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USB4CH User Manual - Symmetric Research

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2. DB15 pin Analog signal Description Diagonal pairs 1 Channel 0 differential input 9 Channel 0 differential input 2 AGND 10 AGND 3 Channel 1 differential input 11 Channel 1 differential input 4 AGND 12 AGND 5 Channel 2 differential input 13 Channel 2 differential input 6 AGND 14 AGND 7 Channel 3 differential input 15 Channel 3 differential input 8 AGND Figure 9 4 USB4CH analog DB15 pin assignments Note the physical connector pin numbering starts at 1 while the USB4CH channel num bering starts at 0 On the DB15 there are 8 pins across the top row and 7 pins across the bottom These are grouped diagonally for the various channels For example channel 0 are the diagonal DB15 pair pins 1 9 This diagonal grouping keeps differential pairs next to each other when using ribbon cable connectors All of the AGND pins are connected together and can be assigned to channels as convenient See the diagrams in Figures 9 5 and 9 6 for pictorial views of the front panel DB15 and the diagonal pin assignments 88 AAA COMODO _Omomomo ee ee DBI15 PIN NUMBERS Figure 9 5 Analog DB15 pin numbers viewed from front panel E AGND DB15 SIGNALS Figure 9 6 Analog DB15 signals viewed from front panel 89 9 3 Twisted pair cabling Despite the benefits of differential signals there are types of noise
3. 20 1 Software Do you include source code Source code for all of the supplied software is included at no extra cost This in cludes the driver user libraries and applications Free downloads are available at our web site Customers wanting to upgrade to the latest release should download from the web Potential customers who would like to review the software are also encouraged to download for review Only partial circuit diagrams are included with the free web downloads Full circuit diagrams are included only with the CDROM shipped with purchase Other than the circuit diagrams the web releases are complete Does the USB4CH save its data to disk files Yes The three acquisition programs DVM Scope and Blast can each save their data to disk files DVM saves its data in ASC format Scope in DAT and Blast in PAK For details see the Application Programs Files in the respective formats are given the filename extensions ASC DAT or PAK Conversion utilities are supplied to convert from the binary DAT and PAK formats to ASC See the Utilities and Format Conversion chapter 166 What is the ASC file format ASC files are ASCII text Data is organized in columns that can be easily read in text editors and imported into other applications such as spreadsheets In the DVM initialization file there are a number of options to control the ASC header and format to be the most convenient for your work The Scope and Blast
4. Call the Open function XchModel 0x20 lt must be 0x20 for the USB4CH GpsModel 0 lt 0 NONE UserCfgByte 0 lt 0 use power up defaults Sps 130 0 requested sampling rate in Hz handle SrUsbXchOpen DriverName XchModel GpsModel UserCfgByte Sps amp ActualSps returned value amp Error returned value if Error then print out the error code printf Open error ouccured Error code d Error else success print out the actual sampling rate printf the ActualSps is fin ActualSps 130 2083 Hz continue on with other code 60 5 2 SPS rate table lookup Include file SrUsbXch h Prototype int SrUsbXchSpsRateTable int SpsIndex double SpsRate The USBxCH can sample its inputs at various fixed rates The allowed rates are listed in the Rate Table in Chapter 6 This function takes an index into that table and returns the corresponding Sps rate This is a helper function only and does not require a device handle The function parameters are int SrUsbXchSpsRateTable function return If SpsIndex is between 0 and 15 this fuction returns a 1 indicating success 0 if not SpsIndex input parameter The requested table index between 0 and 15 SpsRate pointer to returned value This should be a pointer to a double in your program After returning it will be filled in with the sampling rate in Hz corresponding to the index A code fra
5. Figure 3 1 Typical DVM GUI display 17 3 1 1 DVM starting the program Starting DVM is similar for either the GUI or text only versions From the command line type either of cmd prompt gt DvmGui parameters ini cmd prompt gt DvmCmd parameters ini where the first is for the GUI display and the second for the text only display The parameters ini file is optional If not specified DVM will start up with defaults If you want to run with custom parameters they should be specified in the ini file There is nothing special about the ini filename any filename may be used In fact having several ini files for different setups can be very handy Several program shortcuts are also included in the DVM directory Double click on them to execute Copy the shortcuts to the Windows Desktop or Start menu for easy access if needed You can also make multiple copies of the shortcuts and edit their properties to run with different ini files 18 3 1 2 DVM ini syntax The layout of a DVM ini file is free format ASCII with a simple syntax of the form keyword value Comments are denoted with a semicolon where everything from to the end of line is a comment You can create and edit ini files with text editors such as Windows Notepad or any other favorite editor For a listing of all the DVM ini keywords see the file SR USBXCH Dvm DvmHelpIniSyntax txt Keywords not specified in the ini file will be given default values Here is an examp
6. This can usually be done with utilities provided by the operating system After that set the USBxCH to use the PC clock as its time source Using the PC clock as a central time source in this fashion has its advantages All hardware running in parallel on the PC will have access to the same time base NTP has its inherent inaccuracies One of the primary problems are cable delays Because USB Web or Ethernet delays all depend on the activity of all the attached peripherals NTP time stamping will not have the absolute accuracy of GPS By comparison GPS computes its time signals directly on the USBxCH board with a custom controller giving microsecond accuracy The next two sections cover the steps required to use the NTP time system with the USBxCH 14 1 Synchronizing the PC clock to NTP Each of the operating systems supported by the USBxCH has command line utilities to synchronize the PC clock with NTP The sync is done continuously but is not perfect There are jumps in the PC clock as the background NTP utilities resync the PC clock Work underway 121 14 2 Setting the USBxCH to use the PC clock Once the PC clock is synchronized to NTP time all that is required is to set the USBxCH to use PC time to time stamp its data For programs like Scope set the ini file parameter GPS_MODEL to PC_TIME and you are done Work underway 122 Chapter 15 Power Supply Reliable power is critical to the USBxCH Many seemingly myst
7. int RedLedState The USBxCH has two LEDs on its front panel one yellow and one red Call this function with 1 or 0 to set the states of the two LEDs to on or off The red LED has a power on default to toggle automatically with each GPS PPS tick from the font panel DB25 connector To change it to be user programmable set the UserCfgByte in the Open function appropriately The yellow LED is always available and dedicated to being user programmable 70 5 9 Power good Include file SrUsbXch h Prototype int SrUsbXchPowerGood DEVHANDLE UsbXchHandle This function returns the current status of the POWER GOOD signal If a 1 is returned power is good 0 if not The return of this function is the inverse of the red power status LED on the USBxCH back panel near the 2 1mm power connector If the red LED is ON power is not good and this function returns a 0 Conversely if the red LED is OFF then power is good and this function returns a 1 Note that an ongoing record of the power status is automatically returned once a second in the GetDataAsPackets data stream Users of Blast or Scope will already have the power status information recorded and not need to call this function 71 5 10 Stop acquisition Include file SrUsbXch h Prototype void SrUsbXchStop DEVHANDLE UsbXchHandle This is the matching function to Start and will stop data acquisition It is common for a keyboard press or other signal to call this
8. RunMode Besides specifying the output file format these ini parameters also calibrate the second readout to light level units of 1 to 10 Calibrate into other light intensity units as appro priate ileName ileComment ileShowHeader ileShowIndex DisplayTitle DisplayUnits DisplayPlaces DisplayDigits DisplaySlope DisplayOffset PRrReRR RO RB DvmOutputSolar asc Measuring solar panel response ON ON ON ON CONTINUOUS Light Level OneToTen 6 2 6 02121e 007 0 00147941 156 00 00 00 00 00 00 HMS 39 39 39 39 39 39 12 13 14 15 17 18 468 629 791 953 114 276 Once the data file has been acquired start GnuPlot and issue the commands SET FILE FORMAT and PLOTTING AXIS PARAMETERS DataFile DvmOutputSolar asc ColSample 1 ColVolts 2 ColLight 3 ColSeconds 4 ColTime 5 set xtics nomirror font Helvetica Bold 14 set ytics nomirror font Helvetica Bold 14 set xlabel Sample font Helvetica Bold 18 set ylabel Volts font Helvetica Bold 18 set xrange 0 120 About 2 minutes of data set yrange 0 5 Solar panel outputs 3 3v in strong sunlight PLOT THE SOLAR DATA set title SERiCH UA Solar Panel Data font Helvetica Bold 18 plot DataFile index 1 using ColSample ColVolts linestyle 1 title Solar panel voltage You can also save these commands to a file and run them with the GnuPlot load command see Examples Solar gp The
9. Temp range 0 70 C Board dimensions 5 28 x 6 inches 3 4 5 6 7 130 Figure 17 1 USB4CH specifications table 1 Min max input on any or analog pin within conversion range 2 The USB1 1 and DRAM FIFO bandwidth limit the sampling rate to this maximum Absolute maximum noise floor measured in peak to peak bits Input impedance is set by onboard resistors 51K factory default Absolute min max beyond this damage occurs 10K series R is internal to board Power consumption varies little with conversion rate Sleep mode occurs when Close is executed 17 2 Noise floor The USBxCH noise floor varies with sampling rate This is characteristic of all systems based on sigma delta A D converters where the faster the final data output rate the less time there is for signal averaging The typical performance at various rates is USBxCH Noise Floor Counts vs Samples E 0 A 50 9765 Hz 100 200 300 400 500 Figure 17 2 Noise floor variation with sampling rate These graphs show the peak to peak noise versus time The vertical axes are in counts where 1 count is the 24th bit of the converted result Similar results can be seen running the Scope program in real time If the results from Scope are worse than the plots above you have another noise source in the overall system besides the USBxCH 131 Besides plotting the noise floor as a function of time it is also useful to display the
10. The User Library is written in C and available as a DLL The functions can be called from Visual Basic as well as other programming languages as long as you follow C calling conventions See the User C Library chapter for information on the library functions 167 How do I use the system with LabView Set up LabView VI virtual instrument interfaces to the USB4CH User Library with C calling conventions and you will have access to the library functions Can I run under Linux Yes drivers and applications are provided for Linux However before using them confirm the Linux kernel rev on your machine agrees with the SR supplied driver Once compiled Linux drivers are specific to a particular Linux kernel revision If the kernel rev on your machine does not agree with the SR driver you will have to recompile the driver source on your particular machine Why doesn t the USBxCH work after waking the PC from sleep Some PC motherboard USB hub drivers do not wake up correctly after sleep for self powered peripherals and may even crash the system This is a well known OS level error for several versions of Windows and Linux for which neither Microsoft or Linux provides a solution The USBxCH driver which is layered on top of the OS hub driver works around this problem by automatically disabling itself when the PC goes to sleep This prevents any possibility of crashing on wake up However the price to be paid for this work around is th
11. The following GnuPlot graph made from the Pak2Asc data shows a typical run 8 AA NiMH discharge plot Figure 19 16 8 AA NiMH discharge plot Both the analog battery voltage and the power good status bit red LED are plotted The power good signal when the red LED comes on failed at approximately 7 5 volts as it should Note that although the USB digital portion of the system can function at battery voltages even as low as 3 5 volts the analog subsystems such as the A D reference will begin to fail at 7 5 volts The USBxCH will not meet analog specifications at voltages less than 7 5 volts The elapsed time for this particular run was approximately 22 hours Given their relatively small size and good availability NiMH AA cells are an excellent match for many applications Recharging NiMH batteries is fairly easy While you could remove the 8 AA cells from the battery holder and place them in a commercial recharger you can also recharge them all while in series still in the holder Charging rates are quoted in fractions of a full charge C So for example if the capacity is 2Ah then a C 10 rate would use a constant current of 200ma for charging If you have a lab bench supply the eight AA cells in series can be recharged by applying 12 volts at a current limit of 200ma for 10 hours to the battery holder Disconnect the battery holder from the USBxCH while recharging Actually you should apply the recharging voltage for 12 to 14
12. Things as simple as a wall plug not being turned on are common or if you are running from batteries they may be dead If the green LED is not on check the off board power and correct the problem Once the green LED is on the red LED further indicates whether the USBxCH regulators are within specifications If the red LED is on the on board regulators are not functioning correctly The problem is most likely the off board power supply voltage is too low For example if the power supply is 5 volts the green LED will be on but the red LED will also be on You must raise the power to at least 8 volts for the red LED to turn off The red LED may indicate other conditions besides low power supply voltage For example during power up the on board capacitors are charging and the regulators are momentarily out of specifications In this case the red LED should go off within 2 seconds and then the USBxCH will be ready to run If the red LED stays on permanently there is a problem that must be fixed After verifying the off board voltage is sufficient the red LED may be indicating there is a short on the USBxCH board itself and the current limit is activated Do not run for extended periods with the red LED on Diagnose the problem 15 4 POWER GOOD signal The status of the back panel red LED is also available in software and can be accessed in two ways 125 First an ongoing record of the power status is automatically saved once a second in
13. battery can be connected with one clean quick action Sparks often occur when attaching an active load to a battery with alligator clips Not only will the sparks bounce the power and probably crash the USBxCH it is also dangerous if there are any flammable hazards 124 in the area Use a sealed snap action toggle switch to make the final battery connection Wall transformers batteries and some lab power supplies are floating and not necessarily connected to any ground system In such cases be aware if other devices are using the same floating supply because the USBxCH will be sharing the ground connection with those devices In such installations make sure a heavy ground wire is used so all the devices share the same common ground CPU boards are often serious offenders in this regard They may draw many amps when hitting execution peaks and create inductive ground bounces for all the other devices If your system is behaving unreliably review the ground system carefully 15 3 LED power status indicators On the USBxCH back panel there are two LEDs one green one red Both are near the 2 1mm power connectors and give a visual indication of the power status The green LED will light up if there is any power supply voltage at all Even power as low as 3 volts will light it up to indicate the wall transformer or other supply is energized at some level If the green LED is off then check for very basic problems with the power supply itself
14. 0 79 1268679282 074297 2010 03 15 18 54 42 074297 0000000007 1 26 0 79 1268679282 075065 2010 03 15 18 54 42 075065 0000000008 1 26 0 79 1268679282 075833 2010 03 15 18 54 42 075833 0000000009 1 26 0 79 1268679282 076601 2010 03 15 18 54 42 076601 0000000010 1 26 0 79 1268679282 077369 2010 03 15 18 54 42 077369 0000000011 1 26 0 79 1268679282 078137 2010 03 15 18 54 42 078137 0000000012 1 26 0 79 1268679282 078905 2010 03 15 18 54 42 078905 This particular data was acquired at 1302Hz At that rate the sample period is 1 1302 0 0007680 seconds and you can confirm each time stamp is indeed incrementing by that amount In fact the GPS controlled time stamping is so accurate you can even measure the frequency of the on board 10MHz master A D clock controlling sampling rate with extreme precision If you wish to also see the latitude and longitude displayed as a columns run the conversion utilities with the showall command line option 118 13 11 What does time stamping mean Many users ask if the USBxCH A D master clock or Adrdy signal is synchronized to the PPS tick The answer is NO The USBxCH does not phase lock its master clock or Adrdy to PPS A true statement is The USBxCH uses GPS to time stamp the data it acquires When an A D sample is available the GPS time at which it became available is recorded as part of the data stream This statement should be taken literally For example the time stamp does not even indicate the exa
15. 12 volt 3Ah lead acid weighing in at 2 9 pounds Photo Powering from 3Ah Lead Acid Figure 19 17 Powering from a rechargeable 3Ah lead acid battery Lead acids are typically 12 volts so only one battery is required Although the photo shows alligator clips connecting to the battery itself there is still a toggle switch so power can be cleanly applied to the USBxCH without excessive sparking This photo also shows a voltage divider for monitoring the battery voltage with the USBxCH It is interesting to compare the discharge characteristics of lead acid batteries with NiMH 164 Manufacturer Ah ratings are often poorly specified with regard to discharge rate so real world tests are important Figure 19 18 shows the results of a typical run with the 3Ah lead acid The system actually ran for hours while one might have expected only 30 hours from the Ah rating One explanation is the 3Ah lead acid starts at a higher voltage than the NiMH Another is the low voltage discharge characteristics of lead acid are also better Recharging lead acids is not difficult Any automotive battery charger can be used Most have an initial fast charge cycle followed by a trickle charge for maintenance until use Lead acid discharge plot Figure 19 18 Lead acid battery discharge plot Work underway 165 Chapter 20 Frequently Asked Questions The following FAQ may help if you have general questions about the USBxCH
16. 2 second long At a sampling rate of 130 Hz for example there will be 64 samples for each channel in one buffer While at sampling rate of 2604 Hz there will be 1302 samples for each channel in one buffer For more information on these and other ini keywords refer to the file SR USBXCH Scope ScopeHelpIniSyntax txt 30 3 2 6 Scope DAT output file format The binary DAT file format saves complete information about a data run including analog digital GPS and status parameters like temperature Because binary files are smaller than ASCII CPU and disk bandwidth requirements are reduced when saving data in real time Most users will find it easiest to review DAT files by using the Dat2Asc and View utilities With these utilities you don t need to know the internal binary structure of the DAT file to do offline downstream processing For those who are interested the internal structure of a DAT file is detailed in the include file SR USBXCH Include SrDat h You may also wish to refer to the Dat2Asc c source code for an example of how to decode the DAT data records In general a DAT file is comprised of a 4096 byte header followed by data records The header itself is comprised of a C structure SrDatHdrLayout followed by zero padding to fill out the 4096 bytes The fields in the header include items such as sampling rate number of channels etc All of the the Scope ini keyword values are recorded in the header for a complete r
17. 6 VOLT BATTERY 3v 6v Ov CHO CHO CHO f i AGND NC AGND AGND y CH0 CH0 CH0 3v Ov 6v DVM 6 VOLTS DVM 4 VOLTS DVM 4 VOLTS CORRECT Ch0 clipped at 4 volts Ch0 clipped at 4 volts Figure 19 6 6 volt battery circuit showing clipping depends on ground In these experiments all the DVM channels have been calibrated in volts You can also calibrate for other physical units as in the 10 turn potentiometer experiment For easy ways to plot and print results see the GnuPlot example 146 19 2 Twisted pair for 50 60Hz rejection Work underway 147 19 3 Absolute calibration Work underway 148 19 4 Using DVM with a 10 turn potentiometer Besides volts DVM can also display physical sensor units This example shows how to set up a 10 turn potentiometer with DVM displaying turns Using the same techniques as this example you can easily calibrate to display other desired physical units The circuit for the potentiometer experiment is 10 TURN POTENTIOMETER USBxCH r CHO Vwiper 3v BATTERY CH0 gt 10K TOTAL AGND NO EXTERNAL AGND CONNECTION REQUIRED Figure 19 7 10 turn potentiometer circuit fragment We will assume the battery is a pair of AA cells in series providing 3 volts It is a good idea to keep the end to end potentiometer resistance reasonably high so not too much current is
18. DVM Calibrate program 95 10 1 Full Scale Voltage Span and Counts The USB4CH has 24 bit A D converters with 274 counts spread out over the entire input voltage span of the system TOTAL 24 BIT A D COUNTS 2 24 16 777 216 decimal Counts are returned as 32 bit signed integers Theoretically for zero input volts zero counts should be returned and as the input goes positive or negative the count value goes positive or negative with 22 counts above zero and 22 below zero The USB4CH has 4 volt balanced differential inputs Users are often surprised to learn this implies an input voltage span of 16 volts Positive full scale counts are returned when the analog input is 4 volts AND the input is 4 volts a difference of 8 volts Negative full scale counts are returned when the voltages are reversed resulting in the 16 volt span for the full count range Some of the count values from positive full scale down to negative full scale are Input volts Input volts Counts hex Counts decimal 4 4 0x00 7FFFFF 8 388 607 e 0x00 000002 0 000 002 0 0 0x00 000000 0 000 000 e e OxFF FFFFFE 0 000 002 4 4 OxFF 800000 8 388 608 Figure 10 1 A D counts with balanced differential input Balanced differential inputs have many benefits as discussed in the Analog inputs chapter Having a 16 volt input span also provides an excellent signal to noise ratio with low op amp
19. Linux You can also use the SR utility GpsProg to program a Garmin antenna while connected to the USBxCH rather than a separate RS232 port Both Windows and Linux versions of this SR command line utility are supplied 117 13 10 Seeing the GPS time stamps in Scope and Blast To see the time stamps from Scope or Blast first acquire data to DAT or PAK files and then run either the Dat2Asc or Pak2Asc conversion utilities respectively The time stamps will appear as a column associated with each set of samples The command lines cmd prompt gt Dat2Asc 00000000 dat fw cmd prompt gt Pak2Asc 00000000 pak fw would be typical with the resulting output shown next The analog CHx columns and digi tal data have been omitted to fit on the page The time of each sample point is presented in both in decimal form as Time as Seconds and also YMDHMS formats for easy processing by downstream applications The time in seconds is measured from 1970 01 01 Typical Pak2Asc output Pt CHx PwrH DegC DegF Time in Seconds Time as YMD HMS 0000000000 we aes 1 26 0 79 1268679282 069689 2010 03 15 18 54 42 069689 0000000001 1 26 0 79 1268679282 070457 2010 03 15 18 54 42 070457 0000000002 1 26 0 79 1268679282 071225 2010 03 15 18 54 42 071225 0000000003 1 26 0 79 1268679282 071993 2010 03 15 18 54 42 071993 0000000004 1 26 0 79 1268679282 072761 2010 03 15 18 54 42 072761 0000000005 1 26 0 79 1268679282 073529 2010 03 15 18 54 42 073529 0000000006 1 26
20. TCXO calibration Of course calibrating for the initial TCXO accuracy does not make up for its 2 5ppm variation with temperature If your application is exposed to significant temp variations you should track the time base with the GPS time stamps for an accurate record If you don t have GPS and are using the TCXO as an absolute time base the USBxCH has an on board temp sensor System temperatures are recorded once per second as part of the data stream Do a thermal calibration of the time base at various temps and then use the calibration along with the recorded temp record to make corrections 76 6 3 Interpolation to other sampling rates Some applications may require specific sampling rates such as 100Hz or 250Hz or perhaps to be phase locked with timing marks such as GPS PPS ticks One effective way to achieve these requirements is to interpolate Because sigma delta converters inherently oversample and signal average there is a great deal of smoothing already making interpolation even more accurate The Interpolate utility in the Utilities chapter is one simple way to post process data to various sampling rates and phase lock conditions Of course the interpolator requires data that is sampled at a rate greater than or equal to the final requested output rate to produce accurate results Work underway TT Chapter 7 FIFO Depth and Overflow 7 1 FIFO Depth The USBxCH is equipped with a hardware memory buffer so data ca
21. USB4CH Often the most effective solution for 50 60Hz rejection is to simply use twisted pair for the inputs Do you recommend twisted pair for 50 60Hz rejection Yes Twisted pair along with proper use of the differential inputs is often a very effective way to achieve 50 60Hz rejection Often more effective than any amount of numerical or op amp filtering Ideally the twisted pair would also have a foil shield that is connected to the USB4CH case to provide ESD shielding See the Analog inputs chapter for more information How long can the USB cable be The formal USB specification quotes 6 feet as the maximum You can probably use a longer cable if needed 12 feet being reasonable However you will not be successful using a 100 foot cable That is simply beyond USB capabilities For longer cable runs use USB hubs and repeaters for reliable operation 171 Chapter 21 Extra supplies Extra basic supplies such as cable and connectors may be required depending on the in stallation at a particular site SR can often provide such supplies on request however many customers may want to purchase such parts directly from suppliers themselves This chapter lists a few typical parts and vendors This list is only representative with many other suppliers providing equally good products DigiKey www digikey com 1 800 344 4539 Mouser Electronics www mouser com 1 800 346 6873 JDR Microdevices www jdr com 1 800 538 5000 Abbrev
22. automatically use a text editor to put the following line in a file for D Ai in 207 do Pak2Asc exe i 00000000 pak fw Usually batch files are given a bat extension To execute a batch file type its filename on the command line or double click from Windows Explorer In the for line parameter replacement will be done on the i variable invoking the command following the do on every directory matching the wildcard pattern 20 x The batch file Pak2Asc Convert All bat in the Blast directory implements the for line given above In batch file programming the command following do can even be comprised of many subcommands using For example the following for D Ai in 2077 do cd hi amp ren pak bin amp cd would descend into each directory and rename all the pak files to have a bin extension With batch files you can process a great deal of data very quickly For information about batch file programming search on phrases like command line reference or batch files in the Windows help system Linux also has similar com mand line script programming 38 3 3 5 Blast running in the background For many applications running Blast as a background task is useful Under Windows use the Task Scheduler to setup Blast as a background job With Task Scheduler you can start at a specified time periodically or automatically on startup All quietly in the background while the computer can attend to
23. data conveniently formatted for real time plotting then use this function This is approach Scope and its trace display takes This is a helper function only and does not require a device handle 65 The function parameters for PacketsToColumns are int SrUsbXchPacketsToColumns function return Work underway FinalProcess input parameter Work underway PacketArray pointer to input array This should be a pointer to an array of packets as returned by GetDataAsPackets in the user s program Declare the array to be of type SRUSBXCH_PACKET nPackets input parameter The number of packets in the PacketArray Often this would be the same as the parameter nPacketsReturned from GetDataAsPackets although if you have been saving packets up it should reflect the total number of packets waiting to be processed SampleArray pointer to output array Output pointer to an array of samples in the user s program Declare the array to be of type SRUSBXCH_SAMPLEDATA maxSample input parameter Maximum number of sample entries to return to prevent overwriting the SampleAr ray Do not pass a number larger than the number of entries in SampleArray nSample pointer to returned value Work underway StatusArray pointer to output array Output pointer to an array of status entries in the user s program Declare the array to be of type SRUSBXCH_SAMPLEDATA maxStatus input parameter Maximum number of st
24. have a total resistance of 0 1 ohm Suppose a device sharing the common ground conducts 10ma The voltage generated across Rgnd would be 0 001 volt and this would appear in series with Vsensor from the viewpoint of the USBxCH The Vsensor measurement is at the mercy of other devices and can suffer from crosstalk simply because of the single ended connections Just how big a voltage is 0 001 volts or 1 millivolt It is huge given the 1 microvolt precision of the USBxCH The error caused by a mere 1 millivolt ground bounce would be 1000 times greater than the USBxCH sensitivity To cancel the contribution of the ground noise the input should be used Rather than leaving it unconnected or connected to point B in the figure connect it to point A Since only the difference between the inputs is converted into counts the contribution from RGND is not included in the measurement The improvements provided by differential measurements can be significant and for preci sion results the additional wire is well worth the cost Many active sensors already have differential outputs and making the connections for them is easy USBxCH ACTIVE SENSOR VSENSOR d VSENSOR VSENSOR d GND PWR NO AGND CURRENT and LARGE SIGNAL SWING Figure 9 2 Balanced differential inputs with an active sensor Often active sensors go even further and have balanced differential outputs That means the output is exactly as n
25. of supply voltages we 112 have hooked it up to the USBxCH wall transformer using the daisy chain 2 1mm connector on the USBxCH back panel If you are using an antenna that must be powered from a regulated voltage such as 5 volts do not connect it to the wall transformer The voltage will be too high In those cases you must provide the antenna with its own 5 volts The photo in Figure 13 5 shows the finished cabling with the 2 1mm power and DB25 connectors USBxCH front panel DB25 GARMIN SIGNALS GRAY PPS OUT WHITE RS232 NMEA OUT RA BLUE NMEA IN iy ooo0o000000000 SEER EAN WE crounp YELLOW ENABLE IN BLACK GND RED PWR SHIELD NC 12 volts Ns 2 1mm power daisy chain to USBxCH wall trans GPS 16x HVS Figure 13 4 Garmin GPS 16x HVS wiring 13 5 Determining RS232 polarity Suppose you are using a receiver other than the Garmin 16x It may have a RS232 polarity different than the USBxCH power on default Even within a particular GPS vendor catalog there are likely to be differences between models that must be accommodated To make a successful RS232 connection there are two major considerations The RS232 baud rate and polarity The USBxCH expects a 4800 baud rate signal and the GPS receiver must be configured for that rate Most GPS receivers come with a utility program to set 113 Figure 13 5 Garmin GPS 16x HVS finished cabling their baud rate and you should
26. of them it is relatively easy to post process and generate different displays or data formats If you are writing your own acquisition programs with the User Library we recommend studying the source code for Blast It shows the typical sequence of library function calls and can serve as a guide for development The following sections review each library function one per page Note that all function names are preceded with SrUsbXch so they will be easy to find in source code but that the functions are often referred to only by their base names 56 5 1 Open Include file SrUsbXch h Prototype DEVHANDLE SrUsbXchOpen char DriverName int XchModel int GpsModel int UserCfgByte double Sps double ActualSps int Error This function opens and initializes the USBxCH device driver and hardware If successful the system is ready to go with no other initialization required The Open parameters set the sampling rate and other user selectable features If you want to change the parameters call Close and then Open again with the new settings The DEVHANDLE returned by Open should be passed to the other library functions to specify a particular USBxCH Several systems can be installed on one computer each with its own handle Note that opening a particular USBxCH is exclusive and calls to Open with the same DriverName by other processes will fail until a Close of the handle by the current process is done The function p
27. other tasks Under Linux use the amp command line qualifier The USBxCH on board FIFO makes it unlikely any data will be lost even if the PC cannot serve the Blast background task immediately One problem that comes up with background execution is what to do with screen output The solution is to redirect any screen display to a file with the gt operator The following would be typical cmd prompt gt Blast s4 nokeypress gt report txt Besides saving screen output in the report txt file the Blast nokeypress option will start acquisition with no keyboard interaction required Note that the above Blast command line runs continuously saving files until the process is killed with Task Manager or the taskkill command From Linux use the kill command 39 Chapter 4 Utilities and Format Conversion Besides the DVM Scope and Blast applications several smaller utilities are also provided for use with the USBxCH They cover a number of basic tasks with most intended for processing data offline once it has been acquired Popular utilities are Dat2Asc and Pak2A sc for converting binary DAT and PAK files to ASCII Other utilities are Diag general system hardware diagnostic DevMan USBxCH device driver management Dat2Asc convert Scope binary DAT data files to ASCII Pak2Asc convert Blast binary PAK data files to ASCII Interpolate change time base and sampling rate of saved DAT files View review and display DAT and PAK files NmeaT
28. output file format DVM can save its acquired results to ASCII disk files To turn file saving on set the ini keyword OutputFileName myfile asc The output file may be given any name but it is conventional to use the asc extension for easy identification You can give the empty string or value NONE for no file There are also ini keywords to control the output file format Items such as header format and time display may be selected See the file DvmHelpIniSyntax txt for a complete syntax description The general format of an ASC file is fairly simple Data is laid out in columns one column per channel and one sample point per row DVM ASC output file layout channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD channel 0 channel 1 channel 2 channel 3 HMS YMD etc For DVM each row advances by 1 second If the acquisition units are volts then the voltages from channel 0 will be lined up in the first column Channel numbering starts at O Files in this t
29. packets were available Generally GetDataAs Packets should be called often enough so fewer packets than were requested are returned indicating the USBxCH DRAM FIFO is drained and not creeping toward overflow Error pointer to returned value This parameter will report any errors that occurred A value of 0 indicates success with no errors See the include file SrUsbXch h for a list of possible error codes greater than 0 and their corresponding strings 64 5 5 Convert Packets to Columns Include file SrUsbXch h Prototype int SrUsbXchPacketsToColumns int FinalProcess SRUSBXCH_PACKET PacketArray int nPackets SRUSBXCH_SAMPLEDATA SampleArray int maxSample int nSample SRUSBXCH_STATUSDATA StatusArray int maxStatus int nStatus int Error J The previous function GetDataAsPackets should be used to move data from the USBxCH to the PC While very fast many users will find its native hardware packet format difficult This function PacketsToColumns takes the packets from GetDataAsPackets and converts them to easily accessed arrays of data These arrays are essentially the same as the columns appearing in the output from the Pak2Asc utility Of course real time conversion to column arrays will use CPU horsepower and reduce the maximum sampling rate If you need the maximum bandwidth consider saving packets to disk and then later post processing them This is the approach Blast takes However if you need
30. power at higher supply voltages is dissipated as heat and the board will run hotter Supplies as high as 24 volts are acceptable but cooler electronics is always better and those in the 9 to 12 volt range are ideal Voltages beyond 32 volts simply exceed component specifications and will cause permanent damage even before the board overheats The current consumption of the USBxCH depends somewhat on the sampling rate and other activities of the board Typically it is 100ma for a USB4CH with 5ma variation At power up while on board capacitors are charging the board may draw as much as 350ma The off board power supply must be capable of supplying this amount of inrush current to successfully power up The inrush current surge may last for 2 seconds but no longer Active on board circuitry always limits the total current consumption to 350ma 10 even under most short circuit conditions Besides wall transformers many other supplies meeting the voltage and current require ments are acceptable This includes lab bench supplies as well as batteries For example you may power the USBxCH directly from 12 volt lead acid batteries We have even seen 9 volt transistor radio batteries used Of course the length of time the system will run is directly proportional to the Ah amp hour rating of the battery A 9 volt transistor radio battery will not last very long When running from batteries we highly recommend including a manual switch so the
31. power supply voltages The voltage e is the smallest voltage the ADS1255 A D converter can digitize The USB4CH can be used as a single ended system by connecting the input to ground and applying the signal to the input only However with such a connection noise immu nity is reduced and the count range is cut in half effectively losing one bit of resolution Nevertheless for applications where single ended is appropriate the count values are listed in the table in Figure 10 2 96 Input volts Input volts Counts hex Counts decimal 4 0 0x00 3FFFFF 4 194 303 e 0 0x00 000001 0 000 001 0 0 0x00 000000 0 000 000 e 0 OxFF FFFFFF 0 000 001 4 0 OxFF C00000 4 194 304 Figure 10 2 A D counts with single ended input 10 2 Approximate counts per volt With the total counts and the 16 volt span of the previous section in hand the theoretical counts per volt for the USB4CH is Counts per Volt 2 24 16 1 048 576 counts volt or equivalently Counts per Millivolt 1 049 counts millivolt Counts per Microvolt 1 0 count microvolt where the last two values are rounded Of course the volts per count is just the inverse Volts per Count 16 2 24 1 0 microvolts count Note that because the A D converters have noise floors greater than 24 bits the resolution implied by these numbers may not be fully usable For example at a sampling rate of 100 Hz the system
32. pro grams like Scope and Blast This information is continually recorded and saved in the DAT and PAK files Besides the power status the system temperature is also recorded as described in the next chapter Second you can test the power status by calling the User C Library PowerGood function which returns a 1 if power is good 0 if not The power status is a latched value It is cleared by calling Open and initializing the system If power goes bad at any time during the run the system remembers the event and IsPowerGood will return 0 15 5 Reset and power cycling A hardware jumper is provided on the USBxCH board to force a full power reset cycle This is the most drastic reset possible The power supply performs a momentary power down of the entire board The PC plug and play system will act as if the USBxCH has been unplugged from the system and do a complete restart The power cycle feature is only available if the system is being used as a bare board The power reset header is J940 on the back edge of the board near the molex power connector Placing a short between its two header pins will trigger the reset The short can be made with a header jumper a piece of wire a screwdriver or an open collector output from a logic device Power cycling is particularly useful for field box applications If the field box can only be remotely accessed you may want to provide an internet interface to the power cycle or perhaps periodically take
33. processing ee bk we a a 3 3 5 running in the background 2 202004 10 10 11 11 11 12 14 14 14 4 Utilities and Format Conversion 4 1 4 2 4 3 4 4 4 5 4 6 A T 4 8 4 9 4 10 5 User C Library 5 1 5 2 5 3 5 4 5 0 5 6 Def 5 8 5 9 5 10 pA 6 Sampling rates 6 1 6 2 6 3 DIAS bee La oe e A A et DevMan o sos sa A a RE A Dat ASG e corpa a ae el ee a a AA PARZASO o cs ae e ee a ta a a ca INTERPOLALE ca rm a A A aa o a o EII EE AI MEME a a e a a eee oe e a a it PE TOG ee tee Wk ee Se Mee eo Poe we ee Be be Bete ee Digitale 2 2246 4 ee a bw ke ee eR MA eRe eA o a a MOI ek ws fat dee Yer hs Pe ek a oe Be ee igi A so ce a ee Eee Eee ek ee ae BO ea ee E SPO tate table IU o oo dor wo eae ek ee ee Re ee Be Start BCOUISINION lt lt bake hae et Saw ee eae Se Be es Get Data as Packets us Se ea RA ee we A a Convert Packets to Columns e e e User digital lO read o e 25 8648 dea ee Se a User digital JO write oo so o soca sa bea eR ee a ee es Front panel red and yellow LEDS o Power good ig Soe ee Ri ae gs ee RR E Ge Se RA E SLOD ACQUISITION eos aka dag ee RR p a Oe eae ee Ee d A so og Swe KOR ee Ra HR ee wed BAe eRe es Permitted Tates lt sor cadca amoan a E hanp a aaa Master clock stability ccoo aaoh a eraa a a a E aE S Interpolation to other sampling rates a a a 7 FIFO Depth and Overflow dol FIFO Depth evacrisa A A eR A e
34. programs do not output ASC files directly Too much PC bandwidth is required at high sampling rates to keep up with ASCII formatting in real time Use one of the offline conversion utilities to convert DAT or PAK files to more readable ASCII What is the DAT file format DAT files are binary with the data internally organized as records Some records are purely data while others have GPS time stamping information All data is bit level demuxed and easy to process by downstream programs Utilities are included with the SR software to convert DAT files to ASCII which is then readable in any text editor and can be imported into many applications What is the PAK file format PAK files are binary with the USB4CH 64 byte USB cable packets saved directly to the file This format is useful when you want to save data to disk as fast as possible to maximize bandwidth with the Blast program Decoding a PAK file is difficult and requires detailed knowledge of how the USB4CH formats its data at the bit level Most users should use one of the offline the conversion utilities to convert PAK files to other formats Can I use the USB4CH with Excel or MatLab To interface with these applications convert your DAT or PAK files into ASCII with one of the Utilities and Format Conversion programs and then import ASC files from DVM can be imported directly without a conversion step Is it possible to call a User Library function from Visual Basic
35. results as histograms USBxCH Noise Histogram 130Hz 4096 Readings 60 7 1 1 1 1 50 40 30 Percent of Population 20 6 4 2 0 2 4 6 Output Figure 17 3 Noise floor histogram at 130Hz USBxCH Noise Histogram 1302Hz 4096 Readings Percent of Population a 22 20 18 16 14 12 10 8 6 4 2 0 2 4 6 8 10 12 14 16 18 20 22 Output Figure 17 4 Noise floor histogram at 1302Hz At the higher sampling rate the width of the histogram becomes wider showing the increase 132 in the noise floor with sampling rate At 130Hz the width above the 1 level spans from 4 to 4 counts a peak to peak total of 8 counts or 3 bits At 1302Hz the width spans from 16 to 16 counts a peak to peak total of 32 counts or 5 bits These results are in agreement with the specifications published by TI for the ADS1255 A D converters and include the noise performance of the USBxCH amplifier front end To compare with the TI quoted specs see the TI ADS1255 spec sheet page 13 Table 6 133 17 3 Thermal response Work underway thermal response plot Figure 17 5 Long term thermal response 134 Chapter 18 Circuit Diagrams FREE WEB VERSION PARTIAL CIRCUIT DIAGRAMS This free web copy of the User Manual includes only the Circuit Overview and connector pin assignments Complete circuit diagrams are provided only with purchase of the product I
36. support dev Show device descriptor power Check if power is good led Toggle the yellow LED analog Start A D s and display analog data nmea Start A D s and display NMEA strings equip Start A D s and display equipment info like temp digin Read digital input digout Send digital output dram Run several DRAM FIFO tests rev Get firmware revision number reset Hardware reset USBxCH board with full power cycle gn specifies a time source If not specified the PC clock will be used as the time source See GPS Time Stamping for more information gl gt PCTIME NMEA ZDA lt lt default g2 gt GARMIN NMEA RMC GGA g3 gt TRIMBLE NMEA ZDA GGA driver this option is required only if you are running multiple USBxCH boards on a single PC with the names SrUsbXch0 SrUsbXch9 For a list of installed driver names use the DevMan utility See SetDid for specifying the name associated with a particular board Single board users should not specify this parameter accepting the factory default SrUsbXch0 41 As part of any new installation users should run cmd prompt gt Diag install This carries out a series of tests to confirm the driver is correctly installed and the basic hardware is functioning Windows users may also double click on the Run Diag Install shortcut rather than executing from the command line If you feel the USBxCH has developed a hardware problem after running succes
37. to an output file along with time stamps Data runs for days or months can create a record of light intensity The next section shows how to use GnuPlot with values saved in DvmOutputSolar asc to plot results for reports and presentations Figure 19 12 Measuring light levels with a solar cell 155 19 7 Plotting results with GnuPlot After acquiring data with the USBxCH you may want to plot the values This example GnuPlot is a shows how to use GnuPlot to generate display and report presentations public domain program and can be downloaded for free from or found by searching the web Documentation is included when unpacked Excel and MatLab users may use techniques similar to the ones shown here to import data To use GnuPlot you first need a data file For this example we assume you have the solar cell data collected with DVM as in the previous example The following file fragment from www sourceforge net DvmOutputSolar asc would be typical Sample DO MON Volts OneToTen Time Sec 0 7 1 42 1202171952 468 0 7 1 43 1202171953 629 0 7 1 43 1202171954 791 0 7 1 45 1202171955 953 0 7 1 49 1202171957 114 1 0 2 01 1202171958 276 Time YMD 2008 02 05 2008 02 05 2008 02 05 2008 02 05 2008 02 05 2008 02 05 The DVM ini parameters to create this file format were Solar cell output format and channel 1 calibration DutputF DutputF DutputF DutputF DutputFileShowTimeSec DutputFileShowTimeYmd
38. use It can be mounted on flat wall surfaces and the ends of pipes with flanges and adapters The unit has its antenna and receiver packaged together in a single hockey puck enclosure For connections there is a round multiconductor cable with outputs inputs and power for the puck The following lists the Garmin multiconductor cable wire assignments Garmin wire Color Signal Desc 1 red power 12 VDC power 2 black ground power and signal ground 3 yellow enable on off power on low 4 blue RS232 NMEA in NMEA config programming 5 white RS232 NMEA out NMEA string output 12 6 gray PPS Pulse per second 7 green port 2 data in Garmin reserved not used 8 violet port 2 data out Garmin reserved not used Figure 13 3 Garmin GPS 16x HVS wires To hook up the Garmin 16x its cable must be terminated with suitable connectors In this example we will use a female DB25 connector for signals and a 2 1mm barrel connector for power Note the Garmin cable has only one common ground wire for both power and signals This single ground wire should be connected to a USBxCH DB25 ground pin to avoid ground bounce at the DB25 Figure 13 4 shows the wiring diagram Note also the Garmin cable has a foil shield Garmin recommends not connecting the foil shield to anything because it is part of the antenna system We have followed that recommendation Finally because the 16x HVS can be powered from a wide range
39. use it to set 4800 baud The RS232 polarity is generally less configurable so the USBxCH has provisions to accept inverted or non inverted RS232 RS232 polarity comes in two styles Full 12 volt RS232 or TTL CMOS Typically 12 volt RS232 has inverted polarity while TTL CMOS RS232 is non inverted Even if the signal levels are not 12 volts you may still have inverted outputs You can determine the polarity by studying the output on a scope If the output idles high between characters then the signaling is 12 volt style and the USBxCH should be programmed to idle high You can also probably do this measurement with a multimeter watching activity between bursts of signal Even if not a full 12 volts if the output reads more than a volt or two between bursts of activity you probably have 12 volt inverted idle high signaling If on the other hand the RS232 NMEA string output idles near 0 volts between bursts of activity then you probably have TTL CMOS style signaling and the USBxCH should be programmed to expect non inverted idle low Selecting RS232 idle high or low is programmed with the USBxCH UserCfgByte For most users the easiest way to specify a selection is with the keywords in the Scope ini file If you are writing custom software selections should be specified with the UserCfgByte passed to the User C Library Open function 114 13 6 Determining PPS polarity As with the RS232 polarity GPS receivers also vary in their P
40. used widely in digital cameras and other electronic devices The AA size has excellent power density with 2Ah or more typical Here we will be using Duracell AA batteries which claim 2 6Ah At a drain rate of 100 ma in principle they should be able to power the USBxCH for 26 hours In actual tests they reliably power the system for 22 hours enough for a day of field work The following photo shows the setup Photo Powering from AA NiMh Figure 19 14 Powering from a rechargeable NiMH AA battery pack To hold the 8 AA cells an inexpensive battery holder organized as 4x2 cells in series has been used Since NiMH cells have a fully charged cell voltage of at least 1 2 volts this gives approximately 9 6 volts total This is enough to power the USBxCH In addition to the battery holder there is also an on off toggle switch We recommend using a switch so the power can be applied at one clean instant to the USBxCH Using alligator clips directly as a power switch is unreliable sometimes drawing sparks and causing the system to crash on start up Besides the battery holder and switch there is also a 2 1mm power connector 161 so the battery pack can be quickly connected and disconnected for recharging Determining the discharge characteristics for any particular battery setup is easy have the USBxCH measure and record its own battery voltage giving a detailed plot of the discharge curve One problem is the battery voltage will be g
41. values of the four DB25 digital input pins are returned in the low four bits of the integer pointed to by IoValue For example a value of 0x1 means digital input bit 0 is on and the others off while 0xC means bits 3 4 are on and 1 2 off A code fragment might look like int IoValue lt at the top of the program SrUsbXchUserIoRd hUsbXch amp IoValue 68 5 7 User digital IO write Include file SrUsbXch h Prototype void SrUsbXchUserloWr DEVHANDLE UsbXchHandle int IoValue J This function writes to the front panel DB25 digital outputs The output values are latched until another call to this function is done For information about the DB25 pin assignments and voltage levels see the Digital IO chapter The function parameters are void SrUsbXchUserIoRd function return None DEVHANDLE UsbXchHandle input parameter This should be a device handle from a successful call to Open IoValue input parameter value to write to DB25 The lower four bits of this value are written to the respective DB25 digital output pins Use a voltmeter to measure the pins as you change them A code fragment might look like int IoValue lt at the top of the program IoValue 3 lt set the lower two bits 0 0 1 1 SrUsbXchUserIoWr hUsbXch IoValue 69 5 8 Front panel red and yellow LEDs Include file SrUsbXch h Prototype void SrUsbXchUserLed DEVHANDLE UsbXchHandle int YellowLedState
42. 459 2009 08 11 23 25 000 2 00982 3 01490 0 00347 1 55459 2009 08 11 23 25 06 046 2 00982 3 01492 0 00254 1 55459 2009 08 11 23 25 07 093 2 00981 3 01492 0 00054 1 55459 2009 08 11 23 25 08 140 2 00980 3 01491 0 00007 1 55459 2009 08 11 23 25 187 2 00982 3 01492 0 00129 1 55308 2009 08 11 23 25 10 234 2 00982 3 01492 0 00013 1 55009 2009 08 11 23 25 11 281 2 00982 3 01492 0 00407 1 25474 2009 08 11 23 25 12 328 2 00982 3 01491 0 00589 0 50109 2009 08 11 23 25 375 2 00982 3 01492 0 00309 0 00014 2009 08 11 23 25 421 2 00981 3 01491 0 00084 0 00357 2009 08 11 23 25 15 468 2 00982 3 01492 0 00131 0 05049 2009 08 11 23 25 16 515 00981 01492 0 00067 86903 2009 08 11 25 17 562 2 00982 3 01491 0 00008 1 69047 2009 08 11 23 25 609 2 00981 3 01491 0 00086 2 46758 2009 08 11 23 25 19 656 2 00981 3 01491 0 00142 3 01412 2009 08 11 23 25 20 703 2 00982 3 01491 0 00219 2 68247 2009 08 11 23 25 21 750 1 2 3 4 5 6 7 8 9 Figure 3 3 DVM CMD text screen If you don t even want this amount of display there are ini keywords to turn the display off entirely This can be useful for lower power computers only wanting to save their data to a file The DvmCmd executable size is also smaller than DvmGui Note that DvmCmd uses the same ini keywords as DvmGui You can refine keyword selections with DvmGui and then move over to DvmCmd without change 21 3 1 5 DVM ASC
43. 4CH enclosure down the USB cable shield onto the PC enclosure and hopefully onward to the third wire on the wall power plug If the case of the PC is not grounded in such a fashion it should be Field installations should be equipped with a ground stakes to dissipate the static burst Foil shields connected to properly grounded conductive enclosures form a Faraday cage around the electronic equipment keeping the static discharge on the outside If your equip ment is exposed to ESD building a Faraday cage in this fashion is an effective safeguard and is highly recommended 12 6 User configuration byte The polarity of the timing and GPS signals on the DB25 can be programmed by the user For example you may want to enable or disable the Adrdy signal or change the idle state of PPS These selections can be made with the UserCrfByte passed to the Open function The bit layout of UserCfgByte is shown in the following table Bit Function Values Power on default 0 TriggerPolarity idle low or high idle low 1 reserved 2 Adrdy disabled or enabled disabled 3 reserved 4 PpsPolarity idle low or high idle low 5 PpsLedToggle pps toggle or programmed pps toggle 6 NmeaRxPolarity idle high or low idle high 7 NmeaTxPolarity idle high or low idle high Figure 12 4 USB4CH UserCfgByte bit assignments 107 Most users will specify the values of these configuration bits by setting the value
44. 5 154 POWER GOOD signal se coe aoai omoa o aoa Re a a A a ae 125 15 5 Reset and power cycling aooo a e a 126 196 Curent mie 0 2 e a aa a a a OR a e e ha 126 16 Temp Sensor 127 16 1 Temp records ssor ooe 2b a soea ee ee a eS 127 16 2 System level TC calibration 128 17 Specifications 129 17 1 Bpeciticati ons tables c s se e a a a dw a ee See a a 130 7 2 a IEEE 131 17 3 Thermal response 2 4 54 6424 544 bo oa ea eee Ae eee 134 18 Circuit Diagrams 135 19 Examples and Experiments 141 19 1 Measuring a AA battery 0 0 20002 0202 eee eee 142 19 2 Twisted pair for 50 60Hz rejection lt lt lt ee eee es 147 19 3 Absolute calibration s 2 ee 148 19 4 Using DVM with a 10 turn potentiometer 2 149 19 5 Ratiometric technique e 154 19 6 Measuring light levels with a solar cell o o 155 19 7 Plotting results with GnuPlot kta 156 19 8 Passive geophones o s is eoe ee eee 159 19 9 Multiple USBxCH and network processing o 160 19 10 Powering with batteries o o e eee eee 161 20 Frequently Asked Questions 166 20 1 BOWIE ao ae ek ek a Pe ala A A ws 166 200 HardWare oo a cese m atea opk eF a a ee he a 168 21 Extra supplies 172 31 1 Small Parts Tor cables eto ecs pri acim do da a a a ARO on N S 173 22 Using Adobe PDF effectively 176 23 Getting Technic
45. 6 SADWd OLLVNHHOS UATIONLNOD TWLISIG 8 2 SHOVd OLLVWAHHOS AOWAYHALNI aso MHTAYIAO HYYUDVIA MOOTd HOPasn us 136 a S 6002 OF 19quissag AepsinyL by jo 2 aye 3 8003 yoreasoy oauui s 9 NSC HOPESN v Al Jequiny uawnooq azIg YHOLOJNNOO 8sn DIA Z0 N 70H ONILNNOW am vHIN N 70H ONILNNOW EHN 1 70H ONILNNOW ZHN 70H ONILNNOW a73IHS KC L LUN YEMO4 SNE ASN OL NOILOANNOD ON SI GUYSHL dAJAAMOd ATES SI HOPaSN IHL UND aNd WE anyo oot 001d 8 AdAL ESN oorr Z0T131HS Mains lt lt 197 TaIHS ano y GND dagsn ey 49 wagsn wa si aera wagsn 4 tA HOLOHNNOS SNd 4SN 137 a by JO ar aug 6002 87 1890190 AepseupeM raed AU 800Z yoneesay oaww s 9 NSG HOvaSN v J49aquinyN jJuswNs0q ZIS YOLOANNOO Ol Y3SN DIA 9L ony JIVA sead ooer SINANI IVLIDIC wasn O NIAO SINdLNO IWLIOIA YSN ler 0Lnon 01 TIWVLIOIA INANI YADOIAL YASN YAOOTIULA IM4LMNO AQHA G JASN Aquava ONAS YHDOIAL LNdNI Sdd dD YSN Sdd san INdNI WHWN SID YSN XU WENN Sda N LAdLAO WHWN SdD YHSN XL WENN Sd5A Sdd THNVd INOYA 40 ACIS UNVH LHII4Y4 YOLOANNOOD Scdd FIVON MOTI3A 031 Otea Sda1 TANVd LNOYA AHY ANW MOTTA
46. 9 10 02 at 15 26 13 00000004 file 2009 10 02 at 15 26 13100000005 Keypress abort C SR USBXCH Blast gt Figure 3 9 Blast text screen This particular run did not specify nFiles and thus will create output files forever The endless run was aborted with a q keypress For users preferring to execute by double clicking there are several batch files in the Blast directory with preset options From Windows Explorer double click on these batch files to run The command prompt screen will automatically display and look like the above Copy edit and change the batch files if you wish to run with with other parameters You may also create shortcuts to the batch files 35 3 3 2 Blast output file names Blast output files are saved to disk in the PAK file format This is a binary format com prised of 64 byte packets exactly as received from the USB cable Packet format is briefly summarized in the next section This section describes the output filename conventions When Blast is started a data directory with the name YMDHMS is automatically created YMD stands for year month day and HMS for hours minutes seconds The data directory name is formatted as 2009 05 01 at 23 11 06 which should be read as a Blast run was started on 2009 05 01 at 23 11 06 The YMDHMS convention keeps the data directories well ordered when sorted by name Within a data directory for a particular run Blast creates sequential file na
47. Adrdy This output pin is a buffered version of the ADS1255 A D converter data ready signal indicating when an A D conversion has been completed Adrdy strobes at the same frequency as the analog sampling rate with the rising edge indicating conversion completion Applications can synchronize to the A D sampling rate with this signal This signal is disabled at power on and must be enabled in the UserCfgByte However be aware Adrdy does not indicate the instant at which analog samples are taken With oversampling sigma delta converters like the ADS1255 the output counts is an average of the analog input over the sampling period Adrdy only indicates when the converters have a new sample ready to be moved onward to the PC Trigger This input pin allows the user to control when the USB4CH begins data acqui sition with an external trigger The polarity of the input can be controlled by the user By default the trigger is assumed to idle low with the rising edge indicating the trigger Idleing high with a falling edge indicating the trigger can be selected by programming the UserCfgByte See sections 12 6 and 12 7 below for more details 104 GPS By applying GPS signals from a GPS receiver to these pins you can record GPS time stamp and location information in real time along with the 24 bit analog and digital inputs See chapter 13 for more details on using GPS with the USB4CH 12 4 DB25 pin assignments The digital io signals are availab
48. Arrow This makes it easy to come back from a hyperlink you have followed Alt ForwardArrow and Alt BackArrow go forward and backward through the viewing chain you have recently traversed When viewing the Circuit Diagrams you may wish to rotate them by 90 degrees This can be done quickly with the key combinations Ctrl Shift Plus and Ctrl Shift Minus to rotate back You will probably also want to adjust the page display and zoom level depending on where you are looking in the manual The following may be helpful Alt V P S single page display Alt V P U two up page display Ctrl 0 set zoom to fit page Ctrl 1 set zoom to actual size Ctrl 2 set zoom to fit width Ifthe Adobe Reader single key accelerators is turned on in the General Preferences then you can use the Z key to drag a rectangle around a specific area you would like to view in more detail This can be particularly helpful with the Circuit Diagrams Finally using Ctrl F will bring up the Adobe Reader text search Use the Table of Contents at the beginning of the manual as well as the Adobe text search facility to find specific topics in the Manual 176 Chapter 23 Getting Technical Help Answers to many general questions and resources such as software downloads can be found on the SR web site If you have specific technical questions please email us at General product information www symres com Software downloads www symres com SR technical help email address i
49. BxCH DRAM FIFO from gradually creeping towards overflow If nPacketsReturned is at least occasionally less than nPacketsRequested then you know the PC is keeping up Packet data structures are in a dense multiplexed binary format Analog samples digital input values GPS PPS ticks and NMEA strings system temperature power supply status and error codes are all in the packet data stream For easy post processing use the helper function PacketsToColumns to convert packets to column arrays The function parameters for GetDataAsPackets are unsigned int SrUsbXchGetDataAsPackets function return The same value as nPacketsReturned UsbXchHandle device handle This should be a device handle from a successful call to Open 63 PacketArray pointer to returned array Pointer to an array of type SRDAT_USBPACKET for storing the requested packets nPacketsRequested will be attempted to be read It is the user s responsbility to make sure the PacketArray has been allocated and that fewer packets than the dimension of the array are requested to avoid overwriting nPacketsRequested input parameter The number of packets that will be attempted to read Do not ask for more packets than the size of the PacketArray allocated in your program to avoid overwriting the array nPacketsReturned pointer to returned value Indicates how many packets were actually returned The value may be less than what was requested indicating fewer
50. Dat2Asc are Dat2Asc 100 TimeInfoSample asc Dat2Asc 101 TimelnfoStatus asc Dat2Asc 102 TimeInfoEquip asc Dat2Asc 200 TimeInfoAll asc Dat2Asc 300 Nmea asc Dat2Asc 301 Data asc The last file Dat2Asc 301 Data asc is the name of the final large output file with all of the combined data For csv formats the final data file will be given a csv extension The intermediate files may also have information you find useful Dat2Asc has verbose screen output It reports the input files it processes information about each processing step and the files created To run silently simply redirect the screen output to a report file with cmd prompt gt Dat2Asc 00000000 dat fw gt dat2asc rpt Techniques for automating the processing of data from multiple acquisition runs is covered in the Blast section typical post processing For a ready to go example see the batch file SR USBXCH Utilities Scope Dat2Asc Convert All bat For an example of importing ASCII data into a plotting program see the Examples and Experiments section GnuPlot The techniques used with GnuPlot are similar to those that would be used with other plotting and analysis programs 45 4 4 Pak2Asc Pak2Asc converts the binary PAK files generated by programs like Blast to ASCII format The ASCII output is in columns that are easily readable in a text editor as well as being suitable for importing into spreadsheet and analysis programs The Pak2Asc command line syntax is cm
51. E S 14 15 16 17 18 19 20 21 22 23 24 25 DB25 PIN NUMBERS Figure 12 2 Digital DB25 pin numbers viewed from front panel lt lt Trigger lt lt Adrdy GPS PPS C GPS NMEA RX GPS NMEA TX O Din 0 O lt Din 1 O lt Din 2 Din 3 O lt Dout 0 O lt Dout 0 O Dout 0 Dout 0 s SE EEEEEEEBEEE y Hi GROUND DB25 SIGNALS Figure 12 3 Digital DB25 signals viewed from front panel You can test programming the digital outputs with the utility program Digitallo see Chap ter 4 Measure their values with a multimeter like a Fluke The digital inputs can be viewed in real time with Scope 106 12 5 Static shielding Static electricity discharge ESD is damaging to all solid state equipment The DB25 connector is designed to tolerate small static shocks but users must take reasonable steps to avoid ESD problems If the ESD event is large enough such as a lightning strike there is no hope but reasonable steps against smaller events are also necessary and can avoid failure Even the static discharge from walking across a synthetic carpet in winter will cause severe damage Using shielded multiconductor cable for the digital connections to the DB25 is one of the best preventions possible The foil shield should be connected to the metal DB25 housing When a static discharge hits the cable the jolt will be conducted down the shield onto the USB
52. For divider and gain resistor 169 locations see the A D signal conditioning and A D input amplifiers circuit diagrams Note that SR does not warrant customer modified boards Is it ok to overdrive an analog input Moderate overvoltages less than 20 volts are ok Each input has a 10K series resistor limiting the current that can flow Of course overdriving an input is hard on the system It is better to add suitable front end circuitry to deal with the problems at a particular site rather than having the USB4CH take the brunt of the overload Zener TVS diodes gas arrestor tubes and spark gaps are all useful devices depending on the size of the problem Do static shocks hurt the analog inputs Yes Although the USB4CH analog inputs have resistors and capacitors to help snub static shocks any static discharge is damaging to the system This includes the small sparks generated when walking over a carpet and touching the analog input pins Even the smallest ESD electro static discharge events into the analog input pins will result in degradation System calibration will be modified even if total failure does not occur Before touching the USB4CH first discharge yourself by touching a nearby metal object such as a desk or a computer case Then touch the USB4CH metal enclosure and finally the input connectors for any connections Taking a moment to perform this simple routine will significantly help prevent static damage See the An
53. If you wish to remove the software from your system at this point simply delete the SR USBXCH directory Nothing else is required Later after the device driver has been installed you must use the DevMan utility to completely remove the software The software must be installed in the SR USBXCH directory Installation into other di rectories is not supported Most of the executables can be run from any directory but the shortcuts and batch files have the standard path hardwired into them If you need to reinstall the software rename or delete the current SR USBXCH directory and then run install bat again 10 2 2 Downloading software from the web If you want to upgrade to the latest software version or simply want to review the product the full software package is available for free download from www symres com The web postings contain all the software and User Manual but do not include circuit diagrams Full circuit diagrams are included only on the CD shipped with the system The symres com web site has individual postings for each operating system as a zip file Download the appropriate file Unzip the downloaded file into a temp directory and then run install bat to further unpack the software and create SR USBXCH 2 3 Linux revs The Windows drivers are compatible with all versions of XP 7 Unfortunately Linux drivers are specific to a particular version of the Linux kernel Please compare your OS kernel version with the SR d
54. MEA TX r g g n i 3 A t o ODO BEE EEE EEE EB J 4 2 040004001 1 Hi GROUND DB25 GPS SIGNALS Figure 13 2 DB25 GPS signals viewed from front panel Note that besides having a RX pin to listen to the GPS NMEA output strings the USBxCH also has a TX pin Most GPS receivers are configurable and this allows the USBxCH to program receiver features The TX programming strings are defined as part of the NMEA standard and are an output from the USBxCH point of view Also note that the NMEA RX pin can accept a variety of input voltage levels There is no standard for whether GPS receivers output full 12 volt RS232 or lower level 111 TTL CMOS signals so the DB25 RX pin has been designed to accept to accept a wide range of voltage levels All other DB25 pins expect 3 3 volt digital levels The power on defaults for the signal polarities are given in the last column of the table in Figure 13 1 For an explanation of selecting different polarities with the UseCfgByte see the sections RS232 polarity and PPS polarity 13 4 Using a Garmin 16x HVS with the USBxCH As a specific example this section shows how to connect a Garmin GPS 16x HVS receiver to the USBxCH The Garmin 16x is similar to many GPS receivers and the steps given here should be similar to those for others If you have difficulty making cable connections Symmetric Research offers ready to go antennas The Garmin 16x is a rugged unit designed for outdoor
55. PS antenna interface is provided on the DB25 for precision time stamping of acquired data The USB4CH is self powered Power supplies varying from 8 to 24 volts are acceptable A 110 vac wall transformer is supplied with the system with 220 transformers available on request Various types of batteries can also be used for power As shown above eight AA NiMH batteries will power the USB4CH for over 20 hours See powering with batteries for a discussion Many other configurations are possible The USB4CH can be used with any Windows or Linux computer having a USB port Chapter 2 Getting started Installation of the USBxCH is fairly easy Here are the steps to follow 2 1 Find your CDROM Look for a CD in the shipping box This CD contains the system software and a PDF User Manual with circuit diagrams Support for both Windows and Linux is included on the same disk To install change to the CD directory for the operating system you are going to use and at the command line run cmd prompt gt install bat This will create the directory SR USBXCH on your hard disk and unzip the CD files there This step only copies files to your hard disk No registry entries or driver installation are made with this step If you don t like running install bat from the command line use the shortcut icon available on the CD Once the files are copied to your hard disk examine the subdirectories In particular SR USBXCH Driver will be needed later
56. PS polarity It is most common for PPS to idle low and the rising edge to indicate the PPS tick UserCfgByte PPS IDLE LOW UserCfgByte PPS IDLE HIGH Lp LL A om ye PPS Polarities Figure 13 6 PPS signal polarities However there are receivers that idle high and use the falling edge of PPS to indicate the tick You can accommodate the variation with the USBxCH UserCfgByte The PPS con vention used by a particular receiver can be determined with an oscilloscope or multimeter and observing the behavior between bursts of activity Note that if you have the USBxCH programmed for idle low but the GPS receiver actually idles high your system will appear to work but the time stamps will be off by the width of the PPS pulse The PPS pulse width does not matter to the USBxCH as long as it is greater than 100 nanoseconds Within that constraint it is only the leading PPS edge that signals a tick In practice we have never seen a PPS tick narrower than 10 microseconds or wider than 0 5 sec The 100 ns minimum width is easily met by most receivers Note that if the PPS width is as wide as 0 5 sec you will have trouble determining the polarity with a multimeter Consult the receiver s User Manual in that case As with RS232 polarity for most users the easiest way to make a PPS polarity selection is with the keywords in the Scope ini file If you are writing custom software the UserCfgByte value should be passe
57. Rate Table in Chapter 6 It is not necessary to specify the rate exactly it will be automatically rounded to one of the allowed rates All USBxCH channels are programmed in parallel with the same sampling rate ActualSps pointer to returned value This should be a pointer to a double in your program After returning from Open it will be filled in with the actual sampling rate the USBxCH was programmed with Do not assume the actual sampling is the same as the rate as you requested Only rates from the allowed Rate Table are possible Error pointer to returned value This parameter will report any errors that occurred See the include file SrUsbXch h for a list of possible error code numbers and corresponding strings Note that although Open returns the handle BAD_DEVHANDLE on an error this only 58 indicates a failure did occur The Error return indicates the detailed reason for what went wrong The following page has a typical code sequence for Open Note the use of the C ampersand operator to pass the address of returned parameters a pointer 59 Typical code sequence for open include SrUsbXch h include file allocate parameters at the top of your program DEVHANDLE handle char DriverName SrUsbXch0 int XchModel int GpsModel int UserCfgByte double Sps double ActualSps returned value int Error returned value various code from your program would follow here then
58. Time to display strings from that source forever indicates NMEA strings should be acquired and displayed continuously until a q keypress is made If not specified the NMEA string display will stop after the first string with a valid satellite count is received set sets the PC time from the first valid NMEA string Since NMEA strings are sent from the GPS antenna only once every second the accuracy of the PC clock will be no better than 1 second For more accurate time use the time stamping capabilities of Scope or Blast If you wish to use NmeaTime to periodically set the PC clock set it up as a periodically scheduled task with the operating system OxUC sets the User Configuration Byte You may require the UC byte if you are running from an antenna with non standard signals An example would be for an antenna with inverted RS232 polarity See the GPS Time Stamping chapter for more details 50 driver if you are running a multiboard system specify the name of the USBxCH board NmeaTime should use Must be one of SrUsbXchO 9 If not specified will default to SrUsbXcho0 Note that if the GPS antenna has been programmed to emit more or different strings than are expected by one of the NmeaTime gn options then it will not work correctly You may get truncated versions of the strings if there are too many or the PC time may not be set because there is not enough time information in the strings you are emitting Check the r
59. USB4CH User Manual Manual Revision 2010 06 01 Board Revision E Symmetric Research www symres com FREE WEB VERSION PARTIAL CIRCUIT DIAGRAMS Contents 1 Introduction 2 Getting started Pind your CDROM ocaso e E E ea baw A ee Downloading software from the web o A Be Hee ER Se Ee Hook Up DOWN o rrei ck pa eR eR Ree a ee AN Hook up the USB cable cee te parse aoe eRe eRe ee Re ee Run D AS ck a k Pond ra eR EE ALAS Run DVM or Scope 22255466 bene se HE Rds ee eae edb bawss Linux USB port permissions 2 02000002 eee eee 2 1 2 2 2 3 2 4 2 5 2 6 2 2 8 3 Application Programs 3 1 3 2 A A EN AA S11 starting the propratm e sace e aoc wo ie eani g be ees Dbl M DAE as Ea a a A A 3 13 GUL version lt 4 5 4 62a ee aaa A A 3 1 4 command line version o soo ee ee es 3 1 5 ASC file format e 311 6 Calibrate gt o o saosa mars sa a a a ee Se ROR G DEOPE rd Rod la ak e Ge Be eee de 32 1 startne the programi un a bee ae ed S22 D Syntax oe lw ee ea Ae me A a 3 29 GUISO ria e aS ee ee eee es ee a 3 24 command line versi n iodo ae Se ee G 3 2 5 output file mames o sose sa n aso a aa ar rad 3 2 6 DAT fle format oc oak ee aok a aa a RR Re G P o a e a a ee E ra E 3 8 1 starting the program so cx v sa domk kpaa a ae or kuoria 9 3 2 Output fle mames 2x sa c agot a doa oek ea ER ps ee a Bono PAR DETT o an se caat na a Ee a 3 34 typical post
60. able while the antenna is connected to the USBxCH You cannot set the NMEA RS232 baud rate with GpsProg That is assumed to always be 4800 baud by the USBxCH If your receiver has a different baud rate you will have to use its manufacturer utilities to program it to 4800 Work underway Once your antenna is programmed use the Nmea Time utility to check its NMEA string lineup while connected to the USBxCH Make sure it agrees with that described in the GPS Time stamping chapter Also make sure the PPS is active by watching the USBxCH front panel red led for a 1 second toggle 52 4 9 Digitallo Digitallo is a small command line utility for twiddling the USBxCH front panel DB25 digital IO pins After starting up the user is prompted for output values and they are written to the port Besides programming the output pins the four DB25 input pins are read and displayed on the screen as part of programming each value For the pin number locations see the DB25 pin assignments The Digitallo command line syntax is cmd prompt gt Digitallo driver where driver is optional and indicates the particular USBxCH to program It should be one of SrUsbXch0 9 for multiboard USBxCH installations Output values are specified as single hex digits A value of 3 would result in the bit pattern 0 0 1 1 with the least significant bit on the leftmost DB25 pin while a value of F would result in 1 1 1 1 The values on the pins are latched w
61. accessed on the DB25 front panel connector where besides general purpose inputs and outputs there are also USB4CH timing signals and a GPS interface 12 1 Digital input The USB4CH has four general purpose digital inputs The digital inputs are synchronously sampled and saved automatically along with the 24 bit A D analog inputs No special commands are required with the effect being similar to a mixed signal oscilloscope You can also asynchronously poll the digital inputs with the User library UserloRd func tion which will return the input values at the instant of the call Polling has no effect on the automatic synchronous save which continues on at the analog sampling rate regardless of whether you poll or not The digital inputs use standard 3 3 volt TTL CMOS levels Inputs near 0 volts are saved as a logical 0 while those near 3 3 volts are saved as a logical 1 All four digital inputs are buffered through HC14 Schmitt inverters for noise immunity and slow edge tolerance The USB4CH automatically adds another inversion to the HC14 buffering so the saved digital values agree with the DB25 pins Besides buffering each digital input also has RC filtering for further noise immunity and edge control Depending on the application you may wish to change the RC filtering to be different than the factory setting There is also a pull down resistor on each input so they do not float when left unconnected See the table below for the DB25 pin
62. al Help 177 List of Figures Th 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 6 1 Gl 9 1 9 2 9 3 9 4 9 5 9 6 oa 10 1 10 2 10 3 11 1 11 2 12 1 12 2 12 3 12 4 mini Netbook with USB4CH and geophone 9 DVM sample display 4 2 44440 see 44 ee ee be eA eens 17 DVM GUI screen o ao o oe eS a eG eR ke ae de ee ee eS 20 DVM CMD text sereen ao suossa iaa we a Re RG es 21 DVM Calibrate screen cocinar a a e ee 23 scope sample display s i s sas eke Beda RRA RAS OES wae 25 Scope GUI screen ck kek ea ee hee SH RE ee Ee es 28 Scope CMD sereen s ssc cag ee RO ee 29 Blast sample display avaga daada he eR Re RS 32 Blast text sereem coor eee Ee ea Eo Rae ke ER Le 35 SPS Tae tae ia oe alae amp GL eae ore Bi eal a A he Go Bok 75 FIFO hold out time table oe s sos eee ee es ea ee ee 79 Differential vs single ended signals o o 85 Balanced differential inputs a 86 Two terminal floating sensor connection 87 Analog DB15 pin assignment table o 88 Analog DB15 pin numbers viewed from front panel 89 Analog DB15 pin signals viewed from front panel 89 Magnetic coupling of 50 60Hz noise 90 A D counts with balanced differential input 96 A D counts with single ended input ek we es be a 97 Production input offset spreads o ecs so ee ee ko
63. alog inputs chapter for more information Is the USB4CH connected to system ground Yes The AGND and GND pins on the front panel DB15 and DB25 connectors are connected to power ground and consequently also to PC ground The outer ring of the 2 1mm power supply connector is the USB4CH power supply ground If you use a grounded power supply then the system will also be connected to that ground The wall transformer supplied with the system is an unregulated floating power supply The USB cable ground wire and shield are also connected to the PC Is the system opto isolated No The USB signals are direct wire connections between the PC and USB4CH Users requiring a floating system should use a USB opto isolator from compa nies such as Sea Level 170 Is there an antialias filter The USB4CH amplifier circuitry has solder pads for simple RC filtering at a number of signal nodes The factory default values for these positions are mild so no roll off occurs even for the highest A D sampling rates This type of antialias filtering is intended for protection against RF contamination See the A D signal conditioning circuit diagrams for details What is the 50 60Hz rejection If you need powerline rejection there are three options numerical filters op amp notch filters and twisted pair When numerically filtering use high sam pling rates and then apply the numerical filter Any op amp filters of course must be added in front of the
64. arameters are DEVHANDLE SrUsbXchOpen function return If successful Open will return a valid device handle for subsequent use with other library functions If Open has failed the value BAD _DEVHANDLE will be returned For a more detailed reason for the failure check the Error return argument described below DriverName input string This parameter must point to a C style character string with the USBxCH device name Valid names are SrUsbXch0 SrUsbXch1 57 XchModel input parameter Specifies the USBXCH hardware model The four channel USBxCH is the only model currently available and XchModel must equal 0x20 GpsModel input parameter Specifies the GPS antenna being used with the USBXCH The following values are valid where the constant names are defined in SrUsbXch h SRDAT_GPSMODEL_NONE SRDAT_GPSMODEL_TRIMBLE SRDAT_GPSMODEL_ONCORE SRDAT_GPSMODEL_PCTIME SRDAT_GPSMODEL_GARMIN 5SU0UNRerRO Users that do not have a GPS receiver should use NONE or PCTIME See the Chapter GPS Time stamping for more detail UserCfgByte input parameter This byte specifies a number of digital and GPS configurations for the DB25 con nector on the front panel Among the configurable items are whether to enable or disable the DB25 Adrdy setting the PPS idle state and others See Chapter 12 and the UserCfgByte table SPS input parameter Specifies the sampling rate in Hz This value should be one of the rates from the
65. as supplied by SR will already be programmed with the correct NMEA string line up The first consideration for the NMEA strings is the total number of characters emitted The USBxCH hardware buffer can only hold 255 characters per second A NMEA string lineup less than this must be selected The second consideration is the strings themselves Many NMEA strings do not have sufficient coarse time and location information to provide the quantities needed to compute the time stamp In particular we recommend the antenna be programmed to output the following two strings in this order GPRMC for coarse time and date info GPGGA for location information All other strings should be turned off and not emitted For a description of the Garmin NMEA strings please refer to section 4 2 2 in SR USBXCH Docs GpsSpecs GPS16x TechnicalSpecifications pdf 116 A copy of this Garmin document is included with the SR software distribution for con venience In particular the RMC and GGA string pairs expected by the USB4CH will typically read as GPRMC 185442 A 3608 9181 N 11517 9605 W 000 0 000 0 150310 013 4 Ex 6F GPGGA 185442 3608 9181 N 11517 9605 W 2 10 1 2 880 3 M 26 0 M 70 where the comma separated fields contain the time and location information For example in the RMC sting the A indicates the antenna has lock and the fields are valid while the N indicates the latitude is in the northern hemisphere and so forth Note each string is termi
66. assignments and the Circuit Diagrams chapter for circuit details 103 12 2 Digital output In addition to digital input the USB4CH also has four general purpose digital outputs The four outputs may be set at any time by calling the User Library UserloWr function Once written the outputs stay latched and do not change until another write is done The power on value of the outputs is 0 The digital outputs use standard 3 3 volt TTL CMOS signaling If you program an output to 0 the corresponding DB25 pin will be close to O volts and likewise programming a 1 will result in the output pin being near 3 3 volts All the digital outputs are driven by HC14 inverters and as with the digital inputs the USB4CH automatically adds another inversion so the DB25 pin agrees with the pro grammed logic level Each output also has a 300 ohm series resistor to limit the current that can be drawn from the DB25 pins There is nothing the user can do to one of the outputs that will cause the USB4CH to crash Even direct shorts to ground can be tol erated The 300 ohm resistors also make it easy to connect LEDs as indicators with no additional resistors required See the table below for the DB25 pin assignments and the Circuit Diagrams chapter for circuit details 12 3 Additional digital timing and GPS signals Along with general purpose digital inputs and outputs there are also USB4CH timing signals and a GPS interface on the DB25 The signals are
67. at exactly the same nanosecond and the associated time stamp is the same across all Finally users sometimes ask about using timing signals other than GPS For example there are systems generating PPM pulse per minute signals With appropriate interpretation of the resulting data files these systems can work with the USBxCH With a PPM signal timing marks will simply occur in the output files every minute rather than every second 119 13 12 Driving multiple USBxCH systems from one GPS It is possible to drive several USBxCH systems from one GPS receiver Doing so only requires daisy chaining the GPS NMEA RS232 PPS and ground from one USBxCH system to the next connecting them all in parallel If you choose to daisy chain GPS in this fashion DO NOT use a full width DB25 ribbon cable when connecting one USBxCH DB25 to the next This will unintentionally connect the digital outputs on one system to the next creating contention The DB25 connectors have many signals and you must treat them all appropriately Only daisy chain the NMEA PPS and ground with discrete wires 120 Chapter 14 NTP Time Stamping NTP network time protocol can be used to time stamp data acquired with the USBxCH Although less accurate than GPS NTP is useful for many applications where a GPS an tenna is impossible because of physical location expense or power consumption Using NTP with the USBxCH is straightforward First use NTP to set the PC clock
68. at filename extension is customary but not required If the input file is not in DAT format Dat2Asc will detect it and terminate with an error A full file pathname may be given and then both the input and output are directed to the indicated path If the filename has the form nnnnnnnn dat sequential processing is initiated and Dat2Asc will automatically look for and process the n 1 file For sequential mode the starting filename must be eight decimal digits with a dat extension Note the filename 0 dat has fewer than eight decimal digits and will not initiate sequential processing format specifies the ASCII output format where format may be fw fixed width ASCII columns fw_hex fw with hex instead of decimal fields fw_debug fw with low level debugging info csv comma separated values csv_hex csv with hex instead of decimal fields csv_debug csv with low level debugging info raw record format for debugging only The fixed width formats are easy to view by eye in text editors while the csv formats are easiest to import into downstream processing programs like GnuPlot and Excel A typical Dat2Asc command line for sequential processing might be cmd prompt gt Dat2Asc mydatadirectory 00000000 dat csv 44 this will convert all of the sequential files in mydatadirectory leaving the results there in a single large ASCII file Conversion is a multipass process with intermediate files The names of the files created by
69. atus entries to return to prevent overwriting the StatusAr ray Do not pass a number larger than the number of entries in StatusArray For many applications the StatusArray should be dimensioned at 2 66 nStatus pointer to returned value Work underway Error pointer to returned value This parameter will report any errors that occurred A value of 0 indicates success with no errors See the include file SrUsbXch h for a list of possible error codes greater than 0 and their corresponding strings 67 5 6 User digital IO read Include file SrUsbXch h Prototype void SrUsbXchUserloRd DEVHANDLE UsbXchHandle int IoValue J The DB25 connector on the USBxCH front panel has 4 digital inputs and 4 digital outpus This function performs an asynchronous read of the four digital inputs You don t necessarily need to call this function to read the digital inputs They are au tomatically saved synchronously at the same instant as the analog samples in the DRAM FIFO and can be viewed in real time with programs like Scope Apply a signal to one of the digital input pins to see the Scope digital traces respond For information about the DB25 pin assignments and voltages see the Digital IO chapter The function parameters are void SrUsbXchUserIoRd function return None DEVHANDLE UsbXchHandle input parameter This should be a device handle from a successful call to Open IoValue pointer to return The
70. ay be equally important Issues such as the precision and drift of the master clock as well as analog front end resistor matching are also important For many applications it may be more effective to use the USBxCH on board temperature sensor to perform system level corrections accounting for TC temperature changes rather than pursuing a particular precision reference 81 8 1 Standard reference The reference on the standard USBxCH is populated with a generic REF02 from Texas Instruments The following are a few of its specifications TI part number REFO2AP Technology Buried Zener Reference voltage 5 0 volts Initial accuracy 15 millivolts Max TC 15 ppm C Typical TC 4 ppm C Temp range 40 to 85C Package plastic DIP 8 through hole The output of this reference is buffered and scaled to be suitable for use with the USBxCH ADS1255 A D converters A single REF02 is used to supply the converters for all channels with the same reference voltage see the Circuit Diagrams chapter The package is DIP 8 to reduce mechanical board stress related drift Be aware even though many small monolithic surface mount references advertise excellent TC ppm they have changes with mechanical stress far exceeding their spec sheet claims 8 2 Alternate references High performance versions of the REF02 are available from Cirrus formerly Thaler Cirrus part number VRE3050 Technology Buried Zener Reference voltage 5 0 volts Initial acc
71. bar one terminal of the AA battery to AGND as in the following setup Figure 19 4 AA battery measurement with AGND connection Here we have simply connected the green AGND alligator to the metal thumb tab of the black alligator You will still measure 1 5 volts with DVM as before but now the voltages 144 between the inputs and AGND are different than the floating case Here the input is at 1 5 volts with respect to AGND while the input is at AGND The difference still remains at 1 5 volts but the input is pushed 0 75 volts closer to the 4 volt clipping limit We have effectively put a short across the lower 51K ohm resistor as in the following circuit fragment USBxCH CHO 1 50v 0 00v AA cell 1 5 volts gt AGND CONNECTED TO NEGATIVE AA TERMINAL Figure 19 5 Grounded AA battery circuit To modify the experiment further imagine if instead of a 1 5 volt AA cell we had used a 6 volt battery When floating DVM would report the correct 6 volts with 3 volts above AGND and 3 volts below avoiding clipping But if we connect one of the terminals to AGND the other terminal will be forced to 6 volts with respect to AGND and clipping will occur You can construct a 6 volt battery from 4 AA cells in series The figure on the next page shows some of the results It is also acceptable to use adjustable floating lab supplies less than 20 volts for such expe
72. c 33 55 min 0 56 hrs 39 06 Hz 3355 44 sec 55 92 min 0 93 hrs 32 55 Hz 4026 53 sec 67 11 min 1 12 hrs 19 53 Hz 6710 89 sec 111 85 min 1 86 hrs 13 02 Hz 10066 33 sec 167 77 min 2 80 hrs 6 51 Hz 20132 65 sec 335 54 min 5 59 hrs 3 26 Hz 40265 30 sec 671 09 min 11 18 hrs Figure 7 1 USBxCH FIFO hold out times 79 7 2 FIFO Overflow The USBxCH buffer maintains an Overflow Flag Overflow occurs if the USBxCH has been left unserviced by the PC for so long that the FIFO is completely filled If an overflow occurs then any further A D data is discarded at the USBxCH hardware level Data saved in the FIFO before overflow is preserved and can be read back by the PC This way data from a burst run is not lost The FIFO Overflow Flag OV is sticky Once overflow has occurred the flag stays set until a hardware FIFO reset is done A reset can be forced by stopping and restarting acquisition in programs like Scope or by calling Close and then Open in the User C Library 7 3 FIFO Creep For continuous data acquisition the bandwidth of the PC hard disk and USB interface must all be able on average to keep up with the data acquisition rate of the USBxCH The FIFO allows for the PC to be sporadic in its allocation of bandwidth to service the USBxCH but on average the PC must still be able to keep up In cases where the PC can almost but not quite keep up with offloading data the USBxCH FIFO may creep very slowly toward ful
73. ct instant when the sample was acquired Analog samples acquired with sigma delta A D converters are averaged results over the sampling period The time stamp only indicates when the end of the A D oversampling averaging period occurred Given this understanding exactly how accurate is the time stamp recorded at the end of the oversampling period It depends on two factors The first is obviously the accuracy of the PPS signal itself Most receivers have accuracies in the low microseconds while expensive receivers may be as good as nanoseconds The length of the cable connecting the GPS receiver to the USBxCH can also be a similar issue Two installations with different cable lengths will not deliver their PPS ticks at the same instant at the USBxCH DB25 If you need better accuracy regarding these issues you have no choice but to improve the receiver or cabling The second factor is the accuracy of the USBxCH itself This is guaranteed to be 800 nanoseconds worst case The USBxCH time stamp is computed by a dedicated onboard FPGA controller and is always within 800 ns of the PPS tick No cpu polling interrupt or other activity is involved We are also often asked if the time stamps are the same across all the USBxCH channels Since each channel is clocked from the same master clock and controlled in parallel by the same FPGA there is no skew between channels Each channel has identically the same timing environment Each channel asserts Adrdy
74. d prompt gt Pak2Asc filename format where the filename and format parameters are required Running without parameters or with a will give a usage message The filename and format are as follows filename specifies the PAK input file A pak filename extension is customary but not required If the input file is not in PAK format Pak2Asc will detect it and terminate with an error A full file pathname may be given and then both the input and output are directed to the indicated path If the filename has the form nnnnnnnn pak sequential processing is initiated and Pak2Asc will automatically look for and process the n 1 file For sequential mode the starting filename must be eight decimal digits with a pak extension Note the filename 0 pak has fewer than eight decimal digits and will not initiate sequential processing format specifies the ASCII output format where format may be fw fixed width ASCII columns fw_hex fw with hex instead of decimal fields fw_debug fw with low level debugging info csv comma separated values csv_hex csv with hex instead of decimal fields csv_debug csv with low level debugging info raw packet format for debugging only The fixed width formats are easy to view by eye in text editors while the csv formats are easiest to import into downstream processing programs like GnuPlot and Excel A typical Pak2Asc command line for sequential processing might be cmd prompt gt Pak2Asc myda
75. d to the User C Library Open function 115 13 7 Front panel red LED If you have a GPS antenna hooked up and successfully receiving the front panel red led should toggle on and off once a second in response to the PPS signal If it is not toggling there is a problem with PPS It may be as simple as the GPS receiver taking awhile to get full satellite lock at power on A half hour to get lock from a cold start is not uncommon with many receivers If the receiver has been on for awhile and successfully sending PPS then perhaps the number of satellites has fallen too low or the receiver needs better visibility If you see the red led toggling then you know PPS is being signaled by the antenna It is possible for the front panel red led to be set to program mode with the UserCfgByte and not respond to PPS However the power on default is PPS toggle and GPS users should normally be able to see the red led respond 13 8 Expected NMEA strings Most GPS antennas can be programmed to output a wide variety of RS232 NMEA strings In fact it is even possible to program many antennas with obviously incorrect settings such as emitting more NMEA characters than it is possible for the RS232 baud rate to transmit in 1 second So care is required The USBxCH hardware and software expect particular NMEA strings and the GPS an tenna should be programed accordingly If the antenna is programmed differently the USBxCH may give incorrect results Antenn
76. d with copper ground and power planes the temperature is reasonably uniform from one side to the other This is particularly true if the system is inside a field box along with other equipment 16 1 Where is the temp data stored Temperature recording is done automatically and does not require any special actions by the user The temp reading is reported once per second as part of the GPS NMEA strings A trailing data packet including the temperature power supply condition and other system indicators is tacked onto the end of the once per second NMEA strings If you don t have a GPS antenna you can still get the system status reports by setting the ini file parameter GPS_MODEL to PC_TIME in programs like Scope With Blast specify the corresponding command line argument To see the temp records run the Pak2Asc conversion utility on the PAK data files Plotting the system temp along with the the other analog and digital data is a useful tool to determine how a site is responding to daily temp variations 127 16 2 Temp calibration For those needing the ultimate in TC correction a system level thermal calibration can be performed Once the response to a specific temperatures profile is known it can be used to correct data acquired in the field When performing a TC calibration run several thermal cycles to account for hysteresis 128 Chapter 17 Specifications The table on the following page lists the leading USB4CH operating spec
77. data from all channels the synchronously sampled digital data GPS time stamps and error correction codes 32 FIFO words per sample includes all four channels 78 Since the FIFO buffer has a total size of 4 Meg words 4 194 304 decimal a total of 4 194 304 32 words 131 072 samples can be stored FIFO size in samples 4M 32 131 072 total samples The hold out time is the total number of FIFO samples divided by the sampling rate FIFO BUFFERING TIME in sec 131 072 SPS in Hz So for example if the sampling rate is 100Hz then the FIFO can hold out for a total of 131 072 100 1 310 seconds 21 83 minutes Something is wrong if the PC can t service the USBxCH in 20 minutes The following table summarizes the FIFO depth at the allowed sampling rates These times are the same for any of the USBxCH products regardless of the number of channels Note that at the slower rates data can accumulate for several hours FIFO HOLD OUT TIMES FOR USB4CH with 10 000 MHz master clock SAMPLING RATE FIFO BUFFER HOLD OUT TIME 39062 50 Hz 3 36 sec 0 06 min 0 00 hrs 19531 25 Hz 6 71 sec 0 11 min 0 00 hrs 9765 63 Hz 13 42 sec 0 22 min 0 00 hrs 4882 81 Hz 26 84 sec 0 45 min 0 01 hrs 2604 17 Hz 50 33 sec 0 84 min 0 01 hrs 1302 08 Hz 100 66 sec 1 68 min 0 03 hrs 651 04 Hz 201 33 sec 3 36 min 0 06 hrs 130 21 Hz 1006 63 sec 16 78 min 0 28 hrs 78 13 Hz 1677 72 sec 27 96 min 0 47 hrs 65 10 Hz 2013 27 se
78. display 32 3 3 1 Blast starting the program Start Blast from the command line There is no ini file associated with Blast as with DVM or Scope All user options are specified on the command line The syntax is cmd prompt gt Blast sn gn nFiles nokeypress 0xUC 7 where indicates the parameter is optional Running without any command line pa rameters or will give a usage message The other command line parameters are sn specifies the USBxCH sampling rate and must be one of the following Blast sampling rate table sn gt SPS Hz PACKETS FILE BYTES SECONDS si 19 531250 47 3008 5 s2 32 552083 64 4096 4 s3 39 062500 78 4992 4 s4 65 104167 97 6208 3 s5 78 125000 117 7488 3 s6 130 208333 130 8320 2 s7 651 041667 651 41664 2 s8 1302 083333 1302 83328 2 s9 2604 166667 1302 83328 1 s10 4882 812500 2441 156224 1 s11 9765 625000 4882 312448 1 Specifying the sn sampling rate also automatically sets the output file size The out put PAK files are measured in USB packets with 64 bytes per packet The approximate number of seconds of data in each output file is also listed gn specifies the time source to use and must be one of the following Time source table gO gt NONE g1 gt PCTIME lt lt default g2 gt GARMIN NMEA RMC GGA g3 gt TRIMBLE NMEA ZDA GGA If you have a GPS antenna specify the proper gn number to generate time stamps based on its signals For users with
79. dor 15d3 SYSFS idProduct 5504 MODE 0666 15 Chapter 3 Application Programs The USBxCH comes with three finished acquisition applications DVM Scope and Blast With these programs you can acquire data display it on the screen and save it to disk Even for those planning to write their own custom software running these applications will help you understand how the system works The DVM program presents its data on the screen in familiar digital voltmeter style and is suitable for low sampling rates The Scope program presents its data as horizontal traces in oscilloscope fashion and is suitable for low and medium sampling rates Both DVM and Scope specify their acquisition parameters with initialization files ini files and come in graphical GUI and text only command line versions The Blast program is a minimal command line only program All ofits acquisition parameters are specified on the command line and it saves its data in packet format exactly as received from the USBxCH Blast is appropriate for all sampling rates up to the maximum the system bandwidth can support Source code for each of these programs is included with the system and is also available for download at www symres com The following sections give details about DVM Scope and Blast The Calibrate program is for use with DVM and is also detailed here For information about general utility and format conversion programs see Chapter 4 Utilities and For
80. drawn from the battery With a 10K pot there would be 0 3 ma of current flowing which is reasonable If R is the total end to end potentiometer resistance Ra the resistance above the wiper and R the resistance below the wiper then we have Ra R 1 T 10 R R T 10 where T is the physical number turns at the current setting of the 10 turn potentiometer Of course this assumes the wiper resistance varies linearly with turns The linearity should 149 be available on the potentiometer spec sheet or perhaps even stamped on the side of the unit You could also check the linearity with an experiment like this Using Ohm s law V IR and the equation for Ry the voltage across the wiper would be Vwiper Voat R y Ro Voat R R 7 10 e Voat 10 eT showing Vwiper is directly proportional to the the number of turns T To calibrate DVM for turns we will use the companion program Calibrate to determine the slope and offset parameters The physical setup looks like this Figure 19 8 10 turn potentiometer measurement The potentiometer has been mounted on a simple cardboard enclosure with a green dial made from index paper Connections to the stimulus battery potentiometer and USBxCH have been made with alligator clips The USB cable and computer are not shown Being a 10 turn potentiometer the black knob can spin around and around and it is easy to loose track of which turn it is on let alone measure the exact a
81. e USBxCH driver must be manually restarted after waking from sleep A manual restart can be done either with the SR DevMan utility or with the operating system Device Manager With the DevMan utility use the restart option With the operating system Device Manager go to the SrInstrumenta tion class and toggle the disable enable option to remove the USBxCH yellow exclamation mark 20 2 Hardware Is the USB4CH powered by the USB cable No The USB4CH must be powered by a separate power source like a wall transformer The USB4CH is referred to as a self powered USB peripheral Power sources such as lab bench supplies and batteries are also acceptable 168 Are wall transformers with AC outputs ok No Wall transformers with AC outputs will not work The USB4CH requires a DC power supply The standard wall transformer for the system is an unregulated 9vdc 500ma unit with 2 1mm center positive connector Unregulated 12vdc as well as fully regulated supplies are also acceptable The 50 60Hz ripples from unregulated DC wall transformers are ok if the lows of the ripples are greater than 8 volts See the Specifications for the allowed ranges The ripples will not degrade analog performance What do the back panel green and red LEDs mean The back panel green LED will light up if the USB4CH has any power at all It indicates the wall transformer or other power source is at least energized The back panel red LED further indicates
82. e eS GZ FIFO Qveriow 26 44 4g os Se we A See to PHN Cree sus Pace ee Make wae pak e egies 8 A D reference voltage 8 1 Standard referen ia ee er ee ee 8 2 Alternate references 8 3 TC correction with on board temp sensor e e e 9 Analog inputs Diterential signals coa a Bk we Sle oe bh ee a we eee DB15 pin assignments Twisted pair cabling 2 4 a dob araa A A es ol 8 2 9 3 9 4 Static shielding 40 41 43 44 46 48 49 50 52 53 54 56 57 61 62 63 65 68 69 70 71 72 73 74 75 76 TT 78 78 80 80 81 82 82 83 9 5 9 6 Dl 9 8 TOPE impedance coca be edemas a ARERR he Input voltage range oo eke etos eee ek we ee Pe we eS Opamp SO 22444652 bh a RE ee Dea eR Rae eR OTS RC antialias filtering o oc coes 5680553 6 BBG ea Re EA aaa a 10 Analog DC calibration 10 1 10 2 10 3 Full Scale Voltage Span and Counts 00000 eee eee Approximate counts per volt cio saser sa nea ee Reed Rhee Calibration slope and offs t e a s soe ee 11 Analog AC calibration LT 11 2 Theoretical AC transfer function 0 0 0 00 0000 eee eee Measured transfer function 12 Digital IO 12 1 12 2 12 3 12 4 12 0 12 6 12 7 12 8 12 9 DISIALIADUL lt a RA RA E dee A a A Bees Digital output sosa as A amp Gow RR RRE Additional digital timing and GPS signals 2 DB29 pin GSSIRGINENTS o o sg s eee aa a Ree AR ee et ESIC shielding
83. e screen The functionality is much like an oscilloscope If viewing the AC characteristics of your data is important then Scope is a good match The sampling rates for Scope are user selectable with rates from the low Hz to several kHz supported Analog response is to DC which means even if sampling at kHz DC inputs will still return the same correct DC value over and over on each sample The Scope real time graphical display requires considerable PC CPU horsepower which may limit achieving the highest USBxCH rates For the maximum sampling rates use the Blast program Scope optionally saves its acquired data to DAT disk files The DAT file format is binary with data organized as records that are demuxed at the bit level DAT files contain the entire USBxCH data stream analog digital GPS and system status parameters like temperature For easy post processing two utility programs are provided The Dat2Asc utility converts binary DAT to ASCII text files readable in any text editor Dat2Asc files can also be imported into programs such as GnuPlot Excel and MatLab The View utility displays DAT files as horizontal traces on the screen so users can scroll back and forth reviewing acquired data offline The Scope program comes in two versions A full GUI graphical user interface display and a text only command line version Both versions take their setup parameters from an ini initialization file much like DVM but with different keywords The f
84. e simple and give excellent results To change this example into a ratiometric measurement the battery excitation voltage Vpat is simply measured on another channel at the same time as the wiper voltage From the Vwiper equation above you can see dividing by the battery voltage will give the actual number of physical turns regardless of the absolute values of the voltages Ratiometric measurements are easy to set up with a multichannel DVM The next section shows the results that are possible 153 19 5 Ratiometric technique Work underway 154 19 6 Measuring light levels with a solar cell Sometimes sensors can be made from unexpected devices Any component with a voltage that varies in response to an external stimulus is a candidate Solar cells find their most common use as a power source However the voltage from a cell varies with the light level serving as a light intensity sensor With DVM measurements from a cell can even be calibrated directly into light intensity units As an example the photo below shows a small flexible cell mounted in a cardboard holder for testing This particular cell has a voltage ranging from 0 volts at total darkness to approximately 3 volts at full brightness The cell is connected directly to the USBxCH channel 0 with no signal conditioning required Using the Calibrate program you can set up a DVM readout to be 1 at total darkness and 10 at total brightness You can also have DVM save its values
85. ecord of the acquisition run associated with the DAT file Data records follow the header and may have many different types of data Analog digital GPS and system information are all encoded in the records Each data record starts off with a record tag giving the data type and then the record information The record tag is itself a structure with an integer id indicating the type of record infor mation following the tag structure The following are a few of the record tag types ttdefine SRDAT_TAGID_USBPACKET long BSUT TUSB ttdefine SRDAT_TAGID_USBANALOG long ABUT gt TUBA define SRDAT_TAGID_USBSERIAL long SBUT TUBS define SRDAT_TAGID_USBEQUIP long EBUT TUBE define SRDAT_TAGID_EOF long FOET TEOF Refer to SrDat h for a listing of all the record tags Not all of the record types may appear in a specific DAT file Within a record data may be arranged according to the specific record type See Dat2Asc c for a decoding example Note that because the DAT files have a header they cannot be concatenated from the command line with the gt copy command Instead use the Dat2Asc sequential processing feature to process multiple files 31 3 3 Blast Blast is a USBxCH acquisition program designed to use the minimum PC resources possible It is started from the command line and saves its data to disk as PAK files comprised of native USB binary packets The
86. egative as the output is positive The result is that all the current going out the output is matched by that coming in the output and there is no current at all on AGND The AGND connection is still required to reference the differential signals but with no current flowing on it common mode noise is not an issue 86 To connect a floating sensor to the differential inputs simply hook the two sensor terminals to the pins as in the next figure Here the voltages are automatically self balancing and referenced to AGND because of the USBxCH input circuit A few examples of floating sensors might be geophones microphones magnetic pickups piezo cells etc It would still work if you incorrectly connect the pin to AGND but the inputs would no longer be balanced around AGND and you would be more susceptible to ground noise See the Examples and Experiments chapter for a demo of measuring a floating AA battery in this way USBxCH EQUIVALENT INPUT CIRCUIT VSENSOR 2 VSENSOR VSENSOR 2 lt r NO EXTERNAL AGND CONNECTION REQUIRED USBxCH INTERNAL AGND CONNECTION Figure 9 3 Two terminal floating sensor connection 87 9 2 DB15 pin assignments The DB15 connector on the USB4CH front panel is where the analog input connections should be made The DB15 pins have the AGND inputs for each of the four channels The following table gives the pin assignments
87. ents 91 and their replacement in such cases is expected If you must touch the inputs with your fingers prevent static damage by touching the case immediately before This will bring you and the system to the same potential This simple step will go a long way to preventing trouble A further step is to use shielded cable for the analog inputs The shield should be connected to the case of the USB4CH which in turn is connected to the USB cable shield which is connected onward to the PC case and ultimately to third prong of the wall plug The entire string of shielding forms a Faraday cage and mild ESD events are dissipated away from the sensitive electronics This approach is an excellent defense for installations with mild ESD risk Use round shielded twisted pair multiconductor cable such as that from Belden to make such connections The cable foil shield provides good static protection and the twisted pair is an added benefit for 50 60Hz noise rejection See Chapter 21 Extra supplies for part numbers 9 5 Input impedance Input signals on the USB4CH are connected to the non inverting pins of op amps Because of this the system has an inherently high input impedance of 10M ohms See the TI OPA2277 data sheet in the Docs ChipSpecs directory For most applications an input impedance of 10M ohms is too high for good performance With the tiny signal current implied by high impedance even the smallest noise sources compete and signal to n
88. erious problems are ac tually the result of unstable power The power supply must have sufficient voltage and current for the system to work correctly There must be a solid ground connection between the power source USBxCH PC and other peripherals without a voltage difference between one ground point and another Failure to give adequate consideration to these aspects of the power supply will result in unreliable operation This chapter covers some of the basics 15 1 Power connectors Power connectors for the USBxCH are on the back panel Most users will already be familiar with the wall transformer 2 1mm barrel connector Actually there are two 2 1mm jacks on the back panel connected in parallel This makes it easy to daisy chain several devices from the same wall transformer It does not matter which 2 1mm jack the wall transformer is plugged into and which is used as the daisy chain Besides the 2 1mm power jacks there is also a 4 pin molex power header which is available when using the USBxCH as a bare board It is intended for field box applications where the USBxCH is part of a hardware stack In such applications power is often distributed on discrete wire cables with molex terminations It is important the power cables for the USBxCH be of sufficient gauge 24 gauge stranded wire or larger is recommended The inductance of skinny wires may choke the power supply off when the USBxCH hits an execution peak and demands more power It is
89. ese locations The amplifier front end is not designed to provide antialias filtering with a sharp notch at 50 60Hz Applications requiring powerline noise rejection should use either a custom op amp filter in front of the USB4CH or sample at higher rates and apply numerical filtering Twisted pair input cabling also provides an effective way to reduce 50 60Hz noise 94 Chapter 10 Analog DC calibration The physical quantity measured by the USB4CH is voltage and its A D converters return a count proportional to the input voltage When the input voltage is low a low count value is returned and as the input increases the count value increases The exact relationship between a particular input voltage and the A D counts is referred to as the DC calibration It is well approximated by a straight line with a slope and offset Performing a calibration requires measuring the slope and offset so application software can convert counts into volts As shipped the USB4CH software is only approximately calibrated Programs such as DVM have a typical slope and offset in their ini files These values are reasonably good but for highest accuracy each USB4CH must be calibrated on site by the user Furthermore because the input circuitry varies slightly from channel to channel each of the four channels must be calibrated independently The following sections cover the calculations involved with DC calibration For an easy to use GUI program see the
90. esults of Nmea Time before assuming they are correct Also be aware the NmeaTime utility cannot be run concurrently while Scope or Blast is running Only one program at a time can have the USBxCH device driver open and other programs will be excluded The NmeaTime set option is not intended to time stamp analog data from Scope or Blast It is intended for those who wish to set their PC clock to one second accuracy while booting or at other periodic times as an independent stand alone task Scope and Blast will automatically time stamp data as part of their normal operation A few typical NmeaTime command lines might be cmd prompt gt NmeaTime forever cmd prompt gt NmeaTime g2 cmd prompt gt NmeaTime g2 forever cmd prompt gt NmeaTime g2 set The first will display synthetic ZDA strings from the PC clock continuously until q is pressed Even if a GPS antenna is connected to the system note that the g1 default of the first command displays the synthetic PC clock ZDA strings The second command will display strings from a Garmin antenna until satellite lock is achieved The third command line will continue displaying strings even after satellite lock has been achieved The fourth command will set the PC clock from the Garmin strings quitting once satellite lock has been obtained ol 4 8 GpsProg GpsProg is a command line utility for programing a GPS antenna With it you can set antenna features like NMEA string line up and PPS en
91. eters linear slider 10K ohm MFG part number Alps RSAON1159002 MO part number 688 RSAON1159002 Linear slider pots do not have the accuracy of a 10 turn pot but they are ideal for making linear position measurements Sensors general DK part number Many see their sensors listings MO part number Many see their sensors listings Both DK and MO have extensive selections of sensors that are suitable for use with the USB4CH Temperature and pressure sensors are just a few in their listings They can often provide an easy solution to sensor selection PDF copies of their catalogs are available for download from their web sites Batteries 12 volt lead acid MFG part number BB Battery BP1 2 12 T1 12v 1 2Ah DK part number 522 1007 ND MFG part number Power Sonic 12v 1 4Ah MO part number 547 PS 1212 The batteries above are a small lead acid batteries A good point about lead acid is they are rechargeable A 1 2Ah battery would have enough power to run the USB4CH continuously for approximately 12 hours 175 Chapter 22 Using Adobe PDF effectively Most users will be viewing this this document in Adobe Reader The following tips specif ically for Adobe Reader 8 may help keyboard users navigate the manual more quickly The red text items throughout the manual are hyperlinks Analog inputs is an example If you click on a hyperlink you will go to the referenced item To get back from a hyperlink type Alt Back
92. ets over the USB cable To maximize bandwidth Blast saves these native packets directly to its output files without any processing The output files are all given the PAK filename extension to make them easy to identify PAK stands for packet format A USBxCH packet has considerable internal structure Within the 64 bytes the data could be analog digital GPS PPS GPS NMEA strings system status or error correction codes Each packet has headers to identify its type and substructure For most users the easy way to deal with PAK files is to use the Pak2Asc or View conversion utilities For those who are interested in the binary PAK format here is the layout Work underway 37 3 3 4 Blast typical post processing Beyond Pak2Asc and View users may want to automate post processing data from multiple acquisition runs One way is to use batch files to customize the data flow to exactly fit your needs This section covers a few techniques Suppose you have data from several acquisition runs in YMDHMS directories 2009 09 21 at 11 32 45 2009 09 21 at 11 33 26 2009 09 21 at 11 33 41 2009 09 21 at 11 58 15 2009 09 21 at 13 40 36 2009 09 21 at 15 03 47 2009 09 21 at 15 20 15 where indicates there are many sequential files in each directory It is hard to know what all the directory names are and you probably don t want to type them in with each new set of runs To process all of these directories
93. ferential leads are hooked up in reverse DVM will simply read a negative voltage Also experiment with hooking the battery up to the other channels to see the voltage appear on their respective DVM readouts Unused inputs should normally be left shorted together Performing this test it is important to be aware that while the red and black alligators are much like the test leads of a handheld Fluke multimeter they also may not go more than plus or minus 4 volts with respect to AGND or else clipping will occur Given this constraint how can we be sure the floating AA battery keeps the USBxCH input pins within the 4 volt range of AGND After all there is no obvious AGND connection in Figure 19 1 The answer is a weak ground connection is maintained by the USBxCH internally as shown in the circuit fragment on the following page In this fragment half of the floating battery voltage is above AGND while the other half is below AGND If you physically measure with a handheld voltmeter you will find this is indeed true Because of this weak ground connection you often don t have to make an explicit AGND connection for floating voltages and sensors 143 USBxCH CHO 0 75v AA cell 1 5 volts CHO AGND mie NO EXTERNAL AGND CONNECTION REQUIRED USBxCH INTERNAL AGND CONNECTION Figure 19 3 Floating AA battery circuit What happens if instead of floating we crow
94. files are free format ASCII with a simple syntax of the form keyword value Comments are denoted with a semicolon where everything from to the end of line is a comment You can create and edit ini files with text editors such as Windows Notepad or any other favorite editor For a listing of all the Scope ini keywords see the file SR USBXCH Scope ScopeHelpIniSyntax txt Here is an example of a short ini file short Scope ini file SamplingRate 130 0 requested sampling rate ToggleLed ON ChannelTitle 0 Channel Name 00 analog display names ChannelTitle 1 Signal Generator 0 ChannelTitle 2 Microphone ChannelTitle 3 My custom name DigitalTitle 0 DIGO digital display names DigitalTitle 1 DIG1 DigitalTitle 2 DIG2 DigitalTitle 3 DIG3 OutputFileFormat Dat Dat None OutputFileNaming Sequential Single Sequential Time all other keywords are not specified and stay at default values Keywords not specified in the ini file will be given default values There are no GUI dialogs for setting ini parameters with the exception of a few display settings that can be toggled with Alt menu commands All other Scope parameters are taken from the ini keywords or default values Alt menu commands are available for quick ini file editing and reloading 27 3 2 3 Scope GUI version When run in GUI display mode the Scope screen will look like 5 USBscope ScopeSetup ini ScopeSetup
95. function The function takes only the device handle as a parameter and does not have any other parameters or returns Note that stopping acquisition is not the same as calling Close Stop does not close the device driver To restart the USBxCH with a different sampling rate you must call Close and then Open again to reinitialize 72 5 11 Close Include file SrUsbXch h Prototype int SrUsbXchClose DEVHANDLE UsbXchHandle Close the device driver and release the USBxCH for other applications to use Since only one process can have the USBxCH open at a time it is important to Close the driver when you are done Close is the matching function to Open This function takes only the device handle as a parameter Its return indicates whether the Close was successful or not Usually Close can only fail if handed a bad device handle perhaps from a failed call to Open Although the USBxCH device driver will be closed by the operating system if you exit from an application we recommend using calling Close in your programs to gracefully remove the driver from the Plug and Play system 73 Chapter 6 Sampling rates The USBxCH returns converted analog data at a varitey of programmable rates A partic ular sampling rate is referred to as the SPS samples per second or frequency in Hz To set the sampling rate in programs such as Scope users should specify the appropriate ini keywords or if writing their own programs specify the sa
96. gment might look like double SpsRate lt at the top of the program SrUsbXchRateTable 5 amp SpsRate This would return the SpsRate 39 0625 Hz 61 5 3 Start acquisition Include file SrUsbXch h Prototype void SrUsbXchStart DEVHANDLE UsbXchHandle Once Open has returned a valid device handle acquisition can be started with this function Between the call to Open and Start the USBxCH is in idle mode and not returning data Starting on command is useful for a variety of situations such as controlling acquisition in response to a keypress or other signal The matching function to Start is Stop This function takes only a device handle as a parameter and does not have any other returns or parameters 62 5 4 Get Data as Packets Include file SrUsbXch h Prototype unsigned int SrUsbXchGetDataAsPackets DEVHANDLE UsbXchHandle SRDAT_USBPACKET PacketArray unsigned int nPacketsRequested unsigned int nPacketsReturned int Error dis After Open and Start are successful data can then be retrieved from the USBxCH with calls to GetDataAsPackets The function will attempt to read the requested number of data packets from the USBxCH If fewer packets are ready then those that are ready will be returned The return value nPacketsReturned indicates how many packets were actually read Because data is continually streaming in this function must be called periodically at a sufficient rate to avoid the US
97. has a noise free repeatable count value of 20 bits There are four bits or 2 4 1 0 16 microvolts of noise You may prefer to work in 20 bit counts and 16 microvolts per count for your calculations at that sampling rate The input voltage span depends on the gain setting of the front end op amps The above calculation assumes a gain of 1 on those amplifiers By changing resistors on the board it is possible to run the amplifiers with gains of 1 to 100 with no increase in the noise floor This is discussed in the Analog inputs chapter The full scale input range will be smaller with added gain but the counts per volt will be more sensitive We do not recommend using the ADS1255 PGA feature to increase the counts per volt As 97 with most sigma delta A D converters claiming to have a PGA the ADS1255 implements this function by changing the effective oversampling When doing this the noise floor increases in direct proportion This is in contrast to changing the gain of the USB4CH op amps where the gain can be increased without corresponding noise floor increases 10 3 Calibration slope and offset For the general differential DC transfer function in the Analog inputs chapter A D counts slope V V offset applied to a theoretically perfect USB4CH the slope is the A D counts per volt as in the previous section and the offset is zero So the equation becomes A D counts 1 048 576 V V For most applications the ca
98. hould light up If the green LED is off then there is a basic problem with the wall transformer Check the wall power and connections You must fix it to continue v Is the red LED off The red LED near the 2 1mm power jacks may momentarily light up when power is applied but will go off in a second or two If the red LED stays on it indicates the power is not within specifications and something is wrong Perhaps the wall transformer voltage is low or the USBxCH is suffering a short If the red LED is on the problem must be fixed before the system will function correctly At this point if the green LED is on and the red LED is off then the USBxCH is properly powered and you are ready to connect the USB cable 2 5 Hook up the USB cable Connecting the USB cable is the big event The PC will detect the new USB hardware and prompt you for the location of its driver The steps are v Find the USB cable Find the USB cable included in the shipping box One end of the cable has a flat type A USB connector for the PC The other end has a square type B connector for the USBxCH peripheral v Plug the flat type A end into the PC Plug the flat type A end into your computer Note that the connector is polarized Do not use excessive force and plug it in upside down 12 v Plug the square type B end into the USBxCH The next step is to plug the type B end of the USB cable into the powered up USBxCH Doing so will start a sequence of Plug a
99. hours because battery charging cycles are not 100 efficient Do not charge at more than a C 10 rate with this method Do not continue charging for more than 12 to 14 hours with this method either Do not leave 163 the batteries for extended periods with low rate constant trickle charging applied Failing to observe any of these rules may cause the batteries to become hot and even explode The problem is oxygen builds up internal to the battery once charging is complete We do not recommend fast rate charging at currents greater than C 10 for reliable battery life With any charging method stop charging immediately if the batteries become hot For longer runs and applications where trickle charging is required lead acid batteries are useful They come in a variety of sizes and Ah ratings At one extreme are car batteries Actually rather than car batteries deep discharge marine batteries are often a better match Marine lead acids are designed for complete discharge cycles while car batteries are designed for short bursts of extremely high current Both types are readily available at automotive supply stores Such batteries have an impressive amount of power with 50Ah or more common That represents 500 hours 20 days of continuous operation Of course the battery is probably powering other equipment too so the overall run time will be correspondingly less For more modest applications there are smaller lead acids The following photo shows a
100. iations used below MFG Manufacturer DK DigiKey MO Mouser JDR JDR Microdevices 172 21 1 Small Parts for cables etc Some of the more common small parts used in USB4CH applications are as follows 2 1mm power plug MFG part number CUI Inc PP3 002A DK part number CP3 1000A MFG part number Kobiconn MO part number 1710 2131 These are discrete wire power plugs suitable for soldering wires to They are useful for connecting batteries and other custom power sources to the USB4CH Use these instead of chopping the plug off of your wall transformer Alligator clips MFG part number Mueller BU 30 DK part number 314 1010 ND MFG part number Silvertronic 501793 MO part number 835 501793 The Mueller BU 30 clip has a good spring and strong teeth The connection is wire crimp which should also be soldered for low resistance Making cables with these clips requires skill but they result in inexpensive connections of good quality that are easy to use The Silvertronic part is equivalent to the Mueller DB15 DB25 solder cup Dshell connectors MFG part number generic JDR part number DB15S female DB25S female For making custom analog and digital USB4CH input cables solder cup DB connectors are convenient These are available everywhere including DK and MO The JDR parts are generic and of good quality at a reasonable price 173 Wall transformers MFG part number CUI Inc DPD090050 P5P SZ DK par
101. ifications Many performance questions are discussed in more detail in their respective chapters The small table here lists the primary analog components used on the board Copies of the manufac turer specification sheets are also included in the directory Docs ChipSpecs A D converter ADS1255 Texas Instruments A D voltage reference REFO2AP Texas Instruments Front end op amp OPA2277UA Texas Instruments Temp sensor TCN75 Microchip 129 17 1 Specifications table USB4CH Specs Parameter Comment Min Typ Max Units Analog input Input voltage range 1 4 0 4 0 volts Sampling rate 2 3 26 9 765 625 Hz Resolution 24 bits Noise Floor 3 at 130 Hz 3 bits at 1302 Hz 5 bits Input Impedance 4 51K 10M Q Overvoltage tolerance 5 10K ohm series R 20 0 20 0 volts Digital IO Logic 1 high voltage 3 3 V Logic 0 low voltage 0 0 V Output current 300 ohm series R 11 ma GPS interface NMEA RX baud rate fixed 4800 baud NMEA TX baud rate fixed 4800 baud PPS pulse width 100 unlimited ns Time stamp error worst case 800 ns USB cable USB type bit rate USB 1 1 12 Mbit sec USB cable length 6 feet Power supply Supply voltage 8 12 24 Vdc Supply inrush current 2 s at power up 350 ma Supply current 6 converting 100 ma Supply current 7 sleeping 2 ma General
102. ime report the NMEA strings set PC time for systems with GPS GpsProg program a GPS antenna through the USB port Digitallo twiddle the DB25 digital io bits SetDid set the USB DID for multiboard installations Source code is included and users are encouraged to use it as a starting point for developing their own custom utilities There may be additional utilities available with the software distribution besides those listed above see the ReadMe txt files for information Most of the utilities are command line oriented and have options that may be specified Executing without any options will give a help screen Under Windows shortcut icons are also available that may be double clicked to run with defaults The following sections cover each utility and their options 40 4 1 Diag Diag should be used to verify correct operation of the USBxCH after installation or if you ever have any doubts about the hardware It is the Swiss Army knife of USBxCH hardware maintenance The Diag command line syntax is cmd prompt gt Diag test gn driver where indicates the parameter is optional Running without parameters or with will give a usage message The other command line parameters are test is required and specifies the particular test to run The following are a few of the available tests See the usage message for the full list install Installation test suite dev power led analog nmea debug Debug tests for customer
103. ini Stopped Ctrl R to run Showing 12 bits DER Program Options View Help Ctrl R to run changes amplitude 0735 038 lt 2 651 042 Hz Sat 00000014 dat AS gt lt Figure 3 6 Scope GUI screen The four analog channels are displayed as horizontal traces as well as the digital channels and GPS data too The channel titles and enabling disabling the display of particular channels can be specified in the ini file Across the top of the screen is an Alt menu with various program actions With the Alt menus you can start and stop acquisition edit the ini file and bring up a help screen Speed keys are available for keyboard users As with DVM you can specify the text editor to use To change the Scope sampling rate you must edit and reload the ini file Only rates from the Rate Table are permitted Requested rates not on the rate table will be rounded to the nearest allowed rate The sampling rate and other system parameters appear in the status bar at the bottom of the Scope window 28 3 2 4 Scope command line version If you like the capabilities of ScopeGui such as specifying sampling rates and DAT files but want a text only display then ScopeCmd may be a good match The ScopeCmd screen looks like this x C SR USBXCH Scope gt ScopeCmd exe ScopeSetup ini USBXCH ScopeCmd c SR 2009 Rev 2009 08 10 Generating Scope rpt F 10 02 09 10 15 48 Message Beginning Scopecmd Initializing USBxCH wi
104. ith the same value remaining until the next value is specified Note that programs like Scope and Blast synchronously save the digital inputs along with the analog inputs automatically The effect is the same as a mixed signal digital oscilloscope For most applications you do not need the Digitallo utility to save the digital inputs 53 4 10 SetDid SetDid programs the board level EEPROM DID identifiers for multiboard installations Use this utility to set the driver names when you wish to prepare several boards to be connected to a single PC all at once The SetDid command line syntax is cmd prompt gt SetDid driver 0 9 showa111 where indicates the parameter is optional Running without parameters or with will give a usage message The other command line parameters are driver specifies an existing USBxCH board to program with a new DID This parameter must be one of SrUsbXch0 9 The board driver name will change accordingly when programmed with a new DID 0 9 new DID value to program the board EEPROM with The new DID must be a single digit 0 9 After programming the board will have the new driver name SrUsbXchN where N is the new DID number If you want to program the board back to its original DID you must specify the new driver name when calling SetDid showall scans the PC for all SrUsbXchN that are installed The scan is done by calling Open sequentially on each of the SrUsbXchO 9 sy
105. ive USBxCH board Note that you cannot have two boards with the same DID value connected to the PC at the same time The second board will fail to install In this situation connect the boards one at time programming each with a unique DID number and try again Also note that if you forget the DID number of a particular board then you won t know the driver name for it In this case run SetDid showall to scan for the board For step by step instructions on setting up a multiboard installation see the Examples and Experiments section Multiple USBxCH If the machine registry has become a mess and you need to clean up for a completely new start run DevMan removeall This will delete all USBxCH instances and you will have a clean start for the next plug and play event 55 Chapter 5 User C Library For those writing their own custom software a function library is provided for controlling the USBxCH The library is written in C and follows C calling conventions It is supplied both as a static LIB and a dynamic DLL for either style of linking Programs written in languages such as Basic and LabView can use the DLL library by specifying C calling conventions and including SrUsbXch dll on their search paths If your primary goal is to acquire data and save it to disk we recommend using DVM Scope or Blast for most users These finished programs have been tested and checked for many error conditions Once data has been saved to disk with one
106. jyerd suezz3 TTeM paezernbaiun eupos Dan 6 OWA ON OdA 7 09 8 SHITddNS YAMOd CadvOd AHO HIAVLAHDOV SAL WO9EXA9d TYNOILOSNICIA 0060 aNd TOA aNd t Y30AY3H coer YAdCVaH AdMOd XHION ALVNAALTV ano ano lef 7 ono lo T wwz yoyr HAMOd to6r Mowe NAT Z NIVHO ASIVA ANO ANO anyo A9 SAL 0069 0064 riss an9 IND 1060 tt AND z L oan 4 NO m 819 wyo 0 wwz MOWP B3MOd 0064 ooer HdOTA NOILOJLOYd IVSAJAJA YAMOd SAIYAS T0640 MOVE SNWAL TIVM WNT Z SHUOLOANNOS INANI ATddNsS AAMOd 140 Chapter 19 Examples and Experiments This chapter reviews a few simple experiments with the USBxCH Photos are included with many of the examples These particular experiments were chosen to help you get started quickly with the system on your test bench AA battery Twisted pair Absolute calibration 10 turn potentiometer Ratiometric technique Solar cell light levels GnuPlot Passive geophones Multiple USBxCH Powering with batteries VV Vv VV VV VV VY using a battery as an analog DC test signal twisted pair for 50 60Hz noise rejection absolute voltage calibration with the VREF 399 calibrating DVM in potentiometer turns ratiometic methods versus absolute measuring light levels with a solar cell importing USB4CH data into GnuPlot recording seismic signals with Scope processing data from multiple s
107. l requiring hours or even days before overflow occurs How can you know before then if the PC is not keeping up with the average bandwidth requirements A Partially Full PF flag is maintained for the FIFO The PF flag should be clearing regularly if the PC is keeping up with the average bandwidth requirements at the particular sampling rate Work underway 80 Chapter 8 A D reference voltage All A D converters require a reference voltage to compare their analog input against When the analog input is equal to the reference voltage the converter outputs full counts For other input voltages the reference sets the linear scale for the converter see the Analog DC calibration chapter for details on the DC transfer function Of course for conversions to be reliable the reference must be the same from one power on cycle to the next and stable across temperature changes The USBxCH uses a single precision REF02 part for its reference with the same reference voltage applied to all four converters A DIP 8 plastic through hole package is used for maximum mechanical stability The pinout of the REFO2 is standard across several manufacturers with many grades of performance available A goal of the USBxCH is to achieve absolute voltage accuracy rather than simply ratiometric measurement so the selection of the reference is an important consideration However besides the precision of the analog reference users should be aware other factors m
108. l accuracy of 1 5ppm and frequency stability over the entire temperature range of 2 5ppm Thus at a constant 25 C room temperature Fclkin is actually something between 10MHz 15Hz lt Fclkin lt 10MHz 15Hz while over the full temperature range Fclkin could vary by 25Hz This is better than the average PC computer clock which typically has 100ppm variation And for many applications the TCXO is good enough to provide an absolute time base But what does this all mean As an example suppose a particular master clock initial frequency is high by 1 5ppm The clock period would then be Tclkin 1 10MHz 1 1 5ppm 1 10MHz 1 1 5ppm where the second equal sign uses the first order approximation 1 1 x 1 x If this clock runs for a day the amount of time it will lose is very close to 1 day 1 5ppm 0 129 600 seconds lost This amount of error could represent many samples at high sampling rates At 1kHz the analog sample that would be declared to be at the next day boundary if the TCXO is used as an absolute time base would actually have come 129 samples before the true day boundary occurred If you know the clock is high by 1 5ppm you could account for that fact A good way to calibrate the master clock is to use the USBxCH GPS subsystem see the GPS Time Stamping chapter With GPS time stamping you can count exactly how many samples occur in a day and get an exceptionally accurate initial
109. l connected USBxCH devices after PC sleep removeall deletes all USBxCH registry entries and all driver sys and inf files in the Windows directories If you want to clean the system of earlier driver revisions and force plug and play to load a new driver version then use removeall Many of the tasks addressed by DevMan can also be carried out by hand in the Windows GUI Device Manager Using the DevMan command line program is safer for most users since its operations are specifically targeted at the USBxCH It is difficult to compromise the computer with DevMan while with Windows Device Manager you are exposed to drivers for all the hardware serving the system If you have forgotten the symbolic device name of a particular USBxCH use the showall option to refresh yourself For information on running multiple USBxCH systems on a single PC refer to the Examples and Experiments section Multiple USBxCH 43 43 Dat2Asc DatAsc converts the binary DAT files generated by programs like Scope to ASCII format The ASCII output is in columns that are easily readable in a text editor as well as being suitable for importing into spreadsheet and analysis programs The Dat2Asc command line syntax is cmd prompt gt Dat2Asc filename format where the filename and format parameters are required Running without parameters or with a will give a usage message The filename and format are as follows filename specifies the DAT input file A d
110. le of a short ini file short DVM ini file custom channel O display parameters ChannelTitle 0 Temp any string ChannelUnits 0 Degree F any string ChannelPlaces 0 5 total digits shown including ChannelDigits 0 0 digits after ChannelSlope O 0 0007109 calibration slope ChannelOffset 0 631 757 calibration offset channel 1 2 3 are not specified and stay at default values All DVM parameters are taken from the ini file or default program values Changes to parameters such as the number of digits displayed must be specified in the ini file There are no GUI dialogs for setting ini parameters such as displayed digits To make changes edit and reload the ini file Besides the keywords in the fragment above there are also keywords specifying the output filename time format and similar features See the DvmHelpIniSyntax txt file Note the DVM sampling rate is fixed at 1Hz and is not specified with a keyword DVM is intended for low acquisition rate applications Use Scope or Blast for support at user specified sampling rates 19 3 1 3 DVM GUI version When run in GUI mode the DVM screen will look like Ej USBxCH Digital Volt Meter Program Options Help Sample 33 Voltage Rheostat Position Inches CtrHR acquire data Cirl S stop F1 help Files DymSetup ini Dy mOutput asc Figure 3 2 DVM GUI screen For a USB4CH all four analog channels are displayed as green digi
111. le on the male Dsub 25 pin connector DB25 located on the USB4CH front panel right hand side The pin assignments are DB25 pin Signal USB4CH Power on polarity Top row 1 Din bit 0 input pull down 2 Din bit 1 input pull down 3 Din bit 2 input pull down 4 Din bit 3 input pull down 5 Dout bit 0 output low 6 Dout bit 1 output low 7 Dout bit 2 output low 8 Dout bit 3 output low 9 Trigger input idle low rising edge 10 Adrdy sync pulse output disabled 11 GPS PPS input idle low rising edge 12 GPS RS232 NMEA RX input idle high 13 GPS RS232 NMEA TX output idle high Bottom row 14 25 Ground Figure 12 1 USB4CH digital DB25 pin assignments It is easy to count off pins on the DB25 Looking at the connector from the front all the signal pins are on the top row All the ground pins are on the bottom row Counting from the left on the top row the first four signal pins are the digital inputs the next four signal pins are the digital outputs etc Note that the digital bits are counted starting from 0 while the DB25 pins are counted starting from 1 All signals must be referenced to the ground on the DB25 where each signal should be paired with a matching ground return if possible The following two diagrams show the pins viewed from the front panel 105 10 11 12 1 w aa O Ooo0oo0oo000o0o00000n SEER S S SS SS E
112. libration equation is actually used the other way around given the A D counts one wants to compute the corresponding voltage The DVM program is one example Given the A D counts we have V V 9 53674e 007 A D counts 9 53674e 007 1 1 048 576 and the slope and offset would be entered into the DVM ini file as ChannelSlope x 9 53674e 007 1 1 048 576 ChannelOffset x 0 The ini files shipped with DVM for voltage display use these theoretically perfect values Of course physical components are never perfect and the true slope and offset will be slightly different from this ideal For an exact calibration of any particular USB4CH channel you should perform a physical calibration with the DVM Calibrate program Note that besides calibration into volts it is possible to calibrate A D counts into other physical quantities such as temperature The slope and offset can include the sensor response too The major contribution to offset error on USB4CH boards is the Vj input offset voltage of the front end op amps No op amp is ideal and the Vio parameter measures what input voltage may actually be required to zero the output For the OPA2277 amps used on the USB4CH Vio is 50 microvolts max See the TI spec sheet for this Vio specification 98 as well as other details such as TC temperature variation The following graph shows the offset spreads measured on 10 USB4CH boards for a total of 40 channels at 25 C include g
113. m setting and take another measurement Use the resulting ini file with DVM There is nothing special about a 10 turn potentiometer the same process can be used with any sensor that has a linear response 151 EJUSBXCH Calibration This program calibrates data from a USBxCH To run select channel and enter properties Apply input signals to the USBxCH then click the measure buttons Click save to write the calibration results and exitto end the program Channel 0 v Title Units Places Digits Value A Value B Potentiomet Turns 6 2 10 10 Format Counts A Counts B 654 12 1123 3254255 Measure A Measurement complete for value B Figure 19 10 10 turn potentiometer Calibrate screen i USBxCH Digital Volt Meter Running Program Options Help Sample 114 Potentiometer Channel 1 Channel 2 Channel 3 Ini file Cal ini Output file DvmOutputYolts asc Ctrl R acquire data Ctrl S stop F1 help Figure 19 11 10 turn potentiometer DVM screen 152 No doubt 24 bits is more resolution than is typically needed for the average potentiometer measurement However the idea is to apply these methods to applications that do require high precision Even with this experiment an 8 bit A D would only have an angular resolution of 14 degrees while with 24 bits you can easily achieve 0 1 degree resolution Other types of potentiometers offer linear styles for length measurements while many simple de
114. mat conversion gt DVM enhanced multichannel digital voltmeter gt Calibrate DVM calibration into volts and user units gt Scope horizontal real time trace display gt Blast minimal but fast PAK file acquisition 16 3 1 DVM DVM is an acquisition program for the USBxCH with a display and function much like an enhanced multichannel digital volt meter If hand held instruments such as Fluke meters are familiar then you will find DVM easy to use One feature of DVM is besides displaying values as counts or volts it can also display values in user specified units For example displays reading in degrees C are possible A calibration program is included to easily generate the coefficients for such setups DVM optionally saves its acquired values to ASCII disk files This makes it easy to review experimental results and to import data into spreadsheets etc See the Examples and Experiments chapter for an example of importing data into GnuPlot DVM comes in two versions A full GUI graphical user interface display and a text only command line version Both versions take their setup parameters from an ini initialization file The ini syntax and keywords are the same for both The following sections review details of using the program Ej USBxCH Digital Volt Meter Program Options Help Sample 33 Voltage Rheostat Degree F Pasition Inches Ctrl R acquire data Ctrl S stop F1 help Files DymSetup ini DymOutput asc
115. mbolic device names A list of who responds and who doesn t is displayed Use the showall option before and after programming to check the results are what you expected USB devices are identified by three numbers their VID PID DID numbers standing for the vendor product and device id respectively The VID and PID are fixed for a particular vendor and product while DID numbers are free to change as needed Sometimes the DID is used to indicated a firmware revision however it may also be used to distinguish between multiple devices of the same type connected to a single PC The second meaning is used with the USBxCH where up to 10 boards may be connected to a single PC at a time The multiple devices are referred to as SrUsbXch0 SrUsbXch1 etc where the trailing digit is the same as the DID id number The USBxCH product is shipped from the factory with its on board EEPROM DID pro grammed to 0 This is suitable for computers with a single USBxCH attached All of the ini files supplied with software like Scope and Blast are set up to use the device driver name SrUsbXcho If you wish to run multiple USBxCH on a single PC attach one at a time to the machine and run SetDid to specify the new DID you wish each to have Then create the corresponding 54 ini initialization files or command line arguments to refer to the particular board you desire This way you can run multiple instances of Scope for example with each referring to its respect
116. mented pin grounded and signal connected to the pin configuration except for the inversion To see how differential inputs can reduce ground noise consider the following figure USBxCH A differential connection B single ended Vsensor ae Ground noise current Ground noise sources PC or even adjacent channels Figure 9 1 Differential vs single ended signals The sensor or voltage which is to be connected to the USBxCH is indicated by the battery symbol inside the smaller rectangle The sensor itself is probably not a battery but it has an output that can be idealized as some voltage that varies with time It will also be connected to the USBxCH with wires of unknown length depending on the installation It is reasonable one terminal of the sensor should be connected to the terminal of the USBxCH as shown in the figure But the real question is what to do with the other terminal It could be connected to AGND and the system would work In fact for a single ended system with multiple sensors all of the second terminals would be connected to AGND with a single common wire where sometimes even a chassis might be used The resistance of that common connection is labeled Rgnd in the figure and is where the trouble starts 85 Let s estimate the magnitude of Rgnd 24 gauge stranded wire has a typical resistance of 0 020 ohms per foot and a 5 foot length as might be used in many installations would
117. mes like 2009 05 01 at 23 11 06 00000000 PAK 2009 05 01 at 23 11 06 00000001 PAK 2009 05 01 at 23 11 06 00000002 PAK 2009 05 01 at 23 11 06 00000003 PAK 2009 05 01 at 23 11 06 00000004 PAK 2009 05 01 at 23 11 06 00000005 PAK etc The location is where Blast was started The next time Blast is run a new data directory will be created with the new YMDHMS start time and the sequential file names will start all over again at 00000000 PAK Output files are fixed in size as described in the previous section Use the Pak2Asc utility to convert an entire series of sequential PAK files to ASCII format with one call If necessary PAK files can be concatenated with the copy command Because they are binary you must use the copy b option End of file ctrl z characters are inevitably buried in the binary PAK data and the b option is required to process them correctly PAK files must also be concatenated in acquisition order If two files are concatenated in a different order than they were acquired then the error correction codes will not track As an example if you have a directory with a long sequence of files then the command cmd prompt gt copy b 0 PAK OneSingleFile pak will concatenate all of them into a single PAK file which can be further processed Usually concatenation is not required when using Pak2Asc 36 3 3 3 Blast PAK output file format Data is transmitted from the USBxCH to the PC in 64 byte pack
118. mpling rate in the User C Library Open function Available rates are listed in the Rate table in Figure 6 1 Arbitrary sampling rates cannot be programmed only rates listed on the rate table can be selected Furthermore you cannot program different rates on different channels All the analog and digital inputs on the USBxCH are sampled at the same rate and instant with no channel skew The USBxCH A D chips are sigma delta converters A simple model for their architecture is they oversample their inputs at a high rate and then signal average to produce the final result As the amount of signal averaging increases the final resolution improves at the cost of a lower output sampling rate The input oversampling for the USBxCH TI ADS1255 chips is determined by the on board master clock frequency For a master clock frequency of Fclkin the oversampling rate is Input oversampling rate Fclkin 256 If Fclkin is maximized then oversampling is also maximized and the noise floor at any particular final output rate is minimized because there is more signal averaging The fastest Fclkin the ADS1255 can work with is 10 0 MHz and this is the master clock used on the USBxCH Using the above formula the oversampling rate is Oversampling rate with 10 MHz master clock 39 062 50 Hz All final USBxCH output rates are averages from this 39 kHz oversampling rate 74 6 1 Permitted rates At the chip level a final sampling rate is selected by prog
119. n accumulate on board even if the PC is unable to read it immediately This feature is essential if no data is to be lost during continuous acquisition runs Even if the PC is busy with Ethernet or other activity when new data becomes ready the USBxCH on board memory stores the data until the PC can service the task The buffer is organized as a FIFO First In First Out memory As soon as data is acquired it is placed in the buffer and the PC is notified so it can be read Once read the buffer memory is returned to the end of the FIFO This way there are no latency or fall through times and the FIFO stands only as a guard in case the PC is busy The FIFO is organized as 4M x N bit words where N 4 or 8 depending on the number of USBxCH analog channels In the case of the USB4CH this equates to a total of 2 Mbytes in size An important question is how long can data accumulate before FIFO overflow occurs Knowing this length of time affects both continuous and burst acquisition In continuous mode it defines the amount of time the PC can be away on other tasks At high sampling rates where the PC bandwidth cannot stay up continuously it defines how long a burst mode run can last The FIFO hold out time of course depends on the sampling rate filling more quickly the faster the rate To calculate the hold out time requires first knowing how many words per sample are saved The USBxCH saves 32 words per sample The 32 words include the analog
120. nated with a xx checksum The field values will of course vary depending on when and where you run the system See the Garmin document for details about all the fields When using Scope and Blast you do not have to decode the time and date fields Those programs and their conversion utilities automatically take care of the decoding To simply verify the NMEA strings are being received use the NmeaTime or Diag utilities 13 9 Programming the GPS antenna If you purchase a Garmin or Trimble GPS antenna from Symmetric Research it will already be programmed correctly for the USBxCH Users with other antennas will need to program the baud rate NMEA string lineup and PPS enable to be compatible Note that even the Garmin and Trimble factory defaults are usually not compatible with the USBxCH They tend to output too many strings and have PPS disabled Included with the SR supplied software is a Windows utility from Garmin for setting their basic programmable antenna features It is included with the distribution for convenience Besides programming the NMEA string line up to agree with the previous section also be sure to enable the antenna to output PPS You can find the Garmin programming utility in SR USBXCH Docs GpsSpecs snsrxcfg_200 exe To use this program you will need a computer with an RS232 port and a custom cable See the ReadMe txt file in the GpsSpecs directory for more information Garmin does not supply a programming utility under
121. nd Play events Keep an eye on the PC when plugging it in V Specify the driver directory to Plug and Play After the PC has detected the new hardware you will have to specify where it can find the driver For standard installations this is SR USBXCH Driver Once specified the operating system will complete installation Under Windows this means the Plug and Play PnP manager will do the following Place a copy of the SrUsbXch sys device driver file in the Windows directory windows system32 drivers Place a copy the SrUsbXch inf driver info file in the Windows directory windows inf the info file copy will be given a system generated name like oem1234 inf The only sure way to find it is to compare file contents with the original in SR USBXCH Driver Findstr or grep may help Linux carries out similar steps V Check the Device Manager Once PnP installation is complete check the Device Manager to see the USBxCH listed as an available device under the SR Instrumentation group Suppose you unplug the USBxCH and plug it into a different PC USB port What will happen The PC will act as if new hardware has been detected and ask to reinstall the driver all over again Follow the above steps and all will go fine If plugging and replugging on the very same port nothing will be required After the driver has been installed you will need to know the device name Depending on the number of systems installed this will be S
122. nfo symres com If the USBxCH has a hardware problem run Diag debug and email us the log and report files for a reply 177 Avoid the ditch Cathedral Gorge Panaca Nevada 2006 USB4CH User Manual Copyright Symmetric Research 2004 2010 This material can only be reproduced in whole or part with the written permission of Symmetric Research No guarantee of suitability for any application is made with this document All liabilities are the responsibility of the user Email info symres com Web www symres com 178
123. ngular position The bottom side of the potentiometer is in the next photo with simple wires to the three potentiometer terminals You could easily do this experiment with the potentiometer just 150 lying on the table but the cardboard enclosure and dial are simple to make for more accurate measurements Figure 19 9 10 turn potentiometer photo bottom Next start up the DVM Calibrate program To calibrate first turn the potentiometer knob to its minimum setting aligning the knob with the zero mark on the dial then enter 0 for Value A and click on the Measure A button After that move the potentiometer thru 10 turns to its maximum setting aligning with the zero mark again then enter 10 for Value B and then click on the Measure B button These two measurements define a straight line on a plot of turns versus A D counts Clicking on the Save button will automatically save the ini file Cal ini with the corresponding slope and offset Loading the new Cal ini into DVM will display the potentiometer channel in turns Note when running Calibrate you can enter the Channel Title and Units as Potentiometer and Turns so they will also display The Calibrate screen should look like Figure 19 10 and the resulting DVM screen like Figure 19 11 With practice calibration for other types of sensors should be quick The steps are always the same Put the sensor at its minimum setting and take a measurement Then put the sensor at its maximu
124. nstall the CDROM that came with the product shipment for the full User Manual with complete diagrams Customers who need an update or have lost their original CDROM may obtain copies of the full User Manual by emailing SR at info symres com Use the Adobe Acrobat reader View RotateView Clockwise command to present the dia grams horizontally on the screen TOUR OyervieW o neta tt tt da a 136 o A 137 User dieital IO CORREO id awd weed ened aed eres 138 Analog input GGHMeCtOr dades 139 A NN 140 135 a br jo L 1eayg 6003 82 1990190 Aepsaupea M Tale 3 8003 yoreasey onjamuis 9 NSO HOLEsn Vv Al Jequiny yuswns0q azIS MAIAYSAO LO ond 007 TENNVHO YiAd JALIJANOD d W 118 vz SINANI TIVILNAYAAATO STANNVHO INANI YNOT YOLOANNOO HIVN STA Te LT HOVd OLLVNHHOS 006 ASION MOT YO4 SHAOLWINDAY YVHNIT GYvVOd NO SHYOLOENNOD XH TON NId p ANW AANSOASNVAL TIVM WUT Z HOVLIOA ATddNS HHMOd ATAVLIGHOOV JAA pZ OL 6 vr Ze SHOVd OLLVNHIHOS SLNANI SOTWNW 00 dudo IaL AAYVMGYVH AHSAN SLOdNI WENN CNW Sdd SdD STHART IVNOIS SOWD TIL 3TO0A E SINdINO ANOA ANY SINANI ANOA YOLOANNOO HIVN STA 9T PT SADWVd OLLVNHHOS OI IWLIDIA 002 ATddNS WAMOd 00T AOVIJALNT SANZT Gadds TINA YMATIOULNOO TXA ESA SSAHAdAO YOLOANNOD HdAL ESN O4I4 Wwa AN Z NOIIVHHdO AITOA E wOsSsdoOdd dido NOLSAD T
125. oc ew em cr AR a ek eee OR User configuration byte lt se e toe paie eat emie BY eRe Ree Triggering oe scc caog eaga a ge p ee e Re RUA Programming the front panel red and yellow LEDs Seeing the digital inputs in Scope e 13 GPS Time Stamping 13 1 13 2 13 3 13 4 13 5 13 6 13 7 13 8 13 9 13 10 13 11 13 12 What IS GPS Y cocaina a a Re Required GPS signals coco pare gao a a o ke DB25 pin assignments 2 ee Using a Garmin 16x HVS with the USBxCH Determining RS232 polarity c csa ned dana aadu bee 42 Determining PPS polarity gt s lt a ceso saaara a aa Karp a aa Front panel red LED 2 no ace a moa oaa o ua Re a ee eA a a A Expected NMEA Strings e oe p tate Re e a a e koe e e ee Programming the GPS ant nna gt esoe nocu ee pk ene Doe ee ee Seeing the GPS time stamps in Scope and Blast What does time stamping mean aoaaa e a Driving multiple USBxCH systems from one GPS 14 NTP Time Stamping 14 1 14 2 Gynehromizine the PC clock to NTP cose po Ae O RS eS Setting the USBxCH to use the PC clock a socpp oeae 95 96 97 98 100 101 102 103 103 104 104 105 107 107 108 108 108 109 109 110 110 112 113 115 116 116 117 118 119 120 15 Power Supply 123 ML CONDOTTO sr o hoe Se a A a Re 123 15 2 Voltage and current requirements e 124 15 3 LED power status indicators e 12
126. oise ratio is lost To allow for different input impedances the USB4CH is equipped with resistors in parallel with the inputs See the circuit diagram A D signal conditioning resistors R400 x R401 x The parallel impedance setting resistors are normally populated with 51K ohm values For applications with active sensor outputs this is a good value It draws a reasonable amount of signal current but does not overload the active sensor output either Noise levels are low and issues like the triboelectric effect of input leads are not competing with the signal For applications that require other input impedances such as passive sensors the resistors R400 x R401x should be adjusted appropriately There are SMT 0805 solder pads on the circuit board for making changes Note that if the system is set to 10M ohm input impedance and the A D inputs are allowed to float conversions will be noisy and not pulled to ground reliably To measure the USB4CH noise floor with high input impedance short the inputs to AGND or other low impedance source 92 9 6 Input voltage range The normal full scale input range of the USB4CH is 4 volts as described in the Voltage Span and Counts section of the Analog DC Calibration chapter This is the input range on the pins as measured with respect to AGND The inputs are differential but only as long as the pin voltages are within this range Other input ranges can be accommodated by changing resist
127. olate Interpolate translates data acquired at one sampling rate to another time base Work underway 48 4 6 View View is a GUI application displaying the data from DAT files as horizontal traces on the screen The display looks much like Scope except the user can scroll left and right for a detailed off line review Work underway 49 4 7 NmeaTime NmeaTime reads and displays NMEA strings from the GPS system and optionally also sets the PC clock It is intended as stand alone utility and is not required for time stamping analog data Programs like Scope and Blast will automatically time stamp data with better accuracy because they also process PPS The NmeaTime command line syntax is cmd prompt gt NmeaTime gn forever set OxUC driver 7 where indicates the parameter is optional Running without parameters or with will give a usage message The other command line parameters are gn specifies the type of GPS receiver attached to the system and must be one of the following Time source table gl gt PCTIME NMEA ZDA lt lt default g2 gt GARMIN NMEA RMC GGA g3 gt TRIMBLE NMEA ZDA GGA For details about using GPS with the USBxCH see the GPS Time Stamping chapter Note that even if you have a GPS antenna attached to the system NmeaTime will still default to the g1 PCTIME option with synthetic ZDA strings The correct time source g2 g3 must be specified for Nmea
128. ollowing sections review particular aspects of running Scope E USBscope ScopeSetup ini ScopeSetup ini Stopped Ctrl R to run Showing 12 bits Program Options View Help Geophone CtrHeR to run changes amplitude 0735 038 lt 2 651 042 Hz Sat 00000014 dat lt Figure 3 5 Typical Scope display 25 3 2 1 Scope starting the program Starting Scope is the same for either the GUI or the text only version and is similar to starting DVM From the command line type one of cmd prompt gt ScopeGui parameters ini cmd prompt gt ScopeCmd parameters ini where the first is for the GUI display and the second for the text only display The parameters ini file is optional If not specified Scope will start up with defaults If you want to run with custom parameters they should be specified in the ini file There is nothing special about the ini filename any filename may be used In fact having several ini files for different setups can be very handy The GUI and command line versions of the program use the same ini keywords Several program shortcuts are also included in the Scope directory Double click on them to execute Copy the shortcuts to the desktop or start menu for easy access if needed Make copies of the shortcuts and edit their properties to run with custom ini setups 26 3 2 2 Scope ini syntax The layout of a Scope ini file is similar to that for DVM only the keywords are different Scope ini
129. ooa Re ee ee 99 AC response theoretical sine 2 2 e e 101 AC response physical measurement Setup 102 Digital DB25 pin assignment table a e 105 Digital DB25 pin numbers viewed from front panel 106 Digital DB25 pin signals viewed from front panel 106 Digital DB25 UserCfgByte osa c taceo cami mo ea a a a eee 107 13 1 13 2 13 3 13 4 13 5 13 6 17 1 17 2 17 3 17 4 17 5 19 1 19 2 19 3 19 4 19 5 19 6 19 7 19 8 19 9 19 10 19 11 19 12 19 13 19 14 19 15 19 16 19 17 19 18 GPS DB25 pin assignment table 111 GPS DB25 pin signals viewed from front panel 111 Garmin GPS 16x AVS Wires s coo 2b ee ewe eRe Re Es 112 Garmin GPS 16x HVS wiring 2246 be eee eee eRe 40022 113 Garmin GPS 16x HVS finished cabling o a e 114 PPS sisual polarities o sop He ea ae ey a A Bs 115 Sperihcations table o e ee as ew eae SM we LAA oe bee ee 3 130 Noise floor time domain plots s s se sse se rta re cra ka rona 131 Noise floor histogram at ISO ss s oso o macca daa a a ee 132 Noise floor histogram at 1302Hz s e o sa csa caan 2 0 2 ee eee 132 Long term thermal response sa cac aa o barad parar 134 AA battery test lead setup ooa a ee be a 142 AA battery DVM display screen e 143 AA battery circuit floating 02020000 2 ee ee ee 144 AA battery wi
130. or values on the board For larger input ranges there are solder pads on the input circuit for adding resistor dividers For smaller input ranges the gain of the front end op amp amplifier must be increased The location of the resistor dividers for setting larger ranges is on the circuit diagram page A D signal conditioning resistor pairs R402 x R404 x and R403 x R405 x You can also populate the capacitors in this area of the circuit if RC filtering is required Use matched components to keep the differential inputs balanced One popular larger input range is 10 volts This is fairly common with active sensors with op amp outputs For this range leave R402 x R404 x at their factory 10K values and populate R403 x R405 x with 6 67K ohms You don t have to use exactly 6 67K resistors Values making the input range a little larger than 10 volts will leave a little headroom which may be helpful Note that populating the resistor dividers also sets the input impedance This is usually not a problem for active sensors with low impedance outputs 9 7 Op amp gain There are also solder pads on the board to increase the front end amplifier gain so the input voltage range is smaller than the factory 4 volt default See the circuit diagram pages A D input amplifiers and resistors R410 x R412 x R413 x The resistor R410 x is commonly referred to as the gain setting resistor RG while R412 x and R413 x are the feedback resi
131. ossible the USBxCH can time stamp with NTP network time protocol Although less accurate NTP is useful when the open sky visibility GPS requires is not available NTP time stamping is covered in the next chapter 13 1 What is GPS GPS is a system of orbiting satellites transmitting signals designed to determine location and time at receivers on the surface of the Earth A GPS receiver uses multiple satellites to triangulate its location and then computes precise time by making propagation delay corrections The final time accuracy far exceeds traditional methods like WWV By far the most popular use of GPS is to determine location for travel and mapping However for many applications accurate time is equally essential allowing for the precise correlation of analog data between widely separated installations GPS receivers are surprisingly small often no larger than a hockey puck If your cell phone appears to receive GPS it may not actually have a GPS receiver but only receive GPS information from its base stations True GPS receivers are complete stand alone units that 109 receive satellite signals directly One downside to GPS is buildings cement and other obstacles may all interfer with reception In those cases a long cable may be required to place the GPS receiver where reception is possible Some GPS receivers combine their antenna and receiver into the same enclosure while others separate the two If the antenna and receive
132. out GPS antennas the PCTIME option uses the PC 33 clock as the time source Note that if PCTIME is the time source then the PC clock will provide time even if a GPS antenna is connected to the system To process GPS time you must specify a GPS source For details about using GPS with the USBxCH see the GPS Time Stamping chapter nFiles specifies how many total output files will be created Blast will terminate once nFiles have been written If nFiles is not given the program will create output files forever or until a keypress is made You can also terminate the program from the operating system with Task Manager nokeypress specifies Blast is to start acquiring data with no keypress required The default behavior waits for a keypress to begin acquiring so you can have a chance to read the on screen run time summary message UserCfg is passed to the Open function inside Blast See the User C Library for information about Open and the User configuration byte for bit assignments UserCfg should be a two digit C style hex number like 0x14 When staring up Blast will display a summary report of the parameters it is running with on the screen This gives you an opportunity to verify the system is actually using the parameters specified on the command line A copy of the summary report with the filename 000 Blast Run Summary rpt is also placed in the YMDHMS data directory for a permanent record of the run After the summary display
133. output files will be listed on the screen as they are created Output files are all placed in the YMDHMS data directory for the particular run See the next section for a complete description Each time Blast runs a new data directory is created When running with nFiles not specified output files will be created forever You can terminate the run by pressing q on the keyboard or killing the Blast process with the Task Manager A few typical Blast command lines are blast s3 acquire at 39Hz use PC TIME blast s3 g0 acquire at 39Hz without any time stamps blast s3 g2 acquire at 39Hz with a Garmin antenna blast s10 nokeypress blast s11 0x04 blast s8 100 blast s8 acquire at 4 8kHz no keypress to start acquire at 9 7kHz enable Adrdy on DB25 acquire 100 files at 1 3kHz acquire forever at 1 3kHz q quits NA AAA AA 34 Starting Blast with gt blast s7 g2 nokeypress results in the screen C SR USBXCH Blast gt blast s7 nokeypress USBXCH Blast Acquisition Program c SR 2009 Rev 2009 09 06 sn s7 UserCfgByte 0x00 DriverName SrUsbxXchO XchModel USB4CH GpsModel GARMIN SamplingRate 651 041667 Hz Data directory 2009 10 02 at 15 26 13 nFiles run forever FilePackets 651 FileBytes 41664 FileSeconds 2 Acquisition starting file 2009 10 02 at 15 26 13 00000000 file 2009 10 02 at 15 26 13 00000001 file 2009 10 02 at 15 26 13 00000002 file 2009 10 02 at 15 26 13 00000003 file 200
134. particularly important the ground wire be of sufficient gauge If the ground wire establishes system ground and all signals are referenced to it then any ground bounce will cause false signaling and digital errors 123 15 2 Voltage and current requirements The USBxCH requires only a single positive power supply The supply must be DC AC supplies that are directly from an AC transformer will not work So for example the power from a 9vde 500ma unregulated wall transformer is acceptable while that from a 9vac 500ma wall transformer is not The off board power is conditioned and regulated by active circuitry on the USBxCH In fact there are multiple linear regulators to generate the precision voltages required for 24 bit A D converters See the Power supply circuit diagram pages Off board power may vary over a wide range The minimum is 8 volts and the maximum 24 volts If the power goes below 8 volts the board will detect the error and indicate it by turning on the back panel red LED as well as setting the power status flag to an error If you use an unregulated DC wall transformer it is ok to have 50 60Hz power ripples as long as none of the ripples go below 8 volts AC wall transformers do not meet this requirement and the red LED will light up If possible power supplies in the range of 9 to 12 volts are recommended Because the USBxCH uses linear regulators and consumes approximately 100ma regardless of supply voltage the excess
135. plot command does the serious work everything else is setup Refer to the GnuPlot PDF documentation for details After running the following should appear on the screen SER1CH UA Solar Panel Data a Light very close 4k Solar panel voltage Volts af ye Light off Figure 19 13 GnuPlot graph 157 For including the plot in a report you ll probably want to save it as a PDF file Other formats are possible read about them in the GnuPlot documentation For PDF first run GnuPlot to output a ps PostScript file and then convert this file to PDF The conversion to PDF can be done with either Abobe Acrobat Distiller or the public domain GhostScript In the examples directory we show how to do it with GhostScript commands 158 19 8 Passive geophones Work underway 159 19 9 Multiple USBxCH and network processing Work underway 160 19 10 Powering with batteries For portable applications the USBxCH can be powered from batteries The system requires 100 ma of current at 8 volts or greater and it is entirely possible to run from AA and larger batteries for periods of days Rechargeable batteries are particularly attractive Two popular technologies are NiMH nickel metal hydride and lead acid This example shows how to use eight rechargeable NiMH AA cells to power the system and also a small 3Ah amp hour rechargeable lead acid battery NiMH rechargeable batteries are readily available and
136. r are separated they will be connected by a RF coax cable With either type of packaging there is a final cable from the receiver with digital signals indicating the location and time It is these digital signals the USBxCH requires to time stamp and locate its data Two major GPS manufacturers are Garmin and Trimble Garmin receivers usually com bine the antenna and receiver into the same enclosure while Trimble often has a separate antenna The USBxCH is compatible with both of these brands and many others The general nature of the final GPS digital output is reasonably standard and the USBxCH has programmable features to accommodate several of the common variations As a specific example this chapter will show how to connect a Garmin GPS 16x HVS 13 2 Required GPS signals The USBxCH requires two specific digital outputs from the GPS receiver The first GPS output is a RS232 serial signal This signal has location and coarse time in formation It is comprised of ASCII strings which are emitted once per second in predefined formats with the most popular being NMEA national marine electronics association for mat Because NMEA strings are only emitted once per second it is difficult to determine time to better than one second with them alone and so The second GPS output is a PPS pulse per second TTL CMOS signal The leading edge of this signal is precisely aligned with the global GPS second tick The accuracy of the PPS edge is u
137. rUsbXch0 1 2 3 etc The device name is required for later use with programs and library functions If this is the first USBxCH installed on the computer it will be SrUsbXchO0 lt lt device name 13 To remove the driver use the DevMan utility It will delete the operating system copies of the driver files and corresponding registry entries 2 6 Run Diag After hooking up power and connecting the USB cable run the Diag utility to confirm proper operation This will check the hardware and give an error report if there are any problems Diag can be executed from the command line or by double clicking on the Run Diag Install shortcut icon From the command line type cmd prompt gt Diag install Run Diag without any command line options for a help screen If you feel the system has a hardware problem run Diag debug and email the report and log files to SR 2 7 Run DVM or Scope After running Diag users should test acquiring data with DVM or Scope Each comes in both GUI and command line versions For quick starts with default parameters double click on the shortcut icons When running it is tempting to touch the analog input pins to apply small voltages Avoid the temptation to do this You will inadvertently discharge static electricity into the inputs Even small static shocks such as those from walking on a carpet will do damage Generally the damage is cumulative with calibration and analog performance steadily degraded
138. ramming the ADS1255 Data Rate DR register with the number of averages NumAvg to be performed on the oversampling From the TI ADS1255 data sheet SPS rate Fclkin 256 1 NumAvg SPS rate 39 062 50 NumAvg where the second equation is with a 1OMHz Fclkin master clock The following table gives the possible SPS rates rounded to four decimal places SPS RATES FOR USB4CH 10 000 MHz Fclkin master clock DR 7 0 NumAvg SPS rate 11110000 1 gt 39062 5000 Hz 11100000 2 gt 19531 2500 Hz 11010000 4 gt 9765 6250 Hz 11000000 8 gt 4882 8125 Hz 10110000 15 gt 2604 1667 Hz 10100001 30 gt 1302 0833 Hz 10010010 60 gt 651 0417 Hz 10000010 300 gt 130 2083 Hz 01110010 500 gt 78 1250 Hz 01100011 600 gt 65 1042 Hz 01010011 1000 gt 39 0625 Hz 01000011 e 1200 gt 32 5521 Hz 00110011 2000 gt 19 5313 Hz 00100011 3 3000 gt 13 0208 Hz 00010011 6000 gt 6 5104 Hz 00000011 12000 gt 3 2552 Hz Figure 6 1 USBxCH sampling rates with 10 MHz master clock Only program the DR register with the above values Although it might appear other NumAvg values could be specified in the DR register only the values listed above are valid See the TI ADS1255 spec sheet 75 6 2 Master clock stability Of course all parts have tolerances and the USBxCH master clock is no exception The 10MHz clock used on the USBxCH is a TCXO temperature compensated xtal oscillator with an initia
139. raph here Figure 10 3 Production input offset spreads 99 Chapter 11 Analog AC calibration Suppose you have a sinsuoidal input How does its amplitude and phase get modified by the USB4CH Clearly the response will depend on frequency and one could measure it frequency by frequency to develop a curve While the response can be measured one frequency at a time the AC transfer function can be computed even more quickly and easily by measuring the response to a single square wave step input Since a square edge contains Fourier components of all frequencies the entire response can be computed with one test run This is the method followed here In the experiment a USB4CH DB25 digital output is used as the square wave stimulus and the time base of the input and output will be measured with the GPS timing system See later chapters for details on these capabilities Using these tools the physical measurement of the AC response is easily carried out If you have custom electronics ahead of the USB4CH you can even use the DB25 digital output to measure the response of your front end and USB4CH combined Simply move the DB25 square wave from the USB4CH DB15 analog input to your front end inputs and use the same techniques as reviewed here 100 11 1 Theoretical AC transfer function The dominate component of the USB4CH AC frequency response comes from its A D converters Because all sigma delta converters oversample their input
140. reater than the 4 volt USBxCH input range To solve this use a simple resistive divider to scale the battery voltage into range Keep the divider resistances reasonably high so the divider doesn t drain much additional current from the battery The following circuit is one example What approx 9 6 volts MEASURING BATTERY VOLTAGE Vbat 10 USBxCH 8 AA cells in series Figure 19 15 Dividing battery voltages for USBxCH measurement To acquire the data use the Blast acquisition program at a low sampling rate There really isn t much point to sampling at high rates The following would be typical cmd prompt gt Blast si gi nokeypress The s1 option specifies sampling at 19 5Hz while the g1 option uses the PC clock to time stamp the data After the run use the Pak2Asc utility to convert the binary PAK files to ASCII columns As an alternative to Blast you could also use the DVM program to gather data and even have a real time display of the battery voltage during the run While measuring the battery voltage with Blast check the red LED on the USBxCH back panel near the 2 1mm power connectors When the battery voltage drops low enough the red LED will light up indicating it is too low for the on board regulators to function 162 correctly At this point the run is over and it is time to stop Blast The condition of the red power good LED is also given as a column in the Pak2Asc output file
141. requiring additional mea sures to guard against Two examples are magnetically coupled noise and thermocouple effects Both of these can degrade microvolt measurements By Faraday s Law whenever time varying magnetic flux lines d dt cross the wire loop formed by the input cabling a noise current will be generated While such noise can occur at any frequency by far the most common is 50 60Hz powerline noise At many installations the wall power wiring is close enough and surrounds the work area sufficiently to magnetically couple to the USB4CH input cabling The action is like a transformer with the wall wiring as primary and the USB4CH input cabling as secondary Varying 50 60Hz magnetic flux lines cutting input loop USBxCH CHO CHO AGND Generates EMF across loop and sensor impedance Figure 9 7 Magnetic coupling of 50 60Hz noise Because the voltage generated by the varying flux is in series with the differential loop it is not removed as common mode noise The best defense against this type of noise is to prevent it from entering the system in the first place According to Faraday s Law reducing the area of the cable loop will reduce the EMF voltage generated Placing or binding the leads close to each other as might be done with flat ribbon cable will help However even more effective is using twisted pair cable The EMF generated by magnetic flux lines cutting each small twist has opposite pola
142. riments Even transistor radio 9 volt batteries can be used although their voltage is high enough so clipping will occur even in the floating case The USBxCH inputs will not be damaged or harmed with the 9 volts of overvoltage E Do not attempt to measure high voltages such as 110 220 vac from the wall socket with the USBxCH Not only are such voltages life threatening with the types of connectors on the system you will also instantly destroy the front end circuitry and void the warranty If you must measure high voltages use resistive dividers TVS Zener overvoltage protection and suitably insulated connectors in front of the USBxCH 145 Finally note the USBxCH AGND is connected to its power supply ground as well as the PC ground when making measurements Because of this a ground connection is often present in ways you might not expect For example if you are using a desktop machine AGND is connected through the USB cable ground wire to the PC ground which in turn is probably connected to the PC chassis and the third prong on the wall power At the same time if you use a signal generator also powered from wall power it is probably connected to wall ground This completes a ground loop you probably didn t expect and provides opportunities for noise contributions Review the entire system carefully to avoid hidden ground connections you didn t count on Measured with respect to AGND
143. rity from one twist to the next and cancels out The technique is surprisingly effective see Chapter 19 Examples and Experiments Note that 90 even the flat areas on twisted pair ribbon cable can cause trouble Discrete wire twisted pairs give the best performance Shielded cable is not particularly effective against magnetic coupling You will have better results with simple twisted pair in reducing 50 60Hz noise Shielded cable is excellent for ESD protection and is discussed in the next section Thermocouple effects are another common problem Whenever two dissimilar metals are connected together they generate a temperature dependent junction voltage For a copper to tin lead junction as might occur in a solder joint the voltage is 3 microvolts C This can be a substantial noise contribution at 24 bit sensitivity The way to battle against thermocouple noise is to keep both the and differential inputs exactly balanced with metal to metal junctions If a junction is introduced on the side add one to the side even if it is not needed By keeping the thermocouples exactly the same on the both sides the differential signaling will cancel the two equal sides If the sides are kept in the same thermal bath the cancellation will be exact across all operating temperatures 9 4 Static shielding Electrostatic discharge ESD events directly into the DB15 analog inputs are guaranteed to damage the USB4CH This is not maybe i
144. river build version If they are different you will have to recompile Source code is provided so Linux users can rebuild for their particular kernel SR attempts to stay current with recent kernel revs but does not offer support for older revs 2 4 Hook up power For connecting power to the USBxCH do the following v Find the wall transformer Look for the wall transformer included in the shipping box US customers will have a 110 vac unit while international customers may have a 220 vac unit The output of the wall transformer should be rated at 9vdc 500ma Note that the USBxCH is not powered from the USB cable You must use the supplied wall transformer or other equivalent power source In USB terminology the USBxCH is a self powered device v Plug the wall transformer into the wall Do not plug a 110 volt transformer into 220 power with simple adapters that do not change the wall voltage The wall transformer will simply output the wrong voltage and probably burn up 11 JV Plug the 2 1mm barrel connector into the USBxCH Plug the 2 1mm barrel connector at the other end of the wall transformer cable into either USBxCH back panel power jack There are two jacks on the back panel in parallel for daisy chaining power to other devices if needed Make sure the connector is fully seated into the jack y Is the green LED on If the wall transformer is energized at all the green LED on the back panel near the 2 1mm power jacks s
145. s Apply input signals to the USBxCH then click the measure buttons Click sawe to write the calibration results and exitto end the program Channel lo Ne Title Units Places Digits Value A Value B Voltage Volts 5 3 3 000000 3 000000 Format Counts A Counts B 5 123 3163100 3163532 Measure Measure B Status messages display here Figure 3 4 DVM Calibrate screen To start the program execute either CalGui exe or CalCmd exe from the command line or double click on one of the provided shortcuts Approximate calibration into volts is provided in the DvmSetupVolts ini file included with the software However because 23 all A D converters references and resistors have tolerances precision calibration must be performed on each individual system and channel Absolute calibration requires a lab grade reference with repeatable fixed voltages For such applications the SR VREF 399 heater stabilized precision reference may be useful see www symres com Applications not requiring absolute calibration may find ratiometric techniques helpful See the Examples and Experiments chapter for an absolute calibration demo an example of calibration into physical sensor units and a ratiometric experiment For a discussion of the number of A D counts per volt see the Analog DC calibration chapter 24 3 2 Scope Scope is a USBxCH acquisition program for acquiring and displaying data in real time as horizontal traces on th
146. s and then signal average they impose a strong low pass filter characteristic on the response A normalized average of a sinusoid with many cycles in the averaging window tends towards zero and thus the low pass response Nothing else in the system has a comparable effect In this section the theoretical amplitude response will be reviewed and in the next section the USB4CH response will be experimentally measured for comparison From the TI ADS1255 spec sheet the theoretical transfer function for the A D converter is A f sine x x sinc N Normalization When plotted this gives the curve theoretical AC response graph Figure 11 1 AC response theoretical sinc which has the familiar low pass bouncy ball response one would expect from a finite length numerical average As the input frequency increases when the wavelength agrees with the averaging length the output falls to zero 101 11 2 Measured AC transfer function The experimental setup to measure the AC frequency response is line drawing of response measurement setup Figure 11 2 AC response physical measurement setup Beyond the A D response review the contribution of the op amp and RC signal condition ing front end 102 Chapter 12 Digital IO The USB4CH has digital io in addition to its 24 bit analog inputs The digital interface can be used for simple communication with external equipment and sensors The digital io is
147. s of ini keywords in programs like Scope 12 7 Triggering The leader length is fixed at 100 samples regardless of sampling rate 12 8 Programming the front panel red and yellow LEDs Call the user library function SrUsbXchUserLed to program the front panel red and yellow LEDs Note the red LED can serve two different functions Its power on default is to toggle on and off with every tick of the PPS signal on the DB25 connector The function can be changed to user programmable by changing the PpsLed Toggle bit in the UserCfgByte 12 9 Seeing the digital inputs in Scope Use the Scope application to see the digital inputs in real time The inputs are sampled in real time and saved synchronously along with the 24 bit analog data 108 Chapter 13 GPS Time Stamping If you have a GPS receiver you can probably use it to accurately time stamp data acquired with the USBxCH Using a particular receiver is often only a matter of making the ap propriate cable connections If you don t have a GPS receiver Symmetric Research can provide ready to go antennas with the required cabling Besides GPS time stamping the USBxCH also saves real time GPS latitude and longitude information This can be useful for mobile applications as well as for fixed networks with multiple systems that must know locations to triangulate Both GPS time and location are saved continuously as part of the USBxCH data stream For sites where GPS reception is not p
148. sfully for awhile then run cmd prompt gt Diag debug and email the files SR USBxCH Utilities Diag 300 Diag History log SR USBxCH Utilities Diag 301 Diag Last Run rpt to Symmetric Research for technical help Do not delete earlier entries in the history log They may provide clues for debugging SR help email address info symres com 42 4 2 DevMan DevMan is a command line utility to manage USBxCH device drivers once installed on a PC For initial driver installation rely on the operating system Plug and Play capabilities as described in the Getting started chapter The DevMan command line syntax is cmd prompt gt DevMan showall wakeall removeall where only one optional parameter may be specified at a time and running without any options or with a will give a usage message The parameters are as follows showall scans the registry for all USBxCH references showing both active and inactive instances Also shows the related sys and inf files in the Windows driver directories Plugging a USBxCH into different USB ports on the PC results in an instance of the USB driver each time This option shows all symbolic device names and current status for each instance wakeall if the PC is put into a sleep state while USBxCH devices are plugged in and active they will not be active on wakeup This is an acknowledged OS level error for Windows and self powered USB devices Running DevMan wakeall will wakeup al
149. sole purpose of Blast is to save data to disk quickly It does not have a GUI display or even a real time text display of the data If you need a text display of the data please refer to DvmCmd or ScopeCmd Because it uses the minimum PC resources possible Blast is a good match if you need to make the most of the CPU and disk bandwidth available on a particular computer Use the Pak2Asc and View utilities for easy ways to review PAK output files If you are writing custom software Blast is also a good example to use as a starting point for your source code development By comparison DVM and Scope have much more complicated user interfaces The following sections review particular aspects of running Blast e Command Prompt C SR USBXCH Blast gt blast s7 nokeypress USBXCH Blast Acquisition Program c SR 2009 Rev 2009 09 06 sn s7 UserCfgByte 0x00 DriverName SrUsbXchO XchModel USB4CH GpsModel GARMIN SamplingRate 651 041667 Hz Data directory 2009 10 02 at 15 26 13 nFiles run forever FilePackets 651 FileBytes 41664 FileSeconds 2 Acquisition starting Writing file 2009 10 02 at 15 26 13 00000000 Writing file 2009 10 02 at 15 26 13 00000001 Writing file 2009 10 02 at 15 26 13 00000002 Writing file 2009 10 02 at 15 26 13 00000003 Writing file 2009 10 02 at 15 26 13 00000004 Writing file 2009 10 02 at 15 26 13 00000005 Keypress abort C SR USBXCH Blast gt Figure 3 8 Typical Blast
150. stors RF To keep the differential inputs balanced make the RF resistors are equal and closely matched Assuming equal RF values the transfer function for the differential gain is Vout Vout 1 2 RF RG Vin Vin so with the values RG 1K and RF 10K the differential gain would be 21 When pop ulating for unity gain leave RG empty infinite ohms and set RF O with a zero ohm resistor This avoids offsets due to op amp input bias currents flowing through RF 93 9 8 RC antialias filtering There are number of places on the input circuit where capacitors can be added for simple RC filtering The capacitors are populated at the factory as follows C400 x C401 x These are for snubbing ESD events on the inputs The 47pF value snubs ESD but still does not put much capacitive loading on active sensor outputs which might oscillate if overloaded C406 x C407 x C408 x If your site has radio frequency contamination aliasing into the measured signal these locations can be populated to provide some RC filtering They are left empty at the factory C412 x C413 x Populate these if you wish to roll off the amplifier response Leave these un populated if running the OPA2277 at unity gain C414 x C415 x It is critical these locations are populated with 220pF values to avoid OPA2277 oscillations The capacitive load presented by the input circuit of the ADS1255 must be compensated for with capacitors in th
151. sually within a few microseconds where expensive receivers may even achieve nanosecond accuracy The USBxCH is designed to use PPS in conjunction with the RS232 NMEA strings to time stamp acquired data entirely on board The time stamping is done automatically with a dedicated FPGA Accuracy is maintained regardless of cpu loading interrupts USB activity or other system considerations 13 3 DB25 pin assignments The GPS receiver outputs must be connected to the USBxCH front panel male DB25 connector If your GPS receiver has a cable with wire ends you should use a female DB25 connector to make the connections The following table gives the USBxCH DB25 GPS pin assignments along with a line drawing of the front panel connector in Figure 13 2 These pins are also covered in the Digital IO chapter 110 DB25 pin GPS signal USBxCH Power on polarity Top row 11 PPS input idle low active high 12 RS232 NMEA RX input idle high 13 RS232 NMEA TX output idle high Bottom row 14 25 Ground Figure 13 1 DB25 GPS pin assignment table All signals must be reference to the USBxCH DB25 ground pins This is crucial Any noise glitch or grounding problems with respect to the USBxCH will result in unreliable time stamping It is the user s responsibility to provide clean GPS signals at the front panel DB25 in order to have reliable time stamping lt lt GPS NMEA RX C lt GPS N
152. t is guaranteed Even though the system may appear to continue working correctly at a minimum calibration will be changed with each ESD event Of course drastic ESD events such as lightning strikes deliver irreversible damage that is visible For such installations ground rods gas arrestor tubes TVS zener diodes and cable shielding should all be used as protection However at the other end of the spectrum even a mild spark generated by a finger touch from walking over a carpet will also cause damage and should be protected against Surprisingly the most likely components to be damaged from ESD finger touch events are the series input resistors R402 x R403 x and not the integrated circuits See the circuit diagram page A D signal conditioning Each mild ESD event vaporizes a little bit of the resistor metalization changing the input characteristics The damage is interior to the resistors and will not be visible It is cumulative with each event vaporizing a little more metalization Eventually the resistor is blown open much like a fuse and the channel will appear to have failed If you have a channel go dead it is easy to see if the series input resistors are compromised Measure their resistance with a multimeter such as a Fluke If they measure higher than the value listed on the circuit diagram then they have been damaged and should be replaced One function of the input series resistors is specifically to help guard against ESD ev
153. t number T968 P5P ND 9vdc 500ma 2 1mm plug 110vac input US MFG part number CUI Inc DPDO90050E P5P SZ DK part number T973 P5P ND 9vdc 500ma 2 1mm plug 220vac input Euro Switching regulated wall transformers are not particularly recommended No damage will occur but switching regulators introduce high frequency noise into the system Simple un regulated DC wall transformers listed above provide a low noise supply Linear regulated supplies are equally low noise Twisted pair shielded cable MFG part number Belden 9501 MO part number 566 9501 100 Twisted pair provides reasonable powerline noise immunity for analog inputs This Belden cable also has a foil shield for ESD protection and is jacketed There are a large number of cable types available The above is only one example Double twisted pair shielded cable MFG part number Belden 9502 MO part number 566 9502 100 If necessary cable with multiple twisted pair inside one shield is available There is no particular advantage other than having more connections inside one jacket Potentiometers 10 turn 10K ohm MFG part number Vishay Sfernice 53411103 MO part number 594 53411103 MFG part number Bourns 3540 series DK part number 35405 1 103 ND A 10 turn pot is a simple and reasonably accurate sensor to use when testing the USB4CH or for angular measurements DVM can be easily calibrated into turns or other units if necessary 174 Potentiom
154. tadirectory 00000000 pak csv 46 this will convert all of the sequential files in mydatadirectory leaving the results there in a single large ASCII file Conversion is a multipass process with intermediate files The names of the files created by Pak2Asc are Pak2Asc 100 SamplePackets pak Pak2Asc 101 StatusPackets pak Pak2Asc 200 TimelnfoSample asc Pak2Asc 300 TimelnfoStatus asc Pak2Asc 301 Nmea asc Pak2Asc 400 TimeInfoAll asc Pak2Asc 500 Data asc The last file Pak2Asc 500 Data asc is the name of the final large output file with all of the combined data For csv format the final data file will be given a csv extension The intermediate files may also have information you find useful Pak2Asc has verbose screen output It reports the input files it processes information about each processing step and the output files created To run silently simply redirect the screen output to a report file with cmd prompt gt Pak2Asc 00000000 pak fw gt pak2asc rpt Techniques for automating the processing of data from multiple acquisition runs is covered in the Blast section typical post processing For a ready to go example see the batch file SR USBXCH Utilities Blast Pak2Asc Convert All bat For an example of importing ASCII data into a plotting program see the Examples and Experiments section GnuPlot The techniques used with GnuPlot are similar to those that would be used with other plotting and analysis programs 47 4 5 Interp
155. tal readouts channel titles are on the left and display units on the right The titles and units can be specified independently for each channel in the DVM ini file Across the top of the screen is an Alt menu with various program actions With the Alt menus you can start and stop acquisition edit the ini file and bring up a help screen Each Alt menu item has a speed key for keyboard users Note that even the ini editor can be specified in the ini file Notepad is only the default Users wanting to change the display units will need calibration coefficients The DVM Calibrate program can be used to compute the required slopes and offsets and automatically save them to an ini file 20 3 1 4 DVM command line version If you like the data acquired by DvmGui but only want to run a modest user interface without a full graphical display then the DvmCmd text only version of the program may be useful The DvmCmd output screen looks like this e Command Prompt C SR USBXCH DVM gt DvmCmd exe DvmSetupVoltage ini Ini file DvmSetupVoltage ini Out file DvmOutputVoltage asc Press enter to start acquisition press enter again to Sample Channel O Channel 1 Channel 2 Channel 3 Time YMD HMS Volts Volts Volts Volts 2 00982 3 01491 0 00256 1 55459 2009 08 11 23 25 01 859 2 00982 3 01493 0 00104 1 55459 2009 08 11 23 25 02 906 2 00982 3 01492 0 00004 1 55460 2009 08 11 23 25 03 953 2 00982 3 01492 0 00074 1 55
156. th see Scope rpt for more details srusbxcho USB4CH PCTIME 651 041667 Hz None AtodDriverName AtodModelName GpsModelName TrueSamplingRate TriggerType Press ENTER to start then ENTER again to quit 10 02 09 10 15 52 Message Starting acquisition for first buffer block 00 gt Scope tmp block 01 gt Scope tmp block 02 gt Scope tmp block 03 gt Scope tmp block 04 gt Scope tmp block 05 gt Scope tmp block 06 gt Scope tmp block 07 gt Scope tmp block 08 gt Scope tmp block 09 gt Scope tmp Scope tmp renamed to 00000000 dat Buffer 0000000A block 00 gt Scope tmp 10 02 09 10 15 58 Message Stopping acquisition 10 02 09 10 15 58 Message Ending Scopecmd C SR USBXCH Scope gt Figure 3 7 Scope CMD screen If you don t want even this amount of display there are ini keywords to turn the display off entirely This can be useful for headless node single board computers only wanting to save their data to a file Note that ScopeCmd uses the same ini keywords as ScopeGui You can refine keyword value selections with ScopeGui and then move them over to ScopeCmd without change 29 3 2 5 Scope output file names Scope output files are saved to disk in the DAT file format This is a binary format comprised of a header and data records as described in the next section This section describes the Scope output file name conventions Two ini keywords control the output file names and si
157. th AGND connection 2 20 0 0 ee ee ees 144 AA battery circuit grounded 0 00002002 eee eee 145 AA battery 6 volt circuit 2 2 ee 146 TO CUTA CICULI ia ats fae ah a Oe ee ee eB a a Sa A 149 10 tura photo ROD 2 ae oe ek ee ee ee bo ee Ra we Sew 150 Titi photo DOOM ua Monee Bk ee ee oe ba daa 151 10 turn Calibrate sereen n ooe e s e a ee A ee eA eS 152 10 turn DVM display screen e a so e uoa oaa e ee a k ee 152 Solar cell light level measurements sooo a 155 GuuPlot graph acs sos a Goa a hoac a aa a AA 157 NiMH AA battery pack aaa eee ee eee 161 Battery voltage dividers a acc ea ae a ge kee a ee Ge aa S 162 NiMH AA battery pack discharge plot 2 2200 163 Lead acid SAh battery cas esa ea acp d adoa e 164 Lead acid 3Ah battery discharge plot a a oaa o 165 Chapter 1 Introduction The Symmetric Research USB4CH is a precision 24 bit analog and digital data acquisition system for use with computers having USB ports The system has four independent analog input channels four digital inputs four digital outputs and a GPS interface A key feature of the USB4CH is each of its four analog input channels is equipped with its own 24 bit A D converter This avoids channel crosstalk and skew problems that are common with systems having a single multiplexed A D Some other leading features of the USB4CH are e Simple USB PC interface for plug and play installation e Simultaneous s
158. the system down with a timer for a complete system reset 15 6 Current limiting Power consumption on the USBxCH is current limited The current drawn from the power supply will never be more than 350ma This includes power up inrush current There are active power clamps enforcing a hard limit on the power Normal power consumption after inrush current has subsided should be approximately 100ma If more current is being consumed then something is wrong and should be fixed If the USBxCH is in current limit mode the regulator heat dissipation will be excessive Extended periods at the peak power supply voltage of 24 volts with the back panel red LED continuously on will push the thermal limits of what the board can withstand The system will survive but turn the system off and diagnose the problem 126 Chapter 16 Temp Sensor The USB4CH is equipped with an onboard temperature sensor which records the board temperature once per second With this information you can perform system level tem perature corrections that include the effects of voltage reference op amp and resistor T C drifts The physical temp sensor is a Microchip TCN75 A manufacturer spec sheet is included in the Docs ChipSpecs directory The component has a max error of 2 C from 40 to 120 C Of course the temp sensor does not record the temperature at the exact location of the voltage reference or any other particular component However being a multilayer boar
159. tionship of input volts to counts 9 1 Differential signals The USBxCH has differential analog inputs Although many users are probably more familiar with single ended inputs differential inputs have many benefits Even though the system can be used in single ended fashion differential signaling is recommended for achieving the highest precision The concept of a differential signal is as follows On the USBxCH each analog channel is equipped with three inputs AGND The A D count for the channel is given by the voltage difference between the pins A D counts slope V V offset where the slope and offset are the Analog DC calibration and V V are measured with respect to AGND The advantage of this is any noise which is common on both the and pins is subtracted away and not part of the final returned value Common mode noise rejection with differential signals is a powerful way to reduce ground noise which is present on almost every system Note that the differential pin is not ground It is an input just like the pin with the only difference being its effect on the A D counts is inverted In fact you can reverse the 84 connections on any test setup and all that happens is the count values are inverted Note that if you are making a single ended connection you could just as well tie the pin to AGND and connect the signal to the pin Everything would work the same as the more commonly imple
160. uracy 0 5 millivolts Max TC 0 6 ppm C Typical TC 0 3 ppm C Temp range 40 to 85C Package hybrid DIP SMT 8 This is representative of the very best in the REF02 class Besides having excellent tem perature compensation the hybrid technology has been specifically designed to relieve variations due to mechanical stress There are also acceptable devices comparable with the standard TI part listed above from companies such as Analog Devices Linear Technology etc Check their spec sheets for suitability 82 8 3 TC correction with on board temp sensor Rather than shopping for the most precise reference an alternative is to thermally cali brate the USBxCH Thermal calibration can be used to correct for many system level TC variations as well as the analog reference variations With the USBxCH on board temp sensor the board level temperature is continuously recorded once per second The temp record is automatically saved with the analog data stream so it is always available Once a calibration has been performed it can be used as correction Work underway 83 Chapter 9 Analog inputs This chapter reviews the USBxCH analog inputs General information is given covering the nature of differential inputs the front panel DB15 connector pin assignments appropriate cabling techniques and how to adjust the front end circuitry for custom input ranges and other options See the Analog DC calibration chapter for the exact rela
161. vices can serve as remarkably good sensors for other parameters Silicon diodes as temperature sensors and LEDs as light sensors are examples There is also a huge variety of prepackaged sensors for measuring parameters of every type See your favorite electronics catalog as in the Extra supplies chapter for possibilities Regardless you can use the Calibrate program to create a DVM readout in physical sensor units Some will observe there is a flaw with the core equation we have used in this example It comes from the expression Vwiper Voat 10 T The wiper voltage is not only a function of the physical number of turns T but also depends on Viar Any change in the battery voltage will result in a change in the number of turns reported on the DVM screen regardless of whether the physical turns on the potentiometer changed or not You won t have to work with the system very long before you notice changes in the battery voltage because of discharging or changes in temperature have an effect At 24 bits even a small drift becomes apparent What can be done One solution would be to use a battery or reference that has an extremely constant output across time load and temperature The SR VREF 399 is an example of a stable potentiometer excitation source that would be suitable However for sensors like potentiometers with outputs proportional to their stimulating voltage there is an even better way ratiometric techniques Ratiometric methods ar
162. whether the power is sufficient for the on board regulators to run correctly If the back panel red LED is off then power is ok Conversely if the red led is continuously on something is wrong and must be fixed before the system will run Momentary flashes of the red LED during power up lasting for two seconds or less are normal See the Power Supply chapter for more information After a few seconds if the red LED is off and the green LED is on the system is good Does the USB4CH have any digital buffering Yes It has a 2 Mbyte FIFO buffer for storing data so results can be read back over the USB cable when the PC has available time The FIFO prevents data loss even if the PC is heavily interrupted with other activities such as graphics or networking See the FIFO Depth and Overflow chapter for details on exactly how long the system can hold out before requiring service from the PC What is the analog input voltage range The analog inputs may vary from 4 to 4 volts for valid count values to be returned This is the voltage range on any input pin as measured with respect to AGND The analog inputs are differential with AGND pins See the Analog Inputs chapter for more details on the input range and differential signals For larger full scale input ranges there are solder pads on the board for resistor dividers For smaller full scale ranges the front end amplifier gain may be increased by adjusting the RG and RF resistors
163. with each ESD event If you must touch the input pins touch the metal enclosure immediately before doing so This will help discharge any static Better yet wear an antistatic wrist band clipped onto the front panel See the Analog inputs chapter for details on the analog input voltage ranges and differential signals For introductory hands on usage see the Examples and Experiments chapter 2 8 Linux USB port permissions Many Linux users will have installed the USBxCH driver while logged on as root and all will run fine but when they log on again as a regular user there will be trouble The problem is under Linux there are not only file permissions there are also USB hardware port permissions By default the hardware port permissions are often set to root and if you want to run as a regular user you will have to change them 14 The steps for changing the Linux USB port permissions are covered in the file usr local SR USBXCH Driver 000 ReadMe txt If you are already in the usr local SR USBXCH Driver directory the basic step is to change the udev device rules You can do so by executing cat 40 permissions rules gt gt etc udev rules d 40 permissions rules and then rebooting as a regular user to reload the new rules For Linux experts the contents of the 40 permissions rules file are Contents of 40 permissions rules Symmetric Research USBxCH device create with permission for all users BUS usb SYSFS idVen
164. ynchronous analog and digital recording e High precision 24 bit A D converter per channel e Analog input range of 4 volts balanced differential e Response to true DC sampling rates to 9 7kHz e GPS time stamping with 800 nanosecond accuracy e 2MbFIFO buffer for no analog or digital data loss due to PC latencies e On board continuously recorded temp sensor e Finished ready to go applications as well as User function library e Windows XP 7 and Linux support with kernel mode drivers e Free web software downloads This manual covers the software and hardware aspects of the USB4CH Also see the ReadMe txt files in many of the software directories for further information We hope the USB4CH is a useful tool for your applications Figure 1 1 mini Netbook with USB4CH and geophone One popular USB4CH configuration is with a mini Netbook for portable data acquisition In the photo above the small cylinder is a geophone a passive sensor used for seismic surveys A wide variety of other sensors can be used for applications from DC to 10kHz For software support the Scope program can be used to easily acquire save and display data in real time In this setup the sensor is connected to one analog channel while the other three analog channels are still available The red black alligator pairs are differential inputs for each of the analog inputs The green alligator wire is AGND which is not required for a floating passive sensor A G
165. ype of column format are easily imported into spreadsheets and analysis programs such as GnuPlot Excel or Matlab for plotting and processing See the Examples and Experiments chapter for examples of using the public domain plotting program GnuPlot and many other applications 22 3 1 6 DVM Calibrate Sometimes users are surprised to learn A D converters do not output their results as volts The output from an A D converter is actually a digital integer that is only proportional to the input voltage The conversion from this digital integer to units such as volts is referred to as the calibration The concept of calibration for an A D converter can be carried even further into physical sensor units Suppose you have a sensor like a potentiometer or temperature gauge At the minimum setting the sensor may result in a particular A D count and likewise at its maximum setting another count value These two points define a line and conversion of the count values directly into sensor units such as potentiometer turns or C can be done with a linear transformation having a slope and offset The Calibrate program makes it easy to obtain the slope and offset coefficients for such transformations It allows you to record the transducer min and max settings and then output an ini file for use with DVM The Calibrate screen looks like this FJUSBXCH Calibration This program calibrates data from a USBxCH To run select channel and enter propertie
166. ystems battery power for portable and field apps 141 19 1 Measuring a AA battery With a AA battery and the DVM program you can test many of the USBxCH DC analog input characteristics In this example besides showing basic usage we will also review a few details regarding the three wire differential AGND inputs For additional theory behind differential signals see the Analog inputs chapter The most basic test with a AA battery is to simply connect it between the of an analog channel like this Figure 19 1 Two lead AA battery voltage measurement In this setup we have used a battery holder with tab lugs so the alligator clips can be easily connected with the red and black wires of analog channel 0 connected to the battery terminals The USBxCH green AGND alligator clip is not connected at all leaving the battery floating Note the black input is not ground It is the inverted differential input Since a AA cell has approximately 1 5 volts if you run the DVM program by double clicking on the Run DvmGui Volts shortcut you will see the following on your computer 142 i USBxCH Digital Volt Meter Running Program Options Help Sample 21 Channel 0 Channel 1 Channel 2 Channel 3 Ini file DvmSetupVolts ini Output file DvmOutputvolts asc Ctrl R acquire data Ctrl S stop F1 help 12 23 37 Figure 19 2 DVM with a AA battery hooked up When making this measurement if the dif
167. ze OutputFileNaming ANONE YMDHMS SINGLE OutputFileNbuffers N OutputFileNaming specifies how individual output files are named As Scope runs it fills a temporary file Scope tmp and when full renames it according to NONE turns off file output altogether Use this option if you are setting Scope up for an experiment and don t want to save data yet YMDHMS default creates a data subdirectory for the current Scope run with the name year month day hours minutes seconds as given by the PC clock Within the YMDHMS data directory data is saved to Scope tmp as it comes in When filled the temp file is renamed to nnnnnnnn DAT with an 8 character sequential decimal name starting at 00000000 DAT A new YMDHMS data directory is created for each Scope Ctrl R run and the sequential names will start again at 0 This filename convention is similar to the Blast output filename convention SINGLE renames the temporary file Scope tmp to the single file named Scope dat You or downstream processing must remove Scope dat before the next file is ready or an error will occur OutputFileNbuffers specifies the output file size It controls how many acquisition buffers are saved to Scope tmp file before it is given its permanent name and a new temp file is started N can be any value between 1 and 4 294 967 295 unsigned long The number of data samples per acquisition buffer varies with sampling rate and is selected so each buffer is about 1

USB4CH User Manual - Symmetric Research

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