User Manual
Contents
1. 10 V Examples SET DAC CH1 to 0 V 1 7FFF80 lt LF gt SET DAC CH3 to 2 5 V 3 5FFFA0 lt LF gt SET DAC CH8 to 3 4 V 8 AB8473 lt LF gt 1 1 1 SET ALL DAC CHannel to a DAC VALue HEX ALL lt SPACE gt DAC VAL HEX 0x000000 0xFFFF00 lt LF gt Examples SET ALL DAC CHannels to 0 V ALL 7FFF80 lt LF gt SET ALL DAC CHannels to 10 V ALL FFFF00 lt LF gt 1 2 SET DAC CHannel STATus ON or OFF DAC CH 1 8 lt SPACE gt STAT ON OFF lt LF gt Examples SET DAC CH1 ON 1 ON lt LF gt SET DAC CH5 OFF 5 OFF lt LF gt 1 2 1 SET ALL DAC CHannel to a STATus ON or OFF ALL lt SPACE gt STAT ON OFF lt LF gt Examples SET ALL DAC CHannels ON ALL ON SET ALL DAC CHannels OFF ALL OFF LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC When a SET command is received and processed successfully the device responds with zero 0 followed by a lt CR LF gt This no error replay must be awaited before the next SET command can be send If the SET command cannot be interpreted an error code with a lt CR LF gt is returned the meaning of the error code is as following 0 No error 1 Invalid DAC CHannel 2 Missing DAC VALue or STATus 3 DAC VALue out of range 4 Mistyped 5 Remote writing not allowed local editing is performed Up to sixteen SET commands can be combined in a single line by separating the different command2. High Resolution DAC 6 Local Show Edit DAC Values By using the four top menu items the DAC output voltages can be shown and edited in different number formats During editing DAC values locally remote writing a DAC value is disabled In the Show Edit V mV menu all DAC voltages can be displayed modified on a single page with a resolution of 1 mV On the left separated by a colon the corresponding channel number is indicated the DAC channel 1 and 2 is displayed on the first line the DAC channel 3 and 4 on the second line and so on 12 10 000V 10 000V 34 lt OFF gt V lt OFF gt V 56 8 000V 3 300V 78 10 000V 10 000V The displayed voltages are not measured they are calculated from the set DAC values Since the DAC output voltages can have a maximum voltage error of up to 1 mV the shown voltages may be different to the real DAC output voltages In the Show Edit V V menu the DAC voltages can be edited with a resolution of 1 uV Since only four channels can be displayed simultaneously one has to scroll the display with the rotary knob 5 8 000000 V 6 3 300000 V 7 10 000000 V 8 10 000000 V Because the DAC output voltages can have a maximum voltage error of up to 1 mV the shown voltages may be different to the real DAC output voltages Due to the intrinsic DAC resolution of 1 2 pV the last digit uV may skip some values due to rounding to the nearest possible output voltage In the Sh
3. 150 Hz can clearly be identified in the noise spectra LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC 12 Grounding To prevent ground loops and interferences the DAC output voltages are referred to a common ground which is galvanic isolated from the housing earth and from the computer interface The common DAC output ground can be shifted by up to 20 V with respect to the housing earth The ground reference of the DAC outputs is connected to the experiment e g cryostat via the shields of the BNC cables Due to the galvanic isolation no troublesome ground loop currents can flow over the shielding of the cables If external AC magnetic fields are present loop currents can be induced in shields of the eight BNC cables running from the DAC to the experiment To minimize this effect bring the BNC cables as close as possible or even better twist them In addition the computer interface is also galvanic isolated from the housing earth and it can also be shifted by up to 20 V with respect to the housing earth A switch on the rear side of the device allows the user to select the computer interface between floating or grounded For electrostatic reason also in the floating mode the ground of the computer interface is connected via a 100 kOhm resistor to the housing earth With this grounding concept no optically isolated computer interfaces are needed also in very sensitive experimental
4. For a given decimal DAC Value DACval 0 16 776 960 the output voltage Vout 10 V 10 V can be determined by Vout DACval 838 848 10 LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC 10 Remote Control via Ethernet and TCP IP The LNHR DAC can be easily controlled remotely via the Ethernet port TCP IP by using a web browser If the device is directly connected to computer a crossed X network cable has to be used The IP address can be set via the menu item IP Settings At delivery the IP address is set to 192 168 0 5 and the subnet mask to 255 255 255 0 The embedded web server allows monitoring and controlling the device with a standard web browser When the web page is called the first time the following LabVIEW run time code is automatically loaded from the National Instruments FTP server ftp ftp ni com support labview runtime windows 8 6 1 LVRTE861min exe In that case a second network adapter connected to the internet is needed The web page of the LNHR DAC can be accessed via the web address http IP address LNHR_DAC html e g http 192 168 0 5 LNHR_DAC html LN HR DAC Web Remote Control Panel Physics Basel Low Noise High Resolution DAC Control SP 927 Physics Basel March 2010 Revision 2 4 1 DAC1 DAC2 DAC3 DAC4 DACS5 DAC6 DAC7 DAC8 SPA E Rp LER Or NID 1 ae S JE Ss Sigs Ed nG E e a amp T z 7 A G agw 5 4 400 S 9 4910
5. and the RT State Chart Module The FPGA program is structured in about 20 Sub VIs and the RT code covers around 100 Sub VIs LNHR DAC User s Manual Revision 1 6 Physics Basel
6. gt oS 44M FS Fw SF g aoo F ws ep ks ries aE AN res Seam entire aye KS a Actual DAC Values V 8 666646 7 333293 J 5 999939 4 666586 3 333232 1 999878 0 666525 0 666829 Fiun P2222 333333 Faaa 555555 Me66666 I 777777 Nesssss Actual DAC Values HEX READING ON 1 ON 2 ON 3 ON 4 ONS5 ON 6 ON 7 ON8 DAC1 DAC2 DAC3 DAC4 DAC5 DAC6 DAC7 DAC8 o 0 8 8 Set DAC Values V Set DAC Values HEX Input Format HEX Values 0x000000 0xFFFF00 StM March 2010 Figure 1 Shows the web remote control panel of the LNHR DAC Via the web page the device can be monitored and DAC values status can be manually modified The upper part of the web page READING shows the actual DAC output voltages and the status ON OFF of all the DAC outputs The read DAC values are displayed in voltage 10 000000 V 10 00000 V as well as in hexadecimal values 0x000000 0xFFFF00 LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC While a DAC value is being locally modified by a user writing via the web page and also via RS 232 gets disabled Then the underlying color in the field WRITING changes to red and all the writing fields get disabled and greyed out When remote writing is enabled the color of the WRITING field changes to green A button allows toggling between the two different input formats for the DAC values In the lower row in hexadecim
7. 0 compatible UART Select lower settings to correct connection problems ational Select higher settings for faster performance Defaults Receive Buffer Low 1 U High 14 1 Transmit Buffer Low 1 U High 16 1 COM Port Number COMI 7 LNHR DAC User s Manual Revision 1 6 Physics Basel 9 Low Noise High Resolution DAC All commands must be terminated with a lt RETURNS gt which can be a Line Feed lt LF gt or Carriage Return lt CR gt followed by a Line Feed lt LF gt With a terminal program send a 2 followed by a lt LF gt to the device and you will receive a text with an overview of all ASCII commands All the ASCII commands can be tested simply by using a standard terminal program e g HyperTerminal or Putty on Windows systems The commands are not sensitive to UPPER and lower case typing The terminal program must be configured so that a send line is terminated with a Line Feed lt LF gt or with a Carriage return and Line Feed lt CR LF gt to generate a lt LF gt with the Putty terminal program type a CTRL J To watch the typed commands on the computer monitor the local echo of the terminal program must be turned on 1 SET COMMANDS 1 1 SET aDAC CHannel to a DAC VALue HEX DAC CH 1 8 lt SPACE gt DAC VAL HEX 0x000000 0xFFFFO0 lt LF gt The DAC VAL HEX corresponds to the following voltages 0x7FFF80 0 V OxBFFF40 5 V OxFFFF00 10 V Ox3FFFCO 5 V 0x000000
8. Physics Basel Low Noise High Resolution DAC SP 927 User s Manual Revision 1 6 from serial number 0025 Michael Steinacher November 2013 Nee PRR BASEL Low Noise High Resolution DAC Features Eight DAC voltages with a 10 V range Low noise 0 1 100 Hz Typical 0 5 Vrms 3 3 uVpp 24 bit resolution corresponds to a voltage step size of 1 2 uV Independent DAC channels with a crosstalk isolation of gt 140 dB Output ground is isolated from housing and computer interface LC display for status display and manual control Remote controllable via RS 232 or Ethernet via a web browser LabVIEW drivers included for RS 232 remote control Compact and robust 19 desktop and rack mount housing 2U Height Safety Precautions A The Low Noise High Resolution DAC LNHR DAC is designed for indoors dry laboratory use by qualified and authorized persons only Read this manual carefully before installing and use the LNHR DAC all the safety precautions must be respected Before connecting the device to the mains voltage makes sure that you have the appropriate power supply module 115 Vac or 230 Vac attached to the rear side of the device or properly set the mains section switch 115 Vac 230 Vac Only use a mains power cable with a protection ground earth Make sure that the device is properly grounded Always disconnect the mains cable before replacing the mains fuse on the rear side of the device Do not remove
9. S lt LF gt gt STAT ON OFF LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC Examples QUERY DAC STAT of CH1 1 S lt LF gt gt ON lt CR tLF gt QUERY DAC STAT of CH8 3 S lt LF gt gt 0FF lt CR LF gt 2 2 1 QUERY ALL DAC STATus ON or OFF ALL lt SPACE gt S lt LF gt gt STAT1 STAT2 STATS ON OFF Example QUERY ALL DAC STATus ALL S lt LF gt gt ON OFF ON OFF ON ON ON OFF lt CR LF gt 3 QUERY INFORMATION COMMANDS Several text information and settings can be recalled via the serial interface by the following commands each query command must be terminated with a lt LF gt or lt CR LF gt Shows an overview of the RS 232 ASCII COMMANDS HELP Shows the HELP text as on local LCD SOFT Shows the software release of the device as on local LCD HARD Shows information to the used hardware as on local LCD POWER Shows the status of the power supply voltages as on local LCD STAT Shows the write status 0 Remote writing enabled 5 Disabled SPECS Shows the typical specifications of the device as on local LCD IP Shows the IP Address and the Subnet Mask as on local LCD CONTACT Shows the contact address and further information as on local LCD 4 REMARK For a given output voltage Vout 10 V 10 V the decimal DAC Value DACval 0 16 776 960 is given by DACval Vout 10 838848
10. al values 0x000000 0xFFFF00 and in the upper row in voltages 10 000000 V 10 00000 V Without difficulties the device can be accessed in parallel via RS 232 commands and via a web browser The last written DAC value stays valid until it is changed either via a RS 232 SET command or via an input from the web browser The web page can be used to monitor the device during it is remotely controlled via the serial port The update rate of the web page is relative slow 5 10 times sec and is not suitable for fast reading and writing from to the LNHR DAC LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC 11 Output Noise The typical DAC output noise voltage of the device is only 0 5 Vrms which corresponds to peak to peak noise voltage of about 3 3 uVpp This RMS noise is measured in a frequency band of 0 1 Hz to 100 Hz The noise has a typical 1 f frequency characteristic that s why around 80 of the noise is generated in the low frequency band between 0 1 Hz and 10 Hz The measured noise of your device is appended in the end Measuring such low noise levels is quite challenging short and good cables low vibration environment and an elaborated test setup are mandatory The noise may vary slightly over time and therefore repeated noise measurements must be averaged at least ten 100 sec to get a reasonable value A good portion of the noise is generated from the 10 V reference voltages that
11. any cover Since the internal parts are precisely adjusted do not try to adjust or modify any part of the LNHR DAC The external bias voltage must not exceed 20 V with respect to ground it is internally restricted to 25 V by Zener Diodes When the device is turned off and on again immediately brown out the DAC output voltages can reach peak levels of up to 10 Vpeak Under normal conditions minimum 10 seconds power off almost no spike voltages lt 10 MVpeak occur at the DAC outputs during power on or power off the device Disclaimer Physics Basel hereby disclaims all responsibility for personal injury property damage and fine of penalty which results from misuse not respecting the safety precautions improper maintenance or improper application of this product Compliance with all applicable environment and personnel safety regulations is the sole responsibility of the user LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC 1 Description and Applications The Low Noise High Resolution DAC LNHR DAC generates eight independent low noise and ultra stable voltages The output range of 10 V combined with the 24 bit resolution allows adjusting the voltages with a step size of only 1 2 uV The output voltage noise is well below 1 uVpms typically 0 5 uVrms measured in a frequency range of 0 1 Hz to 100 Hz Each channel can be independently switched ON active driven or OFF grounded b
12. e can find the mains power switch between the mains voltage selector switch and the slot for the fuses When the power is switched on almost no spike voltages lt 10 MVpeak occur at the DAC outputs Under brown out conditions he DAC outputs can reach a peak level of up to 10 Vpeax When the power is switched off all DAC outputs are switched to the OFF state immediately and no spikes occur on the DAC outputs 115 230 Vac 60 50 Hz Pmax 30 W Fuses 115 V 2 x 400 mA slow Fuses 230 V 2 x 200 mA slow L Photo 3 The external and well shielded Transformer amp Rectifier Housing on the rear panel of the LNHR DAC prevents from mains disturbances In the middle of the rear panel green LEDs indicate when the power is switched on and when remote writing DAC values status is enabled Remote reading DAC values status is always allowed During editing DAC values locally remote writing via RS 232 or Ethernet is disabled The connectors for the remote control RS 232 or Ethernet are located on the right When the LNHR DAC is directly connected to a computer crossover cables have to be LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC used For the serial interface RS 232 a so called AT link data cable female female has to be used such a RS 232 cable with a length of three meters is supplied with the device At the top right a rocker switch allows to select between floating compute
13. environment 2 y 15 V Analog 10 V Supply Unit Reference E Line Voltage Status 15 V SupplyStatus 19 4 V Supply 19 4 V SupplyStatus Housing floating from housing D SUB me RS 232 Spin male Computer Board amp FPGA floating from housing LCD amp Encoder Figure 3 The block diagram of the LNHR DAC and its grounding principle If the external bias voltage input is left open the common ground of the DAC outputs is floating with respect to the housing earth and the computer interfaces By driving the external bias voltage the ground of the DAC outputs can be shifted by up to 20 V with respect to the housing earth RJ 45 Ethernet 10 100 Mbps Floating Bias Voltage Vbias nput 20 V Grounded Housing earth LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC 13 Typical Specifications Temperature 25 C 4 h warm up Independent DAC output channels 8 Output voltage range 10 V Output current max 1 mA Resolution 24 bit LSB equal to 1 19 uV Absolute voltage error typ 200 uV max 1 mV Offset voltage error Vout 0 V typ 100 uV max 500 uV Integral nonlinearity INL 80 LSB Drift over 8 h T constant 25 C 10 pV DAC output voltage during power on power off min 10 sec lt 10 MVpeak DAC output voltage during fast power on off brown out max 10 Vpeak ON outp
14. he possibilities to control the device locally and remotely e Software Release Shows the installed firmware release and date e Hardware Version Displays the serial number of the device and the revisions of the installed hardware modules e Power Supply Status The status of the different power supply voltages is shown normally all should be OK Line Voltage OK 15Va Supply OK 15Va Supply OK uC Supply OK e Specifications Shows the typical specifications of the LNHR DAC e Contact Information Displays the contact information of the manufacturer LNHR DAC User s Manual Revision 1 6 Physics Basel 8 Low Noise High Resolution DAC 9 Remote Control via Serial Port The device can be controlled remotely via the serial port RS 232 by using simple ASCII commands A crossed null modem AT link data cable included has to be used to connect the device directly to a computer The Baud rate can be set locally in a range from 300 Baud up to 115 kBaud via the main menu item RS 232 Settings At delivery the baud rate is set to 9 600 bits sec The number of data bits is fixed to eight with one stop bit and the parity is not used The data flow is controlled via the XON XOFF protocol To reach fast update rates use a Baud rate as high as possible For reliable data transfer handshaking between the LNHR DAC and the control software is mandatory Proper handshaking is implemented in the serial port LabVIEW drivers
15. net mask can be done in the same way as editing a DAC value IP Address 192 168 000 005 Subnet Mask 255 255 255 000 After setting new IP values and long pressing the push button the device asks what to do With the rotary knob one can select between two options Escape to MAIN MENU makes no changes and the old IP address and subnet mask remains valid When selecting Save IP amp Restart the modified values are saved permanently and the LNHR DAC is restarted takes about 45 seconds Thereafter the new IP settings are active During restarting the device all DAC channels are switched OFF and they are all reset to an output voltage of 0 V WHAT TO DO NOW Escape to MAIN MENU Save IP amp Restart LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC When selecting the menu item Restart the device the following screen appears WHAT TO DO NOW Escape to MAIN MENU Restart the device If one confirms to restart the device the LNHR DAC is restarted takes about 45 seconds During restarting the device all DAC channels are switched OFF and they are all reset to an output voltage of 0 V It the same procedure as the mains power switch was turned OFF and ON again 8 Local Information Different text information can be accessed via the following main menu items use the rotary knob to scroll through the long texts e HELP General information about the LNHR DAC and t
16. ow Edit DEC val menu the decimal DAC values in a range from 0 10 V to 16 776 960 10 V can be displayed and modified on a single page The resolution of the last digit corresponds to a voltage step of 1 2 uV 12 16776960 16776960 34 lt OFF gt lt OFF gt 56 1677696 11156678 78 0 0 In the Show Edit HEX val menu the hexadecimal DAC values in a range from 0x000000 10 V to OxFFFFOO 10 V can be displayed and modified on a single page The resolution of the last digit corresponds to a voltage step of 1 2 uV 12 XxFFFFOO xFFFFOO 34 x lt OFF gt x lt OFF gt 56 x199980 xAA3CC6 78 x000000 x000000 In all the display formats a DAC channel is switched ON OFF by double click the push button a switched OFF DAC channel is indicated by the text lt OFF gt LNHR DAC User s Manual Revision 1 6 Physics Basel o 6 Low Noise High Resolution DAC Editing a DAC value is performed manually in this way First press the push button then a blinking cursor occurs in the left part of the LCD where the DAC channel numbers are shown With the rotary knob select the DAC channel to be modified by pressing the push button again Then the blinking cursor jumps to the last digit of the selected DAC value Now select the digit to be in or decremented with the rotary knob By pressing the push button again the editing mode gets active In the editing mode the blinking cursor is replaced by an underline curso
17. r and the DAC value is immediately modified by turning the rotary knob left or right One can toggle between the digit selection and the editing mode just by pressing the button Ten seconds after the last user interaction or by long pressing the push button the former selection is retained The system remains in the editing mode until the user presses and holds the push button long 7 Local System Settings The Baud rate of the serial connection can be set in the RS 232 Settings menu item Baud rates from to 300 up to 115 200 can be selected by turning the rotary knob At delivery a Baud rate of 9600 is programmed The data length 8 bit the number of stop bits 1 stop and the parity none are fixed and cannot be changed Baud rate 9600 300 115200 bits s Fix 8 data 1 stop no parity XON XOFF When the Baud rate has been changed by the user and the button is pressed the device asks what to do With the rotary knob one can chose between two options Escape to MAIN MENU makes no changes and the old Baud rate remains valid When choosing Use Save Baud Rate the new Baud rate gets activated and it is saved permanently WHAT TO DO NOW Escape to MAIN MENU Use Save Baud Rate Under the menu item IP Settings the IP address and the subnet mask of the device can be programmed At delivery the private IP address 192 168 000 005 with a subnet mask of 255 255 255 000 is programmed Setting a different IP address or a sub
18. r interface and the ground of the interface hard connected to the housing earth for more details see the chapter Grounding 4 Startup After the mains power cable is connected and the power switch is turned on rear side of the power supply the device starts up and the following message is displayed on the LCD WELCOME Now starting the LN HR DAC software takes about 45 sec Note that during power on the output voltages of the DACs can reach a peak level of up to 7 Vpeak After about 45 seconds the device is ready to run and the following startup information is shown 8 Channel Low Noise High Resolution DAC Physics Basel SP 927 During power up all DAC channels are switched OFF and preset to 0 V After 10 seconds or shortened by pressing the push button the device displays to the main menu 5 Main Menu With the following main menu several settings can be made locally by using the LC display and the rotary push knob Show Edit V mV Show Edit V mV yV Show Edit DEC val Show Edit HEX val HELP RS 232 Settings IP Settings Software Release Hardware Version Power Supply Status Specifications Restart the device Contact Information The main menu can be scrolled up and down by using the rotary knob a menu item can be selected by pressing the push button Leaving a sub menu is done by long pressing the push button LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise
19. s why the noise at DAC output voltages near zero is about 30 smaller than at full range 10 V or 10 V Since the noise level is different from device to device each unit and each channel is qualified for noise performance after production The noise is measured at five different DAC output voltages of 0 V 5 V 10V 5 V and 10 V Therefore a maximum noise voltage of 1 uVrms 6 6 uVpp averaged over ten sweeps 100 sec can be guaranteed t see iaat 1 uV l l LNHE DAC Output Noise 10 v bo Hz 100 nVrms 50 Hz 150 Hz Foe TI POR am 50 nVisart Ha thee aa 600e Bidiv 20 0 H2div x1 10 0HZ 169 9 Hz x2 179 9 Hz 1 AX 5 886 ms Figure 2 A noise measurement by using a low noise AC coupled fgup 0 03 Hz battery powered preamplifier SR560 with a gain of 104 and a bandwidth of 100 Hz This typical noise of 0 5 uV ras is measured at a DAC output voltage of 10 V The upper plot olive green shows the time domain noise signal over 10 second a peak to peak voltage of around 3 3 uVpp can be registered In the lower plot the averaged FFT noise spectra ocher and the integrated noise spectra pink is shown in the frequency domain The integrated RMS noise from 0 1 Hz up to 180 Hz is exactly 0 5 UVrus The noise spectra is generated by using 143 averages 10 sec sweep which corresponds to a total measuring time of almost 25 minutes The unavoidable mains frequency 50 Hz and its third harmonics
20. s with a semicolon For each of the SET commands a separate error code is generated followed by a lt CR LF gt Example SET DAC CH3 to 5V DAC CH3 ON DAC CH4 to OV DAC CH8 OFF 3 3FFFCO 3 ON 4 7FFF80 8 OF F lt LF gt gt 0 lt CR LF gt 0O lt CR LF gt 0 lt CR LF gt 0 lt CR LF gt When using a control software automatic sweep etc it is strongly recommended to read and interpret the error code after each SET command That results in a save data transfer with a handshaking between the device and control software 2 QUERY DATA COMMANDS A QUERY command must be terminated with a question mark followed by a lt LF gt or a lt CR LF gt Only single QUERY commands can be treated If a QUERY command cannot be interpreted the device response with a question mark followed by a lt CR LF gt 2 1 QUERY a DAC VALue HEX of a DAC CHannel DAC CH 1 8 lt SPACE gt V lt LF gt gt DAC VAL HEX 0x000000 0xFFFF00 Examples QUERY DAC VAL of CH1 1 V lt LF gt gt 7FFF80 lt CR LF gt QUERY DAC VAL of CH8 3 V lt LF gt gt 3FFFCO lt CR LF gt 2 1 1 QUERY ALL DAC VALues HEX ALL lt SPACE gt V lt LF gt gt DAC VAL1 DAC VAL2 DAC VAL8 HEX 0x000000 0xFFFF00 Example QUERY ALL DAC VALues ALL V lt LF gt gt 7FFF80 7FFF80 3FFFCO 7FFF80 FFFF00 000000 7FFF80 AB8473 lt CR LF gt 2 2 QUERY a DAC STATus ON or OFF of a DAC CHannel DAC CH 1 8 lt SPACE gt
21. sing earth by applying an external bias voltage This bias voltage has to be connected to the BNC connector Bias Voltage Input on the right Note when using this feature the common ground of the DAC outputs is no longer floating and ground loops may degrade the performance of the device On the most right part of the front panel the LC display and the rotary push knob encoder can be found LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC 3 Rear Panel To minimize the electromagnetic interference from the mains power supply to the DAC outputs the transformers and rectifiers are enclosed in an external box attached to the rear of the LNHR DAC On the back of this Transformer amp Rectifier Housing the mains AC voltage has to be connected via a standard mains connector plug Before connecting the mains voltage makes sure that you have the appropriate power supply module 115 Vac or 230 Vac or properly set the mains voltage selection switch 115 Vac 230 Vac amp Low Noise High Resolution DAC Photo 2 The rear panel of the LNHR DAC with the attached Transformer amp Rectifier Housing on the left The mains fuses are installed just to the left of the mains connector The mains cable must be disconnected before one can open and replace the mains fuses The following slow blow fuses d 5 mm l 20 mm are needed When operating at 115 Vac 2 x 400 mA and at 230 Vac 2 x 200 mA On
22. tion degree 1 no pollution or only dry and non conductive pollution LNHR DAC User s Manual Revision 1 6 Physics Basel Low Noise High Resolution DAC 15 Background The enormous resolution of 24 bit is reached by applying a pulse width modulation PWM on the least significant bit LSB of a commercially available 16 bit DAC chip Texas Instruments DAC8871 To eliminate the parasitic PWM fundamental frequency of 919 Hz the voltage output of the DAC chip is filtered by a low pass Bessel filter f 3a8 75 Hz designed for low noise performance To reach the low noise performance of the LNHR DAC the reference voltages 10 Vref supplied to the DAC chip is crucial To minimize this noise source pretested and selected low noise voltage reference chips are used in this device For further reducing the noise by around a factor of two four of these selected low noise voltage reference chips are combined To increase the linearity a calibration procedure is accomplished on each DAC output after production This is done by using a precision stable and high resolution digital voltmeter Keithley 2010 as reference 2 000 interpolation voltages between 10 V and 10 V are measured and then the linearity error versus DAC value is fit by a high order polynomial correction function The determined polynomial linearization coefficients are then transferred and saved onto the LNHR DAC The 16 bit DAC chip has a typical integral nonlinearit
23. ut source impedance 500 Ohm 1 2 uF OFF output impedance to GND 100 kOhm 1 2 uF Output bandwidth 75 Hz Overshoot 0 V to 10 V Step typ 0 6 max 1 2 Rise time 10 to 90 4 7 ms Settling time for an error lt 0 1 18 ms after no error echo is received Noise 0 1 Hz 100 Hz typ 0 5 Vrms 3 3 UVpp max 1 Vrms 6 6 UVpp DAC output ground is common for all channels and it is galvanic isolated from housing earth and from the computer interface RS 232 and Ethernet Channel to channel crosstalk isolation gt 140 dB Bias voltage DAC output ground to housing earth max 20 V Capacitance of DAC output ground to housing earth 1 5 nF Computer interface ground to housing earth voltage max 20 V Capacitance of computer interface ground to housing earth 1 nF Warm up time 4h Mains voltage supply 115 Vac 230 Vac both 10 5 50 60 Hz Mains power consumption typ 25 W max 30 W DAC update rate via RS 232 115 kBaud 175 DAC values per second Housing 19 width for tabletop use or rack mount Housing dimensions Width 480 mm Height 100 mm 2U Depth 430 mm Weight 8 kg 17 7 lb 14 Operation Conditions Environment Indoors dry laboratories only Ambient temperature between 10 C 50 F and 40 C 104 F Altitude up to 2 000 m 6 561 ft Maximum relative humidity 80 for temperatures up to 31 C 88 F decreases linearly to 50 at a temperature of 40 C 104 F Pollu
24. which are included on a CD at the end of this manual When operating at the highest Baud rate 115 2 kbit sec typical 175 DAC values per second can be transferred to the LNHR DAC with proper handshaking In this case use the following COM port settings on the host computer Make sure that the speed of the serial port Baud rate on the host computer is always the same as configured on the LNHR DAC see p Communications Port COM1 Properties General Port Settings Driver Details Resources Bis per second 115200 sss chapter 7 Local System Settings Data bis 8 If this is violated the LNHR DAC firmware may Party None suum be blocked and no communication is possible a also locally In that case the device has to be ror corte SSE rebooted power off on How control Xon Xoff Mi During power cycling on off of the host computer spurious signals often appear at the serial output and this may also affect and block the firmware of the LNHR DAC Therefore first disconnect the connection to the host computer before switching it on or off i Advanced Restore Defaults To prevent from Buffer Overrun Error when using the serial port LabVIEW drivers in combination with the maximum Baud rate use the following advanced settings of your COM port installed in the host computer r kg Advanced Settings for COM1 os V Use FIFO buffers requires 1655
25. y INL of 1 LSB which corresponds to 256 LSB in the 24 bit system of the LNHR DAC Through the calibration process the INL is reduced by a factor of around three to typical 80 LSB All internal supply voltages are supervised If one fails all DAC outputs are immediately switched OFF This makes sure that no erroneous DAC output voltage can occur which could damage sensitive samples attached to the LNHR DAC A sbRI0 board 9602 from National Instruments is used to control the LNHR DAC and it enables the remote control of the output voltages via Ethernet TCP IP and the serial port RS 232 Also the error corrections for the DAC chips are calculated in real time RT based on the stored polynomial linearization coefficients The web server running on the RT processor of the sbRIO board allows monitoring and controlling of the eight output voltages by using a normal web browser Further a LC display 4 x 20 characters and a rotary push knob allow the local control and setup of the device by the user The FPGA on the sbRIO board performs the time critical SPI bus communication with the eight independent DAC boards and it manages the pulse width modulation of the LSB to increase the resolution of the DAC chips to 24 bit Further some low level routines for driving the LCD and reading the rotary push knob are also implemented in the FPGA The programming of the LNHR DAC is carried out by using the LabVIEW FPGA Module the LabVIEW RT Module
26. y 100 kOhm The device has an alpha numeric display and can be locally as well as remotely controlled via RS 232 or Ethernet Such low noise and ultra fine tunable voltages are often needed for fundamental physics experiments at very low temperatures For those experiments constant DC bias voltages and high resolution sweep voltages with very low fluctuations noise are mandatory e g for driving gate voltages Since the typical load resistances of such gates are very high the output current of the device is relative small 1 mA and the output source resistance is relative high 500 Ohm With an output bandwidth of DC 75 Hz the LNHR DAC can be used for DC biasing for ramping sweeping and for low frequency waveform generation at high impedance loads 2 Front Panel On the left the eight DAC voltages are fed to the front panel via eight BNC connectors A yellow LED above the BNC connector indicates the status ON OFF of the DAC channel The large front panel recesses for the BNC connectors make sure that the outer conductor doesn t make an electrical connection to the housing earth Make sure that the outer conductors of your attached BNC cables do not contact the front panel A 30 oac output on y 10 V DAC output Rout 500 Ohm Common floating GND Photo 1 The front panel of the LNHR DAC with all DAC channel switched on The common floating ground of the DAC voltages can be shifted up to 20 V with respect to the hou
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