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meterbuilder™ mb-1 programmable meter for analog sensors

1. The entries in red in the above table correspond to available MB 1 calibration points At these points the calibration should be exact However the entries in black will undergo linear interpolation Since the transfer function is nonlinear we know there will be some error at these points For an application of this type it is worth evaluating the magnitude of the errors at the intermediate points so that you can determine if the accuracy across the usable range will meet your needs 4 17 2 Error Analysis We can take a look at how well the linear interpolation is doing between calibration points We know that the calibration will be exact for the red entries above which are at multiples of 10 Look at the Vour values for 50 dB and 60 dB If we look at each integral value in that range we have ten data points Because MB 1 uses linear interpolation between calibration points MB 1 will declare the measurement value to be 51 dB when Vour is exactly at 1 10 of the voltage between the 50 dB and 60 dB voltage points Likewise MB 1 will declare the measurement value to be 52 dB when V ovur is exactly 2 1075 of the voltage between the 50 dB and 60 dB voltage points and so forth The first two columns in the table below are copied from the table above and represent the exact SPL and VOUT values calculated usin
2. ALCOHOL SENSOR CURVE RE 38 ALCOHOL SENSOR WIRING RE 39 INTERFACE CIRCUIT FOR ANGULAR VELOCITY SENSOR RE 40 MAGNETIC SENSOR TRANSFER FUNCTION RE 41 CIRCUIT FOR MEASURING RESISTANCE RE 42 INCREASING OHMMETER RANGE RE 43 AFFECT OF MB 1 INPUT RESISTANCE ON MEASUREMENT RE 44 PH FOR DIFFERENT TEMPERATURES VS PH T 100 RE 45 RPM SENSOR INTERFACE RE 46 ADDING MB 1 TO EXISTING INSTRUMENTATION USING A VOLTAGE SENSOR RE 47 ADDING MB 1 TO EXISTING 4 20 MA LOOP INSTRUMENTATION Tables TABLE HALL CURRENT SENSOR CALIBRATION TABLE 2 PORTION OF THE RESISTANCE VS VOLTAGE CALCULATIONS FOR THERMISTOR TABLE 3 VOLTAGE TEMPERATURE CALIBRATION POINTS FOR THERMISTOR TABLE 4 ERROR ANALYSIS FOR TILT SENSOR TABLE 5 LOGIC SIGNALS AND CORRESPONDING ANALOG VOLTAGE FOR DISCRETE TILT SENSOR TABLE 6 CALIBRATION POINTS FOR DISCRETE TILT SENSOR TABLE 7 ERROR ANALYSIS FOR SOUND SENSOR TABLE 8 ALCOHOL SENSOR CALIBRATION POINTS TABLE 9 ERROR AT MIDPOINTS TABLE 10 CALIBRATION METHOD FOR MAGNETIC SENSOR TABLE 11 CALIBRATION POINTS AND CORRESPONDING VOLTAGES FOR OHMMETER APPLICATION TABLE 12 ERROR ANALYSIS FOR OHMMETER EXAMPLE TABLE 13 PH CALIBRATION POINTS FOR T2100 C TABLE 14 SENSOR OUTPUT VOLTAGE AS A FUNCTION OF PH AND TEMPERATURE TABLE 15 PH VALUES FOR DIFFERENT TEMPS CORRESPONDING TO Voyr AT T2100 CASE TABLE 16 ANALOG NEEDLE DEFLECTION FOR T
3. sensitivity see Table 22 To ensure that the MB 1 Amp Mux does not saturate during calibration or operation use the Coupler Setup feature that allows you to view the output of the A to D chain while adjusting the trim pot Set the output of the Amp Mux chain to approximately 30 000 with a voltage of 7 067 volts applied The actual calibration is most easily done by dialing in the calibration voltage at the above two calibration points using a stable voltage source and potentiometer as shown in Figure 4 Note that the 1 5 volt auxiliary power output cannot be used in this case since we need a voltage level greater than 5 volts A 9 volt battery or other stable higher voltage source can be used instead 4 23 3 Analog Meter Calibration Below is a table that shows the sensor output voltage as a function of pH and temperature As mentioned above it can be seen that the 100 case has the largest Vour excursion across the complete pH range The items below in red correspond to our two calibration points Table 14 Sensor Output Voltage as a function of pH and Temperature Vout Vout Vout Vout Vout pH T 100 T 75 T 50 T 25 T 0 0 0407194 0 2054763 0 3702332 0 5349901 0 699747 0 3920452 0 5332654 0 6744856 0 8157058 0 956926 0 743371 0 8610545 0 978738 1 0964215 1 214105 1 0946968 1 1888436 1 2829904 1 3771372 1 471284 1 4460226 1 5166327 1 5872428 1 6578529 1 728463 1 7973484 1 8444218 1 8914952 1 9385686 1 985642 2 1486742 2
4. 100 CASE TABLE 17 ANALOG NEEDLE DEFLECTION FOR T 75 CASE TABLE 18 TRANSFER FUNCTION FOR 10 PRESSURE VALUES FOR VACUUM SENSOR TABLE 19 MB 1 READINGS AND CORRESPONDING PRESSURES FOR INTEGRAL MB 1 READINGS TABLE 20 LOOKUP TABLE FOR INTERPOLATING NON INTEGRAL MB 1 MEASUREMENTS TABLE 21 VACUUM SENSOR CALIBRATION POINTS TABLE 22 MB 1 SPECIFICATIONS OF SPECIAL INTEREST WHEN USING MB 1 WITH ANALOG SENSORS TABLE 23 AVAILABLE MB 1 CALIBRATION POINTS 1 Introduction 1 is not restricted to Amateur Radio applications The calibration routines that were originally designed to improve RF power measurements were expanded allowing 1 to provide generalized measurement capabilities for a wide range of other applications using analog sensors and transducers When combined with MB 1 s other features such as its programmable display devices a programmable averaging window and its alarm trip functions we believe that MB 1 will be useful for a variety of different applications The MeterBuilder website provides an overview on using analog sensors with MB 1 You should also read the Quick Start section of the MB 1 User s Manual to gain a basic understanding of the meter s operation Features like programming the display devices the alarm trip functions the averaging filter and most of MB 1 s other Amateur Radio features are equally applicable for use with analog sensors The overall steps for programming all Generic A
5. 11 2 Calibration Procedure 4 11 3 Using the Liquid Level Sensor with Alarm Functions 4 12 LIGHT LEVEL SENSOR 4 12 1 Overview 4 12 2 Interface Circuit 4 13 FIELD STRENGTH METER USING ELECTROMAGNETIC SIGNAL SENSOR 4 13 1 Overview 4 14 RF AMMETER 4 14 1 Overview 4 15 MEASURING TILT USING AN ACCELEROMETER SENSOR 4 15 1 Overview 4 15 2 Error Analysis 4 15 3 Related Sensors 4 16 MEASURING TILT USING A DISCRETE TILT SENSOR 4 16 1 Overview 4 17 LOGARITHMIC SOUND PRESSURE LEVEL SENSOR 4 17 1 Overview 4 17 2 Error Analysis 4 18 COLOR SENSOR MODULE 4 18 1 Overview 4 18 2 Calibration Procedure 4 18 3 Using the Color Sensor with Alarm Functions 4 19 MEASURING BLOOD ALCOHOL LEVEL USING A NONLINEAR DEVICE 4 19 1 Overview 4 19 2 4 19 3 4 19 4 Error Analysis 4 19 5 Details 4 19 6 Related Sensors 4 20 ANGULAR RATE SENSOR GYROSCOPE 4 20 1 Overview 4 20 2 Interface Circuit 4 20 3 Calibration Procedure 4 21 HALL EFFECT MAGNETIC SENSOR 4 21 1 Overview 4 21 2 Coupler Port Calibration 4 21 3 Panel Meter Calibration 4 21 4 Related Sensors 4 22 OHMMETER EXAMPLE 4 22 1 Overview 4 22 2 Calibration Procedure 4 22 3 Error Analysis 4 22 4 Increasing the Range 4 22 5 Analog Meter Calibration 4 23 MEASURING TEMPERATURE COMPENSATED PH AND OXIDATION REDUCTION POTENTIAL 4 23 1 Overview 4 23 2 Coupler Port Calibration 4 23 3 Analog Meter Calibration 4 24 YAESU FT857 897 EXTERNAL ANALOG METER 4 24 1 Overview 4 25 SOME OTHER SENSORS 4 25 1 Overview 4 2
6. 1722109 2 1957476 2 2192843 2 242821 2 5 2 5 2 5 2 5 2 5 2 8513258 2 8277891 2 8042524 2 7807157 2 757179 3 2026516 3 1555782 3 1085048 3 0614314 3 014358 3 5539774 3 4833673 3 4127572 3 3421471 3 271537 3 9053032 3 8111564 3 7170096 3 6228628 3 528716 4 256629 4 1389455 4 021262 3 9035785 3 785895 4 6079548 4 4667346 4 3255144 4 1842942 4 043074 4 9592806 4 7945237 4 6297668 4 4650099 4 300253 7 0672354 O ON ADU BPWN FP Oo Remember that we calibrated the coupler port for the T 100 case Therefore the digital display readings on the 1 are valid only for the T 100 case However if we create an analog scale for this application using the T 100 case and use the full meter movement range for that case the analog scales for all other temperatures can be temperature corrected by determining what fraction of the analog needle displacement each scale occupies with respect to the T 100 case Below we show how to determine the temperature corrected scales We can use the sensor equation to determine what the pH value is for the temperatures other than T 100 that correspond to Vour T 100 for each integral pH value column 2 in the table above These pH values are shown in the table below for the four temperatures for which we will be creating additional analog scales Table 15 pH Values for Different Temps corresponding to Vour at T 100 Case pH T 75 pH T 50 pH T 25 pH T 0 0 50263 1 08303 1 76075 2 56252 0 5691
7. 300K calibration at the MB 1 calibration point of 30 000 the highest available MB 1 calibration point Then all numeric readings on MB 1 would have to be multiplied by 10 by the user to determine the actual resistance value being measured This would likewise apply to all other calibration points In the figure below it can be seen that at the higher resistance values the 300K input resistance of the MB 1 coupler port becomes significant This resistance can be accounted for by calculating the transfer function taking into account the Unknown R in parallel with the MB 1 input resistance This will give reasonable results for resistances up to 1 Meg Above that value the 300K resistance of the MB 1 input starts to dominate Figure 43 Affect of MB 1 Input Resistance on Measurement Resi 4 22 5 Analog Meter Calibration Most analog ohmmeter scales have a nonlinear scale to account for the nonlinear transfer function of measuring the current directly with an analog meter movement Since the MB 1 measurement and display functions are independent there is no reason why the analog scale can not be linear The figure below shows a linear scale that can be used in the above example A full size copy can be found here 4 23 Measuring Temperature Compensated pH and Oxidation Reduction Potential 4 23 1 Overview This sensor interfaces with either a PH probe or an Oxidation Reduction Potential ORP probe and generates a DC voltage tha
8. 727273 4 375 0 039683 0 652174 2 826087 4 444444 0 044599 0 744681 2 916667 4 5 0 049505 0 833333 3 4 545455 0 098039 1 153846 3 076923 4 6875 0 145631 1 428571 3 148148 4 761905 0 192308 1 666667 3 214286 4 83871 4 22 2 Calibration Procedure To calibrate this application we simply dial in the corresponding voltages for the various calibration points in the above table using a stable voltage source and potentiometer as shown in Figure 4 4 22 3 Error Analysis We can take a look at how well the linear interpolation will at the midpoint of the above calibration points The R and columns from the above table are repeated in the table below in the first two columns Because MB 1 uses linear interpolation between calibration points MB 1 will declare the measurement value to be half way between the corresponding calibration points in the left column when the voltage is exactly half way between the corresponding voltage levels in the Vour column Each entry in the Vy column is the midpoint voltage for the current row and the following row For example the first entry is the voltage half way between the voltage calibration points for 1 and 2 ohms Roect is the resistance value that MB 1 will declare when the voltage equals the corresponding entry For example a resistance of 1 5 ohms which is the midpoint of the first two resistance
9. Alternatively you may set the calibration voltage to a lower value if you want to increase the sensitivity of the sensor antenna combination Calibration is most easily done by dialing in the desired voltage using a stable voltage source and potentiometer as shown in Figure 4 Analog Meter Calibration Any linear scale analog meter with a full scale rating of 1 mA or less will work fine in this application A sample Field Strength Intensity scale is shown here with three scales 0 10 0 100 0 1000 Since we have built in a large amount of resolution during the coupler calibration step we provide three ranges to make use of that resolution Notes A homebrew unit that can be used with MB 1 that has provisions for amplification can be found on N9ZIA s web site 4 14 RF Ammeter 4 14 1 Overview Like an RF power coupler and the other sensors discussed above an RF Current Sensor is really just another form of an analog sensor When you bring up the Coupler Setup screen however you will see that there is a separate choice for the RF Ammeter setup AMPS as shown in the setup screen below This has to do with the way MB 1 processes analog voltages that are either below or above the voltages corresponding to the lowest and highest calibration points respectively This is discussed in detail in 9 3 Suffice it to say here that for multipoint calibrations for both RF Power couplers and RF Ammeter couplers MB 1 will compute po
10. Level Sensor 4 12 1 Overview The sensor used in this example is a ROHM BH1620FVC integrated circuit It generates a DC current proportional to the light intensity level and has a range of more than 5 decades 1 lumen to gt 100 000 lumens In this example we show how to take a sensor with a very wide range and display measurements that fall into each of the five decades with good resolution on an analog meter This example also shows how we can measure quantities larger than the maximum full scale value that MB 1 accommodates 30 000 http media digikey com Photos Rohm 20Photos EV AL BH1620FVC jpg Below is a picture of the light sensor The data sheet can be found here The sensor has a power and ground lead two digital inputs to control the sensitivity and a current output lead that gets connected to an appropriately sized resistor to generate a voltage proportional to the light intensity The generated voltage is fed to an MB 1 coupler input for calibration and measurement 4 12 2 Interface Circuit The sensor connection to MB 1 is shown below Figure 28 Interfacing Light Sensor to MB 1 Shutdown Hi Sensitivity Med Sensitivity Low Sensitivity The appropriate logic signals are applied to leads GC1 and GC2 to provide three different sensitivity settings The output voltage is a function of the sensitivity setting according to the following equation Vout S where S is the Sensitivity Constant and is
11. MB 1 coupler input to amplify the signal excursion 4 20 2 Interface Circuit The blue line in the graph below shows the sensor output voltage for the full range of angular velocities The green line in the graph below shows the sensor output after it has been processed by the Amplifier circuit in Figure 39 The circuit has a gain of 19 1 180K 10K A gain of 19 was chosen since it maximizes the and excursion around the idle voltage 1 35 v without bottoming out at 0 The amplification is provided by op amp2 right Op amp 1 left simply provides a low impedance source of approximately 1 35 volts a virtual ground so that the op amp 2 can amplify the delta between the sensor s idle voltage and the sensor s output when an angular velocity is being measured Since the idle voltage from the sensor is not exactly 1 35 volts adjustable resistor R1 is included so that the virtual ground output of op ampl can be adjusted to match the actual idle voltage of the sensor during calibration Vout vs Angular Speed a e Sensor Output E Amplifier Output Vout volts Angular Speed deg per sec Figure 39 Interface Circuit for Angular Velocity Sensor 1 309 v to Virtual 1 428 v Ground at approx 1 35 To Coupler Input Angular Rate Sensor Sensor output voltage approx 1 35v when idle 4 20 3 Calibration Procedure Coupler Port Calibration First we m
12. POTENTIOMETER MULTIMETER AND RCA CABLES RE 6 TEMPERATURE INPUT DEVICE RE 7 LM34 FEEDING MB 1 8 METER SHUNT RE 9 DC AMMETER APPLICATION RE 10 PROBLEM MEASURING TRANSCEIVER POWER SUPPLY CURRENT USING SHUNT RE 11 MEASURING TRANSCEIVER POWER SUPPLY CURRENT USING AN ISOLATED CURRENT SENSOR RE 12 HALL EFFECT CURRENT SENSOR 13 MAXIM MAX4210E DC POWER SENSOR RE 14 THERMISTOR RESISTANCE 15 NONLINEAR THERMISTOR CIRCUIT AND CALIBRATION PROCEDURE RE 16 VOLTAGE INPUT INTO MB 1 vs TEMPERATURE RE 17 FORCE SENSOR CURVE RE 18 INPUT CIRCUIT TO MEASURE FORCE RE 19 REFLECTANCE SENSOR RE 20 INPUT CIRCUIT TO MEASURE REFLECTANCE RE 21 GREY SCALE FOR CALIBRATING REFLECTANCE SENSOR RE 22 ULTRASONIC DISTANCE SENSOR RE 23 IR DISTANCE SENSOR RE 24 VOLTAGE VS DISTANCE FOR IR SENSOR RE 25 SENSOR REVERSED AND BIASED TO GET INCREASING VOLTAGE VS PARAMETER RE 26 VOLTAGE VS DISTANCE FOR IR SENSOR INVERTED CURVE RE 27 INPUT CIRCUIT TO MEASURE LIQUID LEVEL RE 28 INTERFACING LIGHT SENSOR TO MB 1 RE 29 GRAPHS OF DIFFERENT SENSITIVITY SETTINGS ON LIGHT SENSOR RE 30 CURRENT SENSOR RE 31 SENSOR ORIENTATION RE 32 INTERFACE CIRCUIT FOR DISCRETE TILT SENSOR RE 33 INTERFACE CIRCUIT FOR DISCRETE TILT SENSOR USING D TO A CONVERTER RE 34 OUTPUT VOLTAGE VS SOUND PRESSURE RE 35 FIGURE 36 COLOR SENSOR CURVES FOR RGB SCALE AND SCALE RE 37
13. Regardless of which scale we use R G B or percent the two calibration points can be dialed in with a stable voltage source and potentiometer as shown in Figure 4 You will not be able to achieve the 5 7072 volt setting in the RBG scale using just the potentiometer connected to MB 1 s 5 volt auxiliary power output You can either use a larger voltage source to power the pot during calibration or you can temporarily connect any 1 5 volt battery in series with the pot wiper during calibration This will give your pot battery arrangement a range of approximately 1 5 volts to 6 5 volts If you use the percentage scale both calibration voltages can be achieved directly using just the auxiliary 5 volt source from MB 1 4 18 3 Using the Color Sensor with Alarm Functions The MB 1 alarm functions be used to detect the presence or absence of a color by setting the alarm s high trip point to an appropriate threshold to detect the presence of a color or by setting the alarm s low trip point to an appropriate threshold to detect the absence of a color The alarm trip delay can be set to an appropriate value to accommodate varying conditions of the item s being monitored 4 19 Measuring Blood Alcohol Level Using a Nonlinear Device 4 19 1 Overview The MQ 3 Alcohol Sensor samples the concentration of alcohol in an air sample and changes its resistance as a function of the alcohol concentration A picture is shown below The data sh
14. Temperature Sensor and feed the signal to a coupler port that is calibrated using MB 1 s Generic Meter calibration mode Once calibrated the temperature can be read directly from any of MB 1 s display devices LCD analog meter 7 Segment Displays and Bar Graph The data sheet for the LM34 can be found here The device generates a DC output voltage that is proportional to the temperature in Fahrenheit 10 millivolts per degree We use the LM34D which has a range of 32 to 212 which corresponds to an output voltage range of 320 millivolts to 2 120 volts FIGURE 6 TEMPERATURE INPUT DEVICE Power 5 volts 20 volts output 10 mV degree To program 1 to measure temperature connect the LM34D to the FWD port of one of MB 1 s four coupler ports as shown below FIGURE 7 LM34 FEEDING 1 Power 5 volts 20 volts input to one of the four FWD Coupler Ports output 10 mV degree MB 1 Control Head 4 1 2 Calibration Procedure The Generic Meter example in the MB 1 User s Manual provides a detailed list of steps This application uses the same procedure with the following changes 1 Since we are measuring degrees in Fahrenheit set the Units character to be displayed on the LCD to F for Fahrenheit For the voltages involved in this application you should adjust the side panel coupler trim pot to its maximum sensitivity at least 15 turns CW Since the MB 1 input does not saturate until appr
15. entries will be declared when the measured voltage is the actual resistance that would result in at the corresponding Vy voltage This is calculated simply using the voltage divider formula ERR is the error in ohms between the actual resistance Racr and the declared resistance for each midpoint Finally the last column represents the error as a percentage of the nominal R value The result is reasonable tracking between the MB 1 measurement value and the actual resistance value with a maximum error of 3 8496 For the majority of entries the error is less than 196 Table 12 Error Analysis for Ohmmeter Example ERR R ohms Vour Roect ohms _ ERR 0 004995 1 49975 0 000249626 0 016644 0 00998 0 012468 5 2 499751 0 000249377 0 009976 0 014955 0 017438 5 3 499751 0 000249128 0 007118 0 01992 0 022398 5 4 499751 0 00024888 0 005531 0 024876 0 027348 5 5 499751 0 000248633 0 004521 0 029821 0 032289 5 6 499752 0 000248385 0 003821 0 034757 0 03722 5 7 499752 0 000248139 0 003309 0 039683 0 042141 5 8 499752 0 000247893 0 002916 0 044599 0 047052 5 9 499752 0 000247647 0 002607 0 049505 0 073772 14 97537 0 024630542 0 164474 0 098039 0 121835 24 97561 0 024390244 0 097656 0 145631 0 168969 34 97585 0 024154589 0 069061 0 192308 0 215201 44 97608 0 023923445 0 053191 0 238095 0 260557 54 9763 0 023696682 0 043103 0 283019 0 305061 64 97653 0 023474178 0 036127 0 327103 0 348737 74 97674
16. for the device can be found here The input output curve for this device is shown in Figure 24 As you can see for the useful part of the curve where distance is gt 6 cm the output voltage decreases as distance increases Measurements can not be made below this point because the sensor output voltage must be unique for each parameter value and that is not the case for the transfer function if the region where the distance is less than 6 cm is included Figure 23 IR Distance Sensor Figure 24 Voltage vs Distance for IR Sensor Output 55 HAS TATS LLLL Distance in cm 4 10 2 Calibration Procedure There are two ways to deal with the upside down direction of the transfer function 4 10 2 1 Calibrate and display the reciprocal of the parameter The reciprocal of the curve in Figure 24 Voltage vs Distance for IR Sensor above 10 cm is a monotonically increasing function If we calibrated the meter to measure the reciprocal of the distance this would require us to calculate the reciprocal of the measured value to get the actual distance parameter not elegant However you could make a custom analog meter face with two scales The first scale would be the actual parameter being measured the reciprocal of distance The second scale would be the corresponding distances which could be read directly from the second analog scale which would read from high to low 4 10 2 2 Invert the output and Bias it so th
17. frequency range from 100 Hz to 8 kHz But as stated on the Phidgets website these sensors are not industrial grade sensors and should not be expected to perform as such This example will use this sensor to display sound pressure directly in logarithmic units dB Below is a picture of the sound sensor The data sheet can be found here From the data sheet the equation of the Sound Pressure Level with respect to output voltage V our 18 shown below SPL 16 801 In 200 Vour 9 872 where In is the natural log function The graph for this transfer function is shown below Figure 34 Output voltage vs Sound Pressure Sound Pressures vs Vout 02 03 04 05 06 07 08 09 Vout volts For calibration we need to know the voltages that correspond to the SPL values from 50 dB to 100 dB Solving for Vout in the above equation Vout exp SPL 9 872 16 801 200 A chart of the voltages for these points is shown below Vout Vout 0 054482 0 256055 0 057823 0 271759 0 061369 0 288425 0 065133 0 306113 0 069127 0 324886 0 073367 0 344811 0 077866 0 365957 0 082641 0 3884 0 087709 0 41222 0 093088 0 4375 0 098797 0 464331 0 104856 0 492807 0 111287 0 523029 0 118112 0 555105 0 125355 0 589148 0 133043 0 625279 0 141202 0 663626 0 149862 0 704324 0 159052 0 747518 0 168806 0 793362 0 179159 0 842016 0 190146 0 893655 0 201807 0 94846 0 214184 1 006627 0 227319 1 06836 0 24126
18. industry standard current loop interface of 4 20 mA to encode the magnitude of the parameter being measured One such sensor is the ST420 DI from Electro Sensors A picture of the sensor and its pulser disc are shown below The pulser disc contains magnets that are sensed by the magnetic pulse detector in the sensor In addition to the pulse detector the sensor contains the signal processing circuitry to convert the magnetic pulse counts into a smooth 4 20 mA output The data sheet for this sensor is found here The User s Manual for this sensor provides some additional information that specifies the relationship between RMP and the output current This sensor is available in two standard offerings e ST420 DLL 2 RPM to 200 RPM e ST420 DIH 2 RPM to 2000 RPM This example makes use of the lower speed sensor 5 11 2 Interface Circuit The connection of the sensor to MB 1 is shown in Figure 45 below The current range of 4 mA to 20 mA will produce a voltage input to MB 1 of 1 volt and 5 volts respectively when a 250 ohm resistor is used 1 volt corresponds to the lowest detectable RPM value of 2 RPM 5 volts corresponds to the largest detectable RPM value of 200 RPM Figure 45 RPM Sensor Interface To MB 1 ST 420DI Coupler Sensor Port 5V FS 5 11 3 Calibration Procedure Even though the Vour vs RPM transfer function is linear it does not pass through the origin Therefore we must perform the calibration at two ca
19. is repeated for each integer value in the active range 50 dB to 100 dB As can be seen from the last column none of the errors is greater than 73 dB Table 7 Error Analysis for Sound Sensor Interpolated Vout for which 1 10th MB 1 will Delta for Delta declare this 10 for this the Nominal Nominal dB 10 dB SPL value in Actual Error SPL Vout Exact range Range column 1 SPL Value dB 0 0544818 0 04432 0 00443 0 05448 50 0 0 057823047 0 058913 51 3138528 0 313853 0 061369177 0 063345 52 5323713 0 532371 0 065132781 0 067776 53 6684596 0 66846 0 069127197 0 072208 54 7325669 0 732567 0 073366579 0 07664 55 7332736 0 733274 0 077865951 0 081071 56 6777117 0 677712 0 082641257 0 085503 57 5718736 0 571874 0 08770942 0 089934 58 4208425 0 420843 0 093088399 0 094366 59 2289679 0 228968 0 0987973 0 08036 0 00804 0 0988 60 0 0 104856223 0 106833 61 3138528 0 313853 0 111286769 0 11487 62 5323713 0 532371 0 118111683 0 122906 63 6684596 0 66846 0 12535515 0 130942 64 7325669 0 732567 0 133042839 0 138978 65 7332736 0 733274 0 141201993 0 147014 66 6777117 0 677712 0 149861526 0 15505 67 5718736 0 571874 0 1590521 24 0 163086 68 4208425 0 420843 0 168806357 0 171123 69 2289679 0 228968 0 1791588 0 14573 0 01457 0 17916 70 0 0 190146109 0 193732 71 3138528 0 313853 0 201807251 0 208304 72 5323713 0 532371 0 214183539 0 222877 73 6684596 0 66846 0 227318831 0 23745 74 7325669 0 732567 0 241259674 0 252023 75 7332736 0 733274 0 2
20. jack on Rear Panel Case 2 The current sensor in section 4 4 isolates the lead whose current is being measured from the sensor output leads which feed the MB 1 coupler port The current sensor output is linear but does not pass through the origin The sensor in this example generates an output voltage of approximately 133 millivolts per amp but the idle current output voltage when the current being measured 0 is 500 millivolts Its data sheet can be found here Since this transfer function does not pass through the origin we need two calibration points one at the low end of the scale and one at the high end of the scale As with the example discussed in case 1 above since we know the transfer function we can dial in the corresponding voltages at each of the two calibration points Case 3 For nonlinear sensors if you can characterize the parameter voltage relationship mathematically or if it is given in a spec sheet you can create a simple a grouping of parameter voltage points that line up with MB 1 s available calibration points see the nonlinear temperature sensor example in section 4 7 Using the potentiometer procedure in Figure 4 you can calibrate this series of points by setting the appropriate voltage at each calibration point To calculate measurements when the sensor voltage is at an intermediate voltage point with respect to the discrete calibration points the MB 1 software uses linear interpolation Case 4 T
21. of 1 amps and higher than the largest calibration point of 4 amps in the above example will still be measured and displayed by 1 In these cases MB 1 uses the transfer function characteristics at the lowest and highest calibration points respectively to compute the values Note when performing the coupler setup be sure to follow the procedure for setting the coupler trim pot to ensure that you do not drive the MB 1 Amplifier Mux into saturation This procedure is described in detail in the MB 1 User s Manual Analog Meter Calibration Analog Meter calibration is straight forward and makes use of one or more linear scales depending upon the number of ranges desired A sample RF Ammeter scale is shown here 4 15 Measuring Tilt using an Accelerometer Sensor 4 15 1 Overview This example will measure tilt from 0 degrees to 90 degrees The sensor used is a dual axis sensor but we will use only a single channel A good discussion of how tilt can be measured using an accelerometer is given here but the main point is that the displacement that accelerometer would undergo on a given axis if the acceleration was 1g is identical to the displacement that the accelerometer undergoes when the board is oriented 90 degrees At that point the sensor is undergoing 1g due to gravity even though the sensor is not moving Below is a picture of the accelerometer sensor The data sheet can be found here The figure below shows how
22. the voltage induced in two secondary transformers The induced voltage is proportional to the displacement The displacement or stroke lengths for these sensors is 2mm to 50mm Some LVDTs contain interface circuitry to convert the secondary AC voltages into DC voltages that are more easily processed These AP3 sensors provide such an interface The data sheet for these devices can be found here 5 9 Volumetric Flow Sensor The Omega FPR Flow Sensor measure flow and comes in two models e 5 GPM to 15 GPM e 1 5 GPM to 50 GPM Both models have a 4 20 mA analog output that is proportional to the flow rate The specifications for these sensors can be found here The manual can be found here 5 10 Rotary Torque Transducer The Interface Rotary Torque Transducer rated at 200 Newton Meters generates DC voltage proportional to the torque The analog output is 0 to 5 volt output for CCW torque and a 0 to 5 volt output for CW torque To measure torque in both directions an isolated and regulated 5 volt DC to DC converter or equivalent needs to be inserted in series with the transducer output since MB 1 requires that the coupler input voltages to be positive To measure torque in one direction only the transducer output can be connected directly to MB 1 The data sheet for this device can be found here 5 11 RPM Sensor using an Industry Standard 4 20 mA Current Output 5 11 1 Overview Many industrial sensors use an
23. the Illumination Level The Sensitivity Constants are Sensitivity S Sensitivity Constant Low Medium High We will use the lowest sensitivity setting when measuring the highest light intensity 100 000 lumens To calculate the resistance value we want Vout to be less than 5 volts when the Illumination is 100 000 This limitation is required for the sensor current source to function properly when being powered with 5 volts Vout 0057 10 100 000 R For Vout to be less than 5 volts when the full scale light intensity is present R must be less than 8 8K We will therefore use a standard value of 6 8K Taking into account MB 1s input sensitivity and dynamic range the table below shows the usable range for each sensitivity setting in yellow For example for the high sensitivity setting which is used to measure low 43 light levels we will be able to measure from 1 lumen to 1000 lumens which will generate a Vour from 3 876 millivolts to 3 3876 volts Vout Vout V Ey Hi Sensitivity Med Sensitivity Low Sensitivity 1 0 0003876 0 00003876 10 0 0003876 100 1000 10000 38 76 100000 387 6 38 76 Apply following corrections to MB 1 Digital Readings Multiply by 10 Divide by 10 Graphs for each of the sensitivity settings are plotted on log scales in the chart below Since the sensor is powered from 5 volts the portion of the graphs where the output exceeds 5 volts is not applicable Figur
24. transceiver and to MB 1 since this would effectively short out the power supply Likewise ground loop problems would result if we placed the shunt in the negative leg of the power supply Figure 10 Problem Measuring Transceiver Power Supply Current using Shunt 12 volt E Power Transceiver Supply Connection would cause short MB 1 Control Head To measure current in such applications we can use a sensor that provides isolation between the leads carrying the parameter to be measured and the sensor output leads that feed the MB 1 coupler port For the power supply current measurement example discussed above a Hall Effect current sensor provides the necessary isolation as shown below Figure 11 Measuring Transceiver Power Supply Current using an Isolated Current Sensor Transceiver MB 1 Control Head An example of such a sensor is shown below Its data sheet can be found here This sensor is capable of measuring up to 30 amps DC which provides a good match for the typical transmit mode current draw of 100 watt transceivers powered from 12 volt supplies And surprisingly this sensor is less expensive than most 20 amp and 30 amp meter shunts FIGURE 12 HALL EFFECT CURRENT SENSOR 4 4 2 Calibration Procedure The sensor outputs is a DC voltage that varies linearly with respect to the input current The sensor has a DC offset of approximately 500 millivolts when the current 0 The output increases at a rate of
25. use the empirical approach by applying a series of known forces to the sensor during calibration 4 82 Calibration Procedure Below is a picture of an Interlink 402 sensor It s resistance vs force curve is given below Figure 17 Force Sensor Curve 2111 HE Resistance 100 1000 10 000 Force in grams Figure 18 Input Circuit to Measure Force To measure the pressure with MB 1 using this sensor the circuit in the figure above can be used Since the sensor resistance decreases with increasing pressure this will cause the voltage into MB 1 to increase for increasing pressure again what we want an output whose voltage increases as a function of the parameter being measured If we wanted to calculate the voltages corresponding to various pressures that would be straightforward For example when the pressure is 20 grams the resistance is 30K The voltage at the tap of the sensor and the 10 k resistor would be 5 Volts 30K 30K 10K 3 75 volts We could repeat the calculations at a number of points corresponding to MB 1 calibration points for example 20 grams 30 grams 10 000 grams We could then calibrate MB 1 as we did for the non linear temperature sensor above namely selecting each calibration point dialing in the corresponding voltage with a potentiometer and saving the calibration data potentiometer as shown in Figure 4 But this is a case where the e
26. we need to calibrate the sensor at two points The two end points in the MB 1 column in the table above are 0 and 11 Since 11 is not an available MB 1 calibration point we will use the next higher available calibration point of 20 Since the transfer function is linear if we use calibration points of 0 and 20 the maximum allowable Pressure value of 10 millibars corresponding to an MB 1 reading of 11 will simply be a value that lies on the straight line transfer function Note that during actual operation the vacuum sensor will never produce a voltage that represents a pressure greater than 10 Table 21 Vacuum Sensor Calibration Points Pressure MB 1 Vourt volts Comments millibars Calibration Point 020012 14 000 Used only for calibration Note that the largest voltage in the table above is 14 00 volts which is above the maximum voltage that can be applied to an MB 1 coupler port without saturating it when the coupler trim pots is set to maxim sensitivity see Table 22 To ensure that the MB 1 Amp Mux does not saturate during calibration or operation use the Coupler Setup feature that allows you to view the output of the A to D chain while adjusting the coupler trim pot Set the output of the Amp Mux chain to approximately 30 000 with a voltage of 14 00 volts applied The actual calibration is most easily done by dialing in the calibration voltage at the above two calibration points using a stable voltage source a
27. 0 or 30 millivolts which is the value used in the second column in the table below The third column shows the calculated pressure for the voltages in the second column using the above formula The following table summarizes the MB 1 readings the sensor output voltage Vour and the calculated pressure for 20 segments equally spaced between P 10 and P 10 Table 20 Lookup Table for Interpolating non integral MB 1 Measurements Reading vour Pressure Reading VOUT Pressure 0 2 10E08 po 06 236 402E08 08 248 637E08 09 254 802E08 To use this table simply take the decimal portion of the 1 reading and determine the coefficient in the third column This coefficient will be the same for each of the 11 pressure decades For example assume that MB 1 reads 3 65 We know that the pressure is between 10 and 10 millibars If we look up the fractional part in the above table 65 we see that MB 1 digital reading of 3 65 corresponds approximately to a coefficient of 4 51 Therefore an MB 1 reading of 3 65 corresponds to a pressure of 4 51 x 10 millibars This lookup approach is workable but somewhat cumbersome We come up with a better approach that will allow a direct reading of the pressure when using an analog meter calibrated for this application This is discussed below Calibration Point Since the transfer function equation is linear but does not pass through the origin
28. 0 023255814 0 031017 0 37037 0 391607 84 97696 0 023041475 0 027115 0 412844 0 433695 94 97717 0 02283105 0 024038 A O 0 o C1 100 0 454545 0 505051 112 3596 0 140449438 0 125 125 0 555556 0 603865 137 3626 0 137362637 0 1 150 0 652174 0 698427 162 3656 0 134408602 0 082781 175 0 744681 0 789007 187 3684 0 131578947 0 070225 200 0 833333 0 99359 248 2 0 806452 300 1 153846 1 291209 348 1481 1 851851852 0 531915 400 1 428571 1 547619 448 2759 1 724137931 0 384615 500 1 666667 1 770833 548 3871 1 612903226 0 294118 600 1 875 1 966912 648 4848 1 515151515 0 233645 700 2 058824 2 140523 748 5714 1 428571429 0 19084 800 2 222222 2 295322 848 6486 1 351351351 0 159236 900 2 368421 2 434211 948 7179 1 282051282 0 135135 1000 2 5 2 559524 1048 78 1 219512195 0 116279 1100 2 619048 2 67316 1148 837 1 162790698 0 101215 1200 2 727273 2 77668 1248 889 1 111111111 0 088968 1300 2 826087 2 871377 1348 936 1 063829787 0 078864 1400 2 916667 2 958333 1448 98 1 020408163 0 070423 1500 3 3 038462 1549 02 0 980392157 0 063291 1600 3 076923 3 112536 1649 057 0 943396226 0 057208 1700 3 148148 3 181217 1749 091 0 909090909 0 051975 1800 3 214286 3 245074 1849 123 0 877192982 0 047438 1900 3 275862 3 304598 1949 153 0 847457627 0 043478 2000 3 333333 3 541667 2428 571 71 42857143 2 941176 3000 3 75 3 875 3444 444 55 55555556 1 612903 4000 4 4 083333 4454 545 45 45454545 1 020408 5000 4 166667 4 2261
29. 0 296 of the distance between the tic marks and so forth Since the coupler has been calibrated for a full scale value of 11 when calibrating the Panel Meter the scale type should be set to linear with a full scale value of 11 Rotary Shaft Encoder The Advanced Micro Controls AMCI DC25 encoder is an Absolute Single Turn sensor that generates a DC voltage proportional to the angular displacement The data sheet can be found here 5 3 Linear Position Sensor The Unimeasure family of Linear Position Sensors measure linear distance by measuring the amount a cable is extended from the sensor These units measure distances from as small as 2 inches to as large as 2000 inches These units are basically high resolution multi turn potentiometers The data sheet on this family of sensors can be found here 5 4 Non Contact Infrared Temperature Sensor The Omega OS136 sensor measures the temperature of a surface within in the optical field of view which is 6 1 for this sensor The sensor is internally calibrated for a fixed emissivity of 95 This sensor can be ordered in different temperature ranges either 0 400 F or 300 F 1000 F and different output formats The output formats that will work with MB 1 are V1 0 5 volts DC V2 0 10 volts DC MVC 10 mV C and MVF 10 mV F Details on the sensor can be found here 5 5 High Precision Low Displacement Inductive Linear Sensor The Balluff M8 Linear Sensor provid
30. 5 2 Humidity Sensor 4 25 3 Pressure Sensor Barometer 4 25 4 Wind Direction Sensor SOME INDUSTRIAL SENSORS 5 1 ELEVEN DECADE VACUUM SENSOR 5 1 1 Overview 5 1 2 Coupler Port Calibration 5 1 3 Panel Meter Calibration 5 2 ROTARY SHAFT ENCODER 5 3 LINEAR POSITION SENSOR 5 4 NON CONTACT INFRARED TEMPERATURE SENSOR HIGH PRECISION LOW DISPLACEMENT INDUCTIVE LINEAR SENSOR TIME OF FLIGHT LASER DISTANCE SENSOR SALT WATER CONDUCTIVITY SENSOR LINEAR VARIABLE DISPLACEMENT TRANSFORMERS VOLUMETRIC FLOW SENSOR ROTARY TORQUE TRANSDUCER RPM SENSOR USING AN INDUSTRY STANDARD 4 20 MA CURRENT OUTPUT 5 11 1 Overview 5 11 2 Interface Circuit 5 11 3 Calibration Procedure ADDING MB 1 TO EXISTING MEASUREMENT SYSTEMS INPUT SENSITIVITY AND DYNAMIC RANGE INTERPOLATION SPECIAL CONSIDERATIONS WHEN USING MB 1 WITH ANALOG SENSORS 9 1 AN ADDITIONAL CALIBRATION POINT OF 0 FOR USE WITH ANALOG SENSORS 9 2 ALLOWING A VOLTAGE OF 0 DURING CALIBRATION WITH ANALOG SENSORS 9 3 PROCESSING MEASUREMENTS OUTSIDE OF THE CALIBRATION RANGE 9 3 1 Single Point Calibration Cases 9 3 2 Multipoint Calibration Cases 9 3 5 Dialing In actual Parameter Value during Calibration Figures RE 1 SENSOR WITH LINEAR TRANSFER FUNCTION PASSING THROUGH THE ORIGIN RE 2 SENSORS WITH LINEAR TRANSFER FUNCTIONS NOT PASSING THROUGH THE ORIGIN RE 3 SENSORS WITH NONLINEAR TRANSFER FUNCTIONS RE 4 USING A VOLTAGE SOURCE AND POTENTIOMETER FOR CALIBRATION RE 5
31. 50 kilopascals Barometric pressure is approximately 100 kilopascals with limited variation around that value Because of the broad measurement range the resolution is approximately 1 kilopascal per 10 millivolts If you set you lower and upper ranges to 80 kilopascals and 125 kilopascals during calibration you should be able to get reasonable resolution The analog meter scale for the Barometer must be calibrated as a nonlinear scale since the starting value is not 0 See the discussion for the Panel Meter calibration in the Logarithmic Sound Pressure Level Sensor example above Details on the pressure sensor can be found here The data sheet can be found here 4 25 4 Wind Direction Sensor This sensor measures wind direction by outputting a DC voltage that ranges from 5 to 95 of power supply voltage This corresponds to 250 millivolts to 4 75 volts for 5 volt power When facing North the sensors outputs its minimum voltage The voltage increases linearly as the direction changes to East South West etc Details on the sensor can be found here 5 Some Industrial Sensors The following sensors are used primarily in industrial applications Detailed descriptions are provided for those sensors that cover some new interfacing topics 5 1 Eleven Decade Vacuum Sensor 5 1 1 Overview This example uses an 11 decade Inficon vacuum sensor that can measure pressure from approximately 10 to 10 millibars This corresponds to a rat
32. 56055471 0 266595 76 6777117 0 677712 0 271758654 0 281168 77 5718736 0 571874 0 288424871 0 295741 78 4208425 0 420843 0 306113181 0 310314 79 2289679 0 228968 0 3248863 0 26426 0 02643 0 32489 80 0 0 344810654 0 351312 81 3138528 0 313853 0 365956951 0 377739 82 5323713 0 532371 0 388400092 0 404165 83 6684596 0 66846 0 412219609 0 430591 84 7325669 0 732567 0 437499912 0 457017 85 7332736 0 733274 0 464330588 0 483443 86 6777117 0 677712 0 492806715 0 50987 87 5718736 0 571874 0 523029206 0 536296 88 4208425 0 420843 0 555105159 0 562722 89 2289679 0 228968 0 5891482 0 47921 0 04792 0 58915 90 0 0 625279097 0 637069 91 3138528 0 313853 0 663625757 0 684991 92 5323713 0 532371 0 704324113 0 732912 93 6684596 0 66846 0 747518389 0 780833 94 7325669 0 732567 0 793361651 0 828754 95 7332736 0 733274 0 842016355 0 876676 96 6777117 0 677712 0 89365492 0 924597 97 5718736 0 571874 0 948460337 0 972518 98 4208425 0 420843 99 1 00662682 1 020439 99 2289679 0 228968 100 1 0683605 1 06836 100 0 Coupler Port Calibration Adjust the coupler trim pot for maximum sensitivity There is no chance of overdriving the MB 1 input in this application To calibrate this application set the full scale value to 100 units Then perform calibration at the following points 50 60 70 80 90 and 100 using the corresponding voltage levels shown in red Vour Exact in the table above This is most easily done by dialing in the calibration volt
33. 6 volts using a stable voltage source and potentiometer as shown in Figure 4 Analog Meter Calibration Since we have the option of creating a custom meter face for an analog meter for use with this application we can create 3 different scales that can be read directly based on whether the sensor is set to the low medium or high sensitivity setting The figure below shows such a scale A full size copy can be found here Light Intensity 30000 40000 50000 60000 10000 20000 80000 90000 4000 5000 6000 S s 2000 3000 7000 8000 a 20 200 400 500 600 800 10000 100 900 L 1000 Lumens Even though this meter face has three scales during the Panel Meter calibration you should specify only one linear scale not three The Panel Meter full scale value should be set to 10 000 When reading the analog meter you should use the top scale middle scale or bottom scale when the sensor sensitivity setting is set to low medium or high respectively We use this approach since we have calibrated our coupler above to generate a full scale digital value of 10 000 for all three sensitivity settings To summarize the approach we have used when reading numerical values from MB 1 LEDs or LCD a multiplier factor of 1 1 or 10 needs to be applied to the reading based on the sensitivity setting of the sensor When reading the analog meter the reading can be read directly from the appropriate scale without correction 4 13 Field Strength Me
34. 74 0 07169 0 50922 1 19645 1 640978 1 226409 0 74232 0 169625 2 712782 2 381127 1 993856 1 5357 3 784587 3 535845 3 245392 2 901775 4 856391 4 690563 4 496928 4 26785 5 928196 5 845282 5 748464 5 633925 7 7 7 7 8 071804 8 154718 8 251536 8 366075 9 143609 9 309437 9 503072 9 73215 10 21541 10 46415 10 75461 11 09822 11 28722 11 61887 12 00614 12 4643 12 35902 12 77359 13 25768 13 83037 13 43083 13 92831 14 50922 15 19645 14 50263 15 08303 15 76075 16 56252 O ON DU BPWN FP PRP PR wnr 14 The data from the above table is charted below along with the trend line equations that show pH for T 0 T 25 T 50 and T 75 Y axis vs the pH at 100 X axis pH as a Function of Temperature 661 2 5625 515x 1 7608 547x 1 083 718x 0 5026 pH for T 0 to 100 0 Linear 7 100 pH T 100 The top scale in the analog meter face shown below uses the T 100 case as the reference and spans the entire range of the meter movement Therefore each pH unit for the T2100 is 1 14 the scale deflection as shown below Table 16 Analog Needle Deflection for T 100 Case pH T 100 Deflection 0 0 0 071428571 0 142857143 0 214285714 0 285714286 0 357142857 0 428571429 0 5 0 571428571 ON ADU 0 642857143 0 714285714 0 785714286 0 857142857 0 928571429 1 From the chart above Figure 44 we know the relationship for the pH at a given temperature with respect to the pH a
35. 9 5461 538 38 46153846 0 704225 6000 4 285714 4 330357 6466 667 33 33333333 0 515464 7000 4 375 4 409722 7470 588 29 41176471 0 393701 8000 4 444444 4 472222 8473 684 26 31578947 0 310559 9000 4 5 4 522727 9476 19 23 80952381 0 251256 10000 4 545455 4 616477 12037 04 462 962963 15000 4 6875 4 724702 17162 16 337 8378378 1 968504 20000 4 761905 4 800307 24038 46 961 5384615 4 30000 4 83871 4 22 4 Increasing the Range The highest resistance we can measure with the above configuration is 30K To increase the range the fixed resistor in Figure 41 can be increased Figure 42 below shows the transfer function for two different values of the fixed resistor The curve in blue shows the transfer function when R 1K which was the case covered in the above example The curve in red shows the transfer function when the fixed R 10K With the 10K resistor we can get an upper usable range close to 1 Megohm The tradeoff is that the resolution at the lower end e g 1 100 ohms suffers somewhat Figure 42 Increasing Ohmmeter Range Voltage vs Unknown R e Fixed 1K Fixed R 10K T 1 000 10 000 100 000 1 000 000 Unknown R To implement the higher range since the maximum available MB 1 calibration point is 30 000 scaling would be required during the initial calibration For example we could define the actual measured value as the calibration value 10 This means that we would perform the
36. ERIC and set the full scale value to 8 units Place the sensor in a container of adequate height Add water at each one inch increment from 1 to 8 and save the calibration data at each of these points If you would like to obtain the full range of the sensor 8 5 inches you can set the full scale value to 9 during the setup However since the sensor is not capable of measuring a liquid above 8 5 inches you will have to calculate what the voltage would have been at 9 inches This can be done by extending the data curve in the data sheet until it reaches 9 and extrapolating what the sensor resistance would have been at 9 inches Knowing that value and the value of the fixed resistor above you can calculate the input voltage at the coupler input for this point and dial in the last calibration point using a pot and 5 the volt auxiliary source If you want to extend the range above 8 for best accuracy you should calculate the output resistance curve for your sensor and use it rather than the nominal curve If you add the calibration point for 9 inches you have used a hybrid approach to calibration for this sensor the empirical method for the first 8 points and a calculated value for the last point 9 inches 4 11 3 Using the Liquid Level Sensor with Alarm Functions The MB 1 alarm functions can be used to detect a low or high liquid level condition by setting the alarm s high low or high trip points to the appropriate values 4 12 Light
37. HERMISTOR CIRCUIT AND CALIBRATION PROCEDURE Thermistor 3 SS Fixed R Input to MB 1 FWD Port 42736 Common Nonlinear Temp Application Multipoint calibration 5 Volts Ze 4 E Input to MB 1 FWD Port T A Common Calibration procedure Using an Excel spreadsheet we can calculate the voltage at the Tip of the top circuit as a function of temperature A graph of the function is shown below FIGURE 16 VOLTAGE INPUT INTO MB 1 vs TEMPERATURE Temp Celcius vs voltage Vtip millivolts 100 150 200 250 300 Tcelcius If you are considering using MB 1 for a nonlinear application like this you should have an idea of what your input output function looks like because you want to make sure you have a reasonable resolution over the range you wish to measure We see that the above graph starts to saturate noticeably above 150 While the voltage still increases as the temperature ranges from 300 to 350 the voltage change per degree gets smaller and would result in reduced resolution in this range However in the range 0 to 100 C the slope is fairly large and we could expect reasonable resolution and accuracy within this range 4 7 2 Calibration Procedure The calibration procedure is fairly straightforward Using an Excel spreadsheet we have calculated values for the input voltage vs temperature Let s assume that we want to run a calibration in the rang
38. If we plug in the two closest available MB 1 calibration points 0 and 200 this gives the following calibration point input output values v Angular Velocity 0 0 0 11 volts 200 2 59 volts During calibration these values can be dialed in with a potentiometer powered from the 5 volt auxiliary voltage source as previously discussed Analog Meter Calibration If we design an analog meter scale face the range must be 200 units but when creating the analog scale we can set the tic marks to any value we choose Instead of creating a scale with a starting value of 0 and a full scale value of 200 we can set the starting value to 100 CCW and the full scale value to 100 CW We then calibrate the panel meter as a linear scale panel meter with a full scale value of 200 With this arrangement the angular velocity can be read directly from the analog meter The figure below shows such a scale A full size copy can be found here 4 21 Hall Effect Magnetic Sensor 4 21 1 Overview This example uses a Hall Effect Magnetic Sensor whose DC output voltage varies linearly with respect to the magnetic field Below is a picture of the sensor The data sheet can be found here If you are looking for a good reference on Hall Effect Sensors check this documentation from the Honeywell Corporation PHIDGETS Phadgets com pn 1108 The transfer unction for the magnetic field is Vour 500 200 where is the magn
39. LCD displays the actual value being applied during calibration In some cases it is difficult to perform calibration at the exact calibration point and this feature allows you to dial in the actual parameter value with the front panel pot It is assumed that this value is close to the nominal calibration point By accounting for the actual value of the parameter being calibrated MB 1 can then create a more accurate calibration table This can be done for Power couplers and RF Ammeters since either a square law power couplers or linear law RF Ammeters can be assumed and use to reliably correct the calibration point When used with analog sensors MB 1 can not make any assumptions and thus this correction capability does not apply to Generic Meter Applications
40. P Tx i A E d gt Ti IN m T A T SAVE Re Menu Menu Patent and Copyright Notices Patent Applied For Copyright Material in this document copyrighted 2011 FullWave LLC All firmware and software used in the MB 1 copyrighted 2011 FullWave LLC Table of Contents INTRODUCTION OVERVIEW 2 1 EXAMPLES OF THE FOUR CALIBRATION APPROACHES RESTRICTIONS EXAMPLES USING ANALOG SENSORS 4 1 TEMPERATURE MEASUREMENTS USING A LINEAR DEVICE 4 1 1 Overview 4 1 2 Calibration Procedure 4 2 DC CURRENT MEASUREMENTS USING A METER SHUNT 4 2 1 Overview 422 Calibration Procedure 4 3 NOTES 4 4 DC CURRENT MEASUREMENTS USING AN ISOLATED SENSOR 4 4 1 Overview 4 4 2 Calibration Procedure 4 4 3 Related Sensors 4 5 AC CURRENT MEASUREMENTS USING AN ISOLATED SENSOR 4 5 1 Overview 4 5 2 Calibration Procedure 4 5 3 Related Sensors 4 6 DC POWER MEASUREMENTS 4 6 1 Overview 4 6 2 Calibration Procedure 4 7 TEMPERATURE MEASUREMENTS USING A NONLINEAR DEVICE 4 7 1 Overview 4 7 2 Calibration Procedure 4 7 3 Related Sensors 4 8 PRESSURE FORCE SENSOR USING A NONLINEAR DEVICE 4 8 1 Overview 4 8 2 Calibration Procedure 4 8 3 Related Sensors 4 9 REFLECTANCE SENSOR 4 9 1 Overview 4 9 2 Coupler Calibration Procedure 4 10 MEASURING DISTANCE USING A LINEAR AND NONLINEAR DEVICE 4 10 1 Overview 4 10 2 Calibration Procedure 4 10 3 Related Sensors 4 11 LIQUID LEVEL SENSOR 4 11 1 Overview 4
41. S as shown in the data sheet 4 18 2 Calibration Procedure Below is a picture of the TCS230 sensor The data sheet can be found here The analog output voltage V coron vs color density is shown below for two different scale arrangements These graphs are applicable when the reference voltage is set to 4 95 volts If you want to set the reference voltage exactly to this value you can use the MB 1 5 volt auxiliary power with an appropriate voltage divider but this value is close enough to 5 volts so that the 5 volt auxiliary power source can be used directly without much impact Figure 35 Figure 36 Color Sensor Curves for RGB Scale and Scale Color Intensity Color RGB 0 Intensity VcoLoR VcoLoR Voltage vs Color Intensity RGB 100 150 Color Intensity Voltage vs Color Intensity Percent 40 60 Color Intensity We can represent the color intensity using one of two scale arrangements 1 The color intensity can be represented as an 8 bit value of the R or B intensity In this case the scale would range from 0 255 The color intensity can be represented as a percent in the range 0 to 100 100 would indicate that color being monitored is at its maximum intensity In this case the scale would range from 0 100 We have used Excel s Trend Line feature in the above graphs with a linear fit The R 1 value tells us that the linear fit is an exact fit 1 the data points in th
42. The same is true is case B but in addition since the lower calibration point is not defined when the parameter is less than 200 this tells MB 1 what the valid lower range of the sensor is Figure 3In Figure 3 we also have two cases Both sensors are nonlinear and require multiple calibration points to characterize the sensor When MB 1 reads a voltage between any two calibration points its uses piecewise linear interpolation to calculate the parameter value Therefore sensors with highly nonlinear transfer functions will require a larger number of calibration points for accurate tracking Figure 1 Sensor with Linear Transfer Function passing through the origin Transfer Function is Linear and passes through origin A single calibration point is required Sensor Output Voltage Parameter Figure 2 Sensors with Linear Transfer Functions NOT passing through the origin Case A Transfer Function is Linear but does not pass through the origin Case B Transfer function is valid only when the Parameter is gt 200 and 800 Sensor Output Voltage Calibration of these sensors require two calibration points 600 800 Parameter Figure 3 Sensors with Nonlinear Transfer Functions Both Transfer Functions are nonlinear and require multipoint calibration Sensor Output Voltage Parameter 2 1 Examples of the Four Calibration Approaches This secti
43. age for each of the six calibration points using a stable voltage source and potentiometer as shown in Figure 4 Analog Meter Calibration A Linear scale with a full scale value of 100 could be used for this application However Panel Meters can use the linear scale setup procedure only if the starting value on the scale is 0 If you used a scale with a range from 0 100 this would give you a dead zone from 0 50 since the sensor calibration just covers the range of 50 100 dB which is the usable range of the sensor If you use an existing meter face this is the most straightforward approach But if you decide to design your own meter face you can essentially create a linear scale from 50 100 and calibrate the analog meter as a nonlinear meter scale during the Panel Meter calibration setup procedure The nonlinear scale option must be used since the scale s starting value is not 0 Sound Pressure Level 70 60 80 Above we show custom meter scale for this application The majority of the scale covers the usable range 50 100 A small portion of the scale the section highlighted in yellow is allocated for don t care calibration points that are required as part of the nonlinear scale calibration when the scale does not start at 0 This will become more apparent below To calibrate this scale for use with MB 1 using the Panel Meter calibration routine set the full scale value to 100 and set the number of calib
44. alibrate the application and evaluate its performance without going through a lot of analysis However before expending a lot of the effort on a more complex application spend some time reading the example in section 4 7 which addresses the issue of how a big a dynamic range can reasonably be handled taking into account the nonlinearity of the parameter This will give you some insight into whether MB 1 is s a good match for your application For a sensor to be a candidate for interfacing with MB 1 it must meet the following criteria The sensor must generate a DC voltage or you must be able to derive a DC voltage from the sensor The relationship between the parameter being measured and the DC voltage can be linear or nonlinear The sensor must share a common ground with MB 1 The voltage must have a positive polarity The DC voltage must increase monotonically as a function of the parameter being measured The quantity being measured must be gt 0 since all of MB 1 s calibration points are gt 0 However there are simple work arounds for this especially if you will be designing a custom analog scale for the application The voltage must be compatible with the dynamic range of the coupler ports This issue is discussed in more detail in section 7 4 Examples using Analog Sensors 4 1 Temperature Measurements Using a Linear Device 4 1 1 Overview We use the output from a National Semiconductor LM34 Precision Fahrenheit
45. ansmit mode and receive mode parameters whose values are being output from the Yaesu external jack 101 This is transparent to MB 1 since the full scale values of all of the parameters on the analog scale correspond to the full scale meter deflection Since MB 1 is simply measuring the input signal and linearly driving the analog meter if you wanted to use the Min Max function the Min Max values would represent percent of full scale deflection If you did a long term test as in the above example to monitor for an intermittent sensitivity problem you would have to approximate the value on the appropriate scale to translate the Min Max readings into actual values but in this example since we are looking for a signal dropout interpreting the Min Max readings as percentage full scale values is adequate to determine if a problem was detected 4 25 Some other Sensors 4 25 1 Overview This section lists some miscellaneous sensors we have come across The approaches discussed in the examples above will work for these sensors as well We will update this section periodically 4 25 2 Humidity Sensor This sensor generates a DC output voltage that varies linearly with respect to humidity Details on the humidity sensor can be found here The data sheet can be found here 4 25 3 Pressure Sensor Barometer 3 36 PSI 20 250 KPA HOSN3S ETE Reta This sensor measures absolute pressure and has a range of 20 to 2
46. approximately 133 millivolts Amp Therefore the transfer function is Viout VzERO 133 I where Vzzggo is idle voltage from sensor when the current is 0 nominally 2 5 volts when Vcc 5 volts Therefore a typical sensor will have the following transfer function Viout 5 133 I where I is the current being measured Since the transfer function for this sensor does not pass through the origin 0 sensor voltage when current 0 we need to do calibration at two points namely the two end points If we set the full scale current to 30 amps the two calibration points will then be 0 amps MB 1 s lowest calibration point and 30 amps the full scale value For maximum accuracy Vzggo should be measured for the actual sensor being used and substituted in the equation as shown in the table below Table 1 Hall Current Sensor Calibration Calibration Point Sensor Voltage Viour typical 0 5 volts VzErRo 3 99 typical 4 49 volts During calibration these values can be dialed in with a potentiometer and the 5 volt auxiliary voltage source as previously discussed Adjust the coupler trim pot for maximum sensitivity since there is no chance of overdriving the MB 1 input in this application 4 4 3 Related Sensors Other sensors capable of measuring DC current can be found here 4 5 Current Measurements using an Isolated Sensor 4 5 1 Overview This example is similar to the prev
47. at the voltage seen by MB 1 is always positive This can be done with op amps but the approach we show below accomplishes the same thing and is quick and easy to implement If we reverse the normal polarity of the two sensor output leads and place a 5 volt DC source in series with the sensor output leads so that the voltage will always be positive and 37 monotonically increasing this solves the problem The voltage sources must float with respect to MB 1 s ground A simplified diagram is shown below where BAT1 and BAT2 could easily be implemented with wall warts and 7805 voltage regulators The resultant voltage vs distance curve is shown in Figure 26 Figure 25 Sensor Reversed and Biased to get increasing voltage vs parameter IR Distance Sensor To Tip of Coupler Port To Ground of Coupler Port Figure 26 Voltage vs Distance for IR Sensor Inverted Curve Distance in cm 4 10 3 Related Sensors There are a whole series of sensors that can measure distance using infrared and ultrasonic techniques Some of these can be found here 4 11 Liquid Level Sensor 4 11 1 Overview This application uses a PN 6573P 8 eTtape liquid level sensor that has a useful operating range from approximately 1 inch to 8 5 inches The resistance of the sensor decreases as the height of the fluid column increases The sensor resistance is approximately 385 ohms when the fluid level is 0 and approximately 60 ohms when the f
48. axis Vin 5 5 RL Rin Ry where is the load resistance in series with the sensor 209K If we plug the numbers into Excel it provides us with the expected voltages for all of the calibration points within the sensor advertised range of 0 05mg L 10mg L Table 8 Alcohol Sensor Calibration points Calibration Point Trend Line Ro Vout mg Liter Expression ohms volts 0 05 3 892584 7 785 168 0 130720 0 1 2 440587 4 881 174 0 205298 0 2 1 530208 3 060 417 0 319629 0 3 1 164536 2 329 073 0 411730 0 4 0 959416 1 918 832 0 491110 0 5 0 825540 1 651 079 0 561804 0 730145 1 460 291 0 626014 0 658144 1 316 287 0 685117 0 601538 1 203 076 0 740045 0 555664 1 111 327 0 791470 0 517600 1 035 200 0 839897 0 324527 649 054 1 217873 0 246975 493 950 1 486592 0 203473 406 946 1 696577 0 175081 350 161 1 868871 0 154849 309 699 2 014657 0 139579 279 158 2 140699 0 127574 255 149 2 251434 0 117845 235 690 2 349949 0 109773 219 545 2 438482 O ON DU At this point we can use the approach of connecting a stable voltage source to the end points of a pot and feeding the wiper output of the pot into MB 1 as we did in some of the earlier examples The calibration data would be saved for each point in the above table 4 19 4 Error Analysis We can take a brief look at how well the linear interpolation is doing between calibration points For example we know that if the voltage measured by 1 is exactly
49. ble magnetic field with negative polarity Idle voltage approximately 2 5 volts with no magnetic field applied Maximum sensor voltage approximately 4 7 volts at maximum detectable magnetic field with positive polarity Since MB 1 calibration points are all positive we define the calibration points as follows MB 1 Calibration Point Therefore when reading the MB 1 numeric displays 500 must be subtracted from the MB 1 reading to determine the value of as shown below in Gauss MB 1 Reading 500 We use the empirical method for calibration as shown in the table below Table 10 Calibration Method for Magnetic Sensor MB 1 Condition Calibration Point Approximately 2 Apply Magnet with orientation that reduces sensor voltage as volts magnet is brought closer to sensor Continue to reduce distance between magnet and sensor until minimum voltage is just reached avoid saturation Approximately No external magnetic field applied 2 5 volts Approximately Apply Magnet with orientation that increases sensor voltage as 4 7 volts magnet is brought closer to sensor Continue to reduce distance between magnet and sensor until maximum voltage is just reached avoid saturation 4 21 3 Panel Meter Calibration The maximum signal excursion for this application is 1000 units If we make a custom analog scale we can label the scale to read the magnetic field directly without requiring the s
50. can be calibrated at Not surprisingly these values correspond to the power calibration points used for RF power couplers with one exception discussed below If your application falls outside of this range simply apply a scaling factor when interpreting the output e g x 001 x 1000 etc 9 Special Considerations when using MB 1 with Analog Sensors 9 1 An additional Calibration Point of 0 for use with Analog Sensors For Generic Meter Applications only we also include a calibration point of 0 during the calibration setup routine since this case will be encountered in many world examples For RF Ammeters and Power couplers the minimum calibration point is 05 amps or 05 watts respectively 9 2 Allowing a Voltage of 0 during Calibration with Analog Sensors Another difference you will see is that when calibrating a Generic Meter Application it is valid for the very first calibration point to have DC voltage of 0 associated with This applies to the very fist calibration point used in the Setup routine and is not limited to calibration point 0 As contrasted to the RF Ammeters and Power couplers whose lowest calibration point is 05 the calibration setup routines will declare any calibration point with a calibration voltage of 0 as invalid since an RF Power or RF Ammeter coupler should always produce a nonzero DC output voltage for all calibration points 9 3 Processing Measurements Outside of the Calibration Range 9 3 1 Singl
51. ction to be measured is linear does not pass through the origin and you know the transfer function Case3 The function to be measured is nonlinear and you know the transfer function Case 4 The function to be measured is nonlinear and you do not know the transfer function but you know that the voltage increases as the parameter increases and you know that the DC voltage from the sensor is within the dynamic range of the MB 1 s input circuitry Sample graphs of transfer functions for the first three cases are shown below In Figure 1 the transfer function is linear and passes through the origin In this case MB 1 needs to determine only the slope of the transfer function This can be accomplished by performing the calibration at any point along the line For example if we use the end point MB 1 would be calibrated at 1000 units when 4 volts is applied to the coupler input Once calibrated MB 1 will be able to calculate the parameter value for any input voltage from the sensor In Figure 2 we have two cases Case A is linear but does not pass through the origin Case B is linear and would pass through the origin if extended but the transfer function indicates that the sensor is valid only for parameter values greater than 200 and less than 800 In both these cases the two end points of the transfer function should be used for calibration In case A MB 1 uses the two calibration points to determine the slope and the intercept
52. e 1 to 125 Celsius When we set up the Generic meter calibration we can set the Full Scale value to 125 We can then perform the calibration at temperatures of 0 10 20 100 and 125 For each of these calibration points we simply need to dial in the corresponding voltage that the top circuit in Figure 15 would generate using the circuit shown on the bottom of Figure 15 To calibrate this application we need a series of calibration points in Celsius and the corresponding voltage that the circuit in Figure 15 will generate for each of the calibration points Available MB 1 calibration points that make sense for this application are 0 10 20 30 100 To generate the table we have to know the resistance of the thermistor for each of the calibration points Since the thermistor forms a simple voltage divider with the 3 5K resistor if we could determine the thermistor resistance for each calibration point 0 10 20 we can then determine the corresponding voltage that the coupler input would see But solving for R the Thermistor resistance in terms of the temperature in Equation 1 is difficult Instead we can use Excel to determine the corresponding voltage values by creating a table with fine granularity and then interpolating A portion of the table is shown below where we calculate TCELSIUS in terms of the voltage at the voltage divider tap The two rows in red are rows that span the T 10 calibrat
53. e 29 Graphs of Different Sensitivity Settings on Light Sensor Vout vs Working Range Vout 5 volts Vout volts Er o e EX 0 001 0 0001 0 00001 Coupler Port Calibration e Hi Gain Setting a Med Gain Setting Low Gain Setting 100 1000 100000 Illuminance Lumens Adjust the coupler trim pot for maximum sensitivity There is no chance of overdriving the MB 1 input in this application Since we want to measure up to 100 000 units in this application and since the maximum full scale value that MB 1 supports is 30 000 for the highest range we will set the full scale value to 10 000 and interpret all digital readings as the measurement value divided by 10 This will be used with the sensor s lowest sensitivity setting i e highest light intensity For reading intermediate light levels we use the medium sensitivity setting and will read the numerical values from MB 1directly with no correction Finally for the lowest light readings we use the sensor s highest sensitivity setting This requires us to multiply the digital readings displayed on MB 1 by 10 to determine the actual light intensity We can see from the transfer function equation that the equation is linear and passes through the origin Therefore we need to calibrate this application at a single point namely the full scale value of 10 000 This is most easily done by dialing in the calibration voltage of 3 87
54. e Point Calibration Cases It is only valid to calibrate MB 1 at a single point if the sensor is linear and passes through the origin 0 0 In this case MB 1 can calculate any voltage from the sensor and will calculate the measurement value for any voltage above or below the single calibration point as long as the dynamic range discussed above is not exceeded 9 3 2 Multipoint Calibration Cases This case applies when measurements if the calibration table has two or more points If the sensor voltage is lower than the lowest calibration voltage or higher than the highest calibration voltage MB 1 will bottom out or top out as the voltage is reduced or increased respectively Unlike the single point case described above MB 1 does not have enough information to reliably estimate the parameter undergoing measurement when the sensor voltage is outside of the calibration range For example take the Tilt Sensor application described above The table is repeated below When the sensor voltage is lower than 2 500 volts the measurement will bottom out at 0 degrees If the voltage is greater than 3 500 volts the measurement will top out at 90 degrees Angle XA degrees analog voltage 2 50000 2 67365 2 84202 3 00000 3 14279 3 26604 3 36603 3 43969 3 48481 3 50000 9 3 3 Dialing In actual Parameter Value during Calibration If you look at the detailed calibration steps in the MB 1 User s Manual you will see that line 4 of the
55. e can affixed to an analog meter with a full scale current rating of 1 mA or less The meter can then be connected directly to the Yaesu output in a conventional manner In this case you should insert an appropriate size potentiometer in series with the meter movement This will allow you to set the meter movement for full scale deflection using the Yaesu calibration feature which outputs a signal corresponding to the maximum drive signal If you want to make use of the MB 1 alarm functions or Min Max functions to do some additional processing of the Yaesu parameters you could instead connect the Yaesu analog output to an MB 1 coupler input and calibrate that input as a generic meter function The analog meter with the Yaesu scales would then be driven by MB 1 Why would you want to do this Let s assume you got a radio back from repair due to an infrequent but annoying momentary loss in sensitivity If the MB 1 was monitoring the analog meter output you could set up the Yaesu to display the S meter function in receive mode on the analog output You could then activate a low power signal source e g the calibrator from an older vintage radio to provide a stable readable signal for the Yaesu to receive and monitor the signal level as reported by the Yaesu with MB 1 s Min Max function In such set up you would expect little if any variation in the signal level If after an overnight test the Max function reads 80 e g 80 full scale and t
56. e spec sheet on a straight line We will use the trend line equation on the top graph to display the color intensity as an 8 bit value We will use the trend line equation on the bottom graph to display color intensity as a percent Since the equation does not pass through the origin for either scale arrangement we need to do multipoint calibration Since the equation is linear only two points are required For example to cover the full range of the RGB transfer function which ranges from 0 250 we can perform the calibration at the two closest available MB Icalibration points namely 0 300 The two approaches are show below RGB 8 bit value Displayed Measurement value 0 255 The closest MB 1 calibration point to 0 x axis is 0 The closest MB 1 calibration point that encompasses the entire range on the high end is 300 x axis Using the formula from the top graph the voltages corresponding to these two points are as follows ColorIntenity 0 Vcorog 7 2 mV ColorIntenity 300 V cotor 5 7072 Volts Percentage value Displayed Measurement value 0 100 The closest MB 1 calibration point to 0 x axis is 0 The closest MB 1 calibration point that encompasses the entire range on the high end is 100 X axis Using the formula from the bottom graph the voltages corresponding to these two points are as follows ColorIntenity 0 7 2 mV ColorIntenity 100 4 860 Volts
57. ed on or off by the PT1 and PT2 sensor outputs By picking appropriate values of R1 R2 and R3 we can generate 4 different DC voltages at Vour corresponding to the sensor s four orientations This assumes a 0 volt drop across Q1 and Q2 when turned on In practice you would want to measure Vour for the four states to determine the actual calibration values to account for the Vcg drops and resistor tolerances Coupler Port Calibration Adjust the coupler trim pot for maximum sensitivity There is no chance of overdriving the MB 1 input in this application To calibrate this application set the full scale value to 3 units Then perform calibration at the calibration points shown in the table below These are the two rightmost columns from the table above Digital readings of 0 1 2 and 3 correspond to orientations of down right left and up respectively Table 6 Calibration Points for Discrete Tilt Sensor Orientation in Vou volts Numeric Form 1 2 3 Analog Meter Calibration A sample scale for this application is shown here This is a linear scale and requires that calibration be done at a single calibration point namely the full scale value of 3 In labeling the scale we substitute the text Down Right Left and Up for the four numeric values Admittedly driving LEDs in place of R1 and R2 is a much simpler way to use this particular sensor But if you encounter a sensor with mult
58. eet can be found here While this example measures the alcohol concentration in air the conversion to Blood Alcohol Content BAC should be fairly straightforward if I understand the Wikipedia article on the topic The applicable conversion factor is 1 mg L of exhaled breath alcohol 02 BAC This spec sheet is somewhat different than the ones used in previous examples Instead of graphing resistance vs alcohol concentration the device specs show a resistance ratio vs alcohol concentration The ratio is Rs Ro where Rs is the sensing resistance for a given alcohol concentration and Ro is the sensor resistance when the alcohol concentration is at a know reference value 4 mg Liter I believe that the reason this was done is because there is a large variation in the sensor resistance reference points among samples For example at the reference level of 4 mg Liter the sensor resistance can vary anywhere from 1 Meg to 8 Meg depending on the sample So to use this sensor you have to be able to determine its resistance for the reference concentration of 4 mg Liter What is guaranteed in the spec however is the Rs Ro ratio So again this sensor presents some new issues that we did not have to handle in the earlier examples The spec sheet is shown below The manufacturer spec sheet graphs the data on log scales We plotted the data on linear scales for this example Figure 37 Alcohol Sensor Curve Alcohol Sensor Re
59. ents using the actual pressure values is beyond the display range of MB 1 we must provide the measurement values in log form which is a reasonable approach since this sensor s transfer function is also logarithmic It would be nice to display numerical values from MB 1 ranging from 8 to 3 corresponding to pressures of 10 to 10 respectively But since MB 1 does not display negative values we will use the following translation Table 19 MB 1 Readings and Corresponding Pressures for Integral MB 1 Readings MB 1 Pressure Numerical millibars Reading 1 00E 08 1 00E 07 1 00E 06 1 00E 05 1 00E 04 1 00E 03 1 00E 02 1 00E 01 1 00E 00 1 00E 01 1 00E 02 1 00E 03 BoC AIADNBRWNHE To convert an MB 1 numerical reading to a pressure one would take the numerical reading P 10 MB 1 Reading 8 But this equation is correct only for the integral values displayed on MB 1 as shown in the above table We have to use the actual transfer function to determine the pressure value between integer MB 1 values The equation for pressure in terms of Vour is P 10 1 667xVout 11 33 Since each decade increase of pressure increases Vour by 600 millivolts we can create a lookup table to interpolate non integral MB 1 readings for all 11 decades If we break each decade into 20 segments we can calculate an exact pressure voltage relationship for those 20 points The voltage step for each of these 20 segments is 600 millivolts 2
60. es accurate measurements for small linear displacements in the millimeter range with repeatability in the micrometer range These sensors are used primarily in industrial applications The sensor shown above generates an analog output from 0 10 volts corresponding to displacements of 5mm to 1 5 mm Details on the sensor can be found here 5 6 Time of Flight Laser Distance Sensor The Banner Series of Analog Sensors have a large variety of uses in process control One such sensor referred to as a Time of Flight distance sensor is shown above The data sheet can be found here This sensor determines the distance by emitting light from a laser diode which bounces off the target and is detected by a sensor collocated with the laser Using the speed of light and the round trip time the distance can be measured very accurately The sensor generates a 0 10 volt DC output that varies linearly with respect to the calculated distance and easily processed by MB 1 5 7 Salt Water Conductivity Sensor The A4120 Alliance for Costal Technologies Conductivity Sensor is a high precision conductivity sensor for making measurements in salt water The sensor produces a linear output of 0 5 volts DC corresponding to a conductivity of 0 75 millimhos cm The data sheet can be found here 5 8 Linear Variable Displacement Transformers P3 America LVDTs work by driving a transformer primary with AC voltage and measuring
61. etic field in gauss This sensor is designed to read both polarities of a magnetic field from approximately 500 gauss to 500 gauss The sensor comes with two Neodymium magnets that are capable of generating a magnetic field of at least 500 gauss with both polarities when moved close to the sensor The transfer function is shown on the red data series in the chart below The red curve does not satisfy the MB 1 requirement that the sensor voltage increase monotonically as the parameter value increases But the definition of the magnetic polarities is arbitrary with respect to the sensor If we reverse the sense of the polarity we get the transfer function shown in the blue data series in the chart below The transfer function in blue can therefore be used by MB 1 for calibration All that this reversal means is that we now define the direction of the magnetic field that causes the sensor voltage to increase from its idle 0 gauss value of 2 5 volts as positive and vice versa Figure 40 Magnetic Sensor Transfer Function Magnetic Sensor Vout vs Vout vs normal polarity Vout vs reverse polarity 4 21 2 Coupler Port Calibration The above curves are idealized The sensor sheet indicates that the actual range of the output sensor is 2 volts to 4 7 volts We therefore have 3 well defined calibration points Minimum sensor voltage approximately 2 volts at maximum detecta
62. g the data sheet formula The next column Delta is the difference between VOUT for the next 10 dB step and the current SPL value For example the Delta entry for the SPL 50 row is Vour 60dB 50dB The next column is simply 1 10 of that value Since MB 1 uses linear interpolation adding the 1 10 step to Vour at 50 dB represents the Vour value at which MB 1 will declare the measurement to be 51 dB Adding 2 10 step to VOUT at 50 dB represents the voltage at which MB 1 will declare the measurement to be 52 dB etc These are the entries shown in the blue column below You can see for example that the exact VOUT that corresponds to SPL 51 is 0 057823047 But with linear interpolation MB 1 will declare a measurement of 51 dB at the voltage in the corresponding blue column You can see that the values are somewhat different The blue column therefore represents the voltages at which MB 1 will declare the measurement value to be an integral value in the 50 dB to 100 dB range For the voltage entries in this column we then calculate the exact SPL values corresponding to those voltages using the data sheet formula With the exception of the entries in red at each 10 dB point the Nominal SPL value in column 1 and Actual SPL value in the green column will differ due to the interpolation The difference is the error introduced by the interpolation at that point The error values are shown in the last column This approach
63. half way between two calibration points the software will linearly interpolate and calculate a measurement value exactly half way between the two calibration points The data below shows the midpoint voltage at which the software interpolates the intermediate values between calibration points and the actual voltages for the calibration mid points using the trend formula Table 9 Error at Midpoints Interpolated Exact Voltage Midpoint at Midpoint Calibration Midpoints Values Value 065 0455565533 01656137997 0 09 25 1 352232299 1 361589777 0 69 85 2300691824 2 302063769 0 06 Surprisingly the error at the midpoints is very small less than 2 Given the complexity of the trend line equation and the series resistance term that the voltage divider introduces it is very surprising that the error is so small This is probably not typical of what you would see for an arbitrary nonlinear sensor when used with MB 1 But the point here was to go through some error analysis something you will want to do if you are thinking of using the MB 1 Generic Meter function for a serious application 4 19 5 Details You may have noticed that we never addressed how to determine the calibration of the alcohol sensor itself in other words what is its Ro value of a given sample since it can range from 1 Meg to 8 Meg Good point This appears to be a harder problem than it sounds like If one were serious abou
64. hat corresponds to a particular calibration point Assume that we will calibrate this sensor at 10 degree points 0 10 20 30 90 We need to determine the corresponding voltage XA corresponding to these points Therefore we need to solve for XA in the above equation XA sin 0 2 5 The calibration points and the corresponding sensor output voltages are shown below Angle XA degrees analog voltage 0 2 50000 10 2 67365 20 2 84202 30 3 00000 40 3 14279 50 3 26604 60 3 36603 70 3 43969 80 3 48481 90 3 50000 4 15 2 Error Analysis We can take a look at how well the linear interpolation will do between the above calibration points Because MB 1 uses linear interpolation between calibration points MB 1 will declare the measurement value to be half way between the corresponding calibration points in the left column above when the voltage is exactly half way between the corresponding voltage levels The error analysis is summarized in the table below The numbers in red from the first two columns in the table below are copied from the table above which are the calibration points The next column Midpoint Angle is the midpoint between the two angles in the row below and above the entry in column 1 This is the measurement value that MB 1 will declare when the voltage from the sensor is exactly half way between the XA calibration points in column 2 These voltages are shown in the Midpoint Voltage column The nex
65. he Min function reads 15 e g 15 of full scale your radio still has the problem Similar tests could be done to detect other intermittent conditions such as an RF Power dropout during a long data transmission Admittedly this is a somewhat contrived example but it may spark some ideas on using the Generic Meter function for applications that might not be initially obvious Here is how we would configure MB 1 to interface to the Yaesu and analog meter First it is important to recognize that the Yaesu will generate the same full scale signal to drive an external meter to full scale regardless of which of the 7 parameters are being measured Therefore the easiest approach to take is to view the Yaesu output as a relative signal with a value ranging between 0 no meter deflection and 100 full scale meter deflection In this case we simply have to calibrate the Generic coupler input for a full scale value of 100 and likewise calibrate the external panel meter as a single linear scale analog meter with a full scale value of 100 In effect this makes MB 1 transparent i e the analog meter should respond as if it was connected directly to Yaesu output signal We use the linear scale Panel Meter calibration in this example since we are relying on the meter scale calibrations to give us the correct reading The following describes the steps in detail Coupler Calibration Connect the Yaesu along meter output to the FWD port
66. his approach can be used if we have a sensor that can not be easily characterized mathematically or where there is a large sample to sample variation In this case you can connect the sensor to the coupler port and during calibration you can walk the parameter through its range of values saving the calibration data at discrete points However this approach requires the use of an independent reference during calibration The example below will clarify this Assume that we have distance measuring application where the transfer function is nonlinear and not easily characterized Also assume that there is a large sample to sample variation across sensors We can connect the DC output from the distance sensor to a coupler port Using a simple yard stick or meter stick we then move an object various distances from the senor e g 1 inch two inches 5 inches 20 inches 50 inches and 100 inches saving the calibration data at each point This empirical approach is fast and simple at least in this example since it requires only a simple reference such as a yard stick And since the calibration was performed with the actual sensor this approach also takes care of cases where a wide sample to sample variation exists 3 Restrictions If an application you have in mind is best addressed by the empirical approach case 4 above and if you have a good independent reference against which to measure the parameter of interest you can quickly c
67. hould be less than 4 5 volts Plugging the numbers in we get a Vpour of 4 32 volts which checks out The above discussion can be used to determine component values for other voltage and current combinations as well 4 6 2 Calibration Procedure Adjust the coupler trim pot for maximum sensitivity There is no chance of overdriving the MB 1 input in this application Since the above transfer function is linear and passes through the origin we need to perform the calibration at a single point We can do the calibration at the power corresponding to the maximum voltage and current points namely a power level of 150 watts At that power 0288 15 4 320 volts Calibration at the 150 watt point is most easily done by dialing in the desired voltage at the input to the coupler using a stable voltage source and potentiometer as shown in Figure 4 4 7 Temperature Measurements Using a Nonlinear Device 4 7 1 Overview If you have an interest in measuring parameters with MB 1 that have nonlinear input output relationships this topic may be of interest to you The temperature application described above used a device that generated a DC voltage in a linear relationship with respect to the temperature in Fahrenheit In this application we use a nonlinear temperature device namely a thermistor to map DC voltage into temperature in degrees Celsius If we wanted to measure temperature and a linear device like the LM34
68. ication TABLE 22 MB 1 SPECIFICATIONS OF SPECIAL INTEREST WHEN USING MB 1 WITH ANALOG SENSORS Input Sensitivity DC voltage required to drive the Multiplexer Programmable Gain Amplifier to its maximum output of 32 736 Coupler Port Input resistance Supported Measurements Input Signal Processing Rate Maximum Number of Calibration Points Coupler points Interpolation Digital Filters Alarm Trip Point Low Value Alarm Trip Point High Value Programmable Demo Mode Integrated Simulator One Virtual Port Coupler 8 for simulating Generic Measurements Adjustable Peak Hold Time Min Max Functions All Other Features Approximately 6 14 volts Approximately 300K Instantaneous Value Average Value Peak Value Min Max Functions gt 500 per second 60 Same values as power points for power calibration with the addition of a calibration point for 0 0 30 000 see Table 22 Linear or Square Law Separate Filters for Instantaneous and Average 1 27 500 1 30 000 High must be gt Low 6 Simulation Modes 1 sec 9 9 secs in steps of 1 sec Select the parameter to be processed e g Instantaneous Value and the Min Max feature will capture the Min and Max values for display on any of the available display devices See User s Manual Table 23 Available MB 1 Calibration Points The table above shows the values that a Generic Application
69. io of 10 a range that can only be handled reasonably if we use a logarithmic scale A picture of the sensor is shown below The data sheet can be found here The operating instructions which contain additional specifications can be found here The operating instructions provide the transfer functions for a variety of pressure units The example below uses the millibar equation The implementation for the torr and Pascal units are similar The sensor transfer function for millibars is Vout 6 8 6 log 10 P where P is the pressure in millibars The data points and graph for the 11 decade range transfer function are shown below Table 18 Transfer Function for 10 Pressure Values for Vacuum Sensor Pressure millibars 1 00E 08 2 0000 1 00E 07 2 6000 1 00E 06 3 2000 1 00E 05 3 8000 1 00E 04 4 4000 1 00E 03 5 0000 1 00E 02 5 6000 1 00E 01 6 2000 1 00E 00 6 8000 1 00E 01 7 4000 1 00E 02 8 0000 1 00E 03 8 6000 Vour VS Pressure 10 0000 4 9 0000 8 0000 7 0000 6 0000 5 0000 4 0000 3 0000 2 0000 1 0000 0 0000 T T T T T T T T T T 1 00E 08 1 00 07 1 00E 06 1 00E 05 1 00E 04 1 00E 03 1 00E 02 1 00E 01 1 00E 00 1 00E 01 1 00E 02 1 00E 03 Pressure millibars As can be seen from the above table the sensor output voltage increases at a rate of 600 millivolts per decade 5 1 2 Coupler Port Calibration Since the sensor s range of pressure measurem
70. ion point We can see that 27 10 will correspond to a voltage somewhere between 7 40 volts and 7 50 volts which are the corresponding entries in the first column Excel has FORECAST function that simplifies doing the linear interpolation for these two rows It is used in the rightmost column and determines that the voltage corresponding to 10 is 7487 volts This approach is repeated for each of the 11 calibration points and yields the values in Table 3 below Table 2 Portion of the Resistance vs Voltage Calculations for Thermistor Exact Exact Calibration Voltage TceLcius Point 21862 319 281 1670 8 0170 21500 000 281 5123 8 3623 21147 887 281 8543 8 7043 20805 556 282 1930 9 0430 20472 603 282 5285 9 3785 20148 649 282 8608 9 7108 0 748781 19833 333 283 1902 10 0402 19526 316 283 5165 10 3665 19227 273 283 8400 10 6900 18935 897 284 1607 11 0107 18651 899 284 4787 11 3287 Table 3 Voltage Temperature Calibration Points for Thermistor TceLcius Vpc Using the above table we simply need to dial in the corresponding voltage at the various 0 calibration points and use the calibration setup screens to record these points We have left out some detail such as accounting for the variability from the ideal curve among thermistor samples but hopefully the general concept is clear Application specific programs can always be written for a
71. ious example but makes use of a self powered AC current sensor that can measure up to 100 amps AC The sensor produces 5 volts DC at the full scale rating of 100 amps with a linear transfer function This sensor is electrically isolated from the AC wire whose current is being measured The wire is simply passed through the sensor and inductive coupling is used to generate the DC output voltage that gets fed to MB 1 Phidgets has a family of these sensors ranging from 10 amps AC to 100 amps AC They all work the same way producing 5 volts DC at the full scale rating 4 5 2 Calibration Procedure Below is a picture of the sensor The specifications can be found here Calibration is straightforward with this coupler Adjust the coupler trim pot for maximum sensitivity There is no chance of overdriving the MB 1 input in this application During calibration set the full scale value to 100 or the full scale value corresponding to your sensor Because the transfer function of this sensor is linear and passes through 0 0 this application requires calibration at a single point namely the full scale value During calibration select the full scale value calibration point Then apply 5 volts DC to the coupler input saving the calibration data That is all that is required 4 5 3 Related Sensors Other sensors that can measure AC current can be found here 4 6 DC Power Measurements 4 6 1 Overview There are some applications for insta
72. iple logic outputs that represent the parameter being measured if you want to display the parameter in numeric form or on an analog scale an approach similar to this one could be used Notes In effect the above interface circuit is a simple D to A converter We could have used an 8 bit D to A converter such as the Analog Devices AD558 instead When operated at 5 volts this device generates a full scale voltage of 2 56 volts A simplified schematic using this device for the discrete tilt sensor is shown below We use only the 2 most significant bits Therefore the four generated output voltages will be approximately 0 2 56v 4 2 56v 2 and 2 56v If the AD558 was used to interface to this application these would represent the voltages for the four calibration points Figure 33 Interface Circuit for Discrete Tilt Sensor using D to A Converter For the connections shown in the above diagram these four voltages in increasing order would represent positions of UP RIGHT LEFT and DOWN respectively Using the D to A solution for interfacing to 59 1 starts to make more sense as the number of logic outputs representing the parameter being measured increases above two 4 17 Logarithmic Sound Pressure Level Sensor 4 17 1 Overview This example uses a Phidgets1133 Sound Sensor which produces a DC output voltage that is a nonlinear function of the sound level The sensor is rated at sound pressure levels of 50 dB to 100 dB witha
73. libration points The lower RPM value of 2 and the higher RPM value of 200 are both available MB 1 calibration points and can therefore be used directly as shown in the table below Calibration Point 2 volt 200 5 volts Calibration is most easily done by dialing in the calibration voltages at the corresponding calibration points as shown in Figure 4 6 Adding MB 1 to Existing Measurement Systems In some cases you may wish to add 1 to an existing system that already includes a sensor and display instrumentation You might want to do this to display the measurement on one of MB 1 s display devices to complement the display on the existing instrumentation You may also want to use one or more of MB 1 s processing functions such as Min Max Averaging and Alarm functions that might not be provided by the existing instrumentation If the existing sensor is generating an output voltage MB 1 can be placed in parallel with the existing instrumentation as shown in Figure 46 as long as the 300K input resistance of the MB 1 input circuitry does not adversely impact the existing instrumentation Figure 46 Adding MB 1 to Existing Instrumentation using a Voltage Sensor However if you are using a 4 20 mA loop sensor incorporating MB 1 into the system will take a bit more effort The top circuit in Figure 47 shows an existing 4 20 mA loop based measurement system including the power source the loop sensor and the in
74. luid level is at its maximum value of 8 5 inches with a resistance gradient of 40 ohms per inch However the resistance specs are rated at 10 and a plot of the actual resistance vs level is not perfectly linear Therefore this is a good application for the empirical approach which is simple to do accurately with this application 4 11 2 Calibration Procedure Below is a picture of the sensor The data sheet can be found here Figure 27 Input Circuit to Measure Liquid Level To measure the level of a liquid with MB 1 using this sensor the circuit in the figure above can be used Since the sensor resistance decreases as the level of the liquid increases this will cause the voltage into 1 to increase for increasing pressure which is what we want By picking the fixed resistor value approximately half way between the upper and lower resistance range of the sensor we maximize the voltage swing seen at the input of the coupler port which gives us good resolution To perform the calibration first set the corresponding coupler trim pot to maximum sensitivity max CW travel Since the input stage of MB 1 can not saturate with an input voltage of less than 6 14 volts and since we are using a 5 volts supply setting the trim pot sensitivity to its maximum value will result in maximum accuracy and resolution without the possibility of saturating MB 1 s input circuitry Go into the coupler Setup screen define the coupler type as GEN
75. ly the full scale value of 90 4 15 3 Related Sensors There are a whole series of sensors that can measure acceleration Some of these can be found here This data sheet has the specifications for and Inductive Angle Sensor that generates an analog voltage that varies linearly with respect to the angular displacement and can therefore be used with MB 1 4 16 Measuring Tilt using a Discrete Tilt Sensor 4 16 1 Overview Some sensors have logic outputs that represent the state of the parameter being measured An example of such a sensor is the SHARP GP1S036HEZ which provides 4 output states using two logic outputs Below is a picture of the discrete tilt sensor The data sheet can be found here The logic outputs PT1 and PT2 indicate the sensor s orientation as either an upright right down or left as shown in the table below Table 5 Logic Signals and Corresponding Analog Voltage for Discrete Tilt Sensor Orientation Volts MB 1 Reading ordered in increasing value The circuit diagram below shows how we can derive 4 discrete analog voltages from this sensor for the four discrete orientations We can then use the derived analog voltages to interface to MB 1 Figure 32 Interface Circuit for Discrete Tilt Sensor Sharp GP1S036HEZ Discrete Tilt Sensor Interface Circuit To MB 1 Coupler Oa The two transistors Q1 and Q2 in the interface circuit are turn
76. maximum DC voltage generated from your application is very low you can always add an Operational Amplifier to generate a suitable signal for MB 1 s input circuitry Some references are given in the web site 8 Interpolation When you set up a Generic Meter Application all voltages that are at intermediate voltage levels with respect to the calibration points are linearly interpolated to calculate the parameter being measured The power meter functions associated with RF couplers use a square law interpolation calculated value is the square of the input voltage With power measurements all voltages that are at intermediate voltage levels with respect to the calibration points are interpolated using a square law interpolation If you have a Generic Application whose derived voltage is approximately the square root of the parameter being measured you will gain additional accuracy at intermediate calibration points by calibrating your application as a conventional power meter instead of as a Generic Meter Application If you decide to use this approach you will have to remember that the meter still thinks it is an RF power meter in this mode so you will have to ignore parameters that have no meaning for your Generic Application such as SWR or better yet program the display devices so that these values are not displayed Ignore the w suffix for watts on the LCD and you should be OK using the RF power mode for a square law Generic appl
77. mpirical approach is easier assuming we have some way to apply a series of accurate forces during calibration The advantage of the empirical approach is that it automatically compensates for any variation in the sensor as well as the accuracy of the 5 volt supply and fixed 10K resistor It turns out that the Lincoln Memorial Reverse penny mid 1982 to present weighs 2 5 grams Therefore various combinations of 4 to 40 pennies will give us a reasonable calibration source from 10 grams to 100 grams One liter of water weighs 1000 grams 1 kilogram You get the point depending upon what you are measuring actual calibration using a known input can yield the quickest and most accurate results 4 8 3 Related Sensors There are a whole series of sensors that can measure force and stress Some of these can be found here 4 9 Reflectance Sensor 4 9 1 Overview This example makes use of a QTR 1A reflectance senor This is another example where the sensor characteristics are a little vague so it is difficult to come up with an exact transfer function We therefore use the empirical approach in this example to calibrate the sensor Below is a picture of the Reflectance Sensor Information on the sensor can be found here Figure 19 Reflectance Sensor Figure 20 Input Circuit to Measure Reflectance 47K Vout To MB 1 Coupler Port The sensor connections to MB 1 are shown above As the reflectance increases the cu
78. nce battery powered equipment or solar cell powered systems where the delivered or consumed power measurement is more useful than either the voltage or current measurement This example uses the Maxim MAX4210E real time power monitoring sensor to measure DC power directly This chip uses a current sense amplifier and an analog multiplier to perform a real time multiplication of the current and voltage The sensor outputs a DC voltage that is proportional to the power being monitored MB 1 can be easily calibrated to read the sensor output voltage and can display the power measurement or process the sensor output using the MB 1 averaging Min Max and alarm functions The complete data sheet for this sensor can be found here Application notes which are a little easier to follow are found here Figure 13 Maxim MAX4210E DC Power Sensor Is Vsource 3 AA V Vsource P lt LOAD ower E Source 4v 28v Dc Analog bs Multiplier Coupler Input Power Sensor Measuring DC Power In the figure above the quantity we want to measure namely delivered power is Pprviverep Vsource Is Rsensz is a low resistance shunt that generates a voltage based on the load current Vsense Is For the 4210E device the sense voltage is multiplied by the amplifier gain G which has a value of 25 and the amplifier output is fed to one input of the multiplier The second input to
79. nd potentiometer as shown in Figure 4 Note that the MB 1 5 volt auxiliary power output cannot be used to drive a pot for calibration since a voltage level greater than 5 volts is required Two 9 volt batteries in series or other stable higher voltage source feeding a potentiometer can be used instead 5 1 3 Panel Meter Calibration If we design our own analog meter scale we have the ability to label the scales so that the pressure can be read directly without the translations that had to be done when reading the MB 1 digital displays This requires not only labeling the major tic marks from 10 to 1000 but also spacing the intermediate tic marks between decades with a logarithmic spacing A sample scale is shown below with comments Vacuum millibars 404 10 107 4 10 Each decade or major tic mark simply occupies 1 11th of the full scale range Between each decade we include 4 minor tic marks For example the four tic marks to the right of 10 are 2 x10 4 x108 6 x108 and 8 10 To account for logarithmic behavior of the sensor the minor tic marks must be positioned according to the log of the tic mark value For example for a linear scale the 2 x10 tic mark would be placed at 20 of the displacement between the major tic marks But for this logarithmic sensor it must be placed at log 2 301 or 30 1 of the distance between the major tic marks Likewise minor tic mark 4 x10 must be placed at log 4 2 602 or 6
80. ny measurement application In fact many examples are shown on Professor Anderson s Embedded Processor website http www phanderson com including several applications for measuring temperature However the novel concept of the Generic Application feature of 1 is that measurements can be performed on parameters that have complex parameter vs voltage relationships without the need to write an application specific program The calibration can be achieved either through use of calculated voltages at various calibration points as we did here or with the use of a reference measuring device in this example a thermometer would be used This generalized measurement approach will not likely do better than a custom application designed explicitly to measure a single type of parameter but the tradeoff is obviously one of complexity and speed of implementation 4 7 3 Related Sensors There are a whole series of sensors that can measure temperature using linear and nonlinear sensors Some of these can be found here 4 8 Pressure Force Sensor Using a Nonlinear Device 4 8 1 Overview In the previous temperature application we did a bit of analysis to generate a temperature vs voltage chart that was needed for the calibration The pressure sensor in this example is highly nonlinear as well The specification for this sensor is detailed enough so that we could generate a force vs voltage curve However in this example we will
81. of one of the 4 coupler ports Adjust the coupler trim pot for maximum sensitivity There is no chance of overdriving the MB 1 input in this application Bring up the coupler calibration menu for the coupler port being used Specify the coupler type as a GENERIC meter application Set the full scale value to 100 units Configure the Yaesu to apply a full scale signal on its analog meter output port Select a single calibration point of 100 and save the calibration data for the full scale signal being applied by the Yaesu 8 Save the coupler calibration settings to EEProm Panel Meter Calibration Connect the panel meter with the Yaesu scales to an unused panel meter port Enter the Panel Meter Setup screen and choose the appropriate panel meter port Set the calibration type to Linear Adjust the panel meter trim pot slightly beyond full scale deflection Select the number of Power Scales to 1 Set the full scale value to 100 Set the number of SWR scales to 0 Proceed with calibration Calibration is done at a single point namely the full scale value 100 Simply dial the front panel pot until the meter needle reads full scale and save the calibration point 9 Save the Panel Meter calibration data in EEProm This completes the calibration When you select the coupler port connected Yaesu output and analog meter with the Yaesu MB 1 will drive the analog meter The Yaesu menus determine the actual tr
82. on expands on the above overview by providing some examples Case 1 The temperature sensor in section 4 1 application generates 10 mV per degree and has a linear transfer function that passes through the origin Therefore we know from the specs that at 100 degrees the device will generate an output of 1 0 volt To calibrate this device all we have to do is apply 1 0 volt to the coupler port while setting the calibration point to 100 100 degrees This can be done easily using a potentiometer connected to the 5 volt auxiliary power output on the MB 1 rear panel RCA jacks and then adjusting the pot until the pot s wiper voltage is 1 0 volt Figure 4 and Figure 5 below show a circuit that can accomplish this A low resistance potentiometer should be used so that the input resistance of the coupler ports 300 K can be ignored A pair of clip leads connected to the output of the potentiometer lets you monitor the applied voltage with an external Digital Multimeter while performing the calibration Figure 4 Using a Voltage Source and Potentiometer for Calibration To MB 1 Coupler Input 5 Volts To Digital Multimeter 5 volt Auxiliary Low Resistance source from MB 1 Multi turn Pot Rear Panel e g 1K Using Voltage Source and Potentiometer to Dial In Calibration Voltage Figure 5 Potentiometer Multimeter and RCA Cables Connect to FWD Coupler Port being calibrated CRAFTSMAN Connect to 5 volt DC Auxiliary
83. oximately 6 14 volts when the pot is set to its maximum sensitivity and since this application will never generate a DC voltage that comes close to this saturation point setting the trim pot to its maximum sensitivity will provide the best resolution and accuracy Apply a source of 1 00 volt to the FWD port of the coupler being calibrated This is most easily done by dialing in the calibration voltage using a stable voltage source and potentiometer as shown in Figure 4 Using the Coupler setup screens calibrate the meter at a single point at a calibration temperature of 100 This corresponds to the 1 00 volt being applied from step 2 Since the LM34D input device has a linear transfer characteristic that passes through the origin calibration is required at this single point only 4 2 DC Current Measurements using a Meter Shunt 4 2 1 Overview We can use a meter shunt in series with the current we want to measure and feed the generated voltage across the shunt into one of the coupler ports to measure DC current This example makes use of a 20 amp shunt Shunts in this current range typically generate 75 millivolts at the full scale current Like the example above the transfer function is linear and passes through the origin so this application also requires a single calibration point FIGURE 8 METER SHUNT The circuit diagram and suggested calibration procedure is shown in the figure below Figure 9 DC Ammete
84. pler calibration for the highest temperature 100 since this is the case that produces the largest voltage excursion from the sensor across the full pH range more on that below This approach ensures that that the voltage excursions for the other temperatures will be within the100 calibration range and therefore represent measurements that can be processed by MB 1 without bottoming out or topping out We will handle the temperature issue by creating an analog face that has scales for the 100 case as well as the other temperatures listed above To read the temperature corrected pH value all that is required is to read the scale corresponding most closely to the temperature of the sample being measured 4 23 2 Coupler Port Calibration The transfer function for the pH sensor taking both the pH and temperature into account is Vour pH 7 0 257179 0 000941468 T 2 5 where T is the temperature in centigrade Since the equation is linear but does not pass through the origin we need to calibrate the sensor at two points As discussed above the two points that will be used are 0 and 20 The calibration points are shown below Table 13 pH Calibration Points for T 100 C pH volts 022 00407194 7 0672354 Note that the largest voltage in the table above is 7 067 volts which is above the maximum voltage that can be applied to an MB 1 coupler port without saturating it when the coupler trim pots is set to maxim
85. pplications are basically the same Since the User s Manual provides the step by step procedure for calibrating a simple Generic Meter Application i e a simple DC voltmeter those detailed steps are not repeated here The examples below are not intended to show you how to create a 10 digital thermometer using MB 1 Instead the intent is to illustrate how MB 1 can interface to a variety of analog sensors with different characteristics using different techniques If you have an analog sensor that you would like to use for a particular application it is likely that you will be able to interface it to MB 1 using one or more of the approaches shown in the examples below 2 Overview Assume you have an application that either generates a DC voltage or you have an application from which a DC voltage can be derived The transfer function that relates the parameter of interest to the DC voltage generated by the sensor can be a complex non linear function But if there are no discontinuities in the transfer function and if you can identify discrete calibration points for the parameter of interest you should be able to calibrate MB 1 to measure the parameter The different approaches for integrating analog sensors with MB 1 can be categorized into four general categories Case 1 The function to be measured is linear and passes through the origin the generated DC voltage is 0 when parameter is 0 and you know the transfer function Case2 The fun
86. r Application Meter Shunt 00375 ohms Power Supply Input to MB 1 FWD Port Common DC Ammeter Application Adjust pot to 75 my Tip Vol ae Input to 1 FWD Port i Common Calibration procedure 4 2 2 Calibration Procedure The detailed Generic Meter example in the main User s Manual provides a detailed list of steps This application uses the same procedure with the following changes 1 Since we are measuring current in amps set the Units character to A for amps 2 20 amp full scale shunt select a somewhat larger Full Scale value when doing the coupler setup 30 amps for example For the low voltages involved in this application 75 mV full scale you should adjust the side panel coupler trim pot to its maximum sensitivity at least 15 turns CW During calibration apply a source of 75 millivolts to the coupler input port being calibrated This is most easily done by dialing in the calibration voltage using a stable voltage source and potentiometer as shown in Figure 4 Using the Coupler setup screens calibrate the meter at a single point 20 amps This corresponds to the 75 mV that is being applied from step 4 4 3 Notes The 75 millivolt full scale voltage generated by the sensor is close to minimum full scale voltage where MB 1 can still provide reasonable resolution see section 7 To improve resolution for this application an amplifier could be used but a simpler app
87. ration points to 10 During Panel Meter calibration you will be prompted to calibrate the meter scale at 10 points 10 20 30 100 For calibration points 10 40 you must advance the needle beyond its 0 resting point Furthermore you must advance the needle forward slightly after calibrating each of these phantom points since the software integrity checks require the ADC value to be monotonically increasing for all of the calibration points including these don t care points As long as each of the four calibration points 10 40 are in the yellow region and each calibration point has a larger deflection than the preceding calibration point you will be OK Once you reach the calibration points for 50 dB and above calibrate the meter in the normal fashion by simply dialing the needle to each calibration point on the scale and pressing the SELECT menu button to save the calibration point After calibration any value from 50 100 will read correctly Any value less than 50 will read in the yellow portion of the scale effectively indicating an underrange which is a valid indication for this application 4 18 Color Sensor Module 4 18 1 Overview This application uses a TCS230 color sensor that produces an output voltage that varies linearly with respect to the color intensity of one of three colors red green blue The color to be monitored is selected by applying logic 0 or logic 1 signals to terminals So and
88. roach is to place two shunts in series The voltage drop as seen by the load in minimally affected and the full scale voltage available to MB 1 is doubled to 150 millivolts If you use this approach use a low resistance device such as a copper or brass strip to connect the two shunts in series A more flexible and less expensive approach for measuring DC current using MB 1 is given in the next example using an isolated current sensor 44 DC Current Measurements using an Isolated Sensor 4 4 1 Overview This example uses an isolated current sensor that allows isolation of the sensor leads from the MB 1 ground For Generic Meter applications the negative lead of the sensor output must be connected to the MB 1 ground For example in the meter shunt example above the meter shunt common lead must be connected to the MB 1 common ground There are some applications where this restriction may prevent you from measuring a parameter with a particular sensor when other grounds and common leads are also connected to MB 1 s ground For example in the figure below assume you want to measure your transceiver s power supply current with 1 using a Current Shunt as discussed in the previous example As be seen the figure below the transceiver s ground is already connected to MB 1 s ground via the coupler Therefore the series shunt can not be used to measure the power supply current when a coupler is also connected to the
89. rrent flow in the transistor increase which decreases Since the MB 1 measurements must track the direction of with respect to the up down sense of the parameter we will define low measurements to have high reflectance toward white and high measurements to have low reflectance toward black An inverting Op Am could be inserted if desired to change the sense of the direction 4 9 2 Coupler Calibration Procedure Below is a simple grey scale created with Microsoft Word A full size copy is available on the Downloads page Figure 21 Grey Scale for Calibrating Reflectance Sensor To calibrate the sensor we set a full scale value of 10 during the coupler setup routine and then save calibration data points at integer values ranging from 0 10 The calibration is done at each calibration point with the sensor viewing the corresponding grey scale value in the above chart at a fixed distance Analog Meter Calibration A Linear scale with a full scale value of 10 can be used for this application Legends for Low Reflectance and High Reflectance are included on each end of the scale to clarify the meaning of low and high readings A sample scale is shown here 4 10 Measuring Distance Using a Linear and Nonlinear Device 4 10 1 Overview In the examples above we have dealt with linear sensors and nonlinear sensors and examined different approaches for performing the calibration This example sho
90. satisfies the desired range using such a device simplifies things considerably since the calibration needs to be performed at a single point However we use a thermistor in this sample application since it provides a good example of how MB 1 can be used to measure a parameter that has a nonlinear function The device we use is a Vishay BC1482 thermistor The data sheet for a nearly identical device can be found here The resistance vs temperature transfer function is fairly complex It is given by the following formula Equation 1 Tkelvin 1 0 A B In Rtherm 10 0 C In Rtherm 10 0 2 D In Rtherm 10 0 3 where In is the natural logarithm function and A D are constants for a specific device 354016e 3 569107e 4 626311e 6 675278 7 convert to Celsius we use the following formula T Celsius Tinea 273 15 A plot of Resistance vs Temperature for the thermistor is shown below As expected the function is nonlinear FIGURE 14 THERMISTOR RESISTANCE Thermistor Resistance vs Temp Celcius Resistance ohms Temp C To measure temperature with MB 1 the top circuit in the figure below can be used Since the thermistor resistance decreases with increasing temperature this will cause the voltage into MB 1 to increase for increasing temperature which is what we want a monotonically increasing input function FIGURE 15 NONLINEAR T
91. sistance Ratio vs Concentration mg Liter The blue data series is the piecewise graph of the actual points from the manufacturer s spec Since this was almost a straight line on a log graph scale it is worth a little effort to determine if we can characterize the data with an equation Excel s trend line feature is useful for this This Excel feature is usually used to predict trends future data points from the derived equation But if you can get one of Excel s trend types to give a very close match to the data points you can then get access to the actual trend line equation generated by Excel and use that equation to aid in calibration The generated trend line is shown in red in the above figure Excel also computes what is called an R value The closer that value is to 1 0 the better the fit of the trend line The data in the red box shows both the equation of the trend line and the R value which is in fact very close to 1 Therefore we can assume that we have an accurate formula that characterizes our sensor and we will use that instead of a few discrete data points We used the Excel Power trend type to fit these data points Unless you re a Math major try all of the Excel trend types one at a time using trial and error to see which if any gives the best R value That is the approach we used 4 19 2 Wiring The wiring for the alcohol sensor is shown below Since the resistance of the sensor decreases as
92. strumentation In the bottom circuit a 10 ohm resistor which will have minimal impact on the operation of the existing measurement system has been added in series with the loop and the sensed voltage is processed by the circuit shown in this Maxim application note The circuit consisting of two ICs converts the 4 20 mA sensed current through the 10 ohm resistor to 0 to 5 volts DC respectively which is a suitable input to drive MB 1 Figure 47 Adding 1 to Existing 4 20 mA Loop Instrumentation Existing 4 20 mA System Existing Process or Display Instrumentation Existing Power Supply 4 20mA Sensor System Modified to include MB 1 Existing Existing Process or Power Supply 4 20 mA Display Instrumentation 0 5 volt 5 volt DC input to Converter MB 1 from Maxim Coupler Port 7 Input Sensitivity and Dynamic Range If the DC voltage derived from the parameter you are trying to measure is approximately 6 14 volts or more full scale you can derive the full 15 bit resolution from MB 1 15 bits applies to the values on the low end of the range of MB 1 s Amp Mux Depending upon the accuracy you want to achieve as long as the derived DC voltage is at least 2 volts full scale you will still get a minimum low range resolution of 10 bits If you only need to resolve your measurements to 1 part in 10 or one part in 20 even a much lower maximum voltage from your sensor can be tolerated Of course if the
93. t 100 These are just the Trend Line equations We use the Trend Line equation for the T 75 case below This table shows the corresponding values for integral pH values at 75 and the corresponding pH at 100 For example take the pH 0 case at 75 This corresponds to a pH value of 4689 at 100 using the Vour from the sensor as the reference Since we know the full analog meter deflection equation for the T2100 case we can determine the deflection for the pH 0 case at 75 It is 0334 This is done for the other pH values at 75 and for the other temperatures Table 17 Analog Needle Deflection for T 75 Case 0 46893077 0 033495 1 40194066 0 100139 2 33495055 0 166782 3 26796044 0 233426 4 20097033 0 300069 5 13398022 0 366713 6 06699011 0 433356 7 0 5 7 93300989 0 566644 8 86601978 0 633287 9 79902967 0 699931 10 7320396 0 766574 11 6650494 0 833218 12 5980593 0 899861 13 5310692 0 966505 1 2 3 4 5 6 7 8 9 This gives us the temperature corrected pH meter face below 34567891011 4 2 121314 0 0 A full size be found here 4 24 Yaesu FT857 897 External Analog Meter 4 24 1 Overview These two Yaesu radios have an external jack that is intended to drive an external analog meter A full size meter scale of the one shown below can be found here 20 30 40 50 60 70 80 90 zw 5 4 100 10 s 25 50 75 100 8 9 10 1112 43 14 45 0 3 5 7 This meter fac
94. t column subtracts the idle voltage of 2 5 volts We then take the arcsine of that value to determine the actual angle that corresponds to the midpoint voltage This is shown in the Interpolated 54 Measurement Angle column The last column shows the error due to interpolation which is the difference between the Midpoint Column entry and the Interpolated Measurement Angle column The worst case error occurs at the higher angles and is slightly more than 2 degrees Table 4 Error Analysis for Tilt Sensor MB 1 Interpolated Measurement Midpoint Angle for Error XA Midpoint Midpoint Voltage Midpoint in Angle Vout actual Angle Voltage 2 5 values degrees 2 50000 2 67365 2 84202 3 00000 3 14279 3 26604 3 36603 3 43969 3 48481 3 50000 Coupler Port Calibration Adjust the coupler trim pot for maximum sensitivity There is no chance of overdriving the MB 1 input in this application To calibrate this application set the full scale value to 90 units Then perform calibration at the calibration points shown in the above table in columns 1 and 2 This is most easily done by dialing in the calibration voltage for each of the ten calibration points using a stable voltage source and potentiometer as shown in Figure 4 Analog Meter Calibration A sample Tilt scale is shown here with three scales with a full scale reading of 90 This is a linear scale and requires that calibration be done at a single calibration point name
95. t performing this calibration I suppose you could get some liquor of a known proof and an enclosed container of known volumes such that when all of the liquor evaporates the concentration would be 4 mg Liter This is an approximation at best but hopefully this example provided some additional insight on using MB 1 with the family of gas sensors listed above 4 19 6 Related Sensors There are a whole series of sensors that can measure force and stress Some of these are listed below Flammable Gas and Smoke Sensor MQ 2 Data Sheet Methane Gas Sensor MQ 4 Data Sheet LPG and Natural Gas Sensor MQ 5 Data Sheet LPG Isobutane Propane Gas Sensor MQ 6 Data Sheet Carbon Monoxide Gas Sensor MQ 7 Data Sheet Hydrogen Sensor MQ 8 Data Sheet Carbon Monoxide and Flammable Gas Sensor MQ 9 Data Sheet Ozone Gas Sensor MQ 131 Data Sheet Air Quality Gas Sensor MQ 135 Data Sheet Carbon Dioxide MG 811 Data Sheet Other Gas or Air Sensors Advanced Micro Instruments 0 25 Oxygen Sensor Data Sheet General Monitors Toxic Gas Detector Data Sheet General Monitors 5 Gas Detector Data Sheet Safety Systems Technology Infrared CO2 Sensor Data Sheet 4 20 Angular Rate Sensor Gyroscope 4 20 1 Overview This example makes use of an Angular Rate Sensor These sensors generate an output signal that varies linearly with respect to the angular velocity around some axis Below is a picture of
96. t varies linearly with respect to the either the PH or ORP value respectively This example covers the PH case because it is the more complex of the two cases PH measurements require that the temperature be taken into account to arrive at the correct pH value The ORP sensor does not have the temperature issue A picture of the sensor is below The data sheet can be found here There are a couple of new issues encountered in this example The first issue is that the highest PH 14 is not an available MB 1 calibration point The other issue as mentioned above is that the voltage produced by the PH sensor is affected significantly by temperature Therefore it is desirable to provide a method that generates temperature corrected pH measurements Calibration Procedure We handle the first issue by picking a maximum calibration point of 20 which is the first available MB 1 calibration point above 14 We will see that the transfer function for this sensor is linear Therefore if we calibrate at two points namely pH values of 0 and 20 the maximum allowable PH value of 14 will simply be a PH value that lies on the straight line transfer function Note that during actual operation the PH sensor will never produce a voltage that represents a PH greater than 14 Temperature Dependence The temperatures that will be handled by this example are 0 25 50 75 and 100 Other temperatures could have been chosen as well We will set up the cou
97. ter using Electromagnetic Signal Sensor 4 13 1 Overview Any circuit that generates a DC voltage in the presence of an RF field can be used in this example Many circuits can be found with a Google search This example makes use of an Electromagnetic Field sensor specifically designed for this purpose Below is a picture of the RF sensor Specifications for this sensor can be found here The sensor has only three leads power ground and Vour Since the specifications for this device simply indicate that VOUT increases as the RF field increases the best we can do is make a relative field strength meter The device specs state that the range of operation is from 50 Hz to 100 MHz The sensor also has a built in sensitivity pot and comes with its own antenna but that can be replaced with your own antenna to provide increased sensitivity Coupler Port Calibration Since we are using this as a relative strength indicator and since V our from this sensor can never exceed 5 volts this is an easy sensor to calibrate Adjust the coupler trim pot for maximum sensitivity There is no chance of overdriving the MB 1 input in this application The full scale value we select is arbitrary We will select a full scale value of 1000 which provides good resolution We need to perform the calibration for this sensor at a single point namely the full scale value Apply a calibration voltage of 5 volts to the coupler port and save the calibration data
98. the alcohol concentration increases we wire the alcohol sensor to the voltage source which will cause the voltage fed to the MB 1 coupler port to increase as the alcohol concentration increases The spec applies when the Fixed R resistance is 200K The input resistance of an MB 1 port is approximately 300K so placing a 680K resistor in parallel gives a 209K which is probably close enough to satisfy the spec sheet requirement for a 200K load Figure 38 Alcohol Sensor Wiring The heater on the sensor can draw up to 750 milliwatts If you decide to use the 5 volt auxiliary outputs on MB 1 to power the sensor turn off the external Bar Graph display if on so as not to overload the Auxiliary power bus Any external 7 segment displays can be left on since the current draw on those is not as high as the external Bar Graph 4 19 3 Calibration Procedure We have an equation for the graph in Figure 37 Rs Ro 0 5176x 2635 From that we can determine the actual sensor resistance as a function of Ro Rs Ro 0 5176x 26735 Remember that Ro is the sensor resistance when the alcohol concentration is a know reference value 4 mg Liter and can vary from 1 Meg to 8 Meg sample to sample For this example assume that we have a sensor with a known Ro value of 2 Meg We can now determine the voltage seen by the MB 1 coupler port as a function of alcohol concentration Remember that x in the equation above is the alcohol concentration the X
99. the multiplier is a portion of the supply voltage as determined by voltage divider R Vin V SOURCE R3 R2 R3 Finally the output of the multiplier is given by VsENSE Vin Veour Rsense 15 Vsource R2 R3 The maximum permissible Vgensg value is 150 millivolts For a given load current this determines the maximum resistance of the shunt resistor Rsense Assume that the maximum current in this application is 10 amps This gives us an 5 150 10 015 ohms Another constraint is that the sensor output voltage Vpour that represents the power must not exceed 5v or 4 5v Assume that the source voltage powering the load has a maximum value of 15 volts We can now calculate the voltage divider ratio R3 R2 R3 so that Vpour never exceeds 4 5 volts R2 R3 lt Vpour G Vsource 15 Plugging in the numbers from above R2 R3 lt 4 5 25 15 150 080 If we set R2 120K and R3 10K we get a ratio of 0769 which meets the criteria We now have all of the values to determine the transfer function of Vpour vs PDELIVERED Vpovr Rsewsk Is G Vsource R3 R2 R3 Vpovr 015 Is 25 Vsource 0769 Vpovr 0288 Is Vsource Transfer Function Vpour 0288 PDELIVERED As a sanity check at the maximum voltage level 15 volts and current level 10 amps Vpour s
100. the sensor The data sheet can be found here This angular rate sensor will measure the angular velocity in degrees per second around the Z axis as shown in the figure below The sensor s maximum and minimum range is range is 100 per second clockwise and 100 per second counter clockwise When the device is stationary the device outputs a reference voltage of approximately 1 35 volts As the device is rotated CCW the output voltage decreases from the idle reference voltage by 65 millivolts per degree per second As the device is rotated CW the output voltage increases from the idle reference voltage by 65 millivolts per degree per second This corresponds to a voltage range from 1 35 065 1 285 volts to 1 35 065 1 415 volts corresponding to an angular velocity of 100 per second to 100 per second respectively Therefore the range in the analog output voltage is only 130 millivolts MB 1 can read to millivolt resolution at the low end when the input voltage to MB 1 is small This is the region where MB 1 applies the maximum gain of 32 from the Amplifier Mux that processes the coupler input voltage But since the working voltage range from the output of this sensor is in the vicinity of 1 35 volts MB 1 s resolution will be in the multi millivolt range which is not good enough to give resolution of 1 per second Therefore to provide the improved resolution we will insert an interface circuit between the sensor and the
101. the sensor would be mounted When the inclination angle is 90 X arrow pointing straight down the X axis acceleration is 1g Figure 31 Sensor Orientation Horizontal Hookup is straightforward Description Self Test see data sheet Not used Not Used Y Axis acceleration not used Y Axis acceleration connect to coupler input 5 volt common from MB 1 Aux Power 5 volts from MB 1 Aux Power A 1 uF capacitor should be connected between XA and ground to reduce noise With no acceleration or tilt the idle output voltage is Vcc 2 When powered with 5 volts this sensor generates 1000 millivolts per g Therefore the transfer function is XA 2 5 1 0 2 5 where XA is the analog output voltage in volts and a is the acceleration in g units This is a linear function but the above equation applies for acceleration not tilt From the above equation we know that the output voltage at 0 degrees no tilt will be the idle output voltage of 2 5 volts Vcc 2 At 90 degrees the sensor sees an acceleration of 1g Therefore the analog output voltage will be 2 5v 1000 mv g 1g 3 5 volts But between the two end points the output voltage varies as the arcsine of the acceleration see Application notes for details Therefore 0 arcsine a arcsine XA 2 5 Using the approach we have used in other examples we want to determine the corresponding voltage t
102. ubtraction of 500 as was required when using the MB 1 numeric display values All that is required is a single linear scale of 1000 units full scale with the lower end of the scale is labeled 500 and the upper end of the scale is labeled 500 A sample scale is shown below Magnetic Field E 100 O 100 200 200 300 4 21 4 Related Sensors There are a whole series of sensors that can measure magnetic fields Some of these can be found here Another magnetic sensor the Analog Devices AD22151 has more advanced capabilities than most of the sensors listed above The Analog Devices sensor allows you to control the sensitivity of the sensor It can also be configured for unipolar or bipolar operation 4 22 Ohmmeter Example 4 22 1 Overview This example uses the simple circuit shown below to measure an unknown resistance Vour the voltage at the tap of the voltage divider increases as the unknown resistance increases Figure 41 Circuit for Measuring Resistance We can calculate the voltage for several resistance values corresponding to available MB 1 calibration points These are shown in the table below Table 11 Calibration points and Corresponding Voltages for Ohmmeter Application Vout Vout Vout Vout 0 004995 0 238095 1 875 3 275862 0 00998 0 283019 2 058824 3 333333 0 014955 0 327103 2 222222 3 75 0 01992 0 37037 2 368421 4 0 024876 0 412844 2 5 4 166667 0 029821 0 454545 2 619048 4 285714 0 034757 0 555556 2
103. ust adjust to match the actual reference voltage of the sensor With the sensor a stationary position measure the output voltage of op amp 2 with a multimeter Adjust R1 until this voltage is 0 Read the actual reference voltage by measuring the output voltage at op ampl It will probably be somewhat different from the nominal value of 1 35 volts If that is the case change the equations below and substitute the actual reference voltage for 1 35 The remainder of this example is done using the nominal reference voltage value of 1 35 Since 1 is 0 based we must start the low end of the range at 0 If we set up the calibration with a full scale value of 200 our digital readings on MB 1 will vary from 0 200 To read the actual angular velocity using the digital displays subtract 100 from MB 1 s digital reading If you are adding an analog meter to MB 1 for this application the scale can be created with the actual sensor limits 100 deg sec CCW to 100 deg sec CW allowing the analog meter to be read directly If we add a trend line to the amplified signal and display its formula we get Vout 0124 v 1 35 where v is the angular velocity Since the curve is a straight line we need to calibrate at only two points We need two points instead of one since the equation does not pass through the origin 0 0 With the 100 deg sec offset discussed above the equation becomes Vout 0124 v 100 1 35 0124 v 0 11
104. wer and current measurements respectively for all encountered voltage levels including voltages lower or higher than the voltages corresponding to the smallest and largest calibration points That is not the case for multipoint calibrations identified as GENERIC in the setup screen Below is a picture of the RF Current sensor used in an MFJ RF current meter You will also find circuits for several RF current sensors on the Internet They are relatively easy to build Figure 30 RF Current Sensor Even though an ideal current sensor has a linear transfer function that passes through the origin and could therefore be calibrated at a single point there is some advantage in terms of accuracy to calibrating the coupler at multiple points for the same reason we calibrate an RF Power coupler at multiple points namely real world couplers are not ideal devices RF Sensor Calibration The following figure and table are taken from the MB 1 User s Manual The figure shows one method of calibrating this application using a reference RF power meter in tandem with the RF current sensor When driving a 50 ohm resistive load the RF current can be calculated knowing the power level as read from the reference Power Meter Multiple values are selected in the table below to ensure that we characterize the coupler over its low medium and high operating range Reference RF Watt Meter As mentioned above RF currents less than the lowest calibration point
105. ws distance measurement applications Both linear and nonlinear sensors are available for measuring distance We briefly discuss the linear device but concentrate on the nonlinear device because it brings in a new wrinkle namely the fact that the output voltage while well within MB 1 s input range is decreasing as a function of distance and MB 1 requires that the input voltage that it reads increases as the parameter being measured increases We have not had to deal with this issue so far Using a Linear Distance Sensor Maxbotix Ultrasonic Rangefinder LV EZ1 EZ 1 The data sheet can be found here This sensor shown in Figure 22 is an ultrasonic device that produces a linear output voltage per unit distance The output is given by Vour 512 where Vcc is the supply voltage For a 5 volt supply this corresponds to 9 8 millivolts per inch There is nothing new we can learn from calibrating this device compared with the above examples We can either program a single point for example 980 mV corresponding to a calibration point of 100 inches or we can use the empirical method although you might need to take into account the beam width issues as the distance increases if using the empirical method Figure 22 Ultrasonic Distance Sensor Using a Nonlinear Distance Sensor Sharp IR distance sensor This sensor shown in Figure 23 is an IR sensor with a highly nonlinear transfer function The data sheet

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meterbuilder™ mb-1 programmable meter for analog sensors