I need to log voltage drops across 20 resistances connected in series. The supply current is 30mA. How would I go about wiring this to a pair of CB37 boards?
File Attachment:
I need to log voltage drops across 20 resistances connected in series. The supply current is 30mA. How would I go about wiring this to a pair of CB37 boards?
.png%3Fitok=PHGBxf6M "EEV Blog Reviews LabJack T7-Pro & Software Tools")
.jpg%3Fitok=B1YcuDFK)
.png%3Fitok=Ybt-OlgU "LabJack + JEDI One Can Create a Powerful Distributed DAQ Ecosystem")
You would need to connect an AIN on each side of the resistances (at each of the voltages) you want to measure. You will not be able to measure all of the voltage drops with how your circuit is currently laid out since some measurements would exceed the common mode range of the T7 inputs:
https://labjack.com/support/app-notes/differential-analog-inputs#the-com...
https://labjack.com/support/datasheets/t-series/appendix-a-3-2-3-t7-sign...
Some possible solutions are described in this section about measuring batteries in series:
https://labjack.com/support/app-notes/differential-analog-inputs#measuri...
Can you recommend an instrumentation amplifier for my application?
AD8227 maybe?
You have 20*49 = 980 ohms. Driving 30mA through 980 ohms means your power supply will produce 29.4 volts. The voltages on either side of R1 will be 29.4 and 27.93 volts (a difference of 1.47 volts). That suggest to me you will have to provide the max single supply of 0/36 volts to this amp, and even then you need to find a caculator/simulator to see if these conditions are valid.
Another option is to look for an instrumention amplifier or difference amplifier that is designed to handle high common mode voltage. I don't have a specific suggestion, but know that the semi companies do much such things that can handle a small difference with high common mode, without requiring a high power supply voltage.
Can you drive less current? If you did 10 mA, you could just wire all the voltages directly to the T7 AIN.