Why do I get 15V from the DAQ after the reading?

[Rafi2003]

Hi,

I'm using NI6250 to measure 2 voltages over a shunt resistance.  I'm using a differential input, ch5 for one resistor (wires go to AI_5&AI_12), ch6 for the other (wires go to AI_6&AI_13).

The Problem:  After reading voltage form ch5 I measure 15 volts in my circuit.  This voltage is arriving from the DAQ !!.   When I read the voltage from ch6, the voltage disappear.

Do I have a defective card?  Can anybody suggest any explanation to that?

Thank

Rafi

[Rafi2003]

I made a mistake in the differential inputs specifications:  The actual wiring is as follow:

ai5 & ai13

ai6 & ai14

Thanks

[Joe_S]

Hello Rafi,

The issue that could be causing you to see the wrong reading could come from a few different places.  Have you used a multimeter to measure the voltage across your resistors to make sure you are getting what you expect?  Also, have you tried measuring other sources with your DAQ card such as a power supply or function generator?

If both of those are working as expected, the issue could be with the grounding you are using in your system.  You can try looking at this tutorial for information about connecting your signals.  There is also a section about Connecting Analog Input Signals in Chapter 4 of the DAQ user manual that you could read. Let me know if either of these help!

Regards,

Joe S.