Why is my differential AI channel floating to 10 volts?

[JonathanS]

Hello,

I am using a USB-6229 DAQ with LabVIEW 7.1 and the lastest DAQmx drivers.  I am trying to measure a thermocouple reading and getting bad results.  When checking the analog channel (wired differentially), MAX reports that the differential voltage across the channel is 10.6 volts.  Is this a hardware problem, or is there something I can do to alleviate it?

Thanks,

Jon

[JonathanS]

Just to be clear, as I did not mention it before: I have both terminals shorted to each other with a wire, and yet the DAQ still reads 10 volts.  If I ground either terminal to the chassis or AI GND, the voltage immediately drops to zero.  However, after a few seconds, measured voltage increases to 10.6V again.

[JonathanS]

Another excellent NI support req.:

https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

(for anyone interested)

Thanks,

Jon

[dansch]

Hi Jon,

Were you able to solve the problem by adding in a bias resistor? I assume this is something you have tried based on your reference to the Developer Zone tutorial. I just want to make sure that things are working properly for you now. Thanks!

[JonathanS]

Yup, all working and thank you for the followup.  That was one of those field wiring techniques we've never quite needed before due to chassis connections (read: dumb luck).  But that was the exact tutorial I needed.]

-Jon