DAQmx

[The New-Guy]

I have Labview 7.1 and am working with a PCMIA 6036 board, trying out DAQmx.  I have been dealing with an issue

on the AI for the last couple of days and am stumped.  I am trying to read two continuous differential inputs on A0 and

A1, one being a voltage across a current shunt (A0) and the other a Strain Gauge transdeucer (A1).  The base problem

is that I cannot get anything on A1 except apparently cross-talk.  If I try either of these signal on just A0, they work fine.

When I hook-up to A1, however, the A1 tracks the A0.  When I give an input on the strain gauge (A1), absolutely nothing.

I've tried every permutation of indexing, and have moved the A1 over to A2 and then A5.  Same thing.  This is continuous

reading, 1000 samples/sec and reading 10 samples at a time.  Tried reading 1 sample at a time, faster and slower sample

rates and even software timed loops.  Any help on this issue?

[Wayne.C]

A channel configured in DIFF mode uses 2 AI inputs.  One input is connected to + signal and second input connected to - signal.  In your case you will be connecting a total of 4 analog inputs.  Suggest you read documentation for your device.

[The New-Guy]

Yes, I am doing that.  Sorry I didn't elaborate.  So, back to my question....

[johnsold]

Do the transducers have differing common mode voltages? How big are the common mode voltages? Have you provided a resistive path to ground for amplifier input bias currents?

Lynn

[The New-Guy]

The common mode voltage between the wires may be different, as I have not twisted them (yet).  I have not purposely provided a resistive ground path either.  I do have a 60hz ripple that I will try to eliminate later, hopefully with a software filter. 

In my original message, I stated that I can read this signal normally if that is what I put on A0 (differential, CH0 (+/-)).            

When I put that transdeucer, or anything else (i.e. current shunt), that second channel follows the CH0, with the 60Hz ripple.  This same configuration works with traditional DAQ, that is what is confusing me.

[Abhinav T]

Hi,

Have you been through the troubleshooting steps in this Knowledge base article?

Hope this helps!