different voltage readings

[frostkiller]

Hi community members,

I recently put together a program using LabView 8.0 that runs on my Dell laptop computer. 

I am continuously collecting data from four different channels - Ai in., 100Hz, 100s/channel

I am collecting data from:

1) Linear encoder #1

2) Linear encoder #2

3) Load cell output, after signal conditioning - always in tension, so voltage output is always positive

4) Load cell excitation voltage - DC

My questions:

A) For some reason the voltage that I read with a DMM directly on (4) w.r.t. Ground is off by 2v. All other voltages are not offset. Why?

B) When I run the program on a Sony Vio laptop, signals from (3) are very noisy +/- .2V. Why? All other signals the same, (4) is still offset by 2v.

Thank you for your attention and any valuable input

-Erick

[tbd · Accepted solution]

Hi Erick,

      Sometimes it's simplest to use the Measurement and Automation Explorer (MAX.) to get things working.  There you can setup a quick Data-acq. (for NI hardware.)  Do you use differential-input mode?  Is the load-cell output DC?  If yes to both, then it is surprising that the DMM measures differently than the DAQ-device.

Open MAX (Start\Programs\NI\Measure...), find your (NI) hardware, open test-panel...

If the problem isn't solved by using differential-inputs - what NI-DAQ hardware is connected?

Luck/Cheers!

Message Edited by tbd on 04-19-2009 04:51 PM

[frostkiller]

Yes! you are right, I did have my measurment mode set to single ended. I changed it to differential and it works like a charm.

Thank you tbd 

[tbd]

Very happy to hear it - thanks Erick.