Hi all,
I faced this problem while sampling simultaneously from the first three analog input channels of the A/D board ( UEI ,Powerdaq,PD2-MFS-8-800-14DG). Whenever the first channel ( AIN 0) signal was going above 5~6 volt, the signal from the channel next to it (AIN1), was showing a lower value than expected( after sampling). I connected an oscilloscope in parallel with the channels and the sampled value was less than oscilloscope value for AIN1 ( for example if true value is 1.8 v, it was giving me 1.6 V). But whenever I swapped the channels this problem was solved. I am using Matlab for this and defined same range( +10,-10 V) for all the channels.
The datasheet of the A/D board is attached herewith. I will be glad if anyone can throw any light on this.
Thanks
Samik

 

In the manual, table 5.3c, (p.48), which signal source type are you using?

 

In the manual, table 5.3c, (p.48), which signal source type are you using?

I am using differential mode.......thanks Ron H

 

What is the common mode voltage of your differential input signal?

 

What is the common mode voltage of your differential input signal?

Dear Ron H
The ai0 channel is connected toa pressure transducer which is already grounded, so the common mode voltage is 0. (row I,column II in table 5.3 c)

 

Dear Ron H
The ai0 channel is connected toa pressure transducer which is already grounded, so the common mode voltage is 0. (row I,column II in table 5.3 c)

Is there a current path between your signal source ground and your A/D ground? In other words, is the transducer ground connected to the A/D ground? Somewhere, there has to be a path for A/D input current to return to A/D ground.

 

Is there a current path between your signal source ground and your A/D ground? In other words, is the transducer ground connected to the A/D ground? Somewhere, there has to be a path for A/D input current to return to A/D ground.

The A/D board is connected to computer ground , and both transducer gnd and comp gnd are at same level.