Voltage Not Matching Meter At Terminals on SCB68 with PCI 6254

[MU123]

The setup:   I have a PCI 6254 measuring 10 channels, all differential hook up. 0-4 and 16-19, using 2 SCB-68s and shielded cables and such.  Inputs 0-4 have pressure transducers that put out 0 -10 V all with the same common.  The setup seams to work but I have a strange occurrence.  When I put 30 PSI to input three I get 6.149 VDC measured with a meter on the SCB-68 and something very close to that when I look at the raw voltage coming out of Labviw (2010 BTW).  If I supply 30 psi to input two it see the voltage according to LV to be 6.04 VDC on channel three.  The voltage with the meter is still 6.149 VDC on channel three.  So LV is thinking the pressure went down on that station but I have verified with an external gage that it has not.

So I have two things that I am curious about:

1: Why do the channels interfere with each other?

2: Why do I not get the same voltage when measured with a meter?

Could there be noise in my NI cable between the SCB and the card?

[GarPar · Accepted solution]

Hi MU123-

     It sounds like what you are seeing is ghosting.  Here is a great KnowledgeBase article that discusses this phenomenon and how to avoid it.

     Let us know how this helps out.  Best of luck with your application!

[MU123]

Thanks!  That was it.  Changed the settling rate and slowed the samples some to make some room and that got rid of it.  If I had searched ghosting I probably would have found it.  Your help is much appreciated.