noise spike between two DAQ devices

[moods]

I am having two data acquisition systems measuring a number of channels. The low speed system is using two SCXI chassis and scanning about 128 channels at 200 Hz. The low speed computer is using a PCI-6259 MIO board.

Eight (8) of the channels are Tee'd off to a high speed data acquisition device at 8000 Hz. On the high speed computer, there is a discerete spike at 5 ms (corresponding to 200 Hz). The high speed computer has a PCI-6133 S-Series board (differential mode measurement).

When I change the low speed scan rate to 100 Hz, the spike on the high speed computer is at 10 ms (corresponding to 100 Hz).

My question is whether any digital lines controlling the SCXI chassis are inducing this spike which is being picked up by the high speed board.

The two DAQ boards are installed in two different computers and are not connected in anyway except for the eight (8) analog voltage signals that are Tee'd off and connected.

Any ideas to resolve this problem would be appreciated.

Thanks,

Regards,

Sudarshan.

561-714-1641

[aeastet · Accepted solution]

This could me many things but my first guess would be ground loop. Are the computer plugged into two different plugs? If so this can cause a ground loop. after that it could be many other things.

Shielding

lose connections

interference

etc...

[moods]

Tim,

 Thanks. I thought of doing that long time ago. Got distracted on other instrumentation issues and never thought of it again. It is surprising how a totally different set of eyes that are not deep in the fox hole can point out the solution in the right direction.

 Thanks again for the help. I was considering some really horrible options compared to having them powered on the same AC line.

Regards,

Sudarshan

[aeastet]

Glad it was that easy.