AC motor noise on thermocouple

[marcDAQ]

Hello

Our hydraulic test stand uses a 500KW 3phase AC motor.

I am trying to record hydraulic temperatures using several type T thermocouples.
When the AC drive is shut off everything is fine.

When the drive is running the temperatures fluctuate easily 100C. All over the place from noise.

Our desktop has a PCI-6224 DAQ card. It's connected to a SC-2345 board with SCC-TC02 for signal conditioning.
The thermocouple leads are 30feet of so.

Any suggestions on how to get rid of this noise. I'm sure it's from the field of the large AC motor.

Thanks

Marc

[RavensFan]

A few things I would recommend.

1.  Use ungrounded thermocouples.  I've seen grounded thermocouples cause ground loop problems in the past.

2.  Use shielded thermocouple and ground only one end of the shield.

3.  Acquire the thermocouple data at a much higher rate and average the results

[StevenA]

I agree with everything ravans fan said... Also, isolated inputs is a good idea. 

[hecmar.arreola]

I have an SC-2345 block that I use, and I find that if I properly ground it to facility ground it eliminates a lot of noise.  Isolated inputs help out a lot for noise.  If things are really bad and I need something done quick-and-dirty I goto a laptop setup and run my test on battery power.