SCXI-1122 RTD Noise

[rreverol]

I am using SCXI-1122 to acquire RTD signals.The system has been working for while but a few days ago there is noise in some of the RTD signals. The temperature variation due to noise is about 0.5 ºC and it appears to be intermittent. All cables are shielded, the shield is connected to the SCXI-1322 chassis ground. What can I do to avoid that noise. I am using the internal current source (1mA) for all signals.

Mensaje editado por rreverol

[Henrik_Volkers]

What has changed?

Shielding and isolation checked?

[rreverol]

Henrik,

Thanks for your answer. The shielding has not changed, it is connected to SCXI-1122 chassis. I have already checked isolation in the SCXI-1322 terminal box as well as in field connectors. I'll recheck anyway.

Should I expect a damaged DAQ board or signal conditioner SCXI-1122?  I am using PCI6259. Should I focus just in the noise source?

Roberto. 

[Henrik_Volkers]

Roberto,

what I mean with changes is much more subtil. Has there been any changes in the hole setup? 

New setpoints in a power converter, a new oven nearby.... 

Groundloops?

Is your shielding connected on one side, or on both? 

About isolation, did you test it with hot sensors? 

How does the noise look like? Try the highest samplerate you can get or hook up a scope.

[rreverol]

Henrik,

I have been looking for a new noise source but I haven't found anything yet. I had a ground loop. I eliminated it and everything was OK, but just one day after that the noise appeared again. I had the shield connected to the chassis ground and to the reactor ground (where the RTD is located), I just disconnected the shield from the reactor ground to eliminate de groundloop.

I'll look at the signal at a higher sample rate and tell you more about the noise.

What is a hot sensor? How can I test isolation with it?

Regards and thank you for your help,

Roberto.

[Henrik_Volkers]

hot sensor: don't do the isolation tests while the reactor is cold ....

The conductivity of your isolation materials will change with temperature...