RTD Measurement issues NI9205

[bradbb2005]

Please excuse me if what I say may be confusing, as I haven't done much work with LABView.

So our setup is as follows:

RTD --> Connection Panel --> Signal Conditioner (RTD in, 0-10V out) --> NI9205 Module (Total length: from 50' up to 200')

We have approx 15 RTDs, each output from the signal conditioner is connected to the individual channels on the 9205 card, the commons are all connected together.

This system has been functioning fine as far as I know for a while, and some aspects are still OK.

The issue:

I will use Ti_0-3 (Temperature inlet) as reference for the example.

So we go ahead and calibrate in LV Ti_0-3 from -50 - 300 degrees C, using approx 15 data points.

After Cal, all temps read basically the same ie. 15.0, 15.1, 15.1, 15.0; Ti_0-3 respectively.

When we start our equipment and get it up and running, the temps randomly read differently than each other ie. 11.1, 13.2, 12.1, 12.2; Ti_0-3 respectively. And when checked with a calibrated process calibrator (Fluke), the temps read say 12.1, but LV is displaying the temps wrong for those first 2 channels, and if we put the process calibrator on it and source, it is off by the same amount from -50 up to 300. We then would have to go and recalibrate to get the values correct, but they still change after.

It is not a fluctuation like a loose connection on the RTD, it is like the Calibration gets screwed up.

More info:

RTDs are 3-wire PT100

I think LV version is 2010

System was not built by myself.

I cannot give a copy of of the program for debugging.

Please let me know if there is any additional info needed to help with this issue.

Thank you in advance,

Brad

[FuManWho]

Hey Bradbb2005,

What exactly is the circuit set up of your set up?

Also what happens when you try removing one of the incorrect RTDs, does the other incorect RTD change?

What happens if you don't have anything connected to those channels?

[bradbb2005]

What do you mean by circuit set up? in Labview or physical connections?

If I remember correctly, the values for the other RTDs stay the same - no change.

If I have nothing connected to the channel, the temp defaults to -50.

Sometimes this problem can be fixed by merely unplugging the rtd connection, then plugging it back in, but that is not always the case (as that would lean towards a connection issue)

Is running the RTD to a Signal Conditioner, then to the 9205 a proper way to do it? or is there a better way? I am just wondering if there is too much happening between the actual RTD and the input to LabView.

[FuManWho]

Hi bradbb2005,

I meant circuit setup from the rtd to the DAQ device.

I had some questions to help clarify what you are doing:

Are you using a scale to automatically convert voltage to temperature?
What is the voltage range that is being inputted into the device?
What are the raw voltage measurements that you are getting in compared to measured?