AI GND connection in the sc2345?

[markudm]

I am a new user trying to set my sc-2345 with a SCC tc02 module to measure temperature with a K type tc. The data acquisition card is a 6024E pcmcia card. The TC is working correctly but displaying a noisy signal. I want to try grounding the tc by connecting the GND terminal on the tc02 module to the AI GND. My question is: where is the AI GND terminal in the SC-2345? Do I have to go through a SCCft01 feedthrough module?

[Tesla1977]

afaik the ground terminal on the SC-2345 is made for connecting the shield of a thermocouple wire.
I know that GND on TC-02 and DGND on the screw terminal of SC-2345 is the same ground.
How noisy are your signals?

[Tom_W_[DE]]

Hi markudm-

Grounding the thermocouple may actually be counter-productive as the SCC carrier communicates in NRSE mode with the card. Referencing the TC to ground may actually induce more noise into your measurement if the GND itself is noisy.

Thermocouple readings are by nature rather noisy. I second themad's question: how noisy are your readings?

Regards-

[markudm]

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@Tom W. wrote:
Hi markudm-

Grounding the thermocouple may actually be counter-productive as the SCC carrier communicates in NRSE mode with the card. Referencing the TC to ground may actually induce more noise into your measurement if the GND itself is noisy.

Thermocouple readings are by nature rather noisy. I second themad's question: how noisy are your readings?

Regards-

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OK, thanks for your help. I guess I can live with the noise, about +- 0.25 deg C. I'm reacting to my experience with unconditioned TC signals through the AMUX 64 board, where grounding the negative lead always seemed to take care of excessive noise.

Mark S.

[Tom_W_[DE]]

Hi markudm-

I would say that the noise level you are seeing is pretty small, especially for normal TC operation. As you probably know, TC measurements in general are very sensitive to movements and connections because of the very small voltage levels expected in operation.

To answer your original question, the GND pin on the SCC-TC02 is not a direct connection to the AIGND terminal on your DAQ board. Rather it is a reference to the internal supplies provided by the DAQ card for operation of the SCC module.

In order to connect to AIGND directly for testing you would need a feedthrough module such as the SCC-FT01.

Please let us know if you have any additional questions.

Thanks-