switching thermocouples - Can I?

[hofmann]

Hi,

I have a problem. I have a DAQ system with a SCXI-1001 to adquire 256 thermocouples measurement and I want to expand it to more than 1 thousand. I thinking about use some multiplexer/matrix module but I´m afraid about the accuracy of measurement.

Can I connect the thermocouple directly in multiplexer/matrix without a signal conditioning before?

Can I use the signal conditioning after the multiplexer/matrix?

And what type of multiplexer will give better results, a FET one or a relay one?

Information: My signal condition is made by one SCXI-1303 module.

[ninlmartijn]

Hello,

there is a knowledge base about switching and thermocouple measurements. A switch is usually combined with a DMM (pc or PXI based) for temperature measurements. Please refer to the following link for this topic; https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000x0dBCAQ&l=en-US

A FET or SSR (solid state relais) switch have a unlimited lifetime. In your case you must consider the voltage which is created by the switch itself (EMF) this will introduce a error in your reading. Some mechnical relays and some SSR switches gives the best results here. All switch considerations can be found here; http://zone.ni.com/devzone/cda/tut/p/id/4197 

If you have any questions, please let me know.

Best regards,

Martijn