I have an application where I need to measure the temperature of a surface at various points (approximately 20 to 30 points).
I'm using a cDAQ chassis with multiple NI9211 modules.
The surface to be measured is made of copper. I'm concerned that there may be some spurious signals generated between channels if the thermocouples are not electrically isolated from the surface.
Do I need to use thermocouples with an insulated junction?
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You are absolutely correcct in thinking that you need some isolation. Without it, you will get bad readings and interference between different thermocouples. To get your isolation, you will want to use a high-thermal, low-electrical connectivity material. Vendors such as Omega sell both cements and greases with these properties. Hope this helps and good luck in your application!
There are also sheathed thermocouples that come in grounded and ungrounded versions. In the ungrounded case, the junction has no electrical connection to the sheath. Advantage is electrical isolation, disadvantage is a slower response time which may or may not be an issue in your application.