Christian writes:

Dear all,

I am having a vacuum setup with a Ni-NiCr-Thermocouple inside, which consists
of two welded wires. The question is, if it is allowed to ground the
thermocouple in the welded point, i.e. to attach it to the metallic sample
holder, where the temperature should be measured (reference point outside at
room temperature).

When the thermocouple is isolated in the vacuum, i.e. not attached to the
ground, the readings are fine. But as soon as the thermocouple is grounded, the
readings become oscure. From my point of view, the grounding of the
thermocouple should have no influence, because a difference in voltage is
measured.

The only possibility, which I considered is, that the device which evaluates
the thermo-voltage is not on the same ground than the metallic sample holder...

So: Is it possible to connect the thermocouple to the ground (metallic sample
holder) without a loss of the thermo-voltage?

Anybody has an idea?

Btw: Isolation of the thermocouple is not possible, because temperature gets to
high or isolation material has low thermal conductivity.

You need to check the specifications of the instrumentation that reads
the thermocouple voltage. It should only be meassuring the difference.

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