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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Thermocouple
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. Christian |
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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. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header is ignored. To contact me, please use the feedback form on the S.E.R FAQ Web sites. |
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