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thermocouple attachment to metal

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thermocouple attachment to metal

Postby TecManager » Mon Mar 27, 2017 3:39 pm

We plan to use several thermocouples type K to measure heat rise on conductive electrical parts, i.e., terminal blocks and fuse blades. My question is, what is the best method to attach the probes to these mtal parts?

I believe the loop on the probe end can be undone and separated out and then fixed to sub straight using solder or spot welds, is this correct?
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Re: thermocouple attachment to metal

Postby Gerry » Thu Mar 30, 2017 12:03 pm

Hi TecManager,

If you separate the wires at the tip of a thermocouple and then independently apply them to a surface for measurement then any difference in temperature between the tips will create a measurement error.

High temperature solder or spot welding should be done so the material surrounding the thermocouple junction, and holding it to the surface, is minimal, to minimize it's thermal mass, and maintain a fast response. However, if the surface being measured has a relatively large area, and is a fairly uniform temperature surface during measurement, this is not such an issue. Bear in mind that, although these are good methods of fixing and providing a high thermally conductive connection between the thermocouple tip and surface to be measured, they could also lead to very noisy measurements depending upon the setup and environment (which means that, if you can't utilize other methods to minimize the noise, you will need another method to attach the thermocouples).

Regards,

Gerry
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Re: thermocouple attachment to metal

Postby TecManager » Thu Mar 30, 2017 12:33 pm

Gary, thank you for your knowledge and comments. I guess I will try and use other methods to attached the thermocouples.

:D
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Re: thermocouple attachment to metal

Postby Glovisol » Tue Apr 04, 2017 1:08 pm

Hi Technical manager,

you mention you have to measure the temperature of elements (fuse blades, etc.) with thermocouples. Please consider that the thermocouple itself is a metal junction where two wires join and these wires go to the Picotech apparatus you are using. If you have voltages on the metal parts to be monitored, these voltages can burn out the Picotech unit and represent a safety hazard.

The solution is to ELECTRICALLY ISOLATE the thermocouples while sticking them to the metal parts to be monitored. According to my experience ( I had similar problems to solve) you can use a BERILLIUM OXIDE WASHER as insulator. Berillium Oxide has the same thermal conductivity as copper, but is an excellent electrical insulator. You can fix the washer to the metal surface with small screws or with epoxy resin and then glue the thermocouple to the washer. You can insulate over 1500 V with this method.

Of course this method also helps in minimising stray noise pick-up, especially if you use a grounded shield (ground at the reading device only) over the thermocouple interconnection wires.
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