TC-08 thermonuclear tip isolation

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kazu14
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Joined: Sat Aug 15, 2020 4:21 am

TC-08 thermonuclear tip isolation

Post by kazu14 »

Hello support,

When I used multiple channels to measure temperature on same conductive surface,
those showed some differences in tempareture.
Then, I tried to solder a tip of multiple K-types on same electrically conductive metal
to ensure no contact issue. But I still see several degree difference among multiple channels.
The metal is electrically floating but shorting multiple channels.
I should not short multiple channels by electrically conductive metal ?
I thought electrical short among channles would be OK as long as those multiple channel common level is within +/-7.5V.
Can you tell me that?

Regards
Kazu :)

Gerry
PICO STAFF
PICO STAFF
Posts: 852
Joined: Mon Aug 11, 2014 11:14 am

Re: TC-08 thermonuclear tip isolation

Post by Gerry »

hi kazu14,

I have re-written this answer for brevity and clarity

This is to some extent to be expected with Type-K thermocouples. If you look here: https://www.picotech.com/library/data-l ... tolerances, you can see that the Class 1 Tolerance values for our Type-K thermocouples are ±1.5 °C or ±T x 0.004 (whichever is greater). So, you can have any 2 thermocouples potentially varying by up to 3°C (and more for highest temperatures), and this is basically, due to the types of metals used for the thermoelectric effect, and their impurities.
That tolerance difference, coupled with the usual manufacturing batch tolerance difference, is enough to give you "several degrees of difference among multiple channels", as you observed.

If you need improved (reduced) temperature spread among your channels then you can get Type-T thermocouples here: https://www.picotech.com/data-logger/tc ... ermocouple, which have tolerances of ±0.5 °C or ±T x 0.004, reducing the tolerance spread you are seeing by up to a factor of 3.

Also, unless you are performing the measurements in a temperature controlled environment (such as an oven) then, if you have a big enough separation between probes, what you are seeing could be partly attributed to thermal currents. So, you may be able to reduce any variation due to currents by taking steps to minimize airflow.

Finally, it would be worth reading the following applications note regarding temperature accuracy, to ensure that you are not making any typical mistakes that might be contributing to the variation: https://www.picotech.com/library/applic ... asurements (in particular lead length, and relatively new versus relatively old, previously stressed thermocouples)

You are correct regarding the Common Mode Range and shorting of channels.

Regards,

Gerry
Gerry
Technical Specialist

kazu14
Newbie
Posts: 0
Joined: Sat Aug 15, 2020 4:21 am

Re: TC-08 thermonuclear tip isolation

Post by kazu14 »

Hello Gerry-san

Thank you very much for your reply.
I understood that the error I saw is something expected and
the measuring way with multiple thermo-couplers electrically shorted is allowed as long as those common mode is within +/-7.5V.

Thank you very much again for your support.

Regards
Kazu
:D

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