TC-08 difference in values

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poutila
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Joined: Mon Feb 24, 2020 4:14 pm

TC-08 difference in values

Post by poutila » Mon Feb 24, 2020 11:53 pm

Hello,
I am getting these values from TC-08 standing on a table
22.22
22.58
22.66

Why is there such a big difference in values that should be almost the same?

Gerry
PICO STAFF
PICO STAFF
Posts: 594
Joined: Mon Aug 11, 2014 11:14 am

Re: TC-08 difference in values

Post by Gerry » Wed Feb 26, 2020 10:28 am

Hi poutila,

The answer is, that if the TC-08 is standing on a Table then the values will not be almost the same, because of the following:
(a) Electrical noise at the input of the TC-08. Thermocouples generate relatively low voltage for relatively high resistance, so there is a large amount of noise generated with the voltage representing the temperature, which will cause a variation in values, even with a constant temperature at the tip of the the thermocouple. With no thermocouple connected the input will float and therefore fluctuate, generating noise.
(b) Air currents. To a much lesser degree, moving objects in a room (e.g. doors, windows, people, etc) create movements of air which can create small changes in the temperature around the Cold Junction Compensation (CJC) thermistor in the TC-08. As the temperature values are calculated relative to the measurement of the CJC thermistor, the measured values at the inputs will correspondingly change. Even with all windows and doors closed, it takes time for the air to settle, so there could still be small movements of air affecting the CJC. However, there will be movements of air around any connected thermocouple that will register as larger changes in temperature values for the inputs.

Regards,

Gerry
Gerry
Technical Specialist

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