A thermocouple is two different metals in contact with each
other that generate a voltage when heated.
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thermocouple effect
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The output of the thermocouple is linear.
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Yes, thermocouple is used in fridges !
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To create a thermocouple one needs thermocouple wire, a means of
spot welding the wire, and wire strippers. A thermocouple is used
to measure temperature.