How does a thermocouple work
???
The simplest part in the system ..... ??
THERMOCOUPLES
A
thermocouple
consists of a BI-metal rod inside of a stainless steel shell. The
BI-metal is a
copper-nickel mix called "copel".
Where the copel connects to the tip of the shell
is called the "
Hot
junction".
Where the copel connects to the copper wire in the
shell is called the "
Cold
junction".
When the pilot flame heats the tip of the
thermocouple, the copel metal produces a direct current (
Millivolt).
The current travels through the copper wire and
energizes the gas valve.
The temperature difference between the hot
junction and the cold junction can be up to 650°
f. The minimum
temperature difference needed to produce required
Millivolt signal is 400° f.
![[pilot]](images/Image1.gif)
To correctly achieve this and to prolong life for the
thermocouple, it is important to position the pilot flame so it
heats the top 3/8" to 1/2" of the thermocouple. It is
significant to have a good soft pilot flame. For every 100°
increase at the hot junction, there is a 50% reduction in
thermocouple life.
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![[pilot]](images/Image2_small.gif) |
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Thermocouple |
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Revised
11/13/06 11:09 PM
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