Garland 40 Series Technical Reference Manual - page 54
Part # GCTRM Rev 3 (12/10/09)
Page 54
Thermocouples And How They Work
Thermocouples are used to generate voltage to hold a
magnet on a pilot safety valve. It plays an important part of
the flame safety system in a gas oven.
The thermocouple uses the combined effects of temperature
change and electricity. It consists of a bimetallic strip joined
at one end (called the hot junction). When the hot junction is
heated, a DC voltage is generated across the two other ends
of the strips (the cold junction).
The thermocouple is used to prove the pilot flame. If the pilot
flame goes out, the thermocouple prevents the main gas
from opening.
The magnitude of the voltage across the cold junction
depends on the:
• Two materials of the bimetallic strip
• Temperature difference between the hot and cold
junctions
The small amount of electricity produced is 20 to 30
millivolts. This millivoltage is used to hold open an
electromagnet assembly in the gas control. If the pilot
goes out, the thermocouple will cool down and no longer
generate electricity and in turn, de-energize the magnet,
closing the valve.
Hot
Junction
Dissimilar
Metals
Cold
Junctions
Negative Positive
Flame