How to test it?

Use your Digital multimeter to connect The wiring of the thermocouple and the two test leads of the digital multimeter are
connected as shown in the figure below, and the digital multimeter selects the range (200 mV).
 
Test results –The display data of the digital multimeter is basically stable above “15.0” mv,when the thermocouple functions normally.
 
It is mainly used to automatically cut off the gas source when the gas stove
is ignited or accidentally extinguished when the gas stove is used to prevent
poisoning, explosion, fire and other accidents caused by gas leakage!
 
Working Principle:

When one end of the thermocouple’s thermal inductor is heated by the flame,
A thermoelectric force is generated, which excites the solenoid valve to work.

The magnetic field of the solenoid valve core generates a magnetic field to drive the valve.
After the valve is absorbed, the valve opens and burns normally.

Once the flame is unexpectedly extinguished, the inductive part of the thermocouple cools,the thermocouple does not generate electric potential.

The coil of solenoid valve loses its magnetic force.
The valve quickly resets and seals the air valve, cuts off the air source, and plays a role of safety protection.