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Thermocouples Applied Thermocouple THERMOCOUPLES IN COMMON APPLIANCES Many gas-fed heating appliances today utilize control valves and thermostats which incorporate automatic shutoff valves for reasons of safety. Ovens, water heaters, space heaters, any appliance that operates by means of a pilot light, has a built-in failsafe mechanism which will prevent the accumulation of dangerous gas in case the pilot light should be accidentally extinguished. Such heating appliances typically employ a main burner which is cycled on and off (with the help of the pilot light) under the control of a thermostatic valve or thermostat. For example, most older model ovens have a gas valve which opens and closes in response to a temperature sensor which is located somewhere inside the oven compartment in order to heat up the compartment to an approximately constant temperature, hence the term thermo(heat)stat(static or unchanging). The TS is simply a temperature sensitive valve. When it opens, gas is allowed to flow through a pipe down to a burner located in the oven's lower, broiler compartment, where it is ignited by the pilot light. Should the pilot light ever be blown out or lose its steady supply of gas, the gas flowing out of the burner will not be ignited and will flow, uncombusted, into the surrounding environment. To prevent such a hazard, the TS needs to "know" if and when the pilot light is not working, and will then withhold the supply of gas to the burner. A thermocouple "senses" when the pilot light is not burning, and the TS "senses" the voltage from the TC. No voltage, no gas, and that's FINAL. The tip of the TC extends into the envelope of flame that serves as the pilot. No flame, no heat in the tip; no heat in the tip, no voltage imposed on the wire that goes from the TC back to the TS. Therefore, no "cooperation".
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