Auto reignition

Auto reignition is a process used in gas burners to control ignition devices based on whether a burner flame is lit. This information can be used to stop an ignition device from sparking, which is no longer necessary after the flame is lit. It can also be used to start the sparking device again if the flame goes out while the burner is still supplying gas, for example, from a gust of wind or vibration.

Most gas ranges and cooktops use sparking devices to ignite the burner flame. This eliminates the need for a pilot flame, which wastes energy. Most of these sparking device-equipped ranges require the user to control the ignition sparking manually, resulting in a three-step process required to operate the burner:

One implementation of a gas burner with auto reignition senses the electrical conductivity of the flame. This nonzero flame conductivity is because combustion of natural gas releases enough free electrons to support a small current in air. An electronic circuit then starts or stops the igniter from sparking, based on whether the flame is lit. This reduces the number of steps to turn a burner on from three to one:

This is an elegant solution, compared to detecting flame via a thermocouple, a photoresistor or a mercury-filled sensor. No extra components or electrical connections between the sparker electrode and the spark module electronics are required.

This convenience and safety feature is found only (as of June 2009) on higher priced gas ranges and cooktops.

Auto reignition lowers the risk of gas leaks:

This feature is especially valuable on gas burners with several different short-term users, less likely to bother with or learn multi-step procedures—for example, gas ranges in rental properties, guest houses, or in office kitchens.

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Wikipedia