What is a Flame Sensor?

If a roll out switch is a master “things have gone horribly wrong, stop the show” switch and thermisters are basically limited to measuring temperature, how do we know the burner is actually making a flame? Sure, the thermister will read heat, but that takes time. Imagine the igniter has failed, it takes maybe 10-40 seconds to register enough heat to confirm a flame. The combustion chamber is now pumped full of a potentially explosive fuel mixture and nothing is happening. We need something much, much faster, we need a flame sensor.   How Not to Detect a Flame The way a person knows something is on fire is usually the bright flames and the fact that sticking their hand near it becomes really painful. This approach doesn’t quite work for a furnace. We could measure the light output, that requires more processing power to interpret the data, some incredibly sensitive hardware to detect the tiniest start of a flame, and it doesn’t work on every fuel type. There are systems that work this way, but it’s a little more expensive. We could measure the temperature, but we run into challenges with making a sensor you can shove in the heart of a flame for years on end without failure. It has been done, but it’s expensive. There are however, laws of physics we can exploit to detect a flame without anywhere near so many challenges. We can detect a […]

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