Right you are. A component called a "flame sensor" is used in the
afterburner and signals the control system as to whether or not the
afterburner is lit. It uses the ultra violet wave lengths of the "fire" to
excite a gas within the sensor. It basically acts as an Off/On switch but
it's signal has a significant impact on the control system and on the
behavior of the engine. Then there is a thermocouple harness downstream of
the combustor which has, maybe 12 or more thermocouple probes, each with at
least 4-5 individual thermocouples (chromel/alumel) at different immersions.
The end result is that there are about 60 individual temperature readings
that are averaged to give one cockpit turbine temperature readout. You're
also right about the price--nothing is cheap.
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