It's better than nothing and may be a little inaccurate due to factors such as
external ambient air flow within the engine area passing over the compressor
pipe
itself; so the reading may be under actuals.
The best sensor is one that is immersed within the compressor free stream. A 'K'
thermistor would suffice. Thermocouples are more accurate and more expensive
and are used on Rotax.
The 914 HMM provides impedance reference graph for the plenum temperature
sensor;
you could possibly splice into this circuit for a piggyback reading, and you
would need to ensure there is no risk of damaging the TCU by doing so. A
comparable
screw in thermocouple sensor itself costs about $8-$25 on ebay.
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