I have a device with 2 mechanical parts. One side is stationary and can be connected to an electronic circuit with power. The second side is an enclosure that can have high ambient temperature (100-120°C). I cannot bring a wire from one side to the other, but I would like to read the internal temperature of the second side. The mechanical parts have facing plates of ~50mmx50mm with a distance of 10mm. Sensor must be able to read from -40°C to 220°C. One of the facing plates will rotate, as it is connected to a motor.
Reliability and low cost are important factors. What type of sensing could be done?
I thought of magnetic coupling with energy harvesting, just like RFID. As the environment will be very noisy and reliability is important, I'd like something with a modulation robust to amplitude variation (FM or better). I thought maybe an oscillator connected with a RTD that would change the impedance of a transformer with a variable frequency could do the job, but I've never done this type of circuit.
Can somebody point me out to a temperature sensing technique that could fit? Or some literature that would help me design such circuit.