I understand mercury and mechanical thermometers. How do electronic thermometers, like the one in my car, measure temperature?
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There are many “electronic thermometers”, e.g.:
– Resistance based (RTDs, Thermistors): the resistance of effectively every material depends on the temperature. Measure it to deduce the temperature. Thermistors are usually semi-conductor based, while RTDs are classical metal wires.
– Thermocouples: interfacing two different materials sometimes causes a voltage. This is most pronounced with doped semi-conductors, but there are many variants. Measure this (pretty small) voltage with a carefully designed amplifier to deduce the temperature.
– Thermal emission: not directly electronic, but everything emits thermal light radiation, usually from radio waves and IR to visible light and UV. Focus on one “color” (wavelength), measure the amount of light of this color something emits, and you can maybe deduce the temperature. “Maybe”, because you still need to know the absorptive behaviour the object has in that color; you can either measure it as well using an IR diode, or use a table of known values.
– Several more. For example you can measure the drop-off voltage of a diode, which depends on temperature as well.
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