eli5: How do electronic thermometers work?

Question

I understand mercury and mechanical thermometers. How do electronic thermometers, like the one in my car, measure temperature?

In: 55

Answer 1

Resistance changes with temperature, most things get higher resistance the hotter they get, but this isn’t the case with the types of sensors used in cars.
They are almost always NTC, negative thermal co-efficient, so higher resistance is lower temperatures.
The electronics measure the resistance, and look up a temperature value to display.

A faulty or missing sensor will often show as infinite resistance / open circuit, and the scaling of the sensors often means it’ll be interpreted as about -40C / -40F. If you see a dash readout saying it’s -40 outside, your sensor might have fallen off. It’s a similar thing for the engine sensors, a fault one can think it is freezing outside, have a high idle and not run very well.