I'm making a device that will operate in cold environment. The ambient temperature will vary between -50℃ and -20℃. The sensor is supposed to monitor the temperature so that the microcontroller in my device decides, whether a battery heating system in the device runs or not. The temperature could change at a speed of 0.2℃/s.
What would be the best sensor type among a digital temperature sensor (like DS18B20), a RTD, and a thermocouple?
The temperature of the battery will not change by 0.2 degrees per second mostly likely. The ambient isn't all that important, I suspect. Accuracy of a degree C or two is probably fine.
Also, you only need to sense accurately at a single point in the temperature scale, assuming that the sole purpose of the sensor is to make the heat/no heat decision.
So I suspect the best system in your situation is a precision thermistor, an ADC on your microcontroller and a single precision resistor to the ADC reference (might be the supply rail). Even a 10 bit ADC will give you 50 or so counts per degree C at mid-scale, and accuracy can be quite good with a 1% thermistor.
You can use the same kind of thermistor that is used in battery packs to monitor charging, mounted similarly.
