Electronics notes/Temperature sensing
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Inexpensive High range of temperature Not highly accurate - assume you won't get better than 1 degree Celcius of resolution, less if you don't calibrate well
Age with time and high-temperature use, so will need occasional recalibration and/or replacement.
They produce voltage due to the thermoelectric effect - on the order of millivolts so most uses, and accurate use, requires amplification (with high input impedance to avoid the measurement affecting the thermocouple itself).
Most resistors vary their resistance with temperature. A thermistor (thermal resistor) does it intentionally, and more pronounced.
NTC: negative temperature coefficient, resistance drops (logarithmically) as its body temperature increases
PTC: positive temperature coefficient,
The basic resistance varies with intent, though is usually somewhere in the range of 1000 - 2000 Ohm
They are frequently used in temperature sensing, temperature regulation, and (over)current protection.
Perhaps the he simplest way to get a voltage from a thermistor (think ADC, comparator) is to have it be one leg of a voltage divider.
A power thermistor is a very low-resistance (NTC) thermistor in series with your main current, as a current limiter and/or (self-resetting) overcurrent protector.
One use is to lessen the sudden inrush current in transformers and such:
- place in series with the primarily coild
- when cold (just switched on) it typically has a few hundred ohm resistance
- and once it warms it (few seconds later) goes to under an ohm.
This lessens the magnitude of the sudden current that can happen right after you switch something on.
The voltage across a diode will decrease by ~2 mV per °C in a fairly linear way.
You need amplification and probably a DAC, accuracy isn't great, but it's very convenient inside FPGAs, processors, and such.