A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. Thermistor is used as temperature sensing element for 3D Printer Extruder and Heat beds
In most RepRaps, a thermistor senses the temperature of the Hot End. Often a second thermistor senses the temperature of the Heated Bed.
Thermistors are resistors that change of resistance with a change in temperature. Good qualities of thermistors are a predictable, accurately known resistance value at every temperature in its operating range. The lowering, or rise, depends on the type of thermistor per degree Kelvin (or Celcius, if you prefer), this is called its coefficient. Positive thermal coefficient (PTC) will increase in resistance with an increase in temperature, negative ones (NTC) will decrease. But the formula in practice is not linear, so sometimes an accurate table of measurements is better than the linear formula. These measurements can usually be found in the datasheet that accompanies the thermistor.
100K ohm +/-1% Thermistor
Glass sealed single end
-40 C to +260 C
Coefficient: NTC, Beta: 3950
In Marlin firmware use 11 for thermistor type
At minimum you will need 1 thermistor per extruder only
If you plan to use heat bed you will need 1 thermistor for extruder too
Eg. for 2 extruder + heat bed setup you will need 3 thermistors