Thermistors

The last temperature sensing device is the thermistor. These are also resistance-based relationship sensors like RTDs, but produce a higher degree of change for a given temperature than an RTD. Essentially, these are resistors that vary based on temperature. They are also used in circuits to alleviate in-rush currents. Whereas an RTD has a linear relationship with a change in temperature, thermistors have a highly nonlinear relationship, and are suitable where a high resolution is needed for a narrow temperature range. There are two types of thermistors: NTC, where resistance decreases as temperatures rise; and PTC, where resistance increases with rising temperatures. The main difference from an RTD materially is the use of ceramics or polymers, whereas metals are the basis of RTDs.  

Thermistors are found in medical devices, scientific equipment, food handling equipment, incubators, and home appliances such are thermostats.