Many manufactures list a Beta (B) constant between 2 temperatures (Example: [3 0/50 = 3890). Some materials provide better stability while others have higher resistances so they can be fabricated into larger or smaller thermistors.

Consequently, there are many different ones to choose from.Įach thermistor material provides a different resistance vs. Unlike RTDs and thermocouples, thermistors do not have standards associated with their resistance vs. R s and the supply voltage, V s, can be adjusted to obtain the desired range of output voltage V o for a given range of temperature.Īdvantages: Large resistance change with temperature, rapid response time, good stability, High resistance eliminates difficulties caused by lead resistance, Low cost and interchangeableĭisadvantages: Non-linear, limited operating temperature range, may be subjected to inaccuracy due to overheating, current source required. A typical thermistor circuit is shown below.įrom the circuit diagram, it is clear that this is a simple voltage divider. Linearizing the resistance-temperature correlation may be accomplished with analog circuitry, or by the application of mathematics using digital computation. Manufacturers commonly provide resistance-temperature data in curves, tables or polynomial expressions. In fact, the maximum temperature of operation is sometimes only 100 or 200☌.

Thermistors cannot be used to measure high temperatures compared to RTDs. Furthermore, unlike RTDs, the resistance of a thermistor decreases with increasing temperature. Unlike RTD’s, the temperature-resistance characteristic of a thermistor is non-linear, and cannot be characterized by a single coefficient. A thermistor is a solid state device and has larger sensitivity than does an RTD. These are most commonly used for temperature measurement.Ī thermistor is similar to an RTD, but a semiconductor material is used instead of a metal. NTC thermistors exhibit the characteristic of resistance falling with increasing temperature. There are two main types of thermistors, positive temperature coefficient (PTC) and negative temperature coefficient (NTC). Thermistors are temperature sensitive semiconductors that exhibit a large change in resistance over a relatively small range of temperature.

Thermostat working principle pdf