What is a thermistor and how does its resistance change with temperature?

There are two main types of thermistors:

Negative Temperature Coefficient (NTC) Thermistors: In NTC thermistors, as the temperature increases, the resistance decreases. This is because the electrical conductivity of the material in the thermistor increases with temperature. NTC thermistors are commonly used for temperature measurement and control applications. They are sensitive over a relatively small temperature range, often within a few degrees Celsius.

Positive Temperature Coefficient (PTC) Thermistors: In PTC thermistors, as the temperature increases, the resistance also increases. This behavior is due to the fact that the material's electrical conductivity decreases with temperature. PTC thermistors can be used in applications where they need to provide a self-limiting effect, such as in overcurrent protection circuits, where their resistance increases when the temperature rises due to increased current flow.

The relationship between resistance and temperature for a thermistor is typically nonlinear, and different thermistors have different resistance-temperature curves. This nonlinearity means that thermistors are most accurate when used within a specified temperature range, where their resistance change is most pronounced.

The resistance-temperature relationship of a thermistor is often described using a mathematical equation called the Steinhart-Hart equation, which is a complex polynomial equation that relates resistance to temperature. This equation allows for accurate temperature calculations based on the measured resistance of the thermistor.

Thermistors are commonly used in various applications, including temperature measurement and control in electronics, automotive systems, medical devices, industrial processes, and more. They provide a cost-effective and reliable way to monitor and regulate temperature in a wide range of scenarios.