As described in the Electronics Tutorials article “Thermistors,” a thermistor is a solid-state temperature sensing device that functions similarly to an electrical resistor but with temperature sensitivity. Made from sensitive semiconductor-based metal oxides, thermistors change their resistance in response to variations in ambient temperature, making them effective transducers. This property allows thermistors to generate an analog output voltage corresponding to temperature changes, making them valuable in various temperature detection circuits. 

Thermistors are constructed using metal oxides formed into ceramic discs or beads, with metallized or sintered leads. Their resistive value varies in proportion to small temperature changes, allowing them to operate effectively as temperature sensors. Thermistors can either have a negative temperature coefficient (NTC), where resistance decreases with rising temperature, or a positive temperature coefficient (PTC), where resistance increases with rising temperature. NTC thermistors are the most commonly used type, as they provide a large negative resistance response to temperature changes, making them ideal for precise temperature measurement and control.

Operating at temperatures up to 200°C, thermistors are highly versatile and can be used to measure the temperature of both liquids and ambient air. They are available in various types, such as bead, disk, and glass-encapsulated thermistors, each characterized by their response time and operating temperature range. For enhanced performance, hermetically sealed thermistors are used to prevent moisture penetration, ensuring accurate resistance readings even in challenging environments.

In addition to temperature sensing, thermistors can be used as current-limiting devices in electrical circuits. By being connected in series with other components, they help control the flow of electrical current based on temperature changes. This dual functionality makes thermistors a valuable component in numerous applications where temperature plays a crucial role.

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