Thermistors are temperature-sensitive resistors that exhibit a significant change in their electrical resistance with temperature variations. They are widely used in measurement and control applications where precise temperature sensing is required. Thermistors are made from ceramic materials that have a high temperature coefficient of resistance (TCR), meaning their resistance changes considerably with temperature.
There are two main types of thermistors: NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient) thermistors.
NTC Thermistors:
NTC thermistors have a negative relationship between resistance and temperature. As the temperature increases, the resistance of an NTC thermistor decreases. NTC thermistors are commonly used for temperature measurement, control, and compensation in a variety of applications, such as:
Temperature sensors in household appliances like ovens, refrigerators, and air conditioners.
Industrial equipment for temperature monitoring and control.
Automotive applications for engine temperature monitoring and climate control.
PTC Thermistors:
PTC thermistors have a positive relationship between resistance and temperature. As the temperature increases, the resistance of a PTC thermistor also increases. PTC thermistors are used in a different set of applications, such as:
Overcurrent protection: PTC thermistors are used as resettable fuses. Their resistance increases sharply when the current exceeds a certain threshold, effectively limiting the current flow and protecting the circuit.
Motor starting applications: PTC thermistors can be used to provide inrush current limiting during the startup of electric motors.
Key characteristics of thermistors include their resistance-temperature relationship, sensitivity (how much the resistance changes per degree of temperature change), and precision. When using thermistors for temperature measurement, it's important to account for their non-linear behavior and calibrate the measurement system accordingly.
Thermistors are often used in combination with bridge circuits or signal conditioning circuits to convert the resistance change into a measurable voltage or current output. Additionally, their small size and fast response time make them suitable for various applications where quick and accurate temperature measurements are required.
In summary, thermistors are valuable components in the field of measurement and instrumentation due to their sensitivity to temperature changes, making them ideal for applications requiring precise temperature monitoring and control.