Learn all about temperature sensors and each of their advantages and disadvantages.
Temperature SensorsTemperature sensors are among the most commonly used sensors. All types of equipment use temperature sensors, ranging from computers, cars, kitchen appliances, air conditioners, and (of course) home thermostats. The five most common types of temperature sensors include:
- RTDs (resistive temperature detectors)
- Digital thermometer ICs
- Analog thermometer ICs
ThermistorAs the name implies, the thermistor (i.e., thermal resistor) is a temperature-sensing device whose resistance is a function of its temperature. Thermistors are available in two types: PTC (positive temperature coefficient) and NTC (negative temperature coefficient). The resistance of a PTC thermistor increases as the temperature increases. In contrast, the resistance of an NTC thermistor decreases as temperature increases, and this type seems to be the most commonly used thermistor. See Figure 1 below. [caption id="" align="alignnone" width="608"] Figure 1. PTC and NTC thermistor electrical symbols.[/caption] It’s important to realize that the relationship between a thermistor’s resistance and its temperature is very non-linear. See Figure 2 below. [caption id="" align="alignnone" width="500"] Figure 2. An NTC thermistor resistance vs. temperature. Image courtesy of Maxim Integrated.[/caption] The standard equation for an NTC thermistor’s resistance as a function of temperature is given by:
- R25C is the thermistor’s nominal resistance at room temperature (25°C). This value is normally provided in the datasheet.
- β (beta) is the thermistor’s material constant in Kelvin. This value is normally provided in the datasheet.
- T is the thermistor’s actual temperature in Celsius.