Temperature Sensors

Temperature Sensors are the device which measures the amount of heat energy or coldness that is generated by an object or system. It allows sensing/detecting any physical change to that temperature producing either an analogue or digital output.

A temperature sensor consists of two basic physical types: Contact temperature sensor types and Non-contact temperature sensor types. Contact types of temperature sensor are required to be in physical contact with the object being sensed and use conduction to monitor changes in temperature. Non-contact types of temperature sensor use convection and radiation to monitor changes in temperature.

A variety of devices are available to measure temperature, the most common of which are thermocouples, thermisters, resistance temperature detectors (RTD), and infrared types. Thermocouples are the most versatile, inexpensive, and have a wide range (up to 1200 deg C typical). These consist of two dissimilar metal wires joined at the ends to create the sensing junction. When used in conjunction with a reference junction, the temperature difference between the reference junction and the actual temperature shows up as a voltage potential.

Thermisters are semiconductor devices whose resistance changes as the temperature changes. They are good for very high sensitivity measurements in a limited range of up to 100 deg C. The relationship between the temperature and the resistance is nonlinear. The RTDs use the phenomenon that the resistance of a metal changes with temperature. They are linear over a wide range and most stable and have better accuracy and resolution than thermocouples. RTDs use precision wire, usually made of platinum, as the sense element.

Infrared type sensors use the radiation heat to sense the temperature from a distance. These noncontact sensors can also be used to sense a field of vision to generate a thermal map of a surface.