Temperature Sensors

Temperature sensors are measurement devices that determine temperature by sensing some physical characteristic, such as electrical resistance, electromagnetic field (EMF), or thermal radiation. There are many different types of products. Examples include thermocouples, resistance temperature detectors (RTDs), thermistors and bimetal switches, temperature sensor kits, and temperature and liquid level sensor combination units. Temperature measurement range, accuracy and stability are the most important specifications to consider when selecting temperature sensors. Additional parameters include probe type, tip and termination style, and electrical output. Products with visual displays and audible alarms are commonly available.

Thermocouples are temperature sensors which consist of two wires, each made of a different metal. The wires are joined at one end to form a junction which is exposed to the medium under measurement. The other ends of the wires are terminated to form a reference junction. Thermocouple temperature sensors are divided into various types, and include devices made of Chromel and Constantan (Type E), iron and Constantan (Type J), Chromel and Alumel (Type K), and copper and Constantan (Type T). Chromel, Alumel and Constantan are registered trademarks of the Hoskin Manufacturing Company. Nobel metal thermocouples are also available from some temperature sensor suppliers.

Resistance temperature detectors (RTDs), thermistors, and bimetal switches are also classified as temperatures sensors. RTD elements are wire windings or other thin-film serpentines that exhibit changes in resistance with changes in temperature. RTD probes are temperature sensors which convert the resistance measurement from an element to a current signal. Thermistors are extremely sensitive, but have a limited temperature range. There are two types of thermistors: negative temperature coefficient (NTC), where the resistance drops nonlinearly with a rise in temperature; and positive temperature coefficient (PTC), where the resistance increases as the temperature rises. Bimetal switches are relatively inexpensive, bimetallic temperature sensors that use creep or snap action for thermal cutoff.

Temperature sensor suppliers may offer both temperature sensor kits and temperature liquid level sensor combination units. Temperature sensor kits include a thermocouple or RTD with a stainless steel temperature probe that can be connected to a programmable controller or indicator. Temperature and liquid level sensor combination units are designed for use with liquid level switches. These temperature sensors may incorporate RTD or thermocouple technology.

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Part Numbers for Temperature Sensors