Temperature Sensors Selection Guide

This article establishes guidelines for the selection of Thermocouples, Resistance Temperature Detectors, Thermistors, Filled Systems, Bimetallic Thermometers, and Radiometeric devices. Main keywords for this article are Temperature Sensors Selection Guide. Temperature Sensors Definitions. temperature detectors rtd. resistance temperature detectors rtd.

For detail of specific instruments refer to following articles:
Thermocouples
Resistance Temperature Detectors (RTD)
Thermistors
Filled Thermal Systems
Bimetallic Thermometers

Temperature Sensors Definitions

For the purpose of understanding this standard, the following definitions apply.
Bimetallic Thermometer Element. A temperature-sensitive strip of metal (or other configuration) made by bonding or mechanically joining two dissimilar strips of metal together in such a manner that
small changes in temperature will cause the composite assembly to distort elastically, and produce a predictable deflection; the element is designed to take advantage of the fact that different metals
have different coefficients of thermal expansion.
Dead Time. The interval of time between initiation of an input change or stimulus and the start of the resulting response.
Filled System Thermometer. Any of several devices consisting of a temperature-sensitive element consisting of a bulb, element sensitive to changes in pressure, a volume-sensitive element partly or
completely filled with a fluid that changes its volume or pressure in a predictable manner with changes in temperature.
Radiometer. An instrument which measures optical power in radiometric units (watts). It measures electromagnetic power linearly over its entire spectral range, while the response of a photometer is
calibrated to reflect the nonlinear response of the human eye over the visible spectrum only.
Reference Junction. That thermocouple junction which is at a known or reference temperature. The reference junction is physically that point at which the thermocouple or thermocouple extension wires
are connected to a device or where the thermocouple is connected to a pair of lead wires, usually copper.
Response Time. An output expressed as a function of time, resulting from the application of a specified input under specified operating conditions.
Resistance Temperature Detectors (RTD). A temperature measuring device in which the sensing element is a resistor of known variation in electrical resistance with temperature.
Thermistor. A temperature transducer constructed from semiconductor material and for which the temperature is converted into a resistance, usually with negative slope and highnonlinearity. Its usual applications are as a nonlinear circuit element (either alone or in combination with a heater), as a temperature compensator in a measurement circuit, or as a temperature-measurement element.
Thermocouple. A temperature measuring instrument that develops an electric voltage when heated because of the combined thermoelectric effect due to dissimilar composition between two electrically connected conductors (usually wires) and to temperature difference between the connection (hot junction) and the other end of the conductors (cold junction).
Thermowell. A thermowell is a pressure-tight receptacle adapted to receive a temperature sensing element and provided with external threads or other means for pressure-tight attachment to a vessel.