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Resistance thermometers are constructed in a number of forms and offer greater stability, accuracy and repeatability in some cases than thermocouples. While thermocouples use the Seebeck effect to generate a voltage, resistance thermometers use electrical resistance and require a power source to operate.
Callendar was the first to design and build an accurate platinum resistance thermometer suitable for use, which allowed scientists and engineers to obtain consistent and accurate results. [1] He conducted experiments and researched thermodynamics, producing and publishing reliable tables on the thermodynamic properties of steam used for ...
The Callendar–Van Dusen equation is an equation that describes the relationship between resistance (R) and temperature (T) of platinum resistance thermometers (RTD). As commonly used for commercial applications of RTD thermometers, the relationship between resistance and temperature is given by the following equations.
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In the 1860s–1870s brothers William and Werner Siemens developed a platinum resistance thermometer, initially to measure temperature in undersea cables, but then adapted for measuring temperatures in metallurgy up to 1000 °C, hence deserving a name of a pyrometer. Around 1890 Henry Louis Le Chatelier developed the thermoelectric pyrometer. [8]
Finding temperature from resistance and characteristics [ edit ] The equation model converts the resistance actually measured in a thermistor to its theoretical bulk temperature, with a closer approximation to actual temperature than simpler models, and valid over the entire working temperature range of the sensor.
For example, in the case of a platinum resistance thermometer, the temperature changes are translated into resistance changes. The PRT must therefore have an electrical power supply. The modulated voltage level at the output of the PRT can then be injected into the optical fiber via the usual type of transmitter.