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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 resistance wire in the thermometer is made of pure platinum (NIST manufactured the wires from platinum bar stock with a chemical purity of 99.999% by weight). [ 77 ] [ 78 ] In addition to laboratory uses, Platinum Resistance Thermometry (PRT) also has many industrial applications, industrial standards include ASTM E1137 and IEC 60751.
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.
A thermistor is a semiconductor type of resistor in which the resistance is strongly dependent on temperature. The word thermistor is a portmanteau of thermal and resistor.The varying resistance with temperature allows these devices to be used as temperature sensors, or to control current as a function of temperature.
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]
These include helium vapor pressure thermometers, helium gas thermometers, standard platinum resistance thermometers (known as SPRTs) and monochromatic radiation thermometers. Although the Kelvin and Celsius temperature scales were (until 2019) defined using the triple point of water ( 273.16 K or 0.01 °C ), it is impractical to use this ...
The SI unit of absolute thermal resistance is kelvins per watt (K/W) or the equivalent degrees Celsius per watt (°C/W) – the two are the same since the intervals are equal: ΔT = 1 K = 1 °C. The thermal resistance of materials is of great interest to electronic engineers because most electrical components generate heat and need to be cooled.