Resistance Thermometer

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resistance thermometer

[ri′zis·təns thər′mäm·əd·ər]
A thermometer in which the sensing element is a resistor whose resistance is an accurately known function of temperature. Also known as electrical resistance thermometer; resistance pyrometer.

Thermometer, Resistance


a temperature-measurement device whose operation is based on the change in the electrical resistance of pure metals, alloys, and semiconductors with temperature. (In metals, the resistance R increases with increasing temperature T, whereas in semiconductors the inverse dependence holds.)

Resistance thermometers made of pure metals, especially platinum, with a temperature coefficient of resistance α = (R1000°C – R0°C)/100R0°C = 0.0039 deg–1, and copper with α = 0.0044 deg–1, are widespread. Such thermometers consist of a metal wire or strip wound onto a rigid quartz, porcelain, or mica form enclosed in a protective sheath of metal, quartz, porcelain, or glass. Two, three, or four leads extend from the head of the thermometer, connecting it to a measuring instrument; thermometers with four leads are the most accurate. Platinum resistance thermometers are used for the measurement of temperatures from – 263° to 1064°C, and copper resistance thermometers are used from –50° to l80°C.

The material and design of a resistance thermometer must provide sufficient sensitivity and stability for the required accuracy and precision of measurement in a given temperature range under particular conditions, such as vibration and aggressive mediums. The accuracy of measurement also depends on the accuracy of the instrument measuring the resistance. Industrial resistance thermometers operate in a unit consisting of bridges, potentiometers, and readout and recording quotient meters with scales calibrated directly in degrees Celsius according to tables for the temperature dependence of resistance for particular types of resistance thermometer. The International Practical Temperature Scale is reproduced by high-accuracy platinum resistance thermometers, which make possible the accurate measurement of temperature and the calibration of other thermometers in the range from 14° to 900°K.

Indium and bronze resistance thermometers are sometimes used in laboratory work in the ranges 4°–300°K and 1°–4°K, respectively.

Semiconductor resistance thermometers made of composite carbon and alloyed germanium are commonly used for the measurement of low temperatures (0.1°–100°K) because of their high sensitivity. This type of resistance thermometer consists of semiconductor strips or films of various sizes and shapes, with welded metal leads, often enclosed in a protective shell. Germanium resistance thermometers are especially accurate in the range from 4.2° to 13.8°K. The use of semiconductor resistance thermometers above 100°K is limited, since their instability and the dispersion of individual characteristics become significant (see).


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References in periodicals archive ?
The uncertainty budget for calibration of platinum resistance thermometers (PRTs) at the TPW is presented in Table 7.
Other applications for platinum alloy precision wire and ribbon include: thermistor and platinum resistance thermometer lead wire; high tensile strength alloys for precision potentiometers; platinum wire for micro-amperage fuses having a core diameter of less than 0.
3] constant-volume gas thermometers (CVGTs); standard platinum resistance thermometers (SPRTs); and radiation thermometers.
27 K (determined either by using a gas thermometer or the specified temperature-vapor pressure relationship of equilibrium-hydrogen--See Table 1), at which capsule standard platinum resistance thermometers (CSPRTs) are calibrated and used for interpolation between the points.
The top and bottom wells can accommodate rhodium-iron resistance thermometers (RIRTs) and the mid-height wells can accommodate either CSPRTs or RIRTs.
During this time, the temperature is monitored with one of the resistance thermometers.
In practice, the three fixed-points are realized in the copper block first, and then the readings of the resistance thermometers are used to set the block temperature to the fixed-point temperatures to calibrate the gas thermometer.
The LTRF was designed to calibrate in-house "reference-standard" resistance thermometers consisting of selected CSPRTs and RIRTs for NIST only.
Significant experimental contributions by NBS began with the work of Hoge and Brickwedde (29), who calibrated an ensemble of resistance thermometers against a gas thermometer to establish a scale (known as the NBS-39 Scale) for the calibration of thermometers from 14K to 83K.
The current NIST calibration capabilities in the cryogenic range cover most types of cryogenic resistance thermometers, including all types of capsule SPRTs for temperatures from 13.
Information similar to that provided for CSPRTs is given for RIRTs and Germanium Resistance Thermometers (GRTs) for the ranges from 0.
General information: New standard reference tables for thermocouples are necessary as a result of the introduction of the new international temperature scale, ITS-90, which interpolates between fixed points by means of a standard platinum resistance thermometer instead of thermocouples.

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