Resistance Thermometer

resistance thermometer

[ri′zis·təns thər′mäm·əd·ər] (engineering) 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 = (R_1000°C – R_0°C)/100R_0°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).

REFERENCES

See references under .

D. I. SHAREVSKAIA

resistance thermometer

thermometer

[ther-mom´ĕ-ter] an instrument for determining temperatures, in principle making use of a substance (such as alcohol or mercury) with a physical property that varies with temperature and is susceptible of measurement on some defined scale.

Temperatures on Celsius and Fahrenheit thermometers related to temperature ranges. From Elkin et al., 2000.axilla thermometer a thermometer" >clinical thermometer that is placed in the axilla.Celsius thermometer one that uses the scale" >Celsius scale.centigrade thermometer one having the interval between two established reference points divided into 100 equal units, such as the thermometer" >Celsius thermometer.clinical thermometer one used to determine the temperature of the human body.electronic thermometer a thermometer" >clinical thermometer that uses a sensor based on thermistors, solid-state electronic devices whose electrical characteristics change with temperature. The reading is recorded within seconds, some having a red light or other device to indicate when maximum temperature is reached. Available models include hand-held, desk-top, and wall-mounted units, all having probes that are inserted orally or rectally.Fahrenheit thermometer one that uses the scale" >Fahrenheit scale.Kelvin thermometer one that uses the scale" >Kelvin scale.oral thermometer a thermometer" >clinical thermometer whose mercury containing bulb is placed under the tongue.recording thermometer a temperature-sensitive instrument by which the temperature to which it is exposed is continuously recorded.rectal thermometer a thermometer" >clinical thermometer that is inserted in the rectum.resistance thermometer one that uses the electric resistance of metals (thermocouple) to determine temperature.self-registering thermometer 1. recording thermometer.2. one that registers the maximum or minimum temperature attained in the measurement.tympanic thermometer an electronic thermometer" >clinical thermometer that gives a digital reading in less than two seconds. Second-generation tympanic thermometers work by monitoring the temperature when the ear opening is sealed.