A thermometer that relies on the increase of electrical resistance of a metal wire with rising temperature, according to the approximate relationship R=R0(1+aT+bT2), where R is the resistance of the wire at temperature T and R0 is the resistance of the wire at a reference temperature, usually 0°C; a and b are constants characteristic of the metal of the wire. The metal most frequently used is platinum and the platinum resistance coil is usually incorporated into one arm of a Wheatstone bridge. The effect of the temperature change on the leads carrying current to the platinum coil is compensated by including a pair of dummy leads within the casing carrying the coil. See also thermistor.
An electrical thermometer that utilizes the change in electrical resistance with temperature (see temperature coefficient of resistance) of a wire to measure the temperature of its surroundings.
It consists of a small coil of wire (usually platinum but other metals may be used at low temperatures) wound on a mica former and enclosed in a sheath of silica or porcelain (see diagram). The change in resistance is determined by placing the coil in one arm of a Wheatstone bridge. Compensating leads are usually added to the other arm of the bridge to compensate for temperature variations in the leads as the coil is usually remote from the measuring instrument. Resistance thermometers can be used over a wide range of temperatures from −200 °C to over 1200 °C.
Resistance thermometer
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