Thermocouples | Resistence Thermometers | Thermistor Probes | Hand Held Sensors
What is a Resistance Thermometer?
The resistance of a conductor varies according to its temperature
and this principle is employed in resistance thermometry. By
specifying a conductor material which displays a stable and
approximately linear temperature coefficient of resistance over the
required range, a reliable thermometer can be made.
Since platinum is chosen for the world standard
resistance thermometer material, the platinum resistance thermometer
(PRT) assembly is the predominant choice for both laboratory
and industry. As a sensing element platinum has many virtues. In a
pure form it will resist contamination and is stable both
mechanically and electrically. The relationship between temperature
and resistance is nearly linear which allows production of
accurately interchangeable detectors.
Materials other than platinum are sometimes used
but only to a limited extent; therefore only PRT assemblies
are offered. The use of the PRT assembly is in practice much
simpler than that of the thermocouple:- copper wires are used
between the sensor and the instrument and since the calibration is
absolute, no reference or C.J.C correction techniques are
required.
Standard PRT detectors have a resistance of
100ohms at 0șC and has a resistance/temperature characteristic which
conforms to the international standard IEC 751 class A or B. The
resistance change over the range 0șC to 100șC is 38.5 ohms and is
referred to the fundamental interval.
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