What is the operating principle of a resistance thermometer based on?
The operating principle of resistance thermometers is based on the property of conductors and semiconductors to change their electrical resistance in response to temperature changes in the medium being measured. To measure temperature, the thermometer is placed in the medium; the immersion depth must be at least 150 mm, even though the length of the sensing element itself is up to 120 mm for platinum thermometers and up to 60 mm for copper ones. Thermometer readings are transmitted via wires to a recording instrument installed in an explosion-proof area.
Potentiometers, balanced bridges, and both simple and automatic ratiometers are used as measuring instruments for resistance thermometers. Balanced bridges offer the lowest accuracy. Resistance thermometers are manufactured using platinum or copper in the form of a wire winding—made of either pure platinum with a diameter of 0.07 ± 0.015 mm or copper (enameled wire with a diameter of 0.01 mm wound on a dielectric frame).
