RESISTANCE TEMPERATURE DETECTORS (RTDs)
Figure 3 shows an RTD protective well and terminal head. The well protects the RTD from
damage by the gas or liquid being measured. Protecting wells are normally made of stainless
steel, carbon steel, Inconel, or cast iron, and they are used for temperatures up to 1100°C.
Figure 3 RTD Protective Well and Terminal Head
Resistance temperature detectors (RTDs) are summarized below.
The resistance of an RTD varies directly with temperature:
As temperature increases, resistance increases.
As temperature decreases, resistance decreases.
RTDs are constructed using a fine, pure, metallic, spring-like wire surrounded by
an insulator and enclosed in a metal sheath.
A change in temperature will cause an RTD to heat or cool, producing a
proportional change in resistance. The change in resistance is measured by a
precision device that is calibrated to give the proper temperature reading.