The temperature measurement with resistance thermometers (RTD) is based on the characteristic of conducting materials to change their electrical resistance with temperature. For metals, the resistance increases with rising temperature. If the relation between temperature and resistance is known, you can determine the temperature by measuring the resistance.
Resistance thermometers change their electrical resistance in dependence on the temperature or, in other words, resistance thermometers use the fact that the electrical resistance of an electrical conductor varies with changing temperature. In order to collect the output signal, the resistance is fed with a constant measuring current and the created voltage drop is measured. Platinum RTDs Pt 100, Pt 500 and Pt 1000 are used as measuring probes. They are standardized acc. to DIN EN 60751. Their resistance is 100 Ω at 0°C. The most different construction types of platinum resistance thermometers are applied in industrial measuring technique.