I. Characteristics
A resistance thermometer is a device that measures temperature by utilizing the change in resistance of a conductor or semiconductor with temperature. It consists of a resistance element (temperature-sensing element), connecting wires, and a display or recording instrument. Conventionally (Guangzhou Xizheng) the resistance element used as a standard is called a standard thermometer, while the resistance element used in operation is simply called a resistance thermometer.
1. High accuracy. Among all commonly used thermometers, it has the highest accuracy.
2. Large output signal and high sensitivity.
3. Wide temperature measurement range and good stability. It can operate in environments with minimal vibration and suitable conditions.
It maintains stability below 0.1℃ for a long time.
4. No reference point is required. The temperature value can be directly calculated from the measured resistance value.
5. Thermistor elements made of fine platinum wire have poor resistance to mechanical shock and vibration.
The components have complex structures and large sizes, therefore, they have long thermal response times.
It is suitable for measuring small, instantaneous temperature regions.
II. Principle
The electrical resistance of a material generally changes with temperature. This characteristic is usually described by the temperature coefficient of resistance. It is defined as the relative change in resistance when the temperature changes by 1 K over a temperature interval, commonly denoted by 'a', and measured in K.
III. Construction of Resistance Temperature Detectors
The basic structure of an industrial resistance temperature detector (RTD) consists of three parts: a temperature sensing element (PT100, PT500, PT1000, etc.), internal leads, and a protective tube. It usually also has components for connecting to external measuring and control devices or mechanical devices. Its appearance is similar to a thermocouple; care must be taken to avoid using it incorrectly.
IV. Internal lead configuration of the thermal resistor
1. The lead method of connecting a wire to each end of the resistance temperature sensor is a two-sided wire system.
2. Connecting two leads to one end of the resistance temperature detector (RTD) element and one lead to the other end is called a three-wire system.
3. Connect two leads to each end of the resistance temperature detector (RTD) element. For accurate measurements, a four-wire system should be used. This lead method not only eliminates the influence of the resistance of the internal leads (Guangzhou Xizheng), but also eliminates the influence of that resistance when the resistance of the connecting wires is the same.
