Introduction
The resistance temperature detector, or RTD, is one of the most frequently used temperature sensors in middle-low temperature range. It features high precision and stable performance. Specifically, the platinum resistance thermometer is the most precise one. It is not only used for various industrial applications, but also is assigned as the standard instrument for temperature measurement.

Principle and material
The resistance temperature detector is based on a physical theory-metal resistance increases along the temperature rising. It is commonly made of pure metal materials like platinum and copper. Other materials like nickel, manganese, and rhodium are also more and more adopted.

Structure
(1) Regular RTD
The temperature is directly measured through the variation of resistance value of the thermal resistor. Therefore, the leading cable of the temperature detector will affect the temperature determination to some degree. To eliminate the influence, three-wire or four-wire configurations are usually adopted.

(2) Sheathed RTD
This kind of resistance temperature detector consists of thermal sensor (the resistor), leading wire, insulating material, and stainless steel casing pipe. The outside diameter is usually 2-8mm, and smaller diameter is also available. Comparing with regular thermal resistors, our sheathed thermal resistor has several advantages.
1. The size is small, and no air gap exists in the pipe. Thus the temperature delay is limited, and the measurement is quite accurate.
2. The anti-vibration and anti-shock performances are excellent.
3. Due to the great flexibility, the resistor can be easily installed.
4. Long service life is expected.

(3) Surface RTD
The surface RTD comes with a special temperature sensor that winded by specially treated resistance wire. The sensor is fixed at the top of the thermometer, so that the resistance temperature detector can measure the real temperature at the surface rapidly and accurately. This kind of RTD is more suitable for the bearing bush and some other parts.

(4) Anti-explosion RTD
This kind of RTD can confined the explosion of explosive gas mixture in a special connecting box, avoiding any significant explosion in the workshops. It can be used for the temperature measuring in dangerous places of B1a~B3c explosion grade.

Components of RTD system
The resistance temperature detector system is usually composed by RTD, connection lead, temperature display instrument. There are two points that should be noticed.
1. The scale divisions of the RTD and display instrument should be identical.
2. In order to eliminate the influence of the leading wire’s temperature variation, the three-wire configuration should be adopted.