A temperature transmitter is an instrument that converts temperature variables into standardized output signals that can be transmitted. Mainly used for measuring and controlling temperature parameters in industrial processes. A transmitter with sensors usually consists of two parts: the sensor and the signal converter. Sensors are mainly thermocouples or thermistors; Signal converters are mainly composed of measurement units, signal processing and conversion units (due to the standardization of industrial thermal resistance and thermocouple calibration tables, signal converters are also called transmitters when they are independent products). Some transmitters have added display units, and some also have fieldbus functions. As shown in Figure 1 on the right: Schematic diagram of temperature transmitter. If the transmitter consists of two sensors used to measure temperature difference, there is a given continuous function relationship between the output signal and the temperature difference. Therefore, it is called a temperature transmitter. There is a given continuous function relationship (usually a linear function) between the output signal of the transmitter and the temperature variable. Early produced transmitters had a linear function relationship between the output signal and the resistance value (or voltage value) of the temperature sensor. The standardized output signals are mainly DC electrical signals of 0mA~10mA and 4mA~20mA (or 1V~5V). Other standardized output signals with special regulations cannot be excluded. Temperature transmitters can be divided into two wire and four wire systems according to the power supply wiring method, except for the RWB type temperature transmitter which is a three wire system. Isolation type temperature transmitters come in both electric unit combination instrument series and miniaturized modular, multi-functional intelligent types. The former does not come with sensors, while the latter two types of transmitters can be easily combined with thermocouples or thermistors to form transmitters with sensors.