Sensors and transmitters play an important role in the field of instruments, meters and industrial automation. The transmitter is different from the sensor, in addition to being able to convert non-electricity into measurable electricity, it also has a certain amplification effect. The characteristics of several types of transmitters are described below
I. Integrated temperature transmitter
The temperature measuring probe is directly installed in the junction box in the form of a solid module, thereby forming an integrated transmitter. Generally, an integrated temperature transmitter is composed of a temperature measuring probe and a two-wire solid electronic unit. Integrated temperature transmitters are generally divided into two types: thermal resistance and thermocouple.
） ( 1 ) 转换单元，线性电路，限流保护，反接保护， V/I转换单元等组成。 Thermal resistance temperature transmitter is composed of reference unit, R / V conversion unit, linear circuit, current limiting protection, reverse connection protection, V / I conversion unit and so on. 转换电路后输出一个与被测温度成线性关系的4 ～ 20mA的恒流信号。 After the temperature-measuring thermal resistance signal is converted and amplified, the non-linear relationship between temperature and resistance is compensated by the linear circuit. After the V / I conversion circuit, a constant current signal of 4 to 20 mA that is linear with the measured temperature is output.
） ( 2 ) 转换，限流保护等电路单元组成。 Thermocouple temperature transmitters are generally composed of circuit units such as reference source, cold junction compensation, amplification unit, linearization processing, disconnection processing, reverse connection protection, V / I conversion, and current limit protection. ～ 20mA电流输出信号。 It firstly amplifies the thermoelectric potential generated by the thermocouple through cold junction compensation, then eliminates the non-linear error of thermoelectric potential and temperature by a linear circuit, and finally amplifies and converts it into a 4-20 mA current output signal. In order to prevent accidents caused by temperature control failure due to broken wires in the thermocouple measurement, a power-off protection circuit is also provided in the transmitter. When the thermocouple is broken or disconnected badly, the transmitter will output a maximum value to make the meter cut off the power.
The integrated temperature transmitter has the advantages of simple structure, saving leads, large output signal, good linearity, simple display instrument, strong anti-interference ability, solid module shock resistance and moisture resistance, reverse connection protection and current limit protection, reliable work, etc. . ～ 20mA信号；可与微机系统或者其它常规仪表匹配使用。 The output of the integrated temperature transmitter is a uniform 4 to 20 mA signal; it can be used in conjunction with a microcomputer system or other conventional instruments.
Second, the pressure transmitter
The pressure transmitter can also be called a differential transmitter, which is mainly composed of a load cell sensor, a module circuit, a display head, a case and a process connection. It can convert the received pressure signals of gas and liquid into standard current and voltage signals, which can be used to provide secondary alarms such as indicator alarm, recorder, regulator, etc. for measurement, instruction and process adjustment. 级电压信号。 The measurement principle is: process pressure and reference pressure are applied to both ends of the integrated silicon pressure sensitive element, and the differential pressure deforms the silicon wafer, so that the fully dynamic Wheatstone bridge made of semiconductor technology on the silicon wafer is external. Driven by a current source, an mV -level voltage signal proportional to pressure is output. Due to the excellent strength of the silicon material, the linearity and variation index of the output signal are relatively high. 级的电压信号，并送往放大倍数很高而又可以互相抵消温度漂移的差动式放大器。 When working, the pressure transmitter converts the measured physical quantity into a voltage signal of the mV level and sends it to a differential amplifier with a high amplification factor and which can offset temperature drift with each other. The amplified signal is converted into a corresponding current signal by voltage-current conversion, and then subjected to non-linear correction, and finally a standard current-voltage signal corresponding to a linear relationship with the input pressure is generated. Pressure transmitters can be divided into general pressure transmitters and differential pressure transmitters according to the pressure measurement range.