Let's talk about the basic knowledge of transmitters.

As we all know, our process control instruments have three major hardware components: transmitters, actuators, and regulators. In fact, in some cases,transmitteris equivalent to a sensor. An actuator is like a valve, while a regulator is a controller, the brain of the entire control system, such as a PID regulator. Today, we will focus on discussing the basic knowledge about transmitters.
　　1. What can a transmitter actually do?
In industrial production, after the measuring elements detect parameters such as pressure, temperature, flow, and liquid level, the transmitter is needed to convert the signals from the measuring elements into a standard signal source (such as a 4~20mA DC power supply) to be sent to display instruments or regulating instruments for display, recording, or adjustment. Therefore, the transmitter is not only a medium for conversion but also a medium of communication.
　　2. What are the advantages of transmitters?
Since regulators are generally located in control rooms that are relatively far away, pressure transmitters have become a composite of signal generation and transmission line driving functions, becoming the heart of the entire control device. With it, the control end and the measurement end are connected, forming a complete control system.
　　3. What types of transmitters are there?

Some transmitters integrate the measurement and transmission units (such as pressure transmitters), while others only have transmission functions (such as temperature transmitters).
Transmitters can be classified by their driving energy into pneumatic transmitters and electric transmitters.
Among them, the most commonly used in industrial production processes aredifferential pressure transmittersandtemperature transmitters..
　　4. Common types and selection principles of differential pressure transmitters
Differential pressure transmitters are used to convert measured parameters such as differential pressure, flow, and liquid level into a unified signal standard and transmit this unified signal to indicating, recording instruments, or regulators, allowing the measured parameters to be displayed on the screen.
The main types include: force balance electric differential pressure transmitters, capacitive differential pressure transmitters.
There are no standardized models for differential pressure transmitters; each manufacturer has its own selection table. The selection of differential pressure transmitters is mainly based on the properties of the measured medium, with considerations for cost savings, ease of installation, and maintenance. For cases where the measured medium is highly viscous, prone to crystallization, and strongly corrosive, it is necessary to choose an isolation type transmitter.
When selecting a differential pressure transmitter, it is important to consider the medium's corrosion on the diaphragm metal, and the diaphragm material must be chosen carefully. The diaphragm materials for transmitters include ordinary stainless steel, 304 stainless steel, 316L stainless steel, tantalum diaphragm materials, etc.
When selecting a differential pressure transmitter, the temperature of the measured medium must be considered. If the temperature is high, generally between 200℃ and 400℃, a high-temperature type must be selected; otherwise, the silicone oil may vaporize and expand, leading to inaccurate measurements.
When selecting a differential pressure transmitter, the working pressure level of the equipment must be considered, and the pressure level of the transmitter must match the application scenario. In terms of the measurement range of the selected transmitter, most transmitters have a certain adjustable range, and it is best to set the operating range within 1/4 to 3/4 of its range to ensure accuracy, which is especially important for micro differential pressure transmitters. In practice, some applications (liquid level measurement) require the measurement range of the transmitter to be shifted, and the measurement range and shift amount should be calculated based on the installation position on site, with positive and negative shifts distinguished.
　　5. Types and advantages of temperature transmitters
Temperature transmitters must be used in conjunction with various thermocouples or resistance temperature detectors, converting the measured temperature linearly into 0~10mA or 4~20mA DC current signals for easy display, recording, and adjustment unit cooperation.
According to the different types of temperature sensors used, temperature transmitters are divided into three types: DC voltage transmitters, resistance temperature transmitters, and thermocouple temperature transmitters.
Their advantages include the use of low-drift, high-gain linear integrated circuits, improving the reliability, stability, and various technical performances of the instruments. At the same time, due to the use of linearization circuits, the output signal of the transmitter can maintain a linear relationship with the measured temperature signal. Moreover, safety spark explosion-proof measures are adopted in the circuit, allowing temperature measurement in hazardous locations.