The History of Transmitter In China
Pressure transmitters are important components in many industrial equipment to control industrial processes and pressure changes. The pressure transmitter is used to measure the liquid level, density and pressure of liquid, gas or steam, and then convert the pressure signal into a 4-20mADC signal output. Pressure transmitters are divided into capacitive pressure transmitters and diffusion silicon pressure transmitters, ceramic pressure transmitters, strain pressure transmitters, etc.
The pressure transmitter is a field instrument that is in direct contact with the measured medium, and often works in environments such as high temperature, low temperature, corrosion, vibration and shock. It is widely used in pressure measurement and field control in petroleum, chemical, electric power, steel, light industry and other industries.
The development of pressure transmitters has generally gone through four stages:
1. The early pressure transmitters used the large displacement working principle, such as the mercury float differential pressure gauges and bellows differential pressure transmitters that were mass-produced. These transmitters have low precision and are cumbersome.
2. In the 1950s, there were force balance differential pressure transmitters with slightly higher accuracy, but the feedback force was small, the structure was complex, and the reliability, stability and vibration resistance were poor.
3. In the mid-1970s, with the emergence of new processes, new materials and new technologies, especially the rapid development of electronic technology, displacement transmitters with small size and simple structure appeared.
4. With the rapid development of science and technology in the 1990s, these transmitters have high measurement accuracy and the gradual development of intelligent digital signal transmission is more conducive to data acquisition.
Different types of pressure transmitters have been developed so far, such as capacitive transmitters, diffused silicon piezoresistive transmitters, differential inductive transmitters and ceramic capacitive transmitters.
In the 1990s, the field bus technology rose rapidly, and the industrial process control system gradually developed to the field bus control system with two-way communication and intelligent instrument control. Thus a new generation of intelligent pressure transmitters have been produced.
Their main features are as follows.
1. Self-compensation functions such as nonlinearity, temperature error, response time, noise and cross-induction, etc.
2. Self-diagnosis function such as self-checking when the power is turned on, and running check during work.
3. The function of two-way communication between the microprocessor and the basic sensor constitutes a closed-loop working system.
4. Information storage and memory functions.
5. Digital output.
Based on the above functions, the precision, stability, repeatability and reliability of the intelligent pressure transmitter have been improved and improved. Its two-way communication capability realizes the status of computer software control and remote setting range.
Intelligent pressure transmitters are mainly divided into two types with HART protocol and with 482 or RS232 interface. The intelligent pressure transmitter with HART protocol superimposes a special frequency signal on the analog signal to realize the simultaneous communication of analog and digital. The intelligent pressure transmitter with RS232 or 485 port internally converts the analog signal A/D to output by D/A through microprocessor calculation.
Nowadays, the research fields of pressure transmitters in various countries in the world are very extensive, and they have penetrated into almost every industry, but they are mainly summarized in the following trends:
1. Intelligence: Due to the emergence of integration, some microprocessors can be added to the integrated circuit, so that the transmitter has functions such as automatic compensation, communication, self-diagnosis, and logical judgment.
2. Integration: Pressure transmitters have been increasingly integrated with other measurement transmitters to form measurement and control systems. Integrated systems increase operational speed and efficiency in process control and factory automation.
3. Miniaturization: The market demand for small pressure transmitters is increasing. This kind of small pressure transmitter can work in extremely harsh environments, and only requires little maintenance and maintenance, and also has a negative impact on the surrounding environment. It is very small and can be placed in various important organs of the human body to collect data without affecting people's normal life.
4. Standardization: The design and manufacture of transmitters have formed certain industry standards.
5. Expansion: Another development trend of pressure transmitters is expanding from the machinery industry to other fields, such as automotive components, medical instruments and energy and environmental control systems.
