是直接与被测介质相接触的现场仪表，常常在高温、低温、腐蚀、振动、冲击等环境中工作。 Pressure transmitters are field instruments that are in direct contact with the measured medium, and often work in high temperature, low temperature, corrosion, vibration, shock and other environments. It is widely used in pressure measurement and field control in petroleum, chemical, power, steel, light industry and other industries. The development of pressure transmitters has gone through four stages:
(1) Early pressure transmitters used large displacement working principles, such as mercury float differential pressure gauges and diaphragm-type differential pressure transmitters that had been mass-produced. These transmitters have low accuracy and bulkiness.
(2) In the 1950s, a slightly more accurate force-balanced differential pressure transmitter was available, 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) The rapid development of science and technology in the 1990s. These transmitters have high measurement accuracy and are gradually developing to intelligent. Digital signal transmission is more conducive to the development of data acquisition. Different types of transmitters, differential inductive transmitters and ceramic capacitive transmitters.
2. Introduction of several pressure transmitters 1. Diffused silicon pressure transmitter In the mid-1990s, Icsensors and Nova of the United States applied silicon cutting and silicon wafer stacking to produce a new type of diffusion silicon pressure sensor. Developed a diffused silicon pressure transmitter with high accuracy, low repeatability and corrosion resistance. In 1992, Jiangsu Xudong Instrument Factory developed a highly cost-effective XDB-Y608 diffused silicon pressure transmitter, which was widely used in many large and medium-sized enterprises across the country.
The process pressure is transmitted to the diffusion silicon diaphragm through the isolation diaphragm and sealing silicone oil, while the pressure at the reference end acts on the other end of the diaphragm. In this way, the pressure difference between the two sides of the diaphragm generates a pressure field, which compresses one part of the diaphragm and stretches the other. In the compression area and the tensile area, two strain resistance plates are used to sense the change in resistance caused by pressure, so that Convert pressure signals to electrical signals. This pressure transmitter can measure any liquid or gaseous medium carried by 316 steel.
2. Capacitive film type pressure transmitter Capacitive film type absolute pressure transmitter has a 20-year history since its birth in the 1980s. Due to its high accuracy, corrosion resistance, pollution resistance, and good stability, it is recognized as a low test at home and abroad. Ideal instrument for vacuum pressure. American company MKS is a major manufacturer of capacitive film pressure transmitters worldwide. Until now, its annual sales have reached hundreds of millions of dollars, involving various fields of the civil industry, and military applications such as the aerospace industry and nuclear industry. Industry plays a unique role.
This pressure transmitter is made by using the principle that the elastic film generates a pressure change under the pressure difference to cause a capacitance change. It consists of a detection part and a conversion circuit. The detection part has a vacuum cavity and a detection cavity. The vacuum chamber is a fully sealed structure. After passing the mass leak detection of the mass spectrometer, the exhaust chamber is exhausted for a long time, and the exhaust pipe is finally sealed. It is also equipped with a getter to eliminate residual gas and maintain high vacuum for a long time. The fixed electrode plate is located in the vacuum cavity, and the lead wire from the electrode plate is out of the cavity. The detection diaphragm is placed between the high-vacuum vacuum chamber and the detection chamber connected to the low-vacuum system to be tested. The detection diaphragm is a movable plate, which forms a flat capacitor with the fixed plate, and has a certain capacitance value. The measured low vacuum pressure enters the detection cavity through the detection hole, and the detection diaphragm is deflected, which changes its distance from the fixed plate, and the capacitance value changes accordingly. Different low vacuum pressure values determine different capacitance values. Finally, the capacitance signal is sent to the circuit conversion part. The circuit conversion part outputs the standard voltage or current signal through the conversion, sorting, and amplification links. This standard electrical signal is derived from a capacitive signal, which is proportional to the vacuum pressure. The vacuum pre-cooling tester uses the CPCD100Z capacitor film pressure transmitter as a vacuum chamber pressure measurement. The signal is output on the panel by a microprocessor. Experiments show that this type of transmitter responds quickly, is stable and reliable, and can be used continuously, which fully meets the requirements of pressure measurement in the test.
3. Ceramic thick film pressure transmitter The ceramic thick film pressure transmitter uses the force-sensitive effect of ceramic thick film resistance. The ceramic thick film pressure chip is used as an elastic element, and the thick film resistor printed and sintered on the ceramic diaphragm is a sensitive resistor, and after precise compensation technology, resistance adjustment technology, and signal processing technology are processed, the pressure signal is directly converted into a standard The current signal is connected to the industrial instrument or computer control system to realize the automatic detection and control of the production process. Porcelain thick film pressure transmitter is mainly composed of ceramic thick film pressure sensor and microprocessor. The sensor is used to measure the pressure change. When pressure is applied to the sensor, the resistance value of the sensor changes, which is detected by the bridge circuit on the sensor chip and converted into a digital signal by the A / D converter and sent to the microprocessor. The microprocessor is the core component of signal processing. It has the functions of linear operation, correction, fault diagnosis and communication. The sensor data memory can store correction coefficients, and the microprocessor uses the data information in the memory to calculate and process to produce an output with high accuracy and excellent characteristics. This transmitter can directly introduce various media including corrosive and non-corrosive gases and liquids to the ceramic diaphragm during the production process, without the need for complicated isolation technology, so the price is low. The elastomer of the pressure transmitter is made of high-aluminum porcelain with extremely stable physical and chemical properties. It has no creep and plastic deformation for long-term work, and its linearity and hysteresis performance are obviously better than other types of pressure transmitters.
4. Ceramic capacitor pressure transmitter The ceramic capacitor pressure transmitter uses a dry ceramic capacitor sensor without an intermediary liquid, so as to obtain high technical performance. The products in the market are mainly German E + H company and American Kavlico company. In the mid-1950s, Harbin Institute of Technology produced a PTM120 pressure transmitter using a ceramic capacitive sensor from Kavlico Company in the United States.It has stable performance and accurate test data, and has invested a lot in pressure measurement in petroleum, chemical, power, steel, and light industry industries. And site control. The working principle of the ceramic capacitor pressure transmitter is different from other capacitive transmitters. The medium pressure directly acts on the ceramic diaphragm, which causes the measurement diaphragm to shift. The capacitance change caused by the diaphragm displacement has a certain linear relationship with the input pressure, which is detected, amplified and output by the electronic components.
3. Intelligent pressure transmitters In the 1990s, fieldbus technology rose rapidly, and industrial process control systems gradually developed towards fieldbus control systems with two-way communication and intelligent instrument control. The result is a new generation of intelligent pressure transmitters. Their main features are as follows.
(1) Self-compensation functions such as non-linearity, temperature error, response time, noise, and cross-induction.
(2) The self-diagnostic function, such as performing a self-test when the power is turned on, enables operation checks during work.
(3) The two-way communication function 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 accuracy, stability, repeatability and reliability of the intelligent pressure transmitter have been improved and improved. Its two-way communication capability enables computer software control and remote range setting.
主要分为带协HART协议的和带482或RS232接口的两种类型。 Intelligent pressure transmitters are mainly divided into two types with HART protocol and 482 or RS232 interface. The intelligent pressure transmitter with HART protocol superimposes a dedicated frequency signal on the analog signal to realize the simultaneous communication of analog and digital. The intelligent pressure transmitter with RS232 or 485 port converts the analog signal A / D internally through microprocessor calculation and output by D / A. The RS232 interface is an asynchronous communication protocol interface and is compatible with many communication protocols. Therefore, the latter is widely used.
4. Representative products of pressure transmitters (1) EJA transmitter product specifications Application type Model capsule range (KPa) Maximum working pressure (MPa)
Differential pressure and level conventional installation EJA110A L 0.5-10 3.5
L (wetted material code is "S") 0.5-10 16
M 1-100 16
H 5-500 16
V 0.14-14MPa 16
The influence of static pressure is ignored. When static pressure (working pressure) is applied, the two resonant beams with the same shape, size, and material have the same deformation, so the frequency changes are the same, so the deviation is automatically cleared (the formula and the figure are similar to the temperature effect).
Excellent unidirectional overpressure characteristics The wetted diaphragm and the capsule body adopt original wave processing technology. When the external pressure is increased to a certain value, the wetted diaphragm can fully contact the body, and the pressure transmitted by the silicone oil to the sensor is no longer It increases with the increase of external force, so as to achieve the protection of the sensor.
Flexible installation can be directly installed without bracket;
For routine use, no three-valve manifold is required.
Microelectronic processing technology (MEMS) is used to fabricate two H-shaped resonant beams with the same shape, size and material at the center and edges of the surface of a single crystal silicon chip. figure 1). When the pressure on the upper and lower surfaces of a single crystal silicon wafer is not equal, deformation will occur, causing the central resonant beam to reduce its frequency due to compressive force and the edge resonance to increase its frequency due to tensile force (see Figure 2).
The difference signal between the two frequencies is directly sent to the CPU for data processing, and then (1) is converted into a 4-20mA output signal by D / A, and the Brain or Hart digital signal is superimposed during communication; (2) the direct output conforms to the fieldbus (Fieldbus Foundation TM ) Standard digital signals.
(2) Rosemount pressure transmitter 1. Product overview:
Rosemount's Model 3051C pressure transmitter sets a new standard in pressure measurement technology. It has unparalleled operational performance, a flexible CoPlanarTM platform, and can be upgraded. The performance indicators of the new 3051C pressure transmitter ensure accuracy and stability under different operating conditions.
Working principle: During operation, the isolation diaphragm and filling liquid on the high and low pressure sides transmit the process pressure to the filling liquid, and then the filling liquid transmits the pressure to the sensing diaphragm in the center of the sensor. The sensing diaphragm is a tensioned elastic element whose displacement varies with the pressure (for GP gauge pressure transmitters, atmospheric pressure is the same as that applied to the low-pressure side of the sensing diaphragm). AP absolute pressure transmitter, the low pressure side always maintains a reference pressure. The maximum displacement of the sensing diaphragm is 0.004 inches (0.1 mm), and the displacement is proportional to the pressure. The capacitor plates on both sides detect the position of the sensing diaphragm. The difference in capacitance between the sensing diaphragm and the capacitive plate is converted into the corresponding current, voltage, or digital HART (High-Speed Addressable Remote Transmitter Data Highway) output signal.
The performance index of the new 3051C applied to the 3051 transmitter guarantees accuracy and stability under different working conditions. The flexible and flexible CoPlanarTM platform design not only provides the best solution for your current application needs, but also fully meets your future technical requirements through the PlantWeb plant management network and fieldbus technology.
Overall performance: ± 0.15%
Accuracy: ± 0.075%
Differential pressure: calibration range from 0.5inH2O to 2000psi
Gauge pressure: calibration range from 2.5inH2O to 2000psi
Absolute pressure: calibration range from 0.167psia to 4000psia
Process isolation diaphragm: stainless steel, Hastelloy CR, Monel R, tantalum (CD, CG only) and gold-plated Monel are compact, sturdy and lightweight, easy to install.
的趋势当今世界各国压力变送器的研究领域十分广泛,几乎渗透到了各个行业,但归纳起来主要有以下几个趋势: V. Trends of Pressure TransmittersThe research fields of pressure transmitters in various countries around the world are very extensive and have penetrated almost all industries, but they are 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) Integrated pressure transmitters have been increasingly integrated with other measurement transmitters to form measurement and control systems. Integrated systems increase operating speed and efficiency in process control and factory automation.
(3) Miniaturization At present, the market has a growing demand for small pressure transmitters. Such small transmitters can work in extremely harsh environments, and only require very little maintenance and maintenance, which affects the surrounding environment. It is also very small and can be placed in various important organs of the human body to collect data without affecting the normal life of the person. Such as the United States Entran company's range of 2 ~ 500PSI transmitter, only 1.27mm in diameter, can be placed in the blood vessels of the human body without major impact on blood circulation.
(4) The design and manufacture of standardized transmitters has formed a certain industry standard. Such as ISO international quality system; American ANSI, ASTM standards, Russia's ГOCT, Japan's J IS standards.
(5) Another development trend of widening pressure transmitters is expanding from the mechanical industry to other fields, such as: automotive components, medical instruments and energy environment control systems.