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Detailed analysis of working principle of pressure transmitter

Post: 2020-02-29

In the current domestic market, there have been resistive type, diffused silicon type, ceramic magnetic type pressure transmitters, and gradually occupied a large number of market positions.The following nanjing hanga electron pressure transmitter working principle analysis, hope to help you.

The basic introduction of pressure transmitter

(1) basic concepts

Pressure transmitter is used to detect fluid pressure (actually pressure), and carry out remote signal transmission, signal transmission to secondary instrument or computer pressure control or monitoring of an automatic control front element, mainly composed of pressure sensor, measuring circuit and process connection.It can convert the physical pressure parameters such as gas and liquid felt by the pressure sensor into standard electrical signals, which can be used for the measurement, indication and process adjustment of the secondary instruments such as the alarm device, recorder and regulator.In China, the pressure transmitter currently used in small automatic control is generally based on piezoresistor principle, that is, the resistance changes after the piezoresistor is compressed, and the pressure can be detected by amplifying and using standard pressure calibration.

(2) basic advantages

First, it is easy to set up and can realize multi-point control.If the pressure signal detected is a continuous signal, the pressure can be set at will. Only the electric control part needs to be set.

Second, it can realize the advanced control of compressor operation and extend the compressor life.By using frequency conversion technology, the compressor can run more smoothly, greatly reduce the number of start-up, extend the service cycle, and be more environmentally friendly and energy-saving.

Third, provide control accuracy and better component reliability.The detection accuracy of the pressure transmitter is several times higher than that of the pressure switch, and the control accuracy is naturally improved accordingly. Because the sensitive elements adopted are of non-mechanical structure, they basically do not need maintenance and can reduce the damage rate.

Ii. Working principle of pressure transmitter

1. Resistance strain gauge pressure transmitter

(1) basic overview.Resistance strain pressure transmitter large signal output, stainless steel structure, with high linearity, small hysteresis error, good temperature performance, stable work, wide range, corrosion resistance and other characteristics, mainly in national defense and industrial automation and other fields are widely used.An important component of the sensor is a resistance strain gauge, which can convert the strain changes on the tested piece into an electrical signal.

(2) working principle.Adsorbed on matrix material, the strain resistance of metal resistance strain gauge changes with mechanical deformation, commonly known as resistance strain effect.In general, the strain gauge is tightly bonded to the matrix producing mechanical strain with special adhesives and agents. As the stress changes on the substrate, the resistance strain gauge also deforms, causing the resistance value of the strain gauge to change and the voltage applied to the resistance to change.The strain gauge has A small change in resistance value when it is subjected to force. Generally, the strain gauge forms A strain bridge, which is amplified by subsequent instrument amplifiers and then transmitted to the processing circuit (usually A/D conversion and CPU) display or actuator.In the application, the value range of resistance should be paid special attention to. The resistance value is too small, the required driving current is too large, and constant heating will lead to too high temperature of the strain gauge, leading to too large change in the resistance value of the strain gauge, obvious output zero drift, and too complicated zero adjustment circuit.However, if the resistance is too high and the impedance is too high, the resistance to external electromagnetic interference will be reduced.(see below)

2. Diffused silicon pressure transmitter

(1) basic overview.The pressure detection element of the diffused silicon pressure transmitter adopts imported diffused silicon or ceramic core, and the sensor signal is converted into 0-10ma or 4-20ma unified output signal by high-performance electronic amplifier.This kind of pressure transmitter can replace traditional remote transmission differential transducer, pressure gauge, hall element, and has the DDZ - and DDZ - transmitter performance.Diffused silicon pressure transmitter has a strong performance, not only can be used with various models of moving coil indicator, digital pressure gauge, electronic potentiometer, but also with various automatic regulation system or computer system.

(2) working principle.When the pressure signal of the medium ACTS on the sensor, the pressure signal is converted into an electrical signal, which is amplified by differential amplification and output amplifier. Finally, the voltage and current of V/A is converted into A standard current output signal of 4-20ma, which is linearly corresponding to the liquid level pressure of the measured medium.

3. Ceramic pressure transmitter

(1) basic overview.Ceramic materials are widely recognized for their high elasticity, corrosion resistance, abrasion resistance, shock resistance and vibration resistance.The working temperature range of ceramics is between -40 ~ 135, with high accuracy and stability.Electrical insulation >2kV, not only strong output signal, and can maintain long-term stability.Such high characteristic, low price advantage, will make ceramic sensor will become the future development direction.

(2) working principle.The pressure of the corrosion-resistant ceramic pressure transmitter ACTS directly on the front surface of the ceramic diaphragm, causing slight deformation of the ceramic diaphragm. The thick film resistance is printed on its back and connected to a wheatstone bridge.The piezosensitive resistor's piezosensitive effect enables the bridge to produce a voltage signal that is highly linear in proportion to the pressure and also proportional to the excitation voltage. The standard signal of 2.0/3.0/3.3mv /V is calibrated according to the different pressure range and compatible with strain sensors.The sensor has high temperature stability and time stability through laser calibration. The sensor is equipped with temperature compensation of 0 ~ 70, and can directly contact with most media.

3. Matters needing attention when the pressure transmitter is working

(1) do not use a voltage higher than 36V on the transmitter, which may cause damage.

(2) the transmitter should not touch the diaphragm with a hard object, which may damage the diaphragm.

(3) the tested medium should not be frozen, otherwise the isolation diaphragm of sensor elements is easy to be damaged, resulting in the failure of the transmitter.

(4) when measuring steam or other high temperature medium, the temperature should not exceed the limit temperature when the transmitter is in use, otherwise heat dissipation device must be used.

(5) when measuring steam or other high-temperature medium, in order to connect the transmitter and the pipe, the heat pipe should be used and the pressure on the pipe should be transferred to the transformer.When the measured medium is water vapor, the heat pipe should be injected with appropriate amount of water to prevent overheating steam directly contact with the transmitter, resulting in damage to the sensor.

(6) in the process of pressure transmission, several points should be noted: the connection between the transmitter and the heat pipe shall not leak;Be careful when opening the valve, lest the tested medium directly impact and damage the sensor diaphragm;The pipeline must be kept clear to avoid the sediment in the pipeline from ejecting and damaging the sensor diaphragm.