The role of the elastic sensitive element is to make the measured pressure on an area and converted to displacement or strain, and then by the displacement sensitive element or strain gauge is converted to a certain relationship with the pressure of the electrical signal. Sometimes the function of these two elements into one, such as piezoresistive sensors in the solid-state pressure sensor.
Pressure is an important process parameter in the consumer process and aerospace, aviation, defense industry, not only the need for it to stop the rapid dynamic measurement, but also the results of the measurement for the digital display and record. Large refineries, chemical plants, power plants and steel mills and other automation also need to pressure parameters transmitted over long distances, and the request for pressure and other parameters, such as temperature, flow, viscosity, etc. together with the conversion to digital signals into the computer.
Pressure sensors are extremely focused and rapid development of a sensor. Pressure sensor development trend is to further improve the dynamic response speed, accuracy and reliability, as well as the completion of digital and intelligent. Commonly used pressure sensors are capacitive pressure sensors, variable magnetoresistive pressure sensors, Hall-type pressure sensors, fiber-optic pressure sensors, resonant pressure sensors and so on.
Voltage-type pressure sensors are:
Piezoresistive sensors,
Variable inductive pressure sensors,
Membrane box pressure sensors,
Variable resistive pressure sensors,
Pressure switches, pressure sensors and so on.
Frequency type pressure sensors include:
Capacitive and elastic wave type pressure sensors.
The most widely used in automobiles are piezoresistive and capacitive pressure sensors and switch type pressure sensors.
A, piezoresistive pressure sensor
Piezoresistive pressure sensor sensing element is located on the surface of the diaphragm piezoresistor and silicon steel diaphragm composition.
The diaphragm is surrounded by four resistors connected to each other, known as the Whiston bridge circuit, such as our daily use of home appliances in the power supply circuit in the rectifier part of the general use of the Whiston bridge diode rectifier circuit.
When the pressure changes, the resistance of the bridge circuit changes, and the 5V voltage at both ends of the bridge changes, which is amplified by the amplifier circuit and converted into a signal output to the receiving device.
The piezoresistive pressure sensor is widely used in cars and trucks because of its small size, high precision and low production cost, and is the most advanced type of intake pressure sensor in the automobile.
However, the disadvantage of semiconductor components is affected by the temperature, so generally need to add transistor temperature compensation circuit.
Electronic control system in the intake pressure sensor and rail pressure sensor most of these pressure sensors.
Second, the membrane box pressure sensor
This sensor is a very thin sheet of metal welded into a pneumatic tank, through the positive or negative gas pressure (i.e., vacuum) so that the membrane box expansion or contraction, diaphragm movement to drive the lever to move the diaphragm through the differential converter, so that it converts the resistance change to form an electrical signal output, the principle of operation is similar to the mechanical high-pressure pump on the smoke limiter.
Three, variable inductance pressure sensor
The pressure sensor is mainly produced by two coils of mutual inductance voltage, when the alternating voltage through a coil, through the mutual inductance effect of the other coil to produce mutual inductance voltage, the tighter the coupling is the greater the output voltage, so when the core to the middle of the coil to move, the output signal increases.
Four, switch-type pressure sensors
Switch-type pressure sensors are widely used, generally divided into thin-film pressure sensors and spring tube pressure sensors.
1) thin-film pressure sensor: this type of sensor is commonly used in automotive alarm circuits, such as storage tank pressure sensor, oil pressure switch, air filter clogging sensor and so on.
This type of sensor is mainly composed of a diaphragm, spring, contacts, etc., when the pressure is lower than the calibration value, the diaphragm in the role of the reset spring downward movement, so that the contact closure, light up the corresponding alarm lights.
2) spring tube pressure sensor
In the previous old models are mainly used in the oil pressure alarm device, such as EQ1090 trucks and WD615 engine oil pressure sensor.
It consists of a moving contact, static contact and tube spring, when the oil pressure is higher than the specified value (generally 0.8 ± 0.05kPa) spring tube is driven by the pressure, deformation is larger, so that the contact is separated, the alarm lamp circuit is cut off, the alarm lamp is extinguished, when the pressure is lower than the specified value, the spring tube deformation is small, the contact is in the state of connecting the alarm lamp to form a circuit, so that the alarm lamp is lit.
Fifth, capacitive pressure sensor
This type of sensor is used with an aluminum oxide diaphragm with the base plate to form a capacitance, when there is pressure on the diaphragm, the diaphragm produces a pressure difference, after the integrated circuit processed to produce a variable frequency signal proportional to the pressure.
In fact, this type of sensor is a gap by changing the capacitance between the two plates to change the resonance frequency changes, the control device according to the frequency of the information can be calculated at the time of the absolute pressure.
This type of pressure sensor in the car more applications.
Pressure sensors in addition to the above part, there are such as variable resistance pressure sensors, differential transformer pressure sensors, and so on, and then introduced one by one!
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