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Pressure sensor principle and application

source:release time:2016-04-09

Pressure sensors are industrial practice, instrumentation control the most commonly used sensors, and is widely used in various industrial automation environment, involving water conservancy and hydropower, railway transportation, production automation, aerospace, military, petrochemical, oil, electricity, shipbuilding, many machine tool industry, piping, etc., Comrade Shenzhen City of quasi-sensing technology technology Co., Ltd. is a brief introduction of some commonly used sensor principle and its application.

Many types of mechanical sensors, such as resistance strain gauge pressure sensors, semiconductor strain gauge pressure sensors, piezoresistive pressure sensors, inductive pressure sensors, capacitive pressure sensors, resonant pressure sensor and capacitive accelerometer sensors. But the most widely used is a piezoresistive pressure sensor, it has a very low price and high accuracy and good linearity. Here we introduce this type of sensor.

1, strain gauge pressure sensor principle and application:

Understanding piezoresistive force sensor, we first recognize what this kind of resistance strain gauge element. Resistance strain gauge is a strain variation on the DUT to convert electrical signals into a sensitive device. It is a major component of the piezoresistive strain sensors. Resistance strain gauge most widely used metal resistance strain gauge and semiconductor strain gauge two kinds. Metal resistance strain gauges have filamentous strain gauge and metal foil-like strain gauge two kinds. Usually a strain gauge closely bonded by a special adhesive and agents in the produce mechanical strain matrix, when the matrix by the force generating stress, strain gauges can together produce deformation, strain gauge resistance change, so applied to the resistor voltage changes. This change in resistance strain gauges when the force generated are usually small, general strain gauges that are composed of strain bridge, and amplified by a follow-up instrumentation amplifier, and then transmitted to the processing circuit (usually the A / D converter and CPU) display or the implementing agency.

1.1, the internal structure of the metal resistance strain gauge: It consists of a base material, metal strain wire or strain foil, the insulating protection sheet and lead components. According to different purposes, the resistance of resistance strain gauge can be designed by the designer, but it should be noted that the range of resistance: the resistance is too small, the required drive current is too large, while strain gauge fever itself causes the temperature is too high different environments, so changes in resistance of the strain gauge is too big, obvious output zero drift, the zero circuit is too complex. And the resistance is too large, the impedance is too high, poor resistance to external electromagnetic interference. Generally they are about tens of ohms to several tens of kilohms.

1.2, the working principle of resistance strain gauge: resistance strain gauge metal working principle of resistance strain is adsorbed on the substrate material with the mechanical deformation resistance changes arising from the phenomenon commonly known as resistance strain effect. The resistance value of the metal conductor can be expressed as:

 
Where: ρ-- resistivity metal conductor (Ω · cm2 / m)
        
S-- conductor cross-sectional area (cm2)
        
L-- conductor length (m)
   
We wire strain gauges, for example, when the wire by external force, its length and cross-sectional area will change, from the above formula can be readily seen, that is, the resistance value will change if the wire by external force and elongation, its length increases, while the cross-sectional area is reduced, the resistance value will increase. When the wire is compressed by external force, reducing the length and cross section increase, the resistance value is reduced. As long as the measured increase in the resistance change (usually to measure the voltage across the resistor), you can get the strain wire strain pressure.

2, ceramic pressure sensor principle and application: corrosion resistant ceramic pressure sensor is not the transmission fluid pressure directly on the front surface of the ceramic diaphragm, the diaphragm will produce slight deformation of the back, thick film resistors printed on the ceramic diaphragm, connected into a Wheatstone bridge circuit is closed, since the piezoresistive effect varistor so that the bridge to produce a highly linear proportional to the pressure, and the excitation voltage is proportional to the voltage signal, the standard signal according to the pressure range of different calibration of 2.0 / 3.0 / 3.3 mV / V, etc., and the strain sensor can be compatible. By laser calibration, the sensor has high temperature stability and time stability, the sensor comes with temperature compensation 0 ~ 70 ℃, and direct contact with the vast majority of media.

Ceramic is a recognized high elasticity, corrosion-resistant materials, wear-resistant, shock and vibration. Thermal stability characteristics of the ceramic and thick film resistors can make its operating temperature range up to -40 ~ 135 ℃, and with high precision and high stability of the measurement. Electrical insulation level> 2kV, the output signal is strong, long-term stability. High features, low price of the ceramic sensor will be the development direction of the pressure sensor, a comprehensive alternative to other types of sensors trend in European countries, in China more and more users use the ceramic sensor replacement diffused silicon pressure sensor.

3, diffused silicon pressure sensor principle and application: the measured medium pressure directly on the sensor diaphragm on (stainless steel or ceramic), the diaphragm to produce micro-displacement is proportional to the medium pressure, the resistance value of the sensor changes, and the use of electronic circuit this change and conversion output corresponding to the standard pressure measurement signal.


4. The piezoelectric pressure sensor principle and application

Piezoelectric material mainly used in piezoelectric sensors include quartz, potassium sodium tartrate and dihydrogen phosphate amine. Wherein the quartz (silicon dioxide) is a natural crystal, the piezoelectric effect is found in this crystal, within a certain temperature range, the piezoelectric properties has always existed, but temperatures in excess of this range, the piezoelectric properties completely disappear (this high temperature is called the "Curie point"). Due to changes in the electric field stress as small changes (also said piezoelectric coefficient is relatively low), quartz gradually so be replaced by other piezoelectric crystal. And potassium sodium tartrate has great piezoelectric sensitivity and piezoelectric coefficient, but it is only to be applied at room temperature and low humidity environment. Dihydrogen phosphate crystals are man, able to withstand high temperatures and relatively high humidity, so together). Under the influence of pressure, titanium receiver diaphragm to produce the deformation, the deformation is silicon - sapphire sensitive components perception after which the bridge output will change, and the magnitude of change is proportional to the measured pressure.
    
The piezoelectric effect is now applied in polycrystalline, such as piezoelectric ceramic barium titanate piezoelectric ceramics, PZT, piezoelectric ceramic niobate, lead magnesium niobate piezoelectric ceramics and so on.
    
The main principle is the piezoelectric effect of the piezoelectric sensor, piezoelectric sensors can not be used for static measurements, because after the charge after the external force, only when the input impedance is infinite loop having stored. The actual situation is not the case, so it determines the piezoelectric sensor can only measure dynamic stress.
    
Piezoelectric sensors are used in measuring acceleration, pressure and force the like. Piezoelectric accelerometer is a commonly used accelerometer. It has a simple structure, small size, light weight, long life and other excellent features. Piezoelectric acceleration sensor vibration and shock measuring aircraft, automobiles, ships, bridges and buildings has been widely used, especially in the field of aviation and aerospace more of its special status. Piezoelectric sensors can also be used to measure the internal combustion engine pressure measurement and vacuum measurement. It can also be used for military industry, for example, use it to measure the pressure shock wave guns firing bullets in the breech in the moment of change of chamber pressure and muzzle. It can be used to measure pressure, it can also be used to measure small pressure.
  
Piezoelectric sensors are also widely used in biomedical measurements, such as the decline of the ventricular catheter damper is made of a piezoelectric sensor is made because the measured dynamic pressure is so common, so the application of piezoelectric sensors is very extensive.
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