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        Time:2009/7/9    Nunbwer:5     【Print】【Copy】 【Close
        Principle and Application of pressure sensors
        Pressure sensor is the most commonly used industrial practice of a sensor, which is widely used in various industrial control environment, involved in water conservancy and hydropower, railway transport, intelligent building, production control, aerospace, military, petrochemical, oil, electric power, ships, machine tools, plumbing and many other industries, following a brief introduction to some common principle and application of sensor

        1, strain gauge pressure sensor and application of the principle

          A wide variety of mechanical sensors, such as the resistance strain gauge pressure sensors, semiconductor strain gauge pressure sensors, piezoresistive pressure sensors, inductive pressure sensors, capacitive pressure sensors, resonant capacitive pressure sensor and acceleration sensors. However, the most widely used piezoresistive pressure sensors, it has a very low price and high accuracy and good linearity.

        Here we are introduced such sensors.

          In understanding the piezoresistive force sensor, we first learn what a resistance strain gauge of this component. Resistance strain gauge is a piece on the measured strain signal conversion into a sensitive device. It is a piezoresistive strain sensor, one of the main components of. Resistance strain gauge is the most widely used metal and semiconductor strain gauge resistance strain gauges of two. Metal resistance strain gauges and strain gauge filament and metal foil strain gauge-like two. Strain gauge is usually through special agents of the stick and have a strong mechanical bond strain in the matrix, when the matrix changes in force occurred when the stress, strain resistance, together also have a deformation, so that the resistance strain gauge to change, so that increase the voltage in the resistance to change. This strain gauge force generated by the resistance change is usually small, the general composition of this strain are strain gauge bridge, and through follow-up to enlarge the instrumentation amplifier, and then transmit them to the processing circuit (usually the A / D conversion and CPU) to show or executive body. Metal resistance strain gauge is the resistance of the internal structure of the structure of strain gauge, which is the matrix material, metal foil strain or strain wire, insulation protection, such as films and pinout parts. According to different purposes, resistance of the resistance strain gauges can be designed by the designer, but the range of resistance should be noted: resistance is too small, the required drive current too much heat at the same time led to the strain gauge itself, the temperature is too high different environment, so that changes in resistance strain gauge is too large output zero drift apparent zero circuit is too complicated. But too much resistance, impedance is too high, anti-electromagnetic interference from outside less. Europe in general are a few dozen to several十千around Europe.

          Resistance of the working principle of strain gauge

          Metal resistance of the working principle of strain gauge is adsorbed on the substrate material on the strain deformation resistance with the mechanical changes resulting from the phenomenon of resistance, commonly referred to as the resistance strain effect. Metal conductor type of resistance that can be used: where: ρ - resistivity of the metal conductor (Ω cm2 / m) S - the cross-sectional area of conductor (cm2) L - the length of conductor (m) of our metal wire resistance strain as an example, when the metal wire by the external force, its length and cross-sectional area will change, from where can easily see that its resistance value will change if the metal wire by the external force and elongation , its length, and reduced cross-sectional area, resistance will increase. When the metal wire by the external force and compression to reduce the length of the cross-section increase in resistance value will be reduced. Increase as long as the measured change in resistance (usually at both ends of the resistance measurement voltage), can access the contingency contingency situation wire

        2, Ceramic Theory and Application of pressure sensors

          Corrosion-resistant ceramic pressure sensor is not the transmission of liquid pressure in the direct effect of the pre-ceramic membrane surface to have a tiny patch deformation, thick-film resistors printed on the back of the ceramic diaphragm, connected into a Wheatstone bridge (closed bridge), as a result of the piezoresistive effect varistor so that a bridge with a high degree of pressure is directly proportional to the linear, with the excitation voltage is also proportional to the voltage signal, the standard pressure range of the signal in accordance with the different calibration for the 2.0 / 3.0 / 3.3 mV / V and so on, and the strain sensor can be compatible. Laser calibration, the sensor has high temperature stability and time stability, self-temperature compensation sensor 0 ~ 70 ℃, and the vast majority of media can be in direct contact. Ceramic is a recognized high elasticity, anti-corrosion, abrasion resistance, impact resistance and vibration of the material. Ceramic thermal stability characteristics and its thick-film resistors can make it up to operating temperature range of -40 ~ 135 ℃, and with measurements of high precision and high stability. The degree of electrical insulation> 2kV, the output signal of strong, long-term stability. High characteristics of low-cost ceramic sensor will be the direction of development of pressure sensors, in Europe and the United States a comprehensive alternative to the trend of other types of sensors, in China, more and more users to replace the proliferation of the use of ceramic sensor silicon pressure sensor.

          3, the proliferation of silicon pressure sensors and application of the principle

          The working principle of the pressure measured directly the role of media in the membrane on the sensor (stainless steel or ceramic), which produce medium pressure diaphragm is proportional to the micro-displacement, so that the sensor resistance changes, and the use of electronic circuit detecting the change, and convert the output of a correspond to the standard measurement of the pressure signal.

        4, Sapphire Principle and Application of pressure sensors

          The use of resistive strain principle, the use of silicon - the semiconductor sensor as sapphire, with a unique measurement characteristics. Sapphire single crystal insulator from the elements, there will be no lag, fatigue and creep phenomena; Sapphire than silicon to strong, high hardness, is not afraid of deformation; Sapphire has a very good flexibility and insulating properties (1000 OC days), therefore, the use of silicon - the semiconductor manufacturing sapphire-sensitive components, is not sensitive to temperature change, even in high temperature conditions, also have very good working properties; Sapphire strong anti-radiation properties; In addition, silicon - the semiconductor sensor sapphire, no drift pn Therefore, fundamentally simplifies the manufacturing process and improve the repeatability, to ensure a high yield.

          Silicon - sapphire semiconductor pressure sensor manufactured sensors and transmitters can work in the worst conditions to work, and high reliability, accuracy, and the temperature error is extremely small, cost-effective.

          Pressure gauge pressure sensor and transmitter diaphragm from two components: measurement of titanium and titanium diaphragm diaphragm receiver. Printing heteroepitaxial strain sensitivity of the sapphire bridge circuit sheet, was welded on the titanium diaphragm measurement. Sent to the receiver under test pressure on the diaphragm (diaphragm and measuring receiver patch strong link between the link). The role of pressure, the resulting titanium diaphragm deformation receiver, the deformation was silicon - Sapphire sensitive sensing element, its output will bridge changes with the magnitude of change is proportional to the measured pressure.

          Sensor circuit to ensure that emergency power supply bridge circuit and strain bridge imbalance signal is converted to a unified signal output (0-5,4-20 mA or 0-5V). Absolute pressure in the pressure sensor and transmitter, the sapphire sheet, with the ceramic glass base with solder connections played the role of the elastic element, the pressure will be measured is converted to strain deformation, so as to achieve the purpose of pressure measurement.

        5, piezoelectric pressure sensors and application of the principle

          The main use of piezoelectric sensors in the piezoelectric materials include quartz, tartaric acid and sodium dihydrogen phosphate amine. Which quartz (silicon dioxide) is a natural crystal, piezoelectric effect is found in such a crystal, to a certain temperature range, there have been piezoelectric nature, but the temperature exceeds this range, the piezoelectric nature disappeared (the high temperature is the so-called "Curie Point"). With the stress changes due to changes in micro-electric field (say, a relatively low piezoelectric coefficient), the quartz gradually been replaced by the piezoelectric crystal. And K-Na tartrate great sensitivity and piezoelectric piezoelectric coefficient, but it can only be at room temperature and relatively low humidity environment can be applied. Amine dihydrogen phosphate crystals are man-made, can withstand high heat and humidity, it has been widely used.

          Piezoelectric effect is also applied to polycrystals, such as the present piezoelectric ceramic, piezoelectric ceramic, including barium titanate, PZT, piezoelectric ceramic department niobate, lead acid magnesium niobate piezoelectric ceramics and so on.

          Piezoelectric effect of piezoelectric sensors is the main working principle, piezoelectric sensors can not be used for static measurements, because of the charge after the external force, only in-the-loop with infinite input impedance when are preserved. The actual situation is not like this, so it is determined that piezoelectric sensors can only dynamic stress measurement.

          Piezoelectric sensors are used in acceleration, pressure and force measurements. Piezoelectric acceleration sensor is an accelerometer used. It has a simple structure, small size, light weight, long life and other outstanding characteristics. Piezoelectric acceleration sensor in aircraft, automobiles, ships, bridges and construction of the vibration and impact measurement 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 the pressure measurement and vacuum measurement. Can also be used for military industry, for example, use it to measure the bore of the gun firing bullets in the chamber pressure of the moment of change and the shock wave pressure muzzle. It can be used to measure pressure can also be used to measure small pressure.

          Piezoelectric sensors are widely used in biomedical measurement, for example, sounded a decline of ventricular catheter is made from the piezoelectric sensor, since the dynamic pressure measurement is so widespread, so the application of piezoelectric sensors is very broad
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