Pressure transmitter selection

I believe that friends in the industrial automation industry are very familiar with pressure transmitters, but do you know pressure transmitters? Faced with various complex working conditions, do you really know how to choose a suitable pressure transmitter? Now let me take you to the brothers and sisters of this big family of pressure transmitters! 　　1　　 simple self-introduction of pressure transmitters. Pressure transmitters are a kind of pressure sensor whose output is the standard signal. It is an instrument that accepts pressure variables and converts them into standard output signals in proportion. It can convert the physical pressure parameters of gas and liquid felt by the load cell sensor into standard electrical signals (such as 4-20mADC, etc.) to provide secondary instruments such as indicator alarms, recorders, regulators, etc. for measurement and indication And process regulation. 2　　The classification of pressure transmitters Generally, the pressure transmitters we talk about are divided according to the principle: 　　capacitive pressure transmitter, resistive pressure transmitter, inductive pressure transmitter, semiconductor pressure transmitter , There are piezoelectric pressure transmitters for high-frequency measurement, etc. Among them, resistive pressure transmitters are the most used. The capacitive pressure transmitter takes Rosemount’s 3051S transmitter as a representative of high-end products.　　The focus of this issue　　Pressure transmitters can be divided into metal, ceramic, diffused silicon, single crystal silicon, sapphire, sputtered film, etc. according to pressure sensitive components.　　○Metal pressure transmitter has poor accuracy, but has little effect on temperature. It is suitable for areas with a wide temperature range and low accuracy requirements.　　○ Ceramic pressure sensors have better accuracy, but are more affected by temperature. Ceramics also have the advantage of impact resistance and corrosion resistance, which can be used in the field of response.　　 ○ The pressure transmission accuracy of diffused silicon is very high, and the temperature drift is also large, so it is generally necessary to perform temperature compensation before it can be used. Moreover, even after the temperature compensation, the pressure above 125°C cannot be measured. However, under normal temperature conditions, the sensitivity coefficient of diffused silicon is 5 times that of ceramics, so it is generally used in the field of high-precision measurement.　　○Single crystal silicon pressure transmitter is the most accurate sensor in industrial practice. It is an upgraded version of diffused silicon, and of course the price is also upgraded. At present, Yokogawa of Japan is the representative in the field of monocrystalline silicon pressure. ○The sapphire pressure transmitter is not sensitive to temperature changes and has good working characteristics even under high temperature conditions; sapphire has strong anti-radiation characteristics; no pn drift; it can work normally under the worst working conditions, and High reliability, good accuracy, minimal temperature error, and overall high cost performance.　　○The sputtering thin film pressure transmitter does not have any adhesive, and it shows higher long-term stability and reliability than the sticky strain gauge sensor; it is less affected by temperature: when the temperature changes 100 ℃, the zero drift is only 0.5%. Its temperature performance is far superior to the diffusion silicon pressure sensor; in addition, it can directly contact with general corrosive media. 3　　The principle of different types of pressure transmitters The principle of capacitive pressure transmitters. When the pressure directly acts on the surface of the measuring diaphragm, the diaphragm produces a small deformation. The high-precision circuit on the measuring diaphragm transforms this small deformation. Become a highly linear voltage signal proportional to the pressure and proportional to the excitation voltage, and then use a dedicated chip to convert this voltage signal into an industry standard 4-20mA current signal or 1-5V voltage signal. The principle of the diffused silicon pressure transmitter The pressure of the measured medium directly acts on the diaphragm of the sensor (usually a 316L diaphragm), causing the diaphragm to produce a micro displacement proportional to the pressure of the medium, and changing the resistance value of the sensor , And use Wheatstone circuit to detect this change, and convert and output a standard measurement signal corresponding to this pressure.　　Principle of single crystal silicon pressure transmitter　　piezoresistive pressure sensor is constructed by using the piezoresistive effect of single crystal silicon. Using single crystal silicon wafer as the elastic element, when the pressure changes, the single crystal silicon produces strain, so that the strain resistance directly diffused on it produces a change proportional to the measured pressure, and then the corresponding voltage output signal is obtained by the bridge circuit .　

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