Pressure transmitter is a commonly used sensor in industrial practice. It is widely used in various industrial self-control environments, involving water conservancy and hydropower, railway transportation, intelligent building, production automation, aerospace, military, petrochemical, oil well, electric power, ship. , machine tools, pipelines and many other industries, the following briefly introduces the principles and applications of some commonly used pressure transmitters.

1. Principle and application of strain gauge pressure transmitter
There are many types of mechanical transmitters, such as resistance strain gauge pressure transmitter, semiconductor strain gauge pressure transmitter, piezoresistive pressure transmitter, inductive pressure transmitter, capacitive pressure transmitter, resonant pressure Transmitter and capacitive accelerometer. However, the application is widely used as a piezoresistive pressure transmitter, which has a very low price, high precision and good linearity.

2. Principle and application of ceramic pressure transmitter
    The corrosion-resistant pressure transmitter has no liquid transfer, the pressure acts directly on the front surface of the ceramic diaphragm, causing a slight deformation of the diaphragm. The thick film resistor is printed on the back of the ceramic diaphragm and connected into a Wheatstone bridge ( Closed bridge), due to the piezoresistive effect of the varistor, the bridge produces a highly linear voltage signal proportional to the pressure, which is proportional to the excitation voltage. The standard signal is calibrated to 2.0 / 3.0 according to the pressure range. 3.3 mV/V, etc., compatible with strain gauge sensors. With laser calibration, the sensor has high temperature stability and time stability. The sensor comes with temperature compensation of 0 to 70 ° C and can be in direct contact with most media.
Ceramic is a recognized material that is highly elastic, resistant to corrosion, abrasion, shock and vibration. The thermal stability of ceramics and its thick film resistance allow it to operate over a temperature range of -40 to 135 ° C, with high precision and high stability. The degree of electrical insulation is >2kV, the output signal is strong, and the long-term stability is good. High-performance, low-priced ceramic sensors will be the development direction of pressure transmitters. There is a trend to replace other types of sensors in Europe and the United States. In China, more and more users use ceramic sensors instead of diffused silicon pressure transmitters.

3. Principle and application of diffused silicon pressure transmitter
  The pressure of the measured medium acts directly on the diaphragm of the sensor (stainless steel or ceramic), causing the diaphragm to produce a micro-displacement proportional to the pressure of the medium, causing the resistance value of the sensor to change, and detecting the change by electronic circuitry, and The conversion outputs a standard measurement signal corresponding to this pressure.

4. Principle and application of sapphire pressure transmitter
    Using strain-resistive operation, silicon-sapphire is used as a semiconductor sensor with unparalleled metrology. The sapphire is composed of a single crystal insulator element, which does not cause hysteresis, fatigue and creep; sapphire is stronger than silicon, has higher hardness and is not afraid of deformation; sapphire has very good elasticity and insulation properties (within 1000 OC), so use Semiconductor sensitive components made of silicon-sapphire are insensitive to temperature changes and have excellent operating characteristics even under high temperature conditions; sapphire has excellent radiation resistance; in addition, silicon-sapphire semiconductor sensitive components have no pn drift. Therefore, the manufacturing process is fundamentally simplified, the repeatability is improved, and high yield is ensured.
    Pressure sensors and transmitters made of silicon-sapphire semiconductor sensitive components operate under harsh operating conditions with high reliability, high accuracy, minimal temperature error, and cost-effectiveness.
    The gauge pressure sensor and pressure transmitter consist of a double diaphragm: a titanium alloy measuring diaphragm and a titanium alloy receiving diaphragm. A sapphire sheet printed with a heterogeneous epitaxial strain sensitive bridge circuit is soldered to the titanium alloy measuring diaphragm. The pressure to be measured is transmitted to the receiving diaphragm (the receiving diaphragm and the measuring diaphragm are firmly connected by a tie rod). Under the action of pressure, the titanium alloy receiving diaphragm is deformed. After the deformation is sensed by the silicon-sapphire sensing element, the bridge output changes, and the magnitude of the change is proportional to the measured pressure.

    The sensor's circuitry ensures power to the strained bridge circuit and converts the strain bridge's unbalanced signal into a uniform electrical signal output (0-5, 4-20mA or 0-5V). In the absolute pressure sensor and pressure transmitter, the sapphire sheet is connected with the ceramic base glass solder to act as an elastic element to convert the measured pressure into strain gauge deformation for pressure measurement.


5. Principle and application of piezoelectric pressure transmitter
     The piezoelectric materials mainly used in piezoelectric transducers include quartz, sodium potassium tartrate and dihydrogen phosphate. Among them, quartz (silicon dioxide) is a kind of natural crystal. The piezoelectric effect is found in this crystal. In a certain temperature range, the piezoelectric property always exists, but after the temperature exceeds this range, the piezoelectric property is completely Disappeared (this high temperature is the so-called "Curie point"). Since the electric field changes little with the change of stress (that is, the piezoelectric coefficient is relatively low), quartz is gradually replaced by other piezoelectric crystals. Potassium sodium tartrate has a large piezoelectric sensitivity and piezoelectric coefficient, but it can only be applied in a low room temperature and humidity environment. Dihydrogen phosphate is an artificial crystal that can withstand high temperatures and relatively high humidity, so it has been widely used.
The piezoelectric effect is also applied to polycrystals, such as the current piezoelectric ceramics, including barium titanate piezoelectric ceramics, PZT, tantalate-based piezoelectric ceramics, lead magnesium niobate piezoelectric ceramics, and the like.
     Piezoelectric effect is the main working principle of piezoelectric transducers. Piezoelectric transducers cannot be used for static measurement because the electric charge after external force is only saved when the loop has an infinite input impedance. This is not the case, so this determines that the piezoelectric sensor can only measure dynamic stresses.
     Piezoelectric transmitters are mainly used in the measurement of acceleration, pressure and force. A piezoelectric accelerometer is a commonly used accelerometer. It has the characteristics of simple structure, small size, light weight and long service life. Piezoelectric accelerometers have found wide application in vibration and shock measurement of aircraft, automobiles, ships, bridges and buildings, especially in the aerospace and aerospace fields. Piezoelectric sensors can also be used to measure the measurement of combustion pressure inside the engine and the measurement of vacuum. It can also be used in the military industry, for example, to measure the change in the pressure of the gun bullet in the moment of firing and the shock wave pressure of the muzzle. It can be used to measure large pressures as well as to measure small pressures.

     Piezoelectric sensors are also widely used in biomedical measurements. For example, ventricular catheter microphones are made of piezoelectric sensors. Because measuring dynamic pressure is so common, piezoelectric transducers are widely used.