Classification of pressure gauges

According to different working principles, pressure gauges can be divided into three types: liquid column type, elastic type and sensor type.

(1). Liquid column pressure gauges, such as U-tube manometers and pipe manometers, etc., convert pressure signals into liquid column height signals based on hydrostatic principles, and often use water, alcohol or mercury as the working medium for pressure measurement. Features: The structure is simple, the readings are intuitive, and the signal cannot be transmitted remotely. It is suitable for low-voltage measurement.

(2). The elastic type, such as the Bourdon tube manometer, converts the pressure signal into the mechanical deformation of the elastic element, and outputs the signal in the form of pointer deflection. However, in more cases, it is required to transmit the signal to the control room. Generally, it is necessary to add conversion components to the existing elastic manometer structure to realize long-distance signal transmission. The signal of the elastic manometer mostly adopts the electric remote transmission method, that is, the deformation or displacement of the elastic element is converted into an electrical signal for output. Common conversion methods include potentiometer type, Hall element type, inductive type, and differential transformer type. Elastic pressure gauges are mostly used in industry.

(3). The principle of the pressure sensor is to convert the pressure signal into some kind of electrical signal. The common ones are: strain type, piezoresistive type, piezoelectric type, and capacitive type.

a. Strain type: The working principle of the strain element is based on the "strain effect" of conductors and semiconductors, that is, when the conductors and semiconductor materials undergo mechanical deformation, their resistance value will change.

b. Piezoresistive: piezoresistive pressure sensor, also known as diffused silicon pressure sensor, is based on the piezoresistive effect of semiconductors. It is different from the body-shaped strain element used in the strain sensor, but is directly made of a diffused piezoresistor on a silicon flat diaphragm according to a certain crystal direction by using an integrated circuit process. The silicon flat diaphragm has good elastic properties when subjected to microwave deformation. The deformation of the diaphragm changes the resistance value of the diffusion resistor.

c. Piezoelectric type: It uses the piezoelectric effect of piezoelectric materials to convert the measured pressure into an electrical signal. It is a commonly used sensor in dynamic pressure detection and is not suitable for measuring slowly changing pressure and static pressure. Piezoelectric elements made of piezoelectric materials will generate charges when they are under pressure, and the charges will disappear when the external force is removed. Within the elastic range, there is a linear relationship between the amount of charge generated by piezoelectric elements and the applied force.

d. Capacitive type: It converts the displacement of the elastic element into the change of capacitance, and uses the pressure measuring diaphragm as the movable plate of the capacitor, which forms a variable capacitor with the fixed plate. When the measured pressure changes, the pressure measuring diaphragm produces a displacement to change the distance between the two plates, and the corresponding capacitance change is measured to know the measured pressure value.