Basic knowledge of pressure gauges for various testing equipment

Basic knowledge of pressure gauge

One, the concept of pressure in the pressure gauge

　　 The concept of pressure here actually refers to the pressure in physics, that is, the size of the pressure per unit area.

　　Absolute pressure: The pressure that is higher than the absolute pressure zero position based on the absolute pressure zero position.

　　正　　 pressure: The pressure is higher than the atmospheric pressure based on the atmospheric pressure.

　　negative　　pressure (vacuum): The pressure is lower than the atmospheric pressure based on the atmospheric pressure.

　　差　　Pressure: The difference between two pressures.

　　表　　Pressure: The pressure is greater or less than the atmospheric pressure based on the atmospheric pressure.

　　 Pressure gauge: Based on atmospheric pressure, it is used to measure instruments that are less than or greater than atmospheric pressure.

Two, pressure gauge

　　In the process of industrial process control and technical measurement, mechanical pressure gauges have become more and more widely used due to their high mechanical strength and convenient production due to their elastic sensitive elements.

　　The elastic sensitive element in the mechanical pressure gauge produces elastic deformation with the change of pressure. Mechanical pressure gauges use sensitive components such as spring tubes (Bourdon tubes), diaphragms, bellows and bellows, and are classified according to this. The measured pressure is generally regarded as relative pressure. Generally, the relative point is selected as atmospheric pressure. The elastic deformation of the elastic element under the action of the medium pressure is amplified by the gear transmission mechanism of the pressure gauge, and the pressure gauge will display the relative value (high or low) relative to the atmospheric pressure. (Guide: Precautions for the operation of wire cutting machine)

　　 The pressure value in the measuring range is displayed by the pointer, and the indication range of the dial is generally set to 270 degrees.

Three, the classification of pressure gauges

　　Pressure gauges can be divided into precision pressure gauges and general pressure gauges according to their measurement accuracy. The measurement accuracy grades of precision pressure gauges are 0.1, 0.16, 0.25, and 0.4 respectively; the measurement accuracy grades of general pressure gauges are 1.0, 1.6, 2.5, and 4.0 grades respectively.

　　Pressure gauges are divided into general pressure gauges, absolute pressure gauges, and differential pressure gauges according to their different standards for indicating pressure. General pressure gauges are based on atmospheric pressure; absolute pressure gauges are based on absolute pressure zero; differential pressure gauges measure the difference between two measured pressures.

　　Pressure gauges are classified into vacuum gauges, pressure vacuum gauges, micro pressure gauges, low pressure gauges, medium pressure gauges and high pressure gauges according to their measuring ranges. The vacuum gauge is used to measure the pressure value less than atmospheric pressure; the pressure vacuum gauge is used to measure the pressure value less than and greater than the atmospheric pressure; the micro pressure gauge is used to measure the pressure value less than 60000 Pa; the low pressure gauge is used to measure the pressure value of 0~6MPa ; The medium pressure gauge is used to measure the pressure value of 10~60MPa; the high pressure gauge is used to measure the pressure value above 100MPa.

　　 The shell of the seismic pressure gauge is made of a fully sealed structure, and the shell is filled with damping oil. Due to its damping effect, it can be used in the measurement place of working environment vibration or medium pressure (load) pulsation.

　　The pressure gauge with electric contact control switch can realize the alarm or control function.

　　The pressure gauge with remote transmission mechanism can provide electrical signals (such as resistance signals or standard DC current signals) needed in industrial engineering.

The isolator (chemical seal) used in the diaphragm meter can isolate the measured medium from the instrument through the isolating diaphragm, so as to measure the pressure of the medium with strong corrosion, high temperature and easy crystallization.

　　The elastic element of the pressure gauge The elastic sensitive element in the mechanical pressure gauge produces elastic deformation with the change of pressure. Mechanical pressure gauges use sensitive components such as spring tubes (Bourdon tubes), diaphragms, bellows, and bellows, and are classified according to this. Sensitive components are generally made of copper alloy, stainless steel or special materials. 

　　Spring tube (Bourdon tube) is divided into C tube, coil tube, spiral tube and other types. Generally, cold work hardening material blank tubes are used, which have high plasticity in the annealed state, and obtain high elasticity and strength after pressure working, cold work hardening and qualitative treatment. Under the action of the pressure in the inner cavity of the spring tube, using its elastic characteristics, the pressure can be conveniently converted into the elastic displacement of the free end of the spring tube. The measuring range of the spring tube is generally 0.1MPa ~ 250MPa.

The diaphragm sensitive element is a circular diaphragm with waves, the diaphragm itself is located between two flanges, or welded on the flange or the edge is clamped between the two flanges. One side of the diaphragm is under the pressure of the measuring medium. In this way, the small bending deformation produced by the diaphragm can be used to indirectly measure the pressure of the medium. The magnitude of the pressure is indicated by the pointer. Compared with the Bourdon tube, the diaphragm has a larger transmission force. Because the diaphragm itself is fixed around the edge, its vibration resistance is better. The diaphragm pressure gauge can achieve high overpressure protection (for example, the diaphragm is attached to the upper flange). The diaphragm can also be coated with a protective coating to improve corrosion resistance. Using open flanges, flushing, openings, etc., diaphragm pressure gauges can be used to measure highly viscous, dirty and crystalline media. The pressure measurement range of the diaphragm pressure gauge is 1600Pa ~ 2.5 MPa. 

　　The sensitive element of the diaphragm box is composed of two diaphragms with a circular wavy cross-section that are buckled together. The pressure of the measuring medium acts on the inside of the capsule cavity, and the resulting deformation can be used to indirectly measure the pressure of the medium. The size of the pressure value is displayed by the pointer. The bellows pressure gauge is generally used to measure the micro pressure of the gas, and has a certain degree of overpressure protection. After several capsule sensitive components are stacked together, they will produce a large transmission force to measure extremely small pressure. The pressure measurement range of the bellows pressure gauge is 250Pa ~ 60000Pa.

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