A pressure meter is an instrument that measures the pressure of the medium in the pipeline. The commonly used pressure measurement methods include liquid column pressure measurement, elastic type pressure measurement and electric pressure measurement. Liquid column pressure measurement is based on hydrostatics, and generally adopts U-shaped tube or single tube filled with water or mercury. The elastic type change method is that when the measured pressure acts on the elastic element, the elastic element will produce corresponding deformation, and the pressure can be measured according to the deformation of the urine and stool; The method of electric pressure measurement is to convert the measured pressure directly into an electrical signal through the conversion element, which is divided into magnetic, piezoelectric, capacitive, inductive and resistance strain forms according to the different conversion elements.
Pressure gauge according to its measuring accuracy can be divided into precision pressure gauge, general pressure gauge; The measuring accuracy of the precision pressure gauge is 0.1, 0.16, 0.25, 0.4. The measuring accuracy of the general pressure gauge is 1.0, 1.6, 2.5, 4.0. Pressure gauge according to its indicating pressure benchmark is different, divided into general pressure gauge, absolute pressure gauge, differential pressure gauge, general pressure gauge to atmospheric pressure as the benchmark, absolute pressure gauge to absolute pressure zero as the benchmark, differential pressure gauge to measure the difference between the two measured pressures. According to its measuring range, the pressure gauge is divided into vacuum gauge, pressure gauge, micro pressure gauge, low pressure gauge, medium pressure gauge and high pressure gauge. The vacuum gauge is used to measure the pressure value of less than atmospheric pressure, the pressure gauge is used to measure the pressure value of less than and greater than atmospheric pressure, the micro pressure gauge is used to measure the pressure value of less than 60000 Pa, and 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 to 60MPa, and the high pressure gauge is used to measure the pressure value of more than 100 mpa. Pressure gauges are divided into pointer pressure gauges and digital pressure gauges according to their display mode. Pressure gauge according to its use function is divided into local indication type pressure gauge and live signal control type pressure gauge, general pressure gauge, vacuum pressure gauge, shock-proof pressure gauge, stainless steel pressure gauge, etc. are local indication type pressure gauge, in addition to indicating pressure, no other control function. Pressure gauges can be divided into general pressure gauges, corrosion-resistant pressure gauges, explosion-proof pressure gauges, special pressure gauges according to the characteristics of the measuring medium. General pressure gauges are used to measure the pressure of liquid, gas or steam without explosion, crystallization or solidification on copper and copper alloy. Corrosion-resistant pressure gauge is used to measure the pressure of corrosive media, commonly used stainless steel pressure gauge, diaphragm pressure gauge, etc. Explosion-proof pressure gauges are used in dangerous places with explosive mixtures in the environment, such as explosion-proof electric contact pressure gauges, explosion-proof transmitters, etc. Special pressure gauge for special medium occasions, due to the particularity of the measured medium, the pressure gauge should have a specified color code, and indicate the name of the special medium, oxygen table must be marked with red "no oil" words, hydrogen with dark green horizontal line color code, ammonia with yellow horizontal line color code and so on. Pressure gauge according to the use of elastic components can be divided into spring tube pressure gauge (C-tube, spiral tube, coil spring tube), diaphragm pressure gauge, diaphragm box pressure gauge and bellows pressure gauge. Pressure gauge installation methods are threaded connection, disc connection, flange connection, clamp connection and so on. Typical pressure gauges are shown below.
The selection of pressure gauge should be based on the requirements of the process production process for pressure measurement, combined with other aspects of the situation, to be comprehensively considered and specific analysis, generally considering the type of instrument, measurement range, accuracy level and the use of the environment and media performance. The selection of the measuring range determines the measuring range of the instrument according to the size of the measured pressure. For elastic pressure gauges, when measuring the stable pressure, the maximum pressure value should not exceed 3/4 of the full scale, when measuring the fluctuating pressure, the maximum pressure value should not exceed 2/3 of the full scale, and the minimum measuring pressure value should not be less than 1/3 of the full scale. The precision selection should be based on the maximum measurement error allowed by the production, and the accuracy level of the instrument should be determined by the principle of economy and practicality. The accuracy of the pressure gauge used in the low-pressure pipeline should not be less than 2.5; The accuracy of pressure gauge used in medium and high pressure pipelines shall not be less than 1.6. Considering the use environment and medium performance, the environmental conditions are harsh, such as high temperature, corrosion, humidity, vibration, etc. The performance of the measured medium, such as the temperature, corrosion, easy crystallization, flammable, explosive, etc., in order to determine the type and model of the pressure gauge. The surface diameter of the pressure gauge indicated on the spot is generally 100mm, and the surface diameter is 200 ~ 250mm in the case of high standards or poor lighting conditions, and the diameter of the disc table is 150mm. After use, the pressure instrument shall be periodically checked according to the relevant regulations and standards of measurement to ensure that the pressure instrument used is within the validity period of the check.