Pressure gauge refers to an instrument that uses elastic elements as sensitive components to measure and indicate pressures higher than ambient pressure. It is widely used in almost all industrial processes and scientific research fields. It can be seen everywhere in fields such as thermal pipelines, oil and gas transmission, water and gas supply systems, vehicle maintenance and repair shops, etc. Especially in industrial process control and technical measurement processes, the elastic sensitive components of mechanical pressure gauges have high mechanical strength and convenient production characteristics, making them increasingly widely used. Working principle: The pressure gauge transmits the pressure deformation to the pointer through the elastic deformation of the sensitive components (Bourdon tube, bellows, bellows) inside the gauge, and then the conversion mechanism of the movement inside the gauge transmits the pressure deformation to the pointer, causing the pointer to rotate to display the pressure. Selection principle: The selection of pressure gauges should be based on the production requirements of the usage process, and specific analysis should be conducted according to the specific situation. On the premise of meeting the process requirements, comprehensive consideration should be given to the principle of conservation. Generally, the following aspects should be considered: 1. Selection of types The selection of instrument types must meet the requirements of process production. For example, whether remote transmission, automatic recording, or alarm are required; Whether the properties of the measured medium (such as temperature, viscosity, corrosiveness, degree of dirt, flammability and explosiveness) have special requirements for the instrument, and whether the on-site environmental conditions (such as humidity, temperature, magnetic field strength, vibration, etc.) have requirements for the type of instrument. Therefore, selecting the appropriate instrument type according to process requirements is an important prerequisite for ensuring the normal operation and safe production of instruments. For example, the spring tube of ordinary pressure gauges is mostly made of copper alloy (alloy steel is used for high-pressure gauges), while the material of the spring tube of ammonia pressure gauges is carbon steel (or stainless steel), and copper alloy is not allowed to be used. Because ammonia reacts chemically with copper and can explode, ordinary pressure gauges cannot be used for ammonia pressure measurement.
Oxygen pressure gauges can be identical in structure and material to regular pressure gauges, except that oxygen pressure gauges must be oil free. Because oil entering the oxygen system can easily cause explosions. When calibrating the oxygen pressure gauge, oil should not be used as the working medium like ordinary pressure gauges, and the oxygen pressure gauge should be strictly avoided from coming into contact with oil stains during storage. If it is necessary to use existing pressure gauges with oil stains to measure oxygen pressure, they must be repeatedly cleaned with carbon tetrachloride before use and carefully inspected until there is no oil stain. 2. In order to ensure the reliable operation of the elastic element within the safe range of elastic deformation, the determination of the measurement range of the pressure gauge must be based on the size of the measured pressure and the speed of pressure change, leaving enough room. Therefore, the upper limit value of the pressure gauge should be higher than the maximum pressure value that may be possible in the process production. According to the "Technical Regulations for Chemical Automation Design", when measuring stable pressure, the maximum working pressure should not exceed 2/3 of the measurement upper limit value; When measuring pulsating pressure, the maximum working pressure should not exceed 1/2 of the measurement upper limit value; When measuring high pressure, the maximum working pressure should not exceed 3/5 of the measurement upper limit. The minimum value of the measured pressure should generally not be less than one-third of the upper limit value of the instrument measurement. To ensure a linear relationship between the output and input of the instrument, the upper and lower limits of the instrument are calculated based on the maximum and minimum values of the measured parameter, and cannot be directly used as the measurement range of the instrument. When selecting the upper limit value of the instrument scale, we should choose from the standard series specified by the country. The standard series of pressure gauge measurement range in China includes: -0.1-0.06, 0.15; 0-1,1.6,2.5,4,6,10X10 "MPa (where n is a natural integer and can be positive or negative). 3. The selection of accuracy level is based on the maximum absolute error allowed by the production process and the selected instrument range. The maximum allowable reference error of the instrument is calculated, and the accuracy of the instrument is determined in the national prescribed accuracy level. Generally speaking, the more precise the instrument selected, the more accurate and reliable the measurement results will be. But it cannot be assumed that the higher the accuracy of the selected instrument, the better, because more precise instruments are generally more expensive, and the operation and maintenance are more complicated.
