Introduction to Pressure Gauge Selection

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The accuracy class of a pressure gauge is an abbreviation for its degree of precision or accuracy. The standard GB/T1226 \"General Pressure Gauges\" refers to it as the instrument’s precision class, while JJG52 \"Spring Tube General Pressure Gauges, Pressure-Vacuum Gauges, and Vacuum Gauges\" calls it the instrument’s accuracy class. The accuracy class of a pressure gauge is expressed as a percentage of the allowable error relative to the gauge’s range; it is generally divided into seven classes: 0.5, 1, 1.5, 2, 2.5, 3, and 4 (classes 3 and 4 are not used in boilers). The smaller the value, the higher the precision of the gauge. For example, for a pressure gauge with a range of 0–2.5 MPa and an accuracy class of 2.5, the allowable error between the pressure value indicated by the pointer and the actual pressure of the medium being measured shall not exceed 2.5 MPa × 2.5% = ±0.0625 MPa ； When the pressure gauge indicates a pressure of 0.8 MPa, the actual air pressure lies between 0.7375 and 0.8625 MPa. It can be seen that the magnitude of the actual error of a pressure gauge is related not only to its precision but also to its range. When the range is the same, the higher the precision (i.e., the smaller the number), the smaller the allowable error of the pressure gauge. At the same accuracy level, the larger the range, the greater the error of the pressure gauge. Selection of pressure gauges: The selection of pressure gauges should be based on the requirements of use. While meeting the technical specifications of the process, it is necessary to take a comprehensive approach guided by the principles of economy and practicality, in order to properly choose the accuracy level, range, type, and model. 1. Determination of the accuracy class of pressure gauges: The accuracy classes for precision pressure gauges are 0.1, 0.16, 0.25, and 0.4 ； The accuracy classes of general-purpose pressure gauges are 1.0, 1.6, 2.5, and 4.0. Method for selecting the accuracy class of a pressure gauge: The accuracy class should be determined based on the requirements arising from the production process, economic practicality, testing methods, etc., as well as the allowable error required for the minimum pressure to be measured. 2. Selection of the pressure gauge range: (1) When measuring a steady pressure, the maximum operating pressure should not exceed 2/3 of the range. (2) When measuring pulsating pressure, the maximum operating pressure should not exceed 1/2 of the range. (3) When measuring high pressures, the maximum operating pressure should not exceed 3/5 of the range. (4) To ensure measurement accuracy, the minimum operating pressure should be no less than 1/3 of the range. Following these principles, after calculating a value based on the maximum pressure to be measured, a value slightly greater than this figure is selected from the pressure gauge range series, and this is the chosen range. Selection of pressure gauge types: Different types of pressure gauges must be chosen depending on the medium being measured and the operating environment. (1) For ordinary media such as air, water, steam, oil, etc., standard pressure gauges can be used. (2) Special pressure gauges are required for special media; for example, ammonia-specific pressure gauges are used for ammonia ； Pressure gauge for oxygen use in oxygen-related applications ； Gauge for hydrogen-related applications ； For acetylene compounds, use acetylene pressure gauges and the like. (3) For general corrosive media and environments with corrosive gases, stainless steel pressure gauges can be used. (4) For measuring the pressure of liquids, gases, or media containing suspended solids that have high viscosity, tend to crystallize, are highly corrosive, or are at high temperatures, diaphragm pressure gauges should be used. (5) Pressure measurement in pulsed media and mechanical vibration applications. Choose a shock-resistant pressure gauge. (6) When remote transmission is required, a remote-transmission type pressure gauge can be used; the remote transmission signals come in current type, resistance type, and voltage type. (7) Electric contact pressure gauges can be used when control and protection requirements are present. (8) When explosion protection is required, an explosion-proof model must be selected, such as an explosion-proof electric contact pressure gauge.