Introduction to Pressure Gauge Selection

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The meaning of the accuracy class of a pressure gauge: 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 accuracy. 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 accuracy 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. II. Pressure gauges are common measuring instruments that are widely used in various production fields. The selection of pressure gauges should be based on the operational requirements, and 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 grade, 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 respectively. 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., in accordance with 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 one is selected from the pressure gauge range series, and that value constitutes the chosen range. 3. Selection of pressure gauge types: Different types of pressure gauges must be used to measure various media and in different operating environments. 1) For common media such as air, water, steam, oil, etc., ordinary pressure gauges can be used. 2) For special media, specialized pressure gauges are required; for example, ammonia-based media require ammonia-specific pressure gauges ； Pressure gauge for oxygen use in oxygen-related applications ； Gauge for hydrogen-related applications ； For acetylene-based applications, acetylene pressure gauges and the like are used. 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) An electric contact pressure gauge 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.