Pressure gauges are common measuring instruments widely used in various production fields. The selection of pressure gauges should be based on usage requirements and should be comprehensively considered in accordance with the principles of economy and practicality, while meeting the requirements of process technology. This includes the selection of accuracy grade, measuring range, type, and model.
Determination of Pressure Gauge Accuracy Grade
The method of selecting the accuracy grade of a pressure gauge is to determine the accuracy grade based on the permissible error required by the measured minimum pressure, according to the requirements of production technology, economic practicality, and detection methods. Generally, pressure gauges, membrane box pressure gauges, and diaphragm pressure gauges for measurement purposes should be selected as 1.6 or 2.5 grades. Precision measuring pressure gauges should be selected as 0.4, 0.25, or 0.16 grades.
Selection of Pressure Gauge Measuring Range
(1) When measuring stable pressure, the maximum working pressure should not exceed two-thirds of the measuring range.
(2) When measuring pulsating pressure, the maximum working pressure should not exceed one-half of the measuring range.
(3) When measuring high pressure, the maximum working pressure should not exceed three-fifths of the measuring range.
(4) To ensure measurement accuracy, the minimum working pressure should not be less than one-third of the measuring range.
According to the above principles, after calculating a value based on the maximum measured pressure, select a measuring range that is slightly larger than the calculated value from the pressure gauge measuring range series.
Selection of Pressure Gauge Type
Different types of pressure gauges should be selected for measuring different media and using environments:
(1) For general media such as air, water, steam, and oil, ordinary pressure gauges can be used.
(2) Special pressure gauges are needed for special media, such as ammonia pressure gauges for ammonia, oxygen pressure gauges for oxygen, and acetylene pressure gauges for acetylene.
(3) For general corrosive media and environments with corrosive gases, stainless steel pressure gauges can be selected.
(4) For pressure measurement of liquids, gases, or media with solid suspended matter that have high viscosity, are prone to crystallization, have high corrosiveness, and high temperature, diaphragm pressure gauges produced by professional pressure gauge suppliers should be used.
(5) Vibration-resistant pressure gauges should be selected for pressure measurement in pulsating media and mechanical vibration environments.
(6) Remote transmission pressure gauges can be selected for remote transmission requirements, and remote transmission signals can be of current, resistance, or voltage types.
(7) Electric contact pressure gauges can be selected for control and protection requirements.
(8) Explosion proof pressure gauge must be selected for explosion-proof requirements, such as explosion-proof electric contact pressure gauges.
The accuracy grade of a pressure gauge is divided according to the percentage of the allowable error to the scale value on the dial. The larger the number of accuracy grades, the larger the allowable error percentage to the scale limit value of the dial. The larger the measuring range of a pressure gauge, the larger the absolute error allowed in the pressure value measured by the pressure gauge of the same accuracy grade.
In industry, the accuracy of commonly used pressure gauges is 2.5 and 1.6 grades, and those with 1.0 and 0.5 grades are high-precision pressure gauges. Some digital pressure gauges now reach an accuracy of 0.25 grade.