In industrial measurements, the quality of the instrument is expressed for convenience. Therefore, we usually use the accuracy class to indicate the degree of accuracy of a device. The accuracy class is the maximum quoted error minus the positive and negative signs and the percentage sign. At the same time, the accuracy class is one of the most important indicators of the quality of an instrument.
Under normal conditions of use, the degree of accuracy of the meter’s measurement results is called the meter’s accuracy: the smaller the quoted error, the more accurate the instrument. However, the citation error is related to the range of the meter, so when using the same accuracy meter, we should adopt a close range to reduce the measurement error.
1. Coefficient
The R5 number system has been adopted for the accuracy class of pressure gauges. In the past, the pressure gauge class 1.5 was not part of the R5 number system, so it had to be abolished. Now we use 1.6, which is the closest to 1.5, instead. Thus, we no longer have to grade pressure gauges to 1.5.
2. Method of Calculation
The accuracy level of the pressure gauge is the percentage of the allowable error of the full range of the pressure gauge.
For example, a pressure gauge full range of 100Mpa, the accuracy level of 1.6, then its allowable error of 100Mpa × 1.6% = ± 1.6Mpa. If the accuracy level is 1.5, then its acceptable error of 100Mpa × 1.5% = ± 1.5Mpa.
Instrument accuracy = (the maximum value of absolute error / instrument range) * 100%
The above calculation formula takes the absolute value and drops the % is the accuracy level we see.
3. Common Pressure Gauge Accuracy Grades
Precision pressure gauges have an accuracy of 0.1, 0.25, and 0.4.
Common pressure gauge accuracy 1.0 grade, 1.6 grade (formerly 1.5 grade), 2.5 grade, 4.0 grade (basically no more).
Pressure gauges with surfaces above 60 are class 1.0 and 1.6.
Pressure gauges with surfaces of 60 and below are class 2.5.
Diaphragm box and diaphragm pressure gauge are also generally class 2.5.
4. Pressure Gauge Accuracy and Indexing
The minimum index of a pressure gauge can be commonly thought of as its resolution, but it is not necessarily the indicator’s accuracy. Because a pressure gauge is a measuring instrument, the measured value is displayed to us. There is a specific error between the measured and actual values, and the range of this error is the accuracy. So the smaller the accuracy value means that the closer the value displayed by the testing instrument is to the actual value, the more credible it is.
5. Pressure Gauge Accuracy Level Inspection
Pressure gauge accuracy level is the abbreviation of pressure gauge accuracy level or accuracy level. For example, (the GB/T1226-2001 “general pressure gauge” national standard called the accuracy level of the instrument. jjg52-1999 “spring tube type general pressure gauge, pressure vacuum gauge, and vacuum gauge” reached the accuracy level of the device.
About the working conditions, the pressure gauge accuracy level test should include the following four items.
5.1 The error of the displayed value
In the measurement range, the error of the indicated value should not be greater than the permissible error specified in Table II.
5.2 Return error
In the measurement range, the return error should be no greater than the absolute value of the permissible error specified in Table II.
5.3 Tap displacement
After tapping the case, the change in the indicated value of the pointer should be no greater than 1/2 of the absolute value of the permissible error, as specified in Table II.
5.4 Smoothness of the deflection of the pointer
Within the measuring range, the deflection of the information should be smooth, without skipping and jamming.
6. Determination of the Accuracy Level of Pressure Gauges
The accuracy levels of precision pressure gauges are 0.1, 0.16, 0.25, and 0.4, respectively. The accuracy level of the general type pressure gauge is 1.0, 1.6, 2.5, and 4.0 level respectively. The method of selecting the accuracy level of the pressure gauge: we should be based on the production process, economical and practical, testing methods and other requirements put forward, according to the minimum value of the measured pressure required to determine the accuracy level of the permissible error.
7. The Choice of Pressure Gauge Range
In stable pressure measurement, the maximum working pressure should not exceed 2/3 of the range.
The maximum working pressure should not exceed 3/5 of the range when measuring high pressure.
To ensure the accuracy of the measurement, the minimum working pressure should not be less than 1/3 of the range.
According to the above principles, the maximum measured pressure to calculate a value from the pressure gauge range series selected is slightly more significant than the value of the value that is the selected range.
8. The choice of Pressure Gauge Types
Measure different media and use the environment to choose different types of pressure gauge
(1) General media, such as air, water, steam, oil, etc., available ordinary pressure gauge.
(2) For special media, you need to use a unique pressure gauge, such as ammonia with an ammonia pressure gauge. Oxygen class with oxygen pressure gauge. Hydrogen class with pressure gauge, acetylene class with acetylene pressure gauge, and so on.
(3) A stainless steel pressure gauge can be used for general corrosive media and gas environments.
(4) The use of diaphragm type pressure gauge for the measurement of viscosity, easy to crystallize, corrosive, high-temperature liquid, gas, or solid floating medium pressure measurement.
(5) For the pressure measurement of pulsating media and mechanical vibration occasions. Selection of vibration-resistant pressure gauge.
(6) The remote transmission requirements can be used when the remote transmission type pressure gauge, remote signal current type, resistance type, and voltage type.
(7) Control protection requirements can be used for the electric contact pressure gauge.
(8) Explosion-proof requirements must be used when the explosion-proof type, such as explosion-proof electric contact pressure gauge.
The accuracy level of the pressure gauge is divided by its permissible error as a percentage of the dial scale value. The greater the accuracy of the grade, the greater the allowable error of the dial scale limit value. The greater the range of the pressure gauge, the same accuracy level of the pressure gauge. It measured the absolute value of the pressure value of the allowable error is more significant.
9. Conclusion
In industry, we often use pressure gauges with an accuracy of 2.5 and 1.6. If it is 1.0 and 0.5 class, it belongs to the high-precision pressure gauge. now there are digital pressure gauges have reached 0.25 class.
The accuracy level of the pressure gauge is divided by its permissible error as a percentage of the dial scale value. The greater the number of accuracy grades, the greater the allowable error as a percentage of the dial scale limit value. The greater the pressure gauge range, the greater the permissible error in the absolute value of the pressure value measured by the indicator of the same accuracy level.
