Why is the accuracy level of a general pressure gauge set to 1.6 instead of 1.5?
We need to understand the basic knowledge of priority number systems in standardization technology. For number systems, the national standard GB/T321 specifies the "priority number system", which uses a common ratio of 10 to the power of 1/n, with powers of 1/5, 1/10, 1/20, 1/40, and 1/80 of 10, respectively. The codes are R5 R10、R20、R40、R80。 The accuracy level of the pressure gauge is based on the R5 number system.
The common ratio of the R5 number system is: 1/5 power of 10=1.60. The numbers in the number system include: 1.0, 1.6, 2.5, 4.0, 6.3, and 10. The previous pressure gauge level of 1.5 did not belong to the R5 number system, so it must be abolished and replaced with 1.6, which is closest to 1.5. So now it is no longer allowed to grade pressure gauges as 1.5.
The ratio of two adjacent numbers is equal to the common ratio of the R5 number system, which is 1.6. For example, 10/6.3=1.6, 6.3/4=1.6, 4/2.5=1.6, 2.5/1.6=1.6, 1.6/1=1.6, and further down: 1/0.63=1.6, 0.63/0.4=1.6, 0.4/0.25=1.6, 0.25/0.16=1.6, 0.25/0.16=1.6.
Of course, if you perform reverse calculation, you can also derive the levels on both sides of a certain accuracy level after rounding. For example, at level 2.5, the one level higher is 2.5 ÷ 1.6=1.6, and the one level lower is 2.5 × 1.6=4. For detailed knowledge about number systems, please refer to the national standards.
At the same time, the corresponding provisions for the accuracy level of pressure gauges are also described in the standard GB/T1226-2010 GB/T 1226-2010 General Pressure Gauge:
The accuracy level of a pressure gauge refers to the percentage of allowable error of the pressure gauge to the full range.
For example, if a pressure gauge has a full range of 100Mpa and an accuracy level of 1.6, its allowable error is 100Mpa × 1.6%=± 1.6Mpa. If the accuracy level is set to 1.5, its allowable error is 100Mpa × 1.5%=± 1.5Mpa.
The accuracy of the instrument measurement results under normal usage conditions is called the accuracy of the instrument. The smaller the reference error, the higher the accuracy of the instrument, and the reference error is related to the range of the instrument. Therefore, when using instruments with the same accuracy, it is often necessary to compress the range to reduce measurement errors. In industrial measurement, in order to facilitate the representation of the quality of instruments, accuracy levels are usually used to indicate the accuracy of instruments. The accuracy level is the maximum citation error minus positive, negative, and percentage signs. Accuracy level is one of the important indicators for measuring the quality of instruments.
In industrial measurement, in order to facilitate the representation of instrument quality, accuracy level is usually used to indicate the accuracy of the instrument. Accuracy level is the maximum reference error minus positive, negative, and percentage signs. Accuracy level is one of the important indicators for measuring the quality of instruments.
Instrument accuracy=(maximum absolute error/instrument range) * 100%
The above calculation formula takes the absolute value and removes% to obtain the accuracy level we see.
According to the current national standard for pressure gauges, the accuracy level is 1.6. For 1.5-level pressure gauges in use, the allowable error is calculated at level 1.6, and the accuracy level may not be changed.
Precision pressure gauges have precision levels of 0.1, 0.25, and 0.4;
The accuracy of ordinary pressure gauges is 1.0 level, 1.6 level (formerly 1.5 level), 2.5 level, 4.0 level (basically no longer available);
Pressure gauges with surfaces above 60 are generally rated at 1.0 and 1.6 levels;
Pressure gauges with surfaces of 60 and below are generally rated at 2.5 levels;
Diaphragm boxes and diaphragm pressure gauges are generally rated at 2.5;
The minimum division of a pressure gauge can be commonly referred to as its resolution, but it does not necessarily mean the accuracy of the gauge.
Because the pressure gauge is a detection instrument, it displays the measured value to us. There is a certain error between the measured value and the true value, and the range of this error is actually the accuracy. Therefore, the smaller the accuracy value, the closer the displayed value of the detection instrument is to the true value, and the higher the credibility.
Accuracy grade inspection of pressure gauge
The precision level of a pressure gauge is the abbreviation for the precision level or accuracy level of a pressure gauge. The national standard GB/T1226-2001 "General Pressure Gauge" refers to it as the precision level of an instrument, while JJG52-1999 "Spring Tube General Pressure Gauge, Pressure Vacuum Gauge, and Vacuum Gauge" refers to it as the accuracy level of an instrument.
Under reference working conditions, the accuracy level inspection of pressure gauges should include the following four items:
1. Indication error
Within the measurement range, the indication error should not exceed the allowable error specified in Table 2.
2. Return error
Within the measurement range, the return error should not exceed the absolute value of the allowable error specified in Table 2.
3. Lightly tap displacement
After tapping the case lightly, the change in pointer reading should not exceed 1/2 of the absolute allowable error specified in Table 2.
4. Pointer deflection stability
Within the measurement range, the pointer deflection should be stable, without jumping or jamming.
The accuracy level of a pressure gauge is expressed as the percentage of allowable error to the pressure gauge range, generally divided into seven levels: 0.5, 1, 1.6, 2, 2.5, and 3.4 (levels 3 and 4 are not used on boilers). The smaller the value, the higher the accuracy. For example, for a pressure gauge with a dial range of 0-2.5MPa and an accuracy level of 2.5, the allowable error between the pressure value indicated by its pointer and the actual pressure value of the measured medium shall not exceed 2.5MPax2.5%=± 0.0625MPa; When the pressure gauge indicates a pressure of 0.8 MPa, the actual air pressure is between 0.7375 and 0.8625 MPa.
From this, it can be seen that the actual error of a pressure gauge is not only related to its accuracy, but also to the range size of the pressure gauge. When the range is the same, the higher the accuracy (i.e. the smaller the number), the smaller the allowable error of the pressure gauge. When the accuracy is the same, the larger the range, the greater the error of the pressure gauge.
Pressure gauges are common measuring instruments widely used in various production fields. The selection of pressure gauges should be based on usage requirements, and on the premise of meeting process technology requirements, it should be comprehensively considered in a practical and economical manner, to achieve a reasonable selection of accuracy level, range, type, and model.
1. Determination of Accuracy Grade of Pressure Gauge
The precision levels of precision pressure gauges are 0.1, 0.16, 0.25, and 0.4, respectively; The accuracy levels of general pressure gauges are 1.0, 1.6, 2.5, and 4.0, respectively. The method for selecting the accuracy level of a pressure gauge should be based on the requirements of production technology, economic practicality, testing methods, etc., and the allowable error required for the minimum value of the measured pressure should be used to determine the accuracy level.
2. Selection of pressure gauge range
(1) When measuring stable pressure, the maximum working pressure should not exceed 2/3 of the range.
(2) When measuring pulsating pressure, the maximum working pressure should not exceed 1/2 of the measuring range
(3) When measuring high pressure, the maximum working pressure should not exceed 3/5 of the 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 pressure being measured, select a value slightly larger than this value from the pressure gauge range series as the selected range.
3. Selection of pressure gauge types
Different types of pressure gauges should be selected for measuring different medium and usage environments
(1) Ordinary pressure gauges can be used for general medium such as air, water, steam, oil, etc.
(2) For special medium, specialized pressure gauges are required, such as ammonia pressure gauges for ammonia; Oxygen pressure gauge for use with oxygen; Pressure gauges for hydrogen gas; Acetylene type uses acetylene pressure gauges, etc.
(3) For general corrosive medium and corrosive gas environments, stainless steel pressure gauges can be used.
(4) For pressure measurement of liquids, gases, or media with high viscosity, easy crystallization, high corrosiveness, and high temperature, diaphragm pressure gauges are selected.
(5) For pressure measurement in pulsed medium and mechanical vibration scenarios. Choose a shock resistant pressure gauge.
(6) When there is a requirement for remote transmission, a remote transmission pressure gauge can be selected. Remote transmission signals include current type, resistance type, and voltage type.
(7) When there is a requirement for control and protection, an electric contact pressure gauge can be used.
(8) When there are explosion-proof requirements, explosion-proof types must be selected, such as explosion-proof electrical contact pressure gauges.
The accuracy level of a pressure gauge is divided by the percentage of its allowable error to the dial scale value, and the larger the accuracy level, the greater the allowable error to the dial scale limit value. The larger the range of a pressure gauge, the greater the allowable error in the absolute value of the pressure measured by a pressure gauge of the same accuracy level.
Usage in industry: The accuracy of commonly used pressure gauges is 2.5 and 1.6 levels. If they are 1.0 and 0.5 levels, they belong to high-precision pressure gauges. Some digital pressure gauges now reach 0.25 levels. The accuracy level of a pressure gauge is divided by the percentage of its allowable error to the dial scale value, and the larger the accuracy level, the greater the allowable error to the dial scale limit value. The larger the range of a pressure gauge, the greater the allowable error in the absolute value of the pressure measured by a pressure gauge of the same accuracy level.
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