Accuracy of pressure gauge

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The accuracy class of pressure gauges uses the R5 series. In the past, 1.5, which falls within the pressure gauge range, was not a number in the R5 series; therefore it had to be eliminated, and 1.6, which is the closest to 1.5, was used in its place. So it is no longer allowed to classify pressure gauges as Class 1.5. Why is the accuracy class of pressure gauges 1.6? Why is grade 1.6 used instead of grade 1.5 in the accuracy classes of general pressure gauges? 　 It is necessary to understand the basic knowledge of priority number systems in standardization technology. For number systems, **the standard GB/T321 defines the “priority number systems,” which use powers of 10 with a base of 10; these include 10^1/5, 10^1/10, 10^1/20, 10^1/40, and 10^1/80, with the corresponding codes being R5, R10, R20, R40, and R80 respectively. The accuracy class of pressure gauges is based on the R5 numbering system. The common ratio of the R5 number system is: 10 to the 1/5 power = 1.60. The numbers in the number system include: 1.0, 1.6, 2.5, 4.0, 6.3, 10. In the past, 1.5, which falls within the pressure gauge range, was not a number in the R5 series; therefore it had to be eliminated, and 1.6, which is the closest to 1.5, was used in its place. So it is no longer allowed to classify pressure gauges as Class 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 it can go on: 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 do the reverse calculation, you can also deduce the grades on either side of a certain accuracy level after rounding. For example, at level 2.5, the level one higher is 2.5÷1.6=1.6 level, and the level one lower is 2.5×1.6=4 level. For detailed knowledge on number systems, please read the **standard**. At the same time, the standard GB/T1226-2010, which pertains to general pressure gauges, also specifies the requirements regarding the accuracy grades of such gauges. If you do not find such information in relevant documents, always follow the latest national standards! What is the difference between pressure gauge accuracy classes 1.6 and 1.5? The accuracy class of a pressure gauge refers to the percentage of the full scale range for which the allowable error is permitted. For example, if a pressure gauge has a full scale range of 100 Mpa and an accuracy class of 1.6, then its allowable error is 100 Mpa × 1.6% = ±1.6 Mpa. If the precision grade is 1.5, then its allowable error is 100 Mpa × 1.5% = ±1.5 Mpa. Under normal operating conditions, the degree of accuracy of the measurements taken by an instrument is referred to as the instrument’s accuracy. The smaller the reference error, the higher the accuracy of the instrument. Since the reference error is related to the instrument’s range, when using instruments with the same level of accuracy, it is common to reduce the range in order to minimize measurement errors. In industrial measurement, to conveniently indicate the quality of a instrument, its accuracy level is typically used to represent the degree of accuracy of that instrument. The accuracy grade is the maximum reference error with the plus and minus signs and percent sign removed. The accuracy class is one of the important indicators for measuring the quality of instruments. In industrial measurement, to indicate the quality of a measuring instrument, its accuracy level is commonly used to represent the degree of accuracy. The accuracy level is obtained by removing the plus or minus sign and the percent sign from the maximum allowable error. The accuracy class is one of the important indicators for measuring the quality of instruments. Instrument accuracy = (Maximum absolute error / Instrument range) * 100%. By taking the absolute value of this formula and removing the % sign, we obtain the accuracy grade that is shown. So how should the existing 1.5 class pressure gauges be defined? According to the current standards for pressure gauges, the accuracy class is 1.6; for pressure gauges of class 1.5 that are in use, the allowable error can be calculated based on the 1.6 class standard, without the need to change the accuracy class. Common accuracy grades for pressure gauges: Precision pressure gauges come in accuracy grades of 0.1, 0.25, and 0.4 ； The accuracy grades for ordinary pressure gauges are 1.0 grade, 1.6 grade (formerly 1.5 grade), 2.5 grade, and 4.0 grade (almost none available anymore) ； Gauge pressure transmitters with a surface pressure of over 60 are generally of grade 1.0 or grade 1.6 ； Gauge pressure transmitters with a scale of 60 and below are generally of class 2.5 ； Diaphragm box and diaphragm pressure gauges are generally also of grade 2.5 ； The difference between pressure gauge accuracy and division. The minimum division of a pressure gauge can be simply considered as its resolution, but it is not necessarily the gauge’s accuracy. Since a pressure gauge is a measuring instrument, it displays the measured values to us. There is a certain error between these measured values and the actual values, and the range of this error is what constitutes the accuracy. The lower the accuracy value, the closer the reading shown by the measuring instrument is to the actual value, meaning its reliability is higher. Inspection of the accuracy class of pressure gauges: The accuracy class of a pressure gauge is an abbreviation for its level of precision or accuracy. The standard GB/T1226-2001 \"General Pressure Gauges\" refers to it as the instrument’s precision class, while JJG52-1999 \"Spring Tube General Pressure Gauges, Pressure-Vacuum Gauges, and Vacuum Gauges\" calls it the instrument’s accuracy class. Under reference operating conditions, the accuracy class verification of pressure gauges shall include the following four items: 1. Indication error – Within the measurement range, the indication error shall not exceed the allowable error specified in Table 2. 2. Return error: Within the measurement range, the return error shall not exceed the absolute value of the allowable error specified in Table 2.  3. Tap displacement: After tapping the watch case, the change in the pointer’s reading should not exceed 1/2 of the absolute value of the allowable error specified in Table 2. 4. Stability of pointer deflection: Within the measurement range, the pointer’s deflection should be stable, without any jumping or sticking. 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, 1.6, 2, 2.5, 3, and 4 (classes 3 and 4 are not used in boilers). The lower 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 is 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. At the same range, 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: Pressure gauges are common measuring instruments that are widely used in various manufacturing fields. The selection of pressure gauges should be based on the application 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 grades 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 the above 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.   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 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-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. Use 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. The accuracy class of a pressure gauge is determined by the percentage of its allowable error relative to the scale values on the gauge face; the higher the accuracy class, the greater the allowable error in relation to the maximum scale value. The larger the range of a pressure gauge, the greater the allowable error in the absolute value of the pressure readings it can provide, for pressure gauges of the same accuracy class. Use in industry: The accuracy grades of pressure gauges commonly used are 2.5 and 1.6; those with grades of 1.0 and 0.5 are considered high-precision pressure gauges. Some digital pressure gauges now achieve an accuracy grade of 0.25. The accuracy class of a pressure gauge is determined by the percentage of its allowable error relative to the scale values on the gauge face; the higher the accuracy class, the greater the allowable error in relation to the maximum scale value. The larger the range of a pressure gauge, the greater the allowable error in the absolute value of the pressure readings it can provide, for pressure gauges of the same accuracy class.