Why is grade 1.6 used instead of grade 1.5 in the accuracy classes of general pressure gauges?

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The accuracy class of pressure gauges uses the R5 scale. 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. Therefore, 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 system,” which uses powers of 10 to the 1/n power; these include 10 to the 1/5, 1/10, 1/20, 1/40, and 1/80 power, with codes of R5, R10, R20, R40, and R80 respectively. The accuracy class of a pressure gauge is determined using the R5 scale. 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. Therefore, 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 perform a reverse calculation, you can also derive the grades on both sides of a certain accuracy grade 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 information on number systems, please refer to the **standards**. 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: Image. If you do not find such information in relevant books, 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 accuracy 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 facilitate the indication of an instrument’s quality, its accuracy level is commonly used to represent the degree of accuracy of the instrument. The accuracy grade is the maximum reference error with the plus and minus signs as well as the 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 gauge, its accuracy level is commonly used to express the degree of accuracy. The accuracy level is obtained by removing the plus and minus signs as well as 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 the result from the above formula and removing the % sign, we obtain the accuracy class that we see. So how should the existing 1.5-grade 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 0.1 grade, 0.25 grade, and 0.4 grade ； 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) ； Pressure gauges for surfaces above 60 are basically of grade 1.0 or grade 1.6 ； Gauge pressure transmitters with a surface rating of 60 and below are basically of class 2.5 ； Diaphragm box and diaphragm pressure gauges are generally also of grade 2.5 ； The difference between the accuracy and resolution of a pressure gauge: The minimum resolution of a pressure gauge can be broadly considered as its resolution; however, it isn’t necessarily indicative of the gauge’s accuracy. Since a pressure gauge is a measuring instrument, it displays the measured values. There is inevitably some error between these measured values and the actual values; this range of error is essentially what we refer to as accuracy. Therefore, the smaller the accuracy value, the closer the reading on the measuring instrument is to the true value, and thus the higher its reliability. 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 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 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 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 production fields. The selection of pressure gauges should be based on the usage 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 these 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 that value constitutes the chosen range. 3. Selection of pressure gauge types: Different types of pressure gauges must be chosen depending on the medium being measured and the operating environment. (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 compounds, use acetylene pressure gauges and the like. (3) For general corrosive media and environments with corrosive gases, stainless steel pressure gauges can be selected. (4) For measuring the pressure of media that have high viscosity, tend to crystallize, are highly corrosive, operate at high temperatures, or contain suspended solids, 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) 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 relative to the maximum scale value. The larger the range of a pressure gauge, the greater the allowable absolute error in the pressure values it measures, for a pressure gauge 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 relative to the maximum scale value. The larger the range of a pressure gauge, the greater the allowable absolute error in the pressure values it measures, for a pressure gauge of the same accuracy class.