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. 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 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 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 derive the grades on either side of a certain accuracy level after rounding. For example, for a level of 2.5, the level one higher is 2.5÷1.6=1.6, and the level one lower is 2.5×1.6=4. For detailed knowledge on number systems, please read 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. 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 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 class 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. Click to view--Summary of Chemical Engineering Skill Training Courses in 2023. In industrial measurement, the accuracy grade is commonly used to indicate the precision of instruments, and it is obtained by removing the plus or minus sign 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%. Taking the absolute value of this formula and removing the % gives us the accuracy grade that we see. So how should the existing 1.5-grade pressure gauges be defined? According to current standards for pressure gauges, the accuracy class is 1.6. For pressure gauges currently in use with an accuracy class of 1.5, the permissible error may be calculated based on class 1.6; thus, the accuracy class need not be changed. Common accuracy grades for pressure gauges: Precision pressure gauges come in accuracy grades of 0.1, 0.25, and 0.4 ； The accuracy classes for ordinary pressure gauges are 1.0, 1.6 (previously 1.5), 2.5, and 4.0 (rarely seen nowadays) ； Gauge pressure transmitters with a surface pressure of over 60 are basically 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 value to us. There is a certain error between the measured value and the actual value, and the range of this error is what constitutes the accuracy. The lower the accuracy value, the closer the reading displayed 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 precision level or accuracy level. The standard GB/T1226-2001 \"General Pressure Gauges\" refers to it as the instrument’s precision level, while standard JJG52-1999 \"Spring Tube General Pressure Gauges, Pressure-Vacuum Gauges, and Vacuum Gauges\" calls it the instrument’s accuracy level. Under reference operating conditions, the inspection of the accuracy class of pressure gauges shall include the following four items: 1. Indication error: Within the measurement range, the indication error shall not exceed the permissible 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. When the range is the same, 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 measurement 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 application requirements. On the premise of meeting process technical requirements, a comprehensive consideration should be given in accordance with the principles of economy and practicality, so as to make a reasonable choice regarding the accuracy class, measurement 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 classes of general-purpose pressure gauges are 1.0, 1.6, 2.5, and 4.0. Method for selecting the accuracy class of a pressure gauge: The accuracy class should be determined based on the allowable error required for the minimum measured pressure, in accordance with requirements stemming from the production process, economic feasibility, testing methods, etc. 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, select from the range of pressure gauge scales a value that is slightly greater than this calculated value; this will be the chosen scale. 3. Selection of pressure gauge types: Different types of pressure gauges should be selected depending on the medium being measured and the operating environment. (1) For common media such as air, water, steam, oil, etc., ordinary pressure gauges can be used. (2) For special media, special pressure gauges must be used; for example, ammonia requires an ammonia-specific pressure gauge ； Pressure gauge for oxygen use in oxygen-related applications ； Pressure gauges for hydrogen gas ； For acetylene, use an acetylene pressure gauge, etc. (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) For pressure measurement in pulsed media and situations involving mechanical vibrations. 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) When control and protection requirements exist, an electric contact pressure gauge can be selected. (8) When explosion-proof requirements apply, an explosion-proof type 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 error in the absolute value of the pressure readings it provides, 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 relative 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 provides, for pressure gauges of the same accuracy class.