Pressure gauge rating issue

The range of the pressure gauge selected is incorrect; there is no pressure gauge with a range of 675 kPa – it should be 600 kPa. A precision of 1.5% is acceptable.

The range of pressure gauges is usually an integer, such as 0.1 MPa, 0.2 MPa, 0.6 MPa, and so on

Speaking purely on the merits of the calculation, 675＞450, and 675×1.5%＝10.125＜12.5; there’s nothing wrong with it – it’s appropriate. Objectively speaking, there are also specification standards for the range of instruments. . . It’s not that the teacher who sets the questions decides what range is desired, and then the factory will produce a device with that range. . . The instrument factory does not have a model with a range of 675 kPa. Is this just theoretical talk? This teacher who creates the questions seems to know too little about the instrumentation industry.

Also, regarding the pressure gauge grades, I’ve seen grades such as 1.0, 1.6, 2.5… I’ve never heard of a 1.5 grade before. The grades are regulated by standards; it’s necessary to check the relevant metrological regulations to find out whether there really is a 1.5 grade specified in the national standards! Accuracy level – one must not make things up arbitrarily; those who do so are nothing but scoundrels and riffraff. :lol

This post was last edited by myface on 2018-11-12 at 15:59. It’s likely an old exam question that hasn’t been updated. A quote from the Internet: “Why is grade 1.6 used instead of grade 1.5 in the accuracy classes of ordinary 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 range of pressure gauge values, 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 as its replacement. 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 information on number systems, please read the **standards**. At the same time, the relevant regulations regarding the accuracy grades of pressure gauges are also specified in the standard GB/T1226-2010 for general pressure gauges; if you do not find such information in relevant books, always follow the latest national standards! " ___________________________________________ Furthermore, JJG52-2013 specifies that: for pressure gauges of class 1.5 in use, the maximum allowable error is calculated as if it were a class 1.6 gauge, while the accuracy class may remain unchanged. ” ##########################################################

This post was last edited by It will be better tomorrow on 2018-11-12 at 16:05. 450/(2/3)=675KPa; the value can be reduced to 600KPa when going downward, and increased to 1000KPa when going upward. Clearly, a range of 600KPa is more appropriate. Since the original specification states that a maximum measurement error of ±12.6 KPa is allowed in actual operation, and the operating pressure under actual conditions is 450 KPa, the calculation is as follows: 12.6/450 = 0.028, which is 2.8%. When using a standard accuracy class of 2.5, the calculated error for a range of 600 KPa exceeds 12.6 KPa ； Therefore, it is required that 12.6/600=0.021; a pressure gauge with an accuracy class of 1.6 must be used. Therefore, choosing a pressure gauge with a rating of 600 KPa and class 1.6 will definitely meet the requirements.

The accuracy of a pressure gauge is determined by its range; if it were calculated based on the process variable, wouldn’t that mean it could be infinitely accurate?

Thank you. I’ve learned some knowledge. Digital pressure measuring instruments, such as pressure transmitters and digital pressure gauges, have accuracy classes of 1.0, 0.5, 0.25 (0.2), 0.1, 0.05, 0.02, and 0.01; mechanical pressure gauges do not have classes of 0.4 and 0.16. As a result, in the range from 0.5 to 0.1, these accuracy classes are too numerous and lack consistency. .