How to choose a precision pressure gauge in pressure gauge verification
How to choose a precision pressure gauge in pressure gauge verification
In the recent assessment of the measurement standard device, we found that some enterprises and county (city) metrological verification personnel are verifying the spring tube type general pressure gauge, vacuum gauge and pressure vacuum gauge, whether it is a level 1.6 or a level 2.5 pressure gauge. , All select 0.4 or 0.25 precision pressure gauges with one specification larger than the measuring range of the gauge to be tested as the standard. Can’t handle JJG52-1999 'Spring.' In the recent assessment of the measurement standard device, we found that: some enterprises and county (city) metrology inspectors are verifying spring tube type general pressure gauges, vacuum gauges and pressure vacuum gauges, no matter it is For the verification of 1.6 or 2.5 grade pressure gauges, the 0.4 grade or 0.25 grade precision pressure gauge which is one specification larger than the range of the gauge being tested is used as the standard device. Cannot handle correctly the 'absolute value of the allowable error of the standard instrument should not be greater than 1/4 of the absolute value of the allowable error of the tested meter' stipulated in the verification regulations of JJG52-1999 'Bronze Tube General Pressure Gauge, Vacuum Gauge and Pressure Vacuum Gauge' , And the relationship between 'The use of spring tube pressure gauges should not exceed 3/4 of the upper limit of measurement' introduced in some measurement reference books, the following are some suggestions for the selection of precision pressure gauges in general pressure gauge verification: 1. When calibrating a 1.6-level pressure gauge, for a metrological verification organization that only has a 0.4-level precision pressure gauge, a standard gauge with the same range as the gauge to be tested should be selected. This only meets the requirements of JJG52-1999 for the allowable error of the standard instrument and the tested meter, and does not meet some mechanical measurement reference books on the spring tube pressure gauge. 'Under a fixed or uniformly varying load, it should be at 1/3 of the upper limit of the instrument measurement. Use within the range of ～3/4' this requirement. Its purpose is to extend the service life of the spring tube pressure gauge and ensure the accuracy of the measurement. It is not a rigid requirement and can be disregarded. However, in order to ensure the accuracy and reliability of the transmission of the measurement value, in the verification work, one is not to use the same standard meter to verify the meter under the same measurement limit for a long time. You can use different measurement limits for alternate verification, or when using the same standard meter. Properly extend the time interval between the two gauges to be checked; the second is to appropriately shorten the calibration cycle of the standard gauge, and replace it with a 0.25-level precision pressure gauge when the standard is updated. 2. When verifying pressure gauges below level 2.5, choose a 0.4-level precision pressure gauge with one size larger than the gauge to be tested as the standard. For example, if you are testing a 1.0 MPa gauge, you can directly select a 1.6 MPa standard gauge, and so on. Through calculation, the whole series can meet the above 1/4 and 3/4 requirements. 3. When calibrating the 1.6-level pressure gauge, the qualified verification agency should choose the 0.25-level precision pressure gauge, which is one specification larger than the upper limit of the gauge to be tested, as the standard. In this way, only use the standard meter with the upper limit of measurement 1.0×10nMPa to verify the rest of the range (90-100)% of the measured range of 0.6×10nMPa, which does not meet the requirements of JJG52-1999. For example, the allowable error of the 0.25-level standard meter with a range of 1.0MPa is: 1.0MPa×(±0.25%)u003d±0.0025MPa The allowable error of (90-100)% of the range of the 1.6-level tested meter with a range of 0.6MPa is in JJG52-1999 The accuracy level specified in Table 1 is one level lower than the accuracy of the tested meter, that is, the allowable error of the 1.6 level meter is calculated as ±2.5%, so the allowable error of this part is: 0.6MPa×(±0.25%)u003d±0.015MPa, which is absolute 1/4 of the value is 0.00375MPa, 0.0025MPa<0.00375MPa, which fully meets the requirements. The remaining part is calculated at ±1.6%, and its value is 0.6MPa×(±1.6%)u003d±0.0096MPa. 1/4 of its absolute value is 0.0024MPa, 0.0025MPa>0.0024MPa, which cannot meet the requirements of the “standard device” in the regulations. The absolute value of the error should not be greater than the requirement of 1/4' of the absolute value of the allowable error of the tested meter. Dealing with this special situation: First, the higher-level verification agency is required to provide the verification data of the 1.0×10nMPa series meter when submitting the 0.25-level precision pressure gauge, and the correction value is introduced when the 0.6×10nMPa series 1.6-level general meter is verified. In this way, it not only meets the aforementioned 1/4 and 3/4 requirements, but also provides a calculation basis for the stability assessment of the measurement standard. The second is to refer to the method in 220.127.116.11 of JJG49-1999 'Bronze Tube Precision Pressure Gauges and Vacuum Gauges' that 'Verify 0.16 (0.06) precision pressure gauges can use the second (1) standard pressure gauge with the corresponding measurement rangeDirectly use the standard meter with the upper limit of measurement of 1.0×10nMPa to check the measuring range of 0.6×10nMPa to be checked. Since the two regulations have completely different requirements for the allowable error of the standard instrument, although the 0.16 (0.06) grade precision pressure gauge is verified by the second (1) standard pressure gauge, it does not meet the relationship between the standard instrument and the tested gauge's allowable error 1/4, but JJG49-1999 is solved by refilling, so you can refer to it when verifying general pressure gauges. Moreover, this treatment also meets the basic requirements of JJF1094-2002 'Evaluation of Characteristics of Measuring Instruments' specification 18.104.22.168 of the basic requirements for conformity evaluation of the indication of measuring instruments 'The absolute value of the uncertainty of the indication error U95 and the maximum allowable error of the assessed measuring instrument The ratio of value MPEV should be less than or equal to 1:3, that is, U95≤(1/3)×MPEV. When the indication error Δ of the evaluated measuring instrument is within its maximum allowable error limit, it can be judged as qualified, that is |Δ |≤MPEV is qualified.' To sum up, when selecting a spring tube precision pressure gauge as the standard for verifying general pressure gauges, it must first meet the 1/4 relationship specified in JJG52-1999, and if it does not meet its requirements, it must meet JJF1094-2002 stipulates the 1/3 relationship, and finally consider the 3/4 relationship in the measurement reference book.
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