Is the accuracy class of 0.15 for LNG mass flow meters referring to the indication error?
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I see that according to 7.1.1.3 of JJG1114-2015, the accuracy level of the calibration device is required to be no less than 0.15 grade, while many specifications related to calibration devices require that the indicated error of such devices be no greater than ±0.5%. Are these two requirements contradictory? Does the accuracy level of a calibration device refer to its indicated error?
The accuracy class of 0.15 for LNG mass flow meters refers to the precision level of the instrument itself, rather than the indication error. This level of accuracy encompasses all error factors, such as the instrument’s linearity, repeatability, etc. The indication error represents the difference between the value indicated by the instrument and the true value; it is usually expressed as a percentage. Therefore, the requirements for calibration devices specified in JJG1114-2015 are not contradictory to the requirement in other standards that the indication error shall not exceed ±0.5%. The accuracy class of a testing device is a comprehensive indicator that takes into account the influence of various error factors, whereas the indication error is the difference between the value output by the instrument and the true value. .