Standards for hydraulic metrology published


In May 2020, ISO published the revised standards series on hydraulic measurement techniques ISO 9110-1 and ISO 9110-2. Part 1, General measurement, principles, der Normenreihe ISO 9110, Hydraulic fluid power - Measurement techniques, defines general principles for the measurement of performance parameters under static or steady-state conditions.
Extensive changes in ISO 9110-1
The revised version combines the determination of uncertainty limits and the classification of uncertainties. The specifications of the uncertainty limits have been renamed.
The sections on the evaluation of the readability of measuring instruments and the calibration of working instruments have been deleted from Part 2 and moved to Part 1.
The extensive changes have resulted in the standard now consisting of 20 pages instead of the original four. A new sub-section has been added to this, which specifies how the local gravity value is calculated. The university background of the US project manager cannot be overlooked.
In the legend to formula (2b), the international standard gravitational value gs should be 9.80665 m/s² instead of 9.808665 m/s².

Measurement of average steady-state pressure in a closed conduit
The extensive changes to Part 2 of the standard, Measurement of average steady-state pressure in a closed conduit, concern, among other things, additional terms and definitions as well as the selection and installation of test equipment. A new section shows how the total measurement uncertainty is determined.
The pressure loss between two pressure measuring points can be determined either metrologically (subsection 5.5) or analytically (subsection 5.6). Subsection 5.7 describes how the required coefficient of friction can alternatively be determined experimentally.
Since the coefficient of friction according to 5.6 can also be determined using the Reynolds number, the measuring method is not absolutely necessary. However, if the method according to 5.7 is used, it must be noted that the constant K for conversion to MPa in formula (6) is not correct (10-4 instead of 10-6). During the development phase the unit of internal diameter d was changed from cm to m, but the factor was not adjusted.