METROLOGICAL COMPETENCE OF LENGTH MEASUREMENTS IN A PRIMARY LEVEL CALIBRATION FACILITY

摘要

Metrological competence is the ability to perform comparative measurements and to disseminate the measurement information over some specified range and within acceptable limits of uncertainty for a designated physical quantity. The acceptable limits of measurement uncertainty have been defined as: (1) The bias of the measurements at the laboratory should be no greater than three times the systematic error at a typical national laboratory, and (2) the precision error of the laboratory measurements should be no greater than ten times those suffered for the same measurements at a typical national laboratory. The paper specifically discusses achievement of metrological competence of length measurements at the Measurement Standards Laboratory (MSL) of KFUPM Research Institute which is Saudi Arabia's first world-class calibration laboratory of primary level. The approach to prove the metrological competence is that an on-going measurement assurance program for gage blocks checks for the precision error of the process and occasional blind tests on national laboratory-calibrated gage blocks ascertain the laboratory bias. It is emphasized that one-time proof of competency is of little value; the evidence should be on a continuing basis. That is, the equipment, the operator, the procedure and the environment—all should play their role in characterizing the measurement process or determining the metrological competence. Measurement is thus a process not an isolated event. Any measurement at hand should be a random draw from a stable probability distribution; only then statements can be made about the health of the process.