Managing Measuring Equipment (Metrology)

1.24.
Measurement is the process of assigning a value to a given physical quantity. Quality is the
capability of a product (or a service) to meet stated and implied needs. Measurements have
significant role in product quality through the testing of products against a relevant specification,
after completion of manufacture. In many cases tests are carried out during manufacture, on the
partially assembled product or on key components, to ensure that the manufacturing process is
going as planned and to enable any necessary process adjustments to be made.
Measurements have definite role in achieving product quality, leading to industrial competi-
tiveness, consumer protection and related benefits. Measurements also have a vital part to play in
enhancing quality in the more global sense of quality of life. The accuracy of an item of measuring
equipment is established by testing that equipment in the appropriate way, using a more accurate
measuring instrument. The accuracy of the measurement standard concerned may in turn be
established, in a similar way, by calibration of the standard against a higher, more accurate
standard, and so on, through an unbroken chain of calibrations, stretching back to the national
measurement standards held at NPL.(measurement traceability). The national measurement
standards held at NPL form the anchor for traceability chains serving different levels and sectors
throughout the country. Traceability of measurement is essential, if accuracy of measurement is to
be meaningfully assigned, and if measurements made on different instruments or at different times
and locations are to be validly combined or intercompared.
Credibility of a measurement result deserves good attention. For example, a laboratory may
possess accurate equipment, properly calibrated, but credibility will be lost if measurements are
carried out with the equipment at the wrong temperature, or if measurement staff is insufficiently
skilled, supervised or briefed in their tasks. Even where a measurement has been carried out
satisfactorily, its usefulness may be undermined due to the result being reported or recorded in an
ambiguous or misleading way. Only when there exists authenticated measurement traceability and
when the measuring equipment is under proper control over all other aspects influencing credibility,
can there be proper measurement assurance, giving overall confidence in a measuring equipment’s
capability to produce correct measurement results.
The management of measuring equipment requires the establishment of a system to
demonstrate one’s capability to provide reliable measurement results. The elements of the system
demand an orderly approach to acquisition, calibration, maintenance, use and periodic recalibration
of all measuring equipment. All equipment used in the measurement of characteristics of the
product which affects its ability to comply with the specified requirement must be controlled,
calibrated and maintained. Measuring equipment shall have the accuracy, stability, range and
resolution required for the intended use. It should be ensured that the risk of measuring equipment
producing results having unacceptable errors remains within acceptable bounds.
It is essential to establish and maintain an effective documented system for the managing,
qualification and use of measuring equipment including measurement standards. The system must
provide for the prevention of errors outside the specified limits of permissible error, by prompt
detection of deficiencies and by timely action for their correction.
In performing measurements and in stating and making use of the results, it is required to
take into account all significant known uncertainties in the measurement process including those
that are attributable to measuring equipment (including measurement standards) and those
contributed by personnel, procedures and environment.
Any item of measuring equipment that has suffered damage ; that has been overloaded or
mishandled ; that shows any malfunction ; whose proper functioning is subject to doubt; that has
exceeded its designated qualification interval; the integrity of whose seal has been violated ; must
be removed from service by segregation, prominent labeling or marking. Such equipment should
not be returned to service until it has been repaired and again qualified.
Access to adjustable devices on measuring equipment, whose setting affects the performance,
has to be sealed or otherwise safeguarded immediately following the calibration and qualification
in order to prevent tampering by unauthorized personnel. Seals must be designed in such a way
that tampering is clearly apparent.
A system for receiving, handling, transporting, storing and despatching the measuring
equipment, must be established and maintained in order to prevent abuse, misuse, damage and
changes in dimensional and functional characteristics.