GPS – Specification of demands on Measurement System


Lecture*: Measurement preparation – capabilities before manufacturing of geometrical products


In order to meet the requirements for adequate testing and assessment of product:

Measurement quality assurance standards, such as ISO 10012, give generic guidelines about metrological confirmation of measurement systems.

GPS standards such as ISO 14978 2002 are intended to ease the communication between manufacturer/supplier and customer/user by faciltating the specification phase of GPS measuring equipment e.g., micrometers, dial gauges, calipers, surface plates, height gauges, gauge blocks, while not necessarily excluding more complicated equipment employed to measurement geometrical characteristics. ______________________________________________________________________________

Sources of errors, accuracy and uncertainty of measurement

The GPS standards, such as [ISO/TS 14253-2:1999 §7], describe various types of errors which regularly show up in measurement results, including systematic and random error, drift and outliers.

A list of typical sources of error & uncertainty in the GPS context is given in [ISO/TS 14253-2:1999 §7]

Measurement errors are quantified in terms of measurement accuracy. Calibration of in principle each element of a measurement system (instrument, method, operator etc) with metrological traceability to absolute measurement references is essential in ensuring quality-assured measurement which in turn assures products with fit-for-purpose quality.


Target uncertainty

The GPS standards refer to a “Procedure for Uncertainty Management – PUMA” to be applied when quantifying a measurand, be it a GPS characteristic of a workpiece or a metrological characteristic of a GPS measuring equipment [ISO/TS 14253-2:1999].

PUMA management refers here to choosing a measurement system with the ‘right’ or ‘fit for purpose’ measurement capability for the task at hand.

Note: Uncertainty management means more than just choosing an appropriate “principle of measurement on the basis of experience and available measurement instruments present in the company” [ISO/TS 14253-2:1999 §6.3]. Above all, the demands on the measurement system have to be matched with the conformity assessment task at hand, such as adapting measurement capability to process capability.

The target uncertainty (UT in GPS notation) is a specification limit on the measurement capability of the measurement system employed.


GPS – Presentation of measurement results
GPS – Use of measurement results. Conformity assessment
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