Fitness for purpose of process measurements
by
Ray Littler
University of Waikato, Hamilton
Coauthors: Derek Christie

Industrial processes depend on good measurements for process control and improvement, and for product quality assessment. New technologies have provided many opportunities to replace existing measurement methods with cheaper and more timely alternatives. It is then natural to seek sensible procedures to evaluate the new systems, especially where the measurements are used for assurance on contractual or safety questions. A practical evaluation scheme needs to cope with applications, sometimes referred to as rationalised testing, in which the new system differs from the old in process sampling points as well as in measurement methods.

We discuss some practical and theoretical issues encountered in the attempt to define an adequate protocol to judge the acceptability of a new measurement system, given comparative data on old and new systems collected during normal process operation. It seems instructive to reflect on the interplay between considerations of scientific integrity, “political” acceptability, and the need to produce a scheme which is simple to understand.

Date received: August 30, 2001