Anybody with a mind to implement (or improve) a metrology function might
feel a bit panicky at the thought of all the work to be done if they read this book
unwarned, and more particularly this chapter. Let the reader’s mind be put at ease
first. All the content is not, fortunately, to be carried out literally. All we want to do
is to offer as broad as possible a survey of the subject by pointing out practically all
the items that require consideration.
And then, is it not normal to start wondering what one really needs?
Experience has taught us, too often alas, that this is not a natural process. Many
industrial difficulties, or many costs, grow out of the inadequacy “means of
measurement/real need”.
1.1. Introduction
Before we start any concrete action, it is primordial to analyze the metrological
needs carefully. There are two kinds:
– The organizational needs for the management of metrology. Are those needs
great enough to require the introduction of full-scale metrology? Are premises or
qualified personnel needed permanently? What possibilities are there in the region?
Chapter written by Jean-Yves ARRIAT – Ascent Consulting – and Klaus-Dieter
SCHITTHELM – Expert in Metrology, Germany.
20 Metrology in Industry
Does someone want to manage metrology on his or her own, with the help of a
someone else, or to handle it to a subcontractor?
– The material needs for the realization of the measurements. In order to realize
measurements correctly, it is necessary to have appropriate means; these means are
found after analysis of the objectives and the possibilities of the instruments and the
connection. In order to define the firm’s needs, it is necessary to answer the
following questions:
1. What are my industrial needs?
– What do I have to measure and what accuracy shall I expect?
2. How can I meet my needs?
– What are the possible measuring methods?
– Which method and principle will be used?
3. Which measuring instruments can be used?
– Which instrument shall I use?
– Can the selected instrument ensure the required accuracy?
4. How is to be used the selected instrument?
– What assembly is to be set up and what procedure is to be followed?
– What technical competence do you have to have to use it?
Then a question of a very different magnitude arises: how am I going to
guarantee the quality of my measurements?
Setting up a metrological function
The three key components of a metrological function have to be under control
(see Chapter 4):
– adequacy of means to needs;
– traceability of the means of measurement to international standards;
– administrative management of the equipment (measuring instruments,
standards, etc.).
The preliminary analysis of the needs will produce a first set of specifications.
There is a good chance that these analysis are going to be a bit theoretical and take
little heed of the notions of profitability. You have to accept the principle which
says that the specifications will evolve and obtain agreement from the major actors
taking part in the drafting of the specifications.
For a new measuring instrument, all the stages from conception to utilization
must be taken into account by the specifications. This is fundamentally the concern
Analysis of the Metrological Requirements Needed to Ensure Quality 21
of the manufacturers, but potential users may sometimes take part in the elaboration
of the specifications.
The specifications for a new measuring laboratory must ignore all of the
environmental characteristics of the measurement (see Chapter 8), and take into
consideration the problems of maintainability (for instance, the maintenance of air
conditioning), of access to the personnel, of user-friendliness, etc.
However big or small the problem is, one must always begin by analyzing one’s
real meterological need.
1.2. Definition of the objectives
The metrological function must be approached as soon as you start thinking
about problems of measurement. Its role may depend on each particular firm (see
Chapter 3), but its chief role is to act as a consultant. It examines the need in a
logical process based on:
– the functional analysis of the measurement (drafting of specifications);
– the analysis of the achievement of the measurement results (and of the level of
accuracy reached);
– the analysis of the risks related to the selected means;
– the analysis of the non-conformities which could be encountered.
This process makes it possible to identify and quantify the means (personnel and
material) to be implemented to take the intended measurements.
It is during these phases that the “tools of quality” will be used. Let us point out
that the analysis of the value (fundamental at the outset) is among the most useful
tools. In order to clearly define the objective, we strongly recommend to use
“brainstorming”, cause/effect diagrams, Pareto, etc., which make analysis and
collective participation easier.
So as to guarantee the quality of its measurements (i.e. a process of management
by quality), the firm sets up a real management of the means of measurement. For
this purpose, the metrological function conducts the management of these means
according to needs that are clearly defined and regularly updated. This involves
examining a large number of actions in order to start up and maintain the supply of
measuring instruments necessary to meet the firm’s needs.
22 Metrology in Industry
The first thing to do regarding the analysis of the supply of material is to work
out:
– the list of physical quantities (e.g. temperature, length, electric resistance, etc.);
– the ranges which need to be covered for each physical quantity (e.g. length
from 0.1 mm to 1,000 mm);
– the permissible uncertainty for each quantity and each range (the uncertainty in
the 0.1 mm to 0.5 mm range will be different from the one which is expected
between 100 mm and 1,000 mm).
Then, for each separate case, it will be necessary to consider and define:
– the analysis of the needs and the choice of the means of measurement;
– the acquisition, the reception and the implementation of these means;
– the traceability of the material of measurement (in the case where materials of
measurement are assigned);
– the traceability of the measurements (which material do they come from?);
– the calibration or the verification of the means and the decisions they entail;
– the exploitation of the calibration results;
– the operations related to the moving of these means (protection, authorization,
etc.);
– the updating of the inventory of these means.
The outcome of this is that the intended objectives must not be mixed up to satisfy:
– the needs for the management of metrology with;
– the needs for the realization of the measurements.
1.3. Choice of the method of measurement
1.3.1. Accounting for the selection of the method
You have to justify the choice of the selected method. It is to be understood by
this that the criteria have to possess as little subjectivity as possible.
This choice must take possible restraints of qualification into consideration. The
fact is that within the scope of some contracts (notably related to safety, public
security, health, etc.) you may have to qualify the method of measurement. This
means it must be subjected to an authenticated description, officially certified tests,
etc., in accordance with the relevant program and by a very precise process.
Besides, the ISO/QS 9000 or TS 16 949 certification process also involves a
description of the selected method.

Fortunately, it is often possible to hang on to the methods which are known and
officially accepted. You must not forget that the great metrology laboratories can be
a great help in this area. In France, for example, these are the laboratories of the
LNE (Laboratoire National de Métrologie et d’Essais), and in Germany, those of the
PTB (Physikalisch-Technische-Bundesanstalt), or calibration laboratories accredited
by the DKD (Deutscher Kalibrierdienst).
Whether the method is qualified or not, it is important, after the metrological
objectives have been set, to make the methodology of the measurement explicit. The
different stages, the conditions of the material and the environment, the operations
that make it possible to get the measurement, i.e. everything related to the carrying
out of these measurements, must be written in a document and will be taken into
account particularly when choosing the operators.
One of the very first principles of quality assurance is to write down what is
being done. This process is simple and allows people to think further about the
choice of the method. There must be a clear distinction between chosing a method
and chosing a measuring instrument. For example, you may want to measure a
dimension on a rubber part: you happen to be close to a three-dimensional
measuring machine and your instant reaction may be to go to this machine without
thinking whether there may be a more suitable method than this one.
1.3.2. Defining the method and the principle to implement
When there are several methods of measurement, it is often difficult to determine
which one will best fit your need if you are not able to classify them.
Our advice is to keep only the two (maybe three) most important criteria in mind
and to draw a table. Let us consider the example of Table 1.1. It makes it possible to
analyze the different methods of measurement that lead to the assessment of the
characteristics of industrial robots.
Two criteria have been selected:
– the principle of measurement (two groups of them here);
– the characteristics measured (two families of them here).
As a rule, there are in metrology three great principles of measurement; the three
of them have advantages and drawbacks. They are:
– differential measurement;
– direct measurement;
– indirect measurement.