Standards for Measurement
Standardization In Metrology
Standardization is a word used to describe the exercise of implementing commonly agreed to rules or requirements to govern the variety of an entity available, for specific reasons. These reasons vary but often include efficiency, safety, quality and enhancing trade. The entities themselves vary widely from a product to a test method to rules for conducting an activity.
What is a Standard?
The process of standardization can have many components but is normally characterized by the building of consensus among various stakeholders (those who stand to be affected by the standardization effort) with respect to the rules to which everyone is to abide. The outcome is usually a ‘standard’ of one form or another. Now the word standard can have different meanings depending on your point of view. The International Standards Organization (ISO), the body chiefly responsible for formulating standards for application internationally, defines a standard as:
A standard is the result of a particular standardization effort approved by a recognized authority. It may take the form of:
A document containing a set of conditions to be fulfilled (in French “norme”)
A fundamental unit or physical constant – examples: ampere, absolute zero (Kelvin) (in French “etalon”)
an object for physical comparison – examples: metre (in French “etalon”)
You will observe that there are three possible options for defining (in English) what constitutes a standard. (Two words are used in French for the same purpose) Clearly, depending on your perspective, a standard can mean different things. Now, Metrology is loosely defined as ‘the science of measurement’ and the metrologist as one whose work is in the field of metrology (a measurement scientist). The Vocabulary of International Metrology (VIM) defines a standard as:
A material measure, measuring instrument, reference material or measuring system intended to define, realize, conserve or reproduce a unit of one or more values of a quantity to serve as a reference.
This definition clearly focuses on the metrologist’s objective, which is to realize a reference for comparison purposes, and falls neatly into parts (2) and (3) of the ISO definition. The first part (1) of the ISO definition is also of relevance to the metrologist however. The specific ‘conditions’, referred to in (1), which are to be fulfilled can be in reference to an instrument, test method or environmental conditions etc. The type of document (standard) produced can be classified according to its purpose.
For clarity it is common to use the terms “document standards” and “measurement standards” to differentiate between the types. Number (1) from the ISO definition refers to documents while (2) and (3) from that definition along with the VIM definition all refer to measurement standards.
Document Standards and Specifications
Document (written) standards may cover many aspects of human endeavor. Some of the most common are:
Nomenclature (names) or symbols
Specification (about a product, process etc)
Method of sampling or inspection
Method of grading or classification
Scheme of simplification or rationalization
Packaging and labeling requirements
Supply and delivery conditions
Code of practice including model byelaws and
Forms including contract forms
Of particular interest to Metrology is the type of document standard termed a specification (Specs). A specification is defined by ISO as follows:
A specification is a concise statement of a set of requirements to be satisfied by a product, a material or a process indicating, whenever appropriate, the procedure by means of which it may be determined whether the requirements given are satisfied.
Basically, it outlines criteria which can be used to access, in an objective and standardized (uniform) manner, whether the requirements defined within it are met. In a field where making trustworthy measurements is critical, standards such as these prove particularly useful.
How are Specifications Useful
Specifications give details of acceptable criteria for accessing a product and this can be particularly useful for acquiring the measuring instruments required for various applications. A broad range of international and national standards exist for a wide variety of measuring instruments used in industry including calipers, micrometers, pipettes, burettes, hydrometers, weights, thermometers etc. These standards are available and can be consulted for ‘expert’ advice on what is required for an instrument to meet the criteria set out by the standard. If more members of industry were more aware of the broad range of standards available and their usefulness in ensuring the acquisition of equipment that is suited to the measurements required, local industry would be much more efficient in terms of cost, measurement accuracy and confidence. This in turn, would have a significant impact on our international competitiveness, particularly in light of the ever increasing impact of the globalizing environment on trade and the economy, not to mention the long term survival of individual firms.
The Information Centre of the Bureau of Standards stores many international and national standards that are readily available to local industry. In addition, the Metrology Section of the Laboratory Services Division stores the national standards of Trinidad and Tobago including Mass, Temperature, Pressure and Length. All of which can be traced to the international standards and national standards of metropolitan countries.
Another essential type of document standard to Metrology is the Method of Test or Analysis. In many cases, these test methods are incorporated as part of product specifications. However, many of these methods are made into standards of their own. Of particular interest to the metrologist are the calibration methods for measurement instruments. These methods outline standardized procedures for determining and ensuring that instruments perform within defined acceptable criteria, and this is essential in metrology. This can also have far reaching effects on efficiency and competitiveness of industry and the economy in a country.
Suitability of Instruments for measurement
When we receive bills for utilities or pay for groceries, we all want to feel assured that we are paying for exactly what we consume (within reasonable bounds, of course). This assurance comes from, among other things, confidence in the instruments used to measure our consumption. Now there are many instruments available for measuring specific quantities. But, not all of them would be relevant for a specific purpose. For example, a market scale would not be appropriate for measuring quantities down to the nearest milligram, which is often required in laboratories. And, even within laboratories, a balance used for measuring milligrams would not be appropriate for measurements requiring accuracies to the nearest tenth of a milligram. What this means is that, depending on one’s knowledge and understanding of the intended purpose and usage of a measurement, an appropriate measuring instrument can be chosen.
Matching instruments to their purpose
Another important factor in choosing an appropriate instrument is knowledge of the appropriate characteristics of the instrument in order to wisely choose an instrument suitable for the environment and usage to which the instrument will be put. This becomes relevant when we consider durability, accuracy and reliability of the instrument when in use. We want that the quality of the instrument chosen meets the need for which it is being utilized. In other words, the instrument inherently has a ‘standard’ which it must meet in order to satisfy the need for which it is being used. But, how does one ensure that an instrument chosen meets the standard? This is done (ideally) by ensuring that the specifications (provided they exist) outlined for an instrument of that type are met by the instrument. This involves the creation and usage (wherever possible) of written specifications detailing the requirements of the various classes of instrument of this type and how it can be determined whether these requirements have been met by an instrument. If more people and organizations were guided by these principles then society as a whole would be much the better off for it.