Metrology, Traceability & Calibration

Metrology is the science of measurement and its application. It represents the basis for trust on the results obtained. The national metrology system of a country represents the infrastructure that enables the performance and application of measurement for purposes that mirror the economic and social core of the nation. 

Purpose of Metrology – legal metrology, industrial metrology and scientific metrology.
These are fields that have been internationally accepted to cover all the technical and practical aspects of measurements.

Metrology cover three main tasks:
a. The definition of internationally accepted system of measurement e.g. Metric system
b. The realisation of units of measurements by scientific method e.g. the realisation of a metre through the use of a laser beam
c. The establishment of traceability through unbroken chain in documenting the uncertainty of a measurement. e.g. the documented relationship between the micrometer in a precision engineering workshop and a primary laboratory for optical length metrology.

The metrology is separated into three categories with different levels of complexity, accuracy and uncertainty.
a. Scientific metrology
b. Industrial metrology
c. Legal metrology

Scientific Metrology deals with the organisation and development of standards and with their maintenance (Highest level) 
Scientific measurements applied in the production of measurement standards the improvement of measurements and in the introduction of new forms. National Metrological Institute /National physical laboratory, India is the custodian of primary standards as decreed by the act and signatory to BIPM. 

Industrial metrology has to ensure the adequate functioning of measurement instruments used in the industry as well as in production and testing process. 
Industrial metrology operations run in accredited laboratories give calibration service to enterprise that operate in accordance with ISO 17025. 
This is the aspect of metrology that applies to production/manufacturing and quality control. Typical are the procedure and interval of calibration and the control of measurement processes and equipment. It describes the metrological activities that take place in the industry. In other words, it is the branch that enhances the industrial development and efficiency through the national calibration services. In India, NABL provides accreditation for calibration and testing laboratories to cater services to industries. 

Legal metrology includes the calibration, control and measurement of measuring devices which can be subject to life or commodity security audited by ministry of trade and industry. 
Example, weighing scales, weights used in shopping malls, Jeweller's scale, gas pumps, volumetric measures are included in these operations. 
Legal metrology governs the legal aspects associated with the measurement and utilizes the force of law. Buying and selling by weight or quantity in the market or in the packages are examples of this. 
Department of weights and measures is the legal authority is each state.

Metrological Traceability: Property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty. 

Industries in India ensure the traceability to the highest international level by using NABL accredited laboratories. 

Device for Measurement:
a. Measuring Instruments: Device used for making measurements, alone or in conjunction with one or more supplementary devices.
b. Measuring Systems: Set of one or more measuring instruments and often other devices, including any reagent and supply, assembled and adapted to give information used to generate measured quantity values within specified intervals for quantities of specified kinds.

Calibration: operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication. 
A basic tool in ensuring traceability of a measurement is measuring instrument calibration. This calibration involves in determining the metrological characteristics of an instrument. It is achieved by means of a direct comparison against standards. The calibration certificate is issued and a sticker is attached (in most cases). Based on this information a user can decide whether the instrument is fit for the application in question. 

Purpose of calibration
To ensure readings from an instrument are consistent with other measurements 
To determine the accuracy of the instrument readings 
To establish the reliability of the instrument i.e. it can be trusted. 

Advantages of Calibration:
The results of a calibration permit either the assignment of values of measurement to the indication or the determination of correctness with respect to indications. 
A calibration may also determine other metrological properties such as the effect of influential quantities. 
The result of a calibration may be recorded in a document, sometimes called the calibration certificate or a calibration report. 

Importance of calibration relevant to Industry:
Any measuring device used in an industry, will suffer with wear & tear and, drift over a period of time, and will go out of calibration which may lead to wrong measurements. Reason for this may be environmental conditions of operation, wrong handling etc. Hence, calibration or verification of a measuring device is of great importance which will help to overcome the following effects
a. To keep the measurements within the specified tolerances
b. To maintain consistent product quality during manufacture
c. To optimize the process and increase capacity
d. To control operation and maintain safety
e. To comply with regulations and quality systems
f. To improve quality of life
g. To maintain universal acceptability-thereby economic growth.

Also, to comply with the regulations and quality systems, industries have to adopt any one the quality systems like ISO9001,ISO 9002,ISO 14001 etc., and are required to maintain the records of systematic and well documented calibration with regard to repeatability , accuracy and uncertainity with a confidence level. 
Therefore, it is very important to have good measurement, calibration and traceability and it is the joint responsibility of National metrology institute and the accredited laboratories to achieve the goal. 

Measurement:
Process of experimentally obtaining one or more quantity values that can reasonably be attributed to a quantity
Measurements are strategically important to the process of nation building. Only those nations have progressed to the point of being called "developed". If, our nation is to attain such status, a national system of measurement that matches with our aspirations must be established. 
Measurement metrology is essential and practical for all facets of human development as it is used in activities ranging from the control of production, purity levels of atmosphere and water, evaluation of health and safety standards related to the quantity of materials , food and other products in order to guarantee just trading practices and the production of the consumer as well as the environment.
 

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