Establishing Calibration System (Metrology)

1.20.
Market forces demand industry to ensure environment for supply of quality products to
customers. Accurate measurements play a crucial role at each stage in the development and
production of quality products. The aim of establishing calibration system is to develop internal
metrology and calibration programmes to assure that the test and measuring instruments are
maintained within desired accuracy. Systematic periodic checking of test and measuring instru-
ments is thus becoming increasingly important to the development and maintenance of market
competitiveness. This process of periodic checking against measuring equipments/standards of
higher accuracy is termed as ‘Calibration’.
An essential condition for establishment of calibration system is that the supplier shall
control, calibrate and maintain inspection measuring and test equipment whether owned by the
supplier, on loan, or provided by the purchaser, to demonstrate the conformance of product to the
specified requirements, and further the equipments shall be used in a manner which ensures that
measurement uncertainty is known and is consistent with the required measurement capability.
Important conditions for this purpose are:
(i) To ensure that the measuring equipment is capable of the desired accuracy and precision.
(ii) The calibration system should provide the means to directly or indirectly trace assigned
values of measurement equipment to values in terms of nationally recognised standards.
(Hi) Calibration should be carried out using measurement systems having adequate accuracy,
stability and range to completely verify the performances of the calibrated item within its specified
uncertainty limits.
(iv) The calibration procedure may be a document prepared internally, or by another agency,
or by the manufacturer or a composite of the three. It is essential to designate and use documented
procedures for all calibrations performed.
The contents for the calibration procedure are :
— Introductory description of the unit to be calibrated
— Preliminary actions prior to starting the calibration
— Measurement method used to verify the performance
— At table giving the specification tolerance of different parameters that can be measured
by the unit and tolerance limits calculated.
— Listing of instructions to be performed.
(v) All test and measuring instruments should be securely and durably labelled, coded or
otherwise identified to indicate its calibration status, viz. date of last calibration, date due for
calibration, and the authenticity of calibration.
(vi) Access to adjustable controls/devices on measuring equipment whose setting affects the
performance, should be sealed after calibration in order to prevent tampering by unauthorised
personnel. Seals should be such that tampering is clearly apparent.
(vii) Test and Measuring equipment should be calibrated at periodic intervals established
with the intent of achieving and maintaining a desired level of accuracy and quality.
(viii) Records should be maintained for all test and measuring equipment included in the
calibration system.
(ix) It must be ensured that the environmental conditions (temperature, relative humidity,
cleanliness, vibration, electromagnetic interference and voltage regulation of electric power) are
suitable for the calibration and are maintained.
(x) Personnel performing calibrations of test and measuring instruments should have
training in the area of job assignment, basic knowledge of metrology and calibration concepts, ability
to follow instructions regarding maintenance and use of measurement equipment and standards.
(xi)The calibration control system should be subject to periodic audits conducted at a
frequency and to the degree that assure compliance with all elements of the system procedures and
documented requirements.