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What is Calibration and Requirements of Instruments Calibration

What is Calibration

The process of measurements needs control. In fact calibration itself can be regarded as a process to establish control on instruments and get confidence.

The set of operations which establish, under specified conditions, the relationships between values indicated by a measuring instrument or system or values represented by a material measure or reference material; & the corresponding values of a quantity realised by a reference standard is called calibration.

Calibration involves checking the operational integrity of a test or measuring equipment or of a measurement standard of unverified accuracy in order to detect, correlate, report or eliminate (by adjustment) any deviation in accuracy, capability or from any other required performance. Calibration can be carried out for three possible purposes.

  1. Determining whether or not a particular instrument or standard is within some established tolerance in respect of its deviation from a reference standard.
  2. Reporting of deviations in measurements from nominal values.
  3. Repairing / adjusting the instrument or standard to bring it back within tolerance.

For a majority of equipment, the instrument calibration result is then compared with process / product requirements; if found beyond specification, corrective repair and / or adjustment and re calibration is performed. If not found beyond specification, compensation or adjustment is optional.

The instruments calibration for fixed value type instruments like reference standards, the attribute value and calibration system measurement uncertainty is determined and reported in a calibration certificate. In all cases, a calibration report is given which states the present position of the instrument with reference to its required performance specifications. In cases where it is not possible to correct the instrument by adjustment, the reading as given in the calibration report should be used and necessary corrections to the readings obtained during a measurement should be made so as to get the correct value of the quantity being measured.

For example, the calibration of a digital voltmeter may be examined. The digital voltmeter is connected to a calibrator whose accuracy is higher than the accuracy of the voltmeter. This calibrator would have been calibrated against a reference standard and the calibration would be valid at the time of calibration of the voltmeter. A voltage is fed to voltmeter from the calibrator. If the voltmeter reads correctly, it is in calibration and does not require any adjustment. If the reading of the voltmeter is outside the calibration specifications or tolerance limits, the voltmeter requires to be adjusted to indicate the correct value. Where the voltmeter does not read correctly but is within the specification limits, the voltmeter may be optionally adjusted. The calibration report giving the readings of the voltmeter.

Requirement of Instruments Calibration

“Measurement is the first step that leads to control and eventually for improvement – If you can’t measure something, you can’t understand it. If you can’t understand it, you can’t control it. If you can’t control it, you can’t improve it.”

Process converts Inputs to Output:


  • Invested Capital
  • Raw Material
  • Human Resources
  • Energy

Output is a product

Why Calibration is required

  • Controlling the process, relation between inputs & output can be controlled
  • To control the process, we need to know the status of the process
  • Measurement gives information regarding status
  • Control of a process can never be better than the measurements made in the process
  • The more accurate the data obtained from the process, with more accuracy the process can be controlled

National Center for Quality Calibration – NCQC is a leading name in field of instrument calibration services in India. NCQC offers services for themal instrument calibration, ph meter calibration, conductivity meter calibration, mass, weights and balance calibration. NCQC is iso/iec 17025 NABL approved calibration services india providing NABL certificate for thermal, mechanical and electro-thechnical instruments.


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