Different Methods of Instrument Calibration


What is Instrument Calibration? Why Should You Calibrate?
The process of evaluating the measurements made by the instrument to be calibrated against an instrument known to be making measurements that surpass the suitable limits of precision and correctness is known as instrument calibration. If any variation is found, then the instrument is calibrated so that it can give exact readings and values. It is common for any instrument to lose its calibration after a long period of usage. After the process of calibration, the instrument is good to use again.

Calibration is necessary for:

  1. A crucial measurement
  2. If the instrument has undergone adverse conditions and cannot give the right reading.
  3. When the output does not match the stand-in instrument.
  4. Drastic change in weather
  5. Cyclic testing of instruments

When are Instruments Calibrated?

Instruments which measure length, temperature, pressure etc should be calibrated against some standard measurement at regular intervals as preferred by the manufacturer. Methods of calibration depend on whether the instrument is calibrated regularly or only occasionally for a special task where a highly calibrated instrument is required.
It is essential to get the instruments calibrated every now and then even if they are in good condition to prevent wrong measurements of extremely crucial measurements.

Methods of Calibration

  • Data Calibration – This method is akin to accredited calibration except that they are not accredited to the ISO standard and not supplemented by data with doubtful measurements.
  • Standard Calibration – This is the method used for instruments which are not critical to quality or do not require accreditation. To make sure the standards are operative, it is necessary to document the process.
  • ISO 17025 Accredited Calibration – This is one of the most rigid forms of calibration. An account of the measurement details is maintained. International Organization of Standardization is a benchmark which shows that the company has maintained its standard rules and regulations to maintain a level of quality. There are 4 things to keep in mind to achieve a level of quality.
  1. Maintaining a Record – When an instrument is being calibrated it is mandatory to maintain a record of every minute detail of the results before and after the calibration.
  2. Accurate List of Instruments – It is necessary to maintain an updated list of instruments if your company abides by ISO Standards. An ISO certification is rejected if the instruments are in the list, but they are not physically available.
  3. Inspect the Documentation – Regular inspection of the calibration process is mandatory other than just documenting the process. The changes can easily be detected if the calibration process is closely audited every single time. It is necessary to document the changes as well as to get an ISO certification.
  4. Well-framed Quality Module – It is necessary to frame a module to keep the quality in check. The quality professionals need to follow the same code according to the module to make sure there is regularity in the calibration processes. Only the companies with clear quality modules which is documented on a regular basis will be eligible for ISO certification.

Calibration Procedures

  • The measurements acquired from the scale are compared with the measurements of the sub-standard instrument and the calibration curve is formed from the obtained values.
  • If the measurements from the instruments are parallel to the substandard then it is a good enough calibration. Otherwise the readings will have to be taken multiple times.
  • Static input is applied to the instruments and depending on the dynamic response the static calibration is built.


Calibrations of an instrument ensures precision, consistent measurements, adheres to the government related standards which results in better and more accurate reading.


Author Bio: Edward Simpson works for RS Calibration Services and has a knack for finding faults in machines and does not rest until they are rectified to perfection. He lives in Pleasanton, CA and loves to write about how machines work and about the importance of proper care and calibration of equipment. When he’s not working or writing, he loves to run to stay fit.

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