To compare the unknown value with respect to known Standard / Master.
In any process of measurement, we check the output of a process or product whether it confirms to requirements.
Before checking, it is very much required to check that the medium / instrument which we are using is giving correct value.
For this, the instrument must be compared with other one instrument/ equipment ( known as master) of which is having. Known value as required.
As this all above, calibration is a process which establish reliability of the measurement taken by the instrument.
As per requirement of ISO-9001 (Quality Management System), any monitoring and measuring equipments shall be calibrated or verified & it shall be traceable to national / international standards.
Considering above requirements, the instrument is required to be calibrated/ verified in such a way, so that the traceable to ational / international standards.
To fulfil the requirement, the master also must be calibrated by more accurate standards. This is a chain type process & linked any accredited laboratory.
For example,
1. 'A' instrument is to be calibrated.
2. 'B' shall be used as master.
3. 'B' is more accurate and calibrated by some other master 'C'.
4. Now, 'C' must be calibrated by National Laboratory or other master 'D' and the 'D' must be calibrated at National Laboratory.
Calibration/verification of an instrument can be done in house or by outside agency
Inhouse calibration :
- Calibration should be done in controlled condition.
- Parameters like temperature, humidity to be considered before & during calibration.
- The master taken for reference shall be calibrated & confirm the requirements specified by relevant standard.