Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar way as possible with a second device. The device with the known or assigned correctness is called the standard. The second device is the unit under test or the test instrument.
The formal definition of calibration by the International Bureau of Weights and Measures is the following:
“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 (of the calibrated instrument or secondary standard) and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication”.
Calibration may be called for:
- A new instrument
- After an instrument has been repaired or modified
- When a specified time period has elapsed
- When a specified usage (operating hours) has elapsed
- Before and/or after a critical measurement
- After an event, for example
- After an instrument has had a shock, vibration, or has been exposed to an adverse condition which potentially may have put it out of calibration or damage it
- Sudden changes in weather
- As specified by a requirement, e.g., customer specification, instrument manufacturer recommendation.
In general use, calibration is often regarded as including the process of adjusting the output or indication on a measurement instrument to agree with value of the applied standard, within a specified accuracy. For example, a thermometer could be calibrated so the error of indication or the correction is determined, and adjusted (e.g. via calibration constants) so that it shows the true temperature in Celsius at specific points on the scale. This is the perception of the instrument’s end-user. However, very few instruments can be adjusted to exactly match the standards they are compared to. For the vast majority of calibrations, the calibration process is actually the comparison of an unknown to a known and recording the results.
NML CALIBRATION SERVICES:
National Metrology Laboratory under Bhutan Standards Bureau is the only calibration laboratory in Bhutan which maintains the national standards and provides the following calibration services:
- Calibration on Weights and Electronic Balances
- Calibration on steel scales and measuring tapes
- Calibration on Volumetric Measures
- Calibration on Liquid in glass Thermometers, Temperature probes and RTDs
- Calibration on Pressure Gauges
The National Metrology Laboratory (NML) has been granted Accreditation by National Accreditation Board for testing & calibration Laboratory (NABL), India for the following few parameters:
- Weights, Electronic Balances and
- Steel scales & measuring tapes.