Why does my instrument need calibrating?

Calibration is the process of comparing the indicated reading of instruments to a known measurement standard to establish the relationship between the values indicated. In other words, instrument calibration in its simplest form can be defined as the comparison of a "known' quantity (the measurement standard) to an "unknown' quantity (the indicated readings of the instrument under test).

BS EN ISO 9001:2008 Clause 7.6 - Control of monitoring and measuring equipment, states that in order to ensure valid results equipment must be calibrated or verified against measurement standards which are traceable to international or national measurement standards.

To provide confidence in the accuracy of calibration results, the measurements must demonstrate traceability. Calibrations should be undertaken by a laboratory which has been independently accredited by an approved third party, or by using equipment with values traceable to national and international standards. Traceability can be defined as a "chain' of comparative measurements, with the final "link in the chain' being provided by the International Bureau of Weights and Measures (BIPM).

Your instrument > Hitek Standard > National Standard > International Standard

Whether you have a simple meter or state-of-the-art systems, Hitek recognise the importance of calibration and will endeavour to meet all of your calibration requirements.

All calibrations undertaken by Hitek are traceable to an appropriate national or international standard. This traceability is independently audited in order to maintain the company's BS EN ISO 9001:2008 certification.

Hitek can also provide an "accredited' calibration service. These calibrations are audited and approved by the United Kingdom Accreditation Service (UKAS) to comply with the requirements of the International Standard ISO/IEC 17025:2005.

An accredited calibration will include an "uncertainty of measurement' for each individual measurement stated on the calibration certificate. This "uncertainty of measurement' component is audited and approved by UKAS and demonstrates the overall accuracy of each individual measurement undertaken during the calibration process.

If an instrument is used to verify the results of other measurement instruments, or is used in a highly critical process, an "accredited' calibration is recommended.

How often should my instrument be calibrated?

Most instruments are calibrated annually, but the following factors should all be carefully considered when determining calibration intervals:

• The application or process in which the instrument is being used - the more critical the application or process, the more important it is to maintain confidence in the instrument being used
• The environment in which the instrument is being used - the more variable the environment in which the instrument is used (temperature, humidity, vibration etc.) , increases the likelihood of an instrument drifting away from its original specification
• Instrument Usage - the more often an instrument is used, wear and tear on the instrument increases, reducing confidence in the accuracy of the instrument measurements. Additionally, if an instrument has remained unused for a significant period, it should be calibrated prior to use to maintain confidence

Hitek are happy to offer advice regarding all aspects of calibration, including the level of calibration required and calibration intervals. For further information please visit www.hitek.co.uk.