Discussion on calibration intervals

Source: Content taken from a Powerpoint presentation used for conferences
Author: Mr. Ouellette
Date: 2001-02-12

Definitions

Calibration Interval

  • Period of time or amount of use between calibrations
  • To ensure equipment remains reliable

Reliable

  • Within sufficient tolerance (or uncertainty) for the tests being done

Stakes

  • Interval too short: Calibration $$$$
  • Interval too long: Risk of bad measurements and repercussions

17025 Requirements

  • [5.5.2] Equipment shall be:
    • capable of achieving accuracy required
    • comply with test/calibration method specifications
    • managed under a calibration program
  • Therefore, need to:
    • define required accuracy
    • identify the equipment that can affect it
    • manage that equipment under a calibration program
  • [5.6.1] Established program and procedure for calibration equipment (that matter).
  • [5.1.1 et 5.1.2] Calibration program, etc., needs to consider many factors; e.g.
    • human factors
    • environmental
    • sampling
    • handling, etc.

CLAS Recommended Practices

  • Calibration at (planned) periodic intervals to ensure acceptable accuracy and reliability
  • Shorten intervals when results of previous calibrations suggest it
  • May lengthen intervals on basis of demonstrated performance
  • Documented procedure for assigning and adjusting calibration intervals
  • Fully documented recall system

How to Establish Calibration Interval

  1. Consider influencing factors and existing knowledge, e.g.,
    • accuracy sought and consequences of error
    • manufacturer’s recommendations
    • accommodation and environment
    • purpose and usage
    • maintenance and servicing
    • trends from previous calibrations
    • frequency of checks
  2. Make an initial choice, considering the factors above (especially the following ones):
    • accuracy sought and consequences of error
    • manufacturer’s recommendations
    • accommodation and environment
    • purpose and usage
  3. Monitor and review, adjust as necessary
    • automatic or staircase method for individual item
    • control chart (enables predictions)
    • adjust based upon performance of a group of similar items
    • in-service checks of critical parameters

References

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