The right calibration interval

How do I find the appropriate or necessary calibration interval?

A "correct" calibration cycle is important in order to continuously prove compliance with the specified quality of the test equipment and thereby verify past measurement results. The risk of erroneous measurements should be minimized and resulting follow-up costs avoided. But how do you find the right calibration interval without losing sight of the economic factors? In the relevant standards, there are only references such as "at fixed intervals" or "regularly". What does this mean and on what basis can a decision be made?

Calibration is a quality assurance measure and economic factors are of secondary importance here - from a compliance point of view, this statement is certainly correct. Management, on the other hand, has the task of avoiding or reducing costs, and this without affecting quality.

The obligation to plan and carry out regular calibration for critical measuring instruments or dimensional standards that directly or indirectly influence product quality can be derived from many regulatory sources. As an example, the EU GMP Guide to Good Manufacturing Practice, Chapter 3.41, states: "Measuring, weighing, recording and control equipment should be calibrated and checked at specified intervals using appropriate methods. Appropriate records of this should be kept." (1) ... or the ISO 9001 with "Calibrated and/or verified at specified intervals or before use." (2).

In the absence of clear regulatory requirements and the simultaneous understandable desire for an easy-to-manage calibration interval system, in practice there are often blanket and overriding stipulations of calibration intervals, such as that all temperature measuring points are to be calibrated annually. However, this seemingly efficient system, which is easy to present especially during audits, does not do justice to the individual measuring point due to the lack of a risk-based approach with regard to process requirements, drift behavior, the type and frequency of use of the measuring technology, environmental conditions and, above all, with regard to criticality (calibration outside). The challenge here is the tightrope walk between individual consideration of a measuring point and, at the same time, cross-departmental consistency in the definition.

 

The following notes can provide guidance in determining the interval that is right for you:

  • Legal requirements for calibrations:

The Betriebssicherheitsverordnung (BetrSichV - German law) requires regular inspection of operating equipment.

The BetrSichV talks about administrative offences in § 22 and criminal offences in § 23 if this is not observed.

 

  • Manufacturer recommendation for calibrations:

"In case of high demands on the measuring accuracy as well as in construction site use with frequent transport stress and large temperature fluctuations, we recommend a relatively short calibration interval of 1 year. If your measuring device is mainly used in laboratory operation and indoor areas without stronger climatic or mechanical stresses, then a calibration interval of 2-3 years is usually sufficient."

 

  • Specifications of your internal quality management system for calibrations:

If you are ISO certified, you will find specifications in your QM manual.

Regulatory guidance can also be found here, under "legal requirements".

 

  • Recommendations of official institutions:

DAkkS-Guideline

The german "Guideline and Examples for Calibration and Monitoring Periods of Equipment for Laboratories in Consumer Health Protection 71 SD 4 027" recommends typical fixed calibration intervals for laboratory equipment. For electronic thermometers, test weights, or manometers, an annual interval is recommended. 

 

ILAC-Guideline

In the "Guidelines for the determination of calibration intervals of measuring instruments" a basic distinction is made between the initial determination of the calibration interval and an adjustment based on data collected during the life cycle.

In the initial determination, criteria such as the manufacturer's recommendation, the planned stress and frequency of use, environmental conditions, the required measurement accuracy, possible tolerances, drift behavior and comparison data should be taken into account.

 

Our conclusion:

If you lack well-founded data on the behavior and drift of the measuring point for determining the interval, the manufacturer's recommendation in the first instance, followed by the DAkkS guideline, provide good orientation. If there are measuring point-specific risk factors, these should be included as early as possible when determining the interval. 


If data or experience from similar measuring points is already available, it is advisable to include these values directly as well.

When determining the calibration interval, it is therefore always necessary to weigh up existing data, values and experience, various criteria specific to the situation, application and device, the risk, possible legal obligations and the costs. 

 

We will be happy to advise you on finding the optimum calibration interval for your test equipment. 

Contact: Tel.: +49 911 817718-0 / e-mail: service@gossenmetrawatt.com

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