• Gossen Metrawatt

Calibration questions and answers

  • Why calibration?

    Measurement results are only meaningful and reliable if the measuring instrument is calibrated. In doing so, the result can be related to a reference through a documented, unbroken chain of calibrations, each of which contributes to the measurement uncertainty. Calibration can also be part of test equipment monitoring, which is required by the following standards, for example:

    • DIN EN ISO 9001:2015
    • DIN VDE 0701-0702: 2021-0608
    • Accident prevention regulation BGV A3 (§51)
  • What is calibration?

    Calibration means the determination and documentation of the deviation of the display of a measuring instrument from the correct value, or of the output variable of a test equipment from the nominal value.

    A measurement is thus carried out in which the test item is compared with the values of an accurate and traceable standard according to a documented procedure. The aim is to detect and document deviations.

    If the display of a measuring device or the output variable of a test equipment is outside the permissible tolerances during calibration, there are two possibilities:

    1. It is readjusted so that the values are within the permissible tolerances and then calibrated again.
    2. The adjustment is deliberately omitted because the user wants to have the measurement deviations of his measuring instrument or his test equipment documented for long-term use over defined periods of time.

    Our calibration laboratories are accredited by the DAkkS according to DIN EN ISO/IEC 17025. The DAkkS writes on its website that accreditation creates, among other things, confidence, security, freedom of trade, and market access.

    Our DAkkS calibrations are also internationally recognized, as DAkkS is a signatory to the multilateral agreement with ILAC (ILAC-MRA). This is indicated by the following logos on our calibration certificates.


  • What is adjustment?

    Adjustment is the process of setting or adjusting an instrument so that the measurement deviations from the nominal value are as small as possible and lie within the instrument specifications. Adjustment is a process that permanently changes the measuring instrument. Unfortunately, this process is often confused with the colloquial "calibration".

  • What does metrological traceability mean?

    Metrological traceability of the measured value means that the result is related to a reference by a documented, unbroken chain of calibrations, each of which contributes to the measurement uncertainty (International Metrology Dictionary, Beuth Verlag GmbH, Berlin 2012).

    Historically, this process is comparable to the "cubit" that was carved in stone or provided as a forged iron rail at the portal of the town hall or the central church:


    Source: Hans Koberger, Regensburg - Altes Rathaus - Masse - 2016, CC BY-SA 4.0


    The merchants could thus at any time compare their scale with the scale of the city i.e. trace back. Today, this process is represented as a traceability pyramid:

    Source: GMC-I Service GmbH, 10.12.2021


    At the top are the most accurate measuring standards (primary standards). These are usually located at the national metrology institutes (in Germany: Physikalisch Technische Bundesanstalt = PTB). The measurement uncertainties are smallest here and the number of calibrations performed is also lower. In the next level are the accredited calibration laboratories. These have somewhat higher measurement uncertainties; the calibration scope is significantly higher. This chain continues correspondingly further down.

  • Who benefits from the DAkkS calibration certificate?

    All customers who have implemented an ISO 9000 QA system.
    This is especially true for smaller companies, as the instruments can be used as a comparison standard for multimeters and handheld calibrators.

    Of course, also for calibration service providers. They are especially valuable for all final test stations where adjustment and calibration work is performed.

    Also companies that have to check or ensure the proper condition of electrical equipment have the assurance that their test equipment, which is relevant for product quality, measures "correctly" and is traceable to national standards.

  • DAkkS calibration certificate or factory calibration certificate?

    Very often the question is asked when the factory calibration, which is less expensive than the DAkkS calibration, would be sufficient as a recalibration measure.

    Factory calibration certificates are issued with standards that are subject to regular test equipment monitoring, and the traceability of the standards used is ensured by regular test equipment monitoring.

    Factory calibration certificates can be considered sufficient if the calibration accuracy of the measuring and test equipment is important, but the equipment does not serve as standards.

    DAkkS calibration certificates are issued with standards whose traceability has been performed by internationally recognized calibrations (e.g. DAkkS, Swiss Accreditation, UKAS or CIPM MRA laboratories). DAkkS calibration certificates can only be issued by laboratories accredited by DAkkS. The corresponding physical quantities must be listed in the scope of accreditation with the DAkkS for the respective laboratory.

    This ensures that a high quality of calibration is guaranteed by regular assessments, traceable standards, precisely defined environmental conditions and specially instructed personnel. These cost- and personnel-intensive measures result in a higher price, but also in the necessary reliability of the measurement results.

    When recalibrating test equipment, which in turn serves as standards for monitoring other measuring and test equipment, a DAkkS calibration is preferable to a factory calibration certificate.

  • Which calibration interval is recommended?

    Calibration interval means the period for repeating the calibration. The user is responsible for this period. The following factors must be taken into account:

    • Measured quantity and permissible tolerance band
    • Stress on the measuring and test equipment / intended use
    • Stability of previous calibrations
    • Required measuring accuracy
    • Determinations of the quality assurance system in the companies

    We recommend a calibration interval of 1 to 3 years. We are also happy to offer advice from our service staff. On request, we will note the date of the next calibration on the calibration certificate.


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