• Gossen Metrawatt
  • Camille Bauer

Calibration Questions and Answers

  • Why is calibration important?

    Test equipment monitoring is specified as an essential element of quality assurance for standard calibration in accordance with the DIN EN ISO 9000-9004 series of standards. Test equipment monitoring must assure that all test equipment used for assuring product quality measures “correctly”.

    Note:

    • In order to ensure that this is the case, test equipment must be calibrated on a regular basis (ISO 9001:2000, paragraph 7.6)

    • Laut DIN VDE 0701-0702: 2008: "Die für die Wiederholprüfung benutzten Messgeräte, sind regelmäßig zu prüfen und zu kalibrieren"

    • "Der Unternehmer hat dafür zu sorgen, dass die elektrischen Anlagen und Betriebsmittel ...in bestimmten Zeitabständen ... auf ihren ordnungsgemäßen Zustand geprüft werden. (Auszug aus §5, (1) der Unfallverhütungsvorschrift BGV A3)

     

    In order to ensure that this is the case, test equipment must be calibrated on a regular basis, and must be retraceable to national standards. Obtained measured values must be documented as well. Retracing of calibration results to national standards has been confirmed for the user in the past by means of a "factory certificate" provided as a standard feature.

     

     

    ILAC = International Laboratory Accreditation Cooperation
    EA = European Cooperation for Accreditaion
    DAkkS = Deutsche AkkreditierungsStelle
    (National Accreditation Body of Germany)

     

    However, international recognition of certificates of this type has become more and more uncertain due to rapidly growing numbers of, in some cases unqualified, calibration service providers. For this reason, ISO9000 inspectors are not only demanding calibration certificates from EA accredited or associated calibration service (European Cooperation for Accreditation) in European countries outside of Germany.

    Our DAkkS calibration laboratory is accredited by the Deutsche AkkreditierungsStelle
    in accordance with DIN EN ISO / IEC 17025 under registration number D-K-15080-01-01.

    This assures that all requirements regarding service provider expertise are adhered to. Personnel assigned to DAkkS laboratories are subjected to examination for adequate capabilities and skills, and are continuously monitored. Beyond this, technical standards such as measuring uncertainty are known, and can be published as well.

  • What is calibration?

    Calibration is a process by means of which
    deviation of the display value from the actual value is determined and documented for a given measuring instrument, or deviation of the output quantity from the nominal value for a given test instrument.

    Measurement is thus performed which allows for a comparison of the device under test to a precise standard which can be traced back to national standards by means of a documented process. The objective of this process is to recognize and document deviations.

    If the value displayed by the measuring instrument, or the output quantity of the test instrument, is found to be outside of the allowable tolerance range during the course of calibration, two options are available:

    1. The instrument is adjusted in order to bring its values back into the allowable tolerance range, and is then recalibrated.
    2. Adjustment is deliberately omitted because the user wants to document measuring deviation for long-term use of his measuring or test instrument during defined periods of time.
  • What is adjustment?

    Adjustment is a process by means of which an instrument is aligned or balanced such that measuring deviation from the setpoint value is as small as possible, and within the allowable tolerances specified for the instrument. The process of adjustment causes permanent change to the measuring instrument.

  • What is traceability?
    Traceability describes a process by means of which the measured value indicated by a measuring instrument can be compared to the national standard for the given measured quantity in one or several steps.
    • Establishment of a link to the German Federal Institute of Physics and Metrology (PTB)
    • Assurance of traceability of measured quantities to SI units
    • Calibration of working standards, as well as on-site calibration benches and test equipment monitoring

    The on-site test benches assigned to the permanent calibration laboratory fulfill the following functions:

    • alibration of measuring instruments and calibrators
      - Devices are calibrated at these test benches either during the course of final manufacturing inspection as a standard routine, or individually when service is required.
    • Calibration of special measuring equipment, for example:
      - Shunts by means of current-voltage method
      - High value resistance, 30 GOhm with
        UM=1000V

    Traceability and organization of our
    DAkkS calibration lab (standards hierarchy)

     

  • Who benefits from the DAkkS calibration certificate?

    All customers who have implemented a QA system in accordance with ISO 9000.
    This is especially true for smaller companies, because instruments with calibration certificates can be used as a comparative standard for multimeters and hand-held calibrators.

    Calibration service providers - the certificate is especially advantageous for final inspection stations at which balancing, adjustment and calibration are performed.

    Companies who are required to test electrical equipment in order to ascertain that it is in good working order can also rest assured that test equipment used for the assurance of product quality measures "correctly" and is traceable to national standards.

  • DAkks calibration certificate or factory calibration certificate?

    We are frequently asked in which cases the relatively inexpensive factory calibration certificate would be adequate in place of the more costly DAkkS certificate.

    Factory calibration certificates are issued based upon the use of standards which are subjected to test equipment monitoring on a regular basis. Traceability of the utilized standards is assured by means of test equipment monitoring at regular intervals.

    Factory calibration certificates are sufficient where calibration accuracy is important for the utilized measuring and test equipment, as long as it is not used as a standard.

    DAkkS calibration certificates are issued based upon the use of standards whose traceability is assured by means of DAkkS certificates or calibration certificates issued by the laboratories of the DAkkS (= German national accreditation body). DAkkS calibration certificates may only be issued by calibration laboratories which have been accredited by the DAkkS and only for specifically accredited measured quantities. This assures the maintenance of high standards of calibration quality by means of regular audits, traceable standards, precisely defined ambient conditions and specially trained personnel. These cost and personnel-intensive measures result in a higher price, but they also assure the reliability required for correct measuring results.

    Due to guaranteed traceability to national standards, DAkkS calibration should be used for the re-calibration of test equipment which itself is used as a standard for the monitoring of other measuring and test equipment.

  • What is the recommended calibration interval?

    In order to continuously perform correct measurements, utilized measuring and test equipment must be monitored and calibrated on a regular basis. The corresponding time period is known as the calibration interval. Users of measuring and test equipment frequently ask how often calibration of this equipment is required.

    There is no single correct answer to this question, because calibration always represents an instantaneous snapshot of actual conditions which is dependent upon a variety of factors including the following:

    • Measured quantity and allowable tolerance range
    • Level of stress to which the equipment is subjected
    • Stability of past calibrations
    • Required measuring accuracy
    • Quality assurance requirements

    In the final analysis, this means that the period of time between any two calibrations must be determined and monitored by the user himself.

    We recommend a calibration interval of 1 to 3 years. In order to assist our customers in making this often costly decision, we offer free consultation services provided by our own employees.

    As a rule, we specify a period of 1 year in our factory calibration certificates. Deviations from this rule should be noted by the customer in the purchase order, as well as in the delivery note.

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