FAQs – Calibration
Activity for determining the relationship between the output values of a measuring device or the values represented by a material measure or a reference material and the associated values of a measured variable specified by standards under specified conditions.[Definition from “International Vocabulary of Basic and General Terms in Metrology”]
The verification of a measuring instrument (including a material measure) includes the tests to be carried out by the competent Verification Authority in accordance with the verification regulations and stamping. The test determines whether the meter submitted meets the verification requirements, ie. whether it complies with the requirements of its nature and metrological characteristics, in particular whether the amounts of measurement error do not exceed the error limit (s). The stamping certifies that the measuring instrument has met these requirements at the time of the test and that, due to its nature, it is expected that it will remain “correct” during handling in accordance with the rules of the technology within the subsequent calibration period.
Which measuring instruments are subject to the mandatory verification and which are exempted is regulated by law.
The word “verification” should be used only in this sense and not – as often customary – for adjustment or calibration.[Definition according to DIN 1319 part 1 06/85]
Adjustment … Activity that puts a measuring instrument into a usable operating condition.[Definition from “International Vocabulary of Basic and General Terms in Metrology”]
Execution and evaluation of the calibration in strict compliance with national or international standards and guidelines. The standards and measuring instruments used, as well as the procedure of the calibration and the algorithms of the evaluation and measurement uncertainty calculation were checked and accepted by the Accreditation Authority and laid down in the accreditation notification. Compliance is regularly monitored through audits and proficiency testing.
As a result, you will receive an ÖKD calibration certificate (with confirmation of conformity and classification of your test equipment, if applicable) and an ÖKD calibration mark to identify your test equipment.
Calibration mark of the Calibration Laboratory of the bvfs
ATTENTION! A calibration mark on a measuring instrument does not guarantee that the instrument will operate without error or meet the requirements of a standard. It’s just proof that the measuring instrument has been calibrated. Whether the measuring instrument is suitable for the respective measuring task always has to be taken from the calibration certificate!
The calibration is carried out in accordance with standards and regulations or according to customer requirements. In general, the scope of factory calibrations is lower.
The accreditation verifies the basics of calibration laboratory work.
ATTENTION! A calibration mark on a measuring instrument does not guarantee that the Instrument will operate without error or meet the requirements of a standard. It’s just proof that the measuring Instrument has been calibrated. Whether the measuring instrument is suitable for the respective measuring task always has to be taken from the calibration certificate!
Traceability is ensured in the sense of the series of standards ISO 9000ff (test equipment monitoring) and EN ISO 17025 by comparing measuring instruments with standards accredited calibration laboratories.
Calibration hierarchy as proof of the traceability of test results to national standards by calibration of the Calibration Laboratory of the bvfs.
Property of a measurement result or the value of a standard to be related to appropriate standards, generally international or national standards, by an uninterrupted chain of comparative measurements with specified uncertainty of measurement.
1. The adjective traceable is often used for this term.
2. The unbroken chain of comparative measurements we called traceability chain.
3. The comparison with higher accuracy norms or with appropriately defined ones
…… physical fixed points is also called connecting.[Definition from “International Vocabulary of Basic and General Terms in Metrology”]
Companies that need to demonstrate the traceability of their measuring equipment (such as accredited testing laboratories) need ÖKD (or equivalent) calibration certificates issued by national metrology institutes for the measuring equipment (but at least for the standards used for internal calibration).
If it is not possible to obtain ÖKD calibrations, factory calibration certificates may be sufficient.
These calibration certificates must show the uncertainty of the calibration according to EA-4/02.
In this case, the user of the measuring device is additionally forced to document in a supplier evaluation the competence of the calibration laboratory which has issued the factory calibration certificate.
If internal calibrations are carried out with a calibrated standard, the measurement uncertainty must also be calculated for these calibrations in order to be able to prove traceability.
Without the indication of the measurement uncertainty of the calibration, proof of traceability is not possible.
Calibrations carried out by accredited Calibration Laboratories as part of their accreditation must be recognized nationally or internationally.
The basis for international recognition is the MULTILATERAL AGREEMENT FOR THE MUTUAL RECOGNITION OF CALIBRATION SHEETS of the European Cooperation for Accreditation (EA), in which the Austrian Calibration Service (ÖKD) was accepted at the first General Assembly of EA on June 23, 1998 in Oslo.
Procedure for the formal recognition of the competence of an organization to carry out specific tasks.[Definition from DGQ Script 11-04 “Quality Management Terms”]
The Calibration Laboratory was accredited by the Federal Ministry for Economic Affairs of the Republic of Austria (BmWA) by the decision Zl. 96 113/12-IX / 6/98 of 13 March 1998.
The BmWA as Accreditation Authority is a signatory of the EA Multilateral Agreement and thus an internationally recognized accreditation athority.
Parameter associated with the measurement result that characterizes the dispersion of the values that could reasonably be associated with the measurand.
- The parameter may be, for example, a standard deviation (or a given multiple thereof), or half the width of an area having a fixed level of confidence.
- Measurement uncertainty generally contains many components. Some of these components can be obtained from the statistical distribution of the results of a series of measurements and characterized by empirical standard deviations. The other components, which can also be characterized by standard deviations, are derived from assumed probabilities, based on experience or other information.
- It is assumed that the measurement result is the best estimate of the value of the measurand, and that all components of the uncertainty contribute to scattering, including those arising from systematic effects, e.g. those that come from correction and reference standards.[Definition from “International Vocabulary of Basic and General Terms in Metrology”]
Literature for determining the measurement uncertainty:
- “Guide to the Expression of Uncertainty in Measurement”
- EA-4/02 “Expression of the Uncertainty of Measurement in Calibration”
- EA-4/02-S1 Supplement to EA-4/02
Calculation of the measurement uncertainty.
1) The measurement uncertainty is the basis of decision for the selection of a test equipment for a measuring task. According to the “golden rule of metrology”, the measurement uncertainty should be less than or equal to one tenth of the tolerance to be tested.
U <= T / 10
In exceptional cases, the measurement uncertainty U may be <= T / 5.
Following this guideline, it can be assumed that the measured values are recorded with sufficient accuracy.
2) The measurement uncertainty of a measurement result (calculated from the parameters of the measuring method used) is used for the conformity assessment of test objects (see also EN ISO 14253-1).
The calibration or measurement result, including measurement uncertainty, is within the specified tolerance zone. -> the measured object meets the requirements.
The calibration or measurement result, including measurement uncertainty, is outside the specified tolerance zone. -> the measured object does not meet the requirements
The calibration or measurement result lies within the tolerance zone, but the calibration or measurement result plus measurement uncertainty is outside the tolerance. -> Neither a match nor a non-match can be shown here.
In this case only helps:
- Measure once again with a smaller measurement uncertainty
- Already in advance with the supplier to make an agreement
- Reject the product
Ability of a measuring instrument to provide values of output near a true value.
(Accuracy is a qualitative term)[Definition from “International Vocabulary of Basic and General Terms in Metrology”]