What is calibration



Checking measuring devices for which there are no legal requirements is not called calibration, but rather calibration. In contrast to oak, it is not a task prescribed by the government. Reasons for calibration are, for example, quality assurance or procedural regulations such as DIN EN ISO 9001: 2000.

Terms

A internal Calibration is a calibration (AK) in which all measuring devices are standardized to a company-internal or organizational standard.

A traceable Calibration is a calibration whose reference or normal is a national standard (for example a measuring device / measurement setup from the Physikalisch-Technische Bundesanstalt or a certified reference material from the Federal Institute for Materials Research and Testing (BAM)).

All measurement results obtained with traceable measuring devices are on the one hand traceable to this national standard and on the other hand consequently also comparable with each other.

Traceable calibrated measuring devices are often referred to as reference measuring devices. The advantage of the measuring devices that can be traced back to national standards (and thus usually also to international standards) is the global comparability of the measurement results.

The Dictionary of Metrology (VIM) defines calibration:

Calibration includes the activities to determine the relationship between the output values ​​of a measuring device [...] and the known values ​​of the measured variable under known conditions.

It should be noted that calibration:

  • no specification test (statement of conformity)
  • no comparison
  • and does not contain any statement about drift,

but, strictly speaking, only represents the actual value recording on the basis of measurement uncertainties. The detailed tests mentioned above are the tasks of test equipment monitoring.

The Calibrate (sometimes incorrectly referred to as "calibration") is a measurement process for determining and documenting the deviation of a measuring device or a material measure with a higher-order standard, and not just in metrology.

Calibration * Determination of the relationship between the measured value or expected value of the output variable and the associated true or correct value of the measured variable present as the input variable for a measuring device under consideration under given conditions. During calibration, there is no intervention that changes the measuring device. * According to DIN 1319 Part 1, January 1995 edition, Title: "Basics of measurement technology" - basic terms - Publisher: DIN German Institute for Standardization e.V.Beuth-Verlag GmbH, Berlin-Vienna-Zurich.

Part of a calibration

  • the definition of the measurement process (environmental conditions, required standards, procedure)
  • Creation of a mathematical model for evaluating the calibration, taking all of them into account known systematic influences
  • an uncertainty analysis using the mathematical model
  • Indication of a complete result, d. H. Calibration value and calibration uncertainty.
  • Draw up a log, too Calibration certificate or Calibration certificate called.

The calibration value for the calibration item is used to correct the measured value. In connection with a normal history, statements can be made about the reliability of the calibration item.

A well-known example is the calibration (if carried out by the verification office, then synonymous with verification) of a scale by applying a standard weight. Taking into account systematic influences (measurement deviation of the standard mass, air pressure, temperature, buoyancy) and random influences, the display of the calibration item, the scales, is compared with the standard mass measurement standard. In order to be able to make a statement about the influence of random influences, the measurement is carried out and statistically evaluated with sufficient frequency. Another approach eliminates randomness through fixed standard test conditions, for example with fixed reference temperatures.

Guidelines and requirements

In addition to the requirements and technical measures of quality assurance and quality management, such as test equipment monitoring and traceable calibration of measuring equipment, the calibration guideline VDI (Association of German Engineers) / VDE (Association of Electrical, Electronics and Information Technology) / DGQ (German Society for Qualität eV) / DKD (German Calibration Service) 2622 general calibration instructions, models for the calculation of measurement uncertainty and the traceability of measured variables for most electrical and electronic instruments.

Calibration versus adjustment

Calibrate
During calibration, a measuring device is checked and the deviation (measurement tolerances) from a (known correct) standard or measurement setup is determined and documented / logged, for example the deviation from the original meter in Paris (or other reference standards from PTB, NPL or DKD, UKAS etc.). Actions beyond the logging do not take place during the calibration. The aim of the calibration is a protocol, the so-called calibration certificate (also calibration certificate).
After a calibration, under no circumstances may changes be made to the (measuring) device, otherwise the calibration (= protocol / documentation) will be worthless. Calibration can only be done by those who have a higher order standard - i.e. who have a (known correct) standard or measurement setup available - and who are capable of logging.

Adjust
When adjusting, the display of a measuring device is corrected, i.e. the measured / displayed value (the so-called actual value) is corrected as well as possible to the correct value, the so-called target value. The aim is to get a correct ad. Basically anyone who is able to operate the measuring device can adjust measurement setups that can be adjusted. An adjustment, for example to the zero display, is often carried out before each measurement using adjusting screws directly on the device. However, an adjustment does not say anything about deviations in the measurement results (setpoint to actual value). This is exactly what the calibration is about. For example, the well-known welded-in clinical thermometers cannot be adjusted, but they can be calibrated.

Both adjustment and calibration are often carried out as part of device maintenance (sometimes also during verification). Note: after each adjustment, a previously carried out calibration is worthless, a new calibration is then absolutely necessary.

See also

  • Calibration, testing, adjustment, metrology, German calibration service (DKD)
  • Error calculation, accuracy class, caliber (disambiguation), absolute measurement
  • Color management calibration,
  • Calibration
  • Estimation quality for cardinal insolvency prognoses

Category: Analytical Chemistry