Questions and answers on the topics of measurement technology, calibration and quality management.
In the field of calibration, calibration is a measuring process that serves to reliably determine and document the deviation of a measuring device from another measuring device or standard. The deviation determined by the measuring device must be taken into account in the subsequent measurements so that the readings can be corrected.
Calibration includes the following steps, among others:
First of all, you should work according to quality assurance standards. According to the ISO 9000 series, production and measuring equipment must be calibrated, controlled and monitored according to recognized methods.
Furthermore, you offer your customers a high standard of confidence with the proper calibration of your measuring equipment.
You also save valuable time and money by regularly documenting and checking your measuring devices. Calibration increases your knowledge of your measuring equipment and enables you to compensate for failures in advance and carry out targeted maintenance.
A traceable standard is used for traceable calibration. The two parameters deviation and calibration uncertainty are assigned to this standard. The result of the calibration is now also expressed with deviation and calibration uncertainty and is therefore traceable. It is therefore not the measuring device that has the property of traceability, but the measurement result.
As mentioned above, calibration is merely the documentation and determination of the deviation of a respective measuring instrument or measuring standard in comparison to a reference standard traceable to national standards.
Calibration , on the other hand, confirms the conformity of a measuring device that is subject to legal metrology with a statutory national regulation. During calibration, the respective measuring device is calibrated by a legally authorized body and provided with a calibration seal and a calibration certificate.
The adjustment or calibration of a measuring device is not a mandatory part of a calibration, but may be necessary before a calibration if the deviation detected is unacceptably high.
According to EU Directive 90/384/EEC, scales must be officially calibrated if they are used as follows:
a) In commercial transactions, when the price of goods is determined by weighing.
b) In the manufacture of medicines in pharmacies and in analyses in medical and pharmaceutical laboratories.
c) For official purposes.
d) In the manufacture of prepackages.
Any person or company is permitted to carry out factory calibrations as long as they have a physical measuring device available.
The biggest difference to DAkkS calibration is the lower procedural effort, which is also reflected in the lower costs. With a factory calibration, significantly fewer measuring points are used for calibration items that do not comply with the DAkkS routine and the evaluation of the measurement results is not as precise and comprehensive as with a DAkkS calibration.
However, auditors do not recognize factory calibrations as proof of calibration due to insufficient documentation and traceability.
However, if you only have outliers in some of your measuring devices and simply do not know whether they are still working properly, then factory calibration is just the thing for you.
Accreditation by the DAkkS confirms that laboratories perform their tasks competently and in accordance with applicable requirements.
In a DAkkS calibration, measurement uncertainties are calculated precisely and assigned directly to each measurement result. Traceable calibration is therefore guaranteed. The ISO 17025 standard is applied and the effort for the process and securing the measurement results is maximized.
The advantages of DAkkS calibration of your measuring equipment are maximum safety, the best possible accuracy, minimum measurement uncertainty and international recognition.
First of all, reference can be made here to the DAkkS ISO standard 17025: “A calibration certificate (or calibration mark) must not contain a recommendation on the calibration interval unless this is done with the customer’s consent.”
Of course, there are also different opinions on the definition of calibration intervals. Therefore, there are also few recommendations or data on which the determination of calibration intervals can be based. External opinions often have an economic background and can therefore only be considered to a limited extent from a quality management perspective.
What is certain, however, is that the accuracy of the measurement results decreases with increasing usage time. This is the so-called drift. In addition, the metrological significance of the calibration result can no longer be guaranteed after a certain period of time without recalibration. The time of a new calibration must therefore be selected so that this does not occur.
If the input and output variables are proportional to each other, a single point is sufficient to describe the calibration relationship.
Input and output variables are interdependent and therefore two measuring points are sufficient to describe the calibration relationship.
Multiple measuring points usually do not allow linear calibration due to existing measurement uncertainties. For this purpose, the correlation of the measurement is described with the help of a balancing line (linear regression).
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