Why the calibration of (force) measuring instruments is important

Everyone involved in measurement technology knows the somewhat flippant ? but very catchy ? statement: ?In the event that you measure a lot, you measure nothing!? What is meant by this is: You can measure a lot. But the values are only useful if you can validate them. In everyday activity, for example, you can be surprised when the scales at home show a big deviation from those at the physician?s or the bicycle speedometer deviates many a huge selection of metres from the GPS instrument. The word also often alludes to your tendency to generate a growing number of data inside our modern world, without thinking about its evaluation. As a way to obtain valid data with which to continue working, it is worthwhile for industrial measuring instruments to be calibrated regularly.
For the individual, the highest accuracy will not be important. In industrial applications, however, it really is precisely this that can make the key difference between rejects and the highest quality ? hence the calibration of the measuring instruments. It serves to match the measuring device with the national standard ? in a nutshell: to check whether the values are correct.
Traceability to the national standard
The keyword here’s thus the traceability to the national standard. Understanding that the respective measuring instrument measures the right value can be of great importance for most applications. For example, ISO 9000 requires that the deviations of the test equipment used ought to be monitored. With an up-to-date calibration, passing the audit is no problem. This avoids the repetition of the audit, production downtime or even a recall ? and therefore reduces stress, time and costs. The expenditure on the calibration has thus quickly covered itself. Everyone is happy.
Besides meeting the audit requirements, traceability may also be required for quality assurance, optimising resource utilisation and reducing energy consumption. Finally, the most convincing reason to have one?s own measuring devices checked relative to the current standard may be the feeling of security: The measuring instruments will continue to provide the correct values!
Certification in accordance with the German accreditation body
The illustration shows how the four calibration sequences relative to DKD-R 3-3 differ.
Uncovered for this may be the calibration certificate of the German accreditation body (Deutsche Akkreditierungsstelle ? DAkkS). WIKA has offered certification for pressure, temperature and electrical measurands (DC current, DC voltage and DC resistance) for quite a while. Because the beginning of 2022, tecsis has been accredited relative to DIN EN ISO / IEC 17025 for the measurand force.
What a DAkkS-certified calibration of force measuring instruments means is shown by the exemplory case of high-end force transducers, which are employed in calibration machines. In their case, the test sequence follows the EN ISO 376 standard. At least eight measuring stages are approached, with a total of five preloads, two upward series and two up-down series. Furthermore, the force transducers are each rotated by 120�, which results in three installation positions. With 65 measured values (eight stages), your time and effort is correspondingly high. The purchase price for this type of calibration goes together with this.
In the case of industrial devices, the question arises as to whether this type of procedure is worthwhile. Alternatively, the DKD-R 3-3 directive could be applied. It describes four test sequences which might be selected in line with the requirements. WIKA and tecsis likewise have DAkkS certification for this.
A further option for regular calibration is the non-standardised 3.1 inspection certificate.
Practical examples
An illustrative exemplory case of the usefulness of regular calibration is the checking of hydraulic compression force transducers. These instruments measure the clamping forces of industrial machines such as for example punches, pneumatic presses, sealing presses, spindle presses, tablet presses and toggle lever presses. Here, calibration provides a contribution to ensuring safe working conditions.
Another example may be the instrumentation for checking the contact forces of welding tongs. Ideally, they are monitored continuously by built-in tension/compression force transducers, however they may also be checked at set intervals using a test set for measuring electrode forces (model FSK01). This ensures the quality of the welding points and reduces wear on the electrodes.
For the tension/compression force transducers mentioned, calibration is also worthwhile, should they be used for monitoring very precise production steps. When pressing in Absurd , for example, both the measuring instruments and their calibration can easily pay back: If an error in that process is not noticed immediately (for example, if only the travel is controlled), thousands of euros in material value can be destroyed within minutes.
Adjustment before calibration can be handy
Depending on instrument, application and regulation, it might be worthwhile to have an adjustment carried out before calibration. In this manner, the user ensures that their measuring instrument achieves the corresponding accuracy during calibration. For the calibration itself, an individual has the option of choosing the type and procedure, both for the own and for third-party products.
Note
On the WIKA website you will find further information on the individual calibration services as well as on WIKA force measuring instruments (offers may also be available in the online shop). In case you have any questions, your contact will gladly assist you to.
Also read our post
Calibration or adjustment ? Where?s the difference?

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