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’s meant by that is: It is possible to measure a lot. But the values are only useful when you can validate them. In everyday life, for example, one may be surprised once the scales in the home show a large deviation from those at the physician?s or the bicycle speedometer deviates many hundreds of metres from the GPS instrument. The saying also often alludes to your tendency to generate an increasing number of data in our modern world, without thinking about its evaluation. In order to obtain valid data with which to keep working, it is worthwhile for industrial measuring instruments to be calibrated regularly.
For the individual, the highest accuracy is probably not important. In industrial applications, however, it is precisely this that can make the key difference between rejects and the best quality ? hence the calibration of the measuring instruments. It serves to complement the measuring device with the national standard ? in a nutshell: to check if the values are correct.
Traceability to the national standard
The keyword here’s thus the traceability to the national standard. Knowing that the respective measuring instrument measures the proper value can be of great importance for most applications. For example, ISO 9000 requires that the deviations of the test equipment used should be monitored. Having 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 thus reduces stress, time and costs. The expenditure on the calibration has thus quickly covered itself. Sleazy are happy.
Besides meeting the audit requirements, traceability can also be necessary for quality assurance, optimising resource utilisation and reducing energy consumption. Finally, the most convincing reason to possess one?s own measuring devices checked in accordance with the current standard may be the feeling of security: The measuring instruments will continue steadily to supply the correct values!
Certification relative to the German accreditation body
The illustration shows how the four calibration sequences relative to DKD-R 3-3 differ.
The highest standard because of 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 example of high-end force transducers, which are used in calibration machines. Within their case, the test sequence follows the EN ISO 376 standard. At Backdoor 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 price for such a calibration goes hand in hand with this.
Regarding industrial devices, the question arises concerning whether such a procedure is worthwhile. Alternatively, the DKD-R 3-3 directive can be applied. It describes four test sequences that can be selected based on the requirements. WIKA and tecsis likewise have DAkkS certification because of this.
A further option for regular calibration is the non-standardised 3.1 inspection certificate.
Practical examples
An illustrative example 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 offers 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 utilizing a test set for measuring electrode forces (model FSK01). This ensures the caliber of the welding points and reduces wear on the electrodes.
For the tension/compression force transducers mentioned, calibration is also worthwhile, should they be utilized for monitoring very precise production steps. When pressing in cellular phone displays, for example, both measuring instruments and their calibration can quickly pay back: If an error in that process is not noticed immediately (for example, only if the travel is controlled), several thousand euros in material value can be destroyed within minutes.
Adjustment before calibration can be handy
Depending on instrument, application and regulation, it could be worthwhile to have an adjustment completed before calibration. In this way, the user means that their measuring instrument achieves the corresponding accuracy during calibration. For the calibration itself, the user has the option of choosing the sort and procedure, both for the own and for third-party products.
Note
On the WIKA website you can find further information on the individual calibration services in addition to on WIKA force measuring instruments (offers are also available in the online shop). Assuming you have any questions, your contact will gladly help you.
Also read our post
Calibration or adjustment ? Where?s the difference?

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