Why the calibration of (force) measuring instruments is important

Everyone involved in measurement technology knows the somewhat flippant ? but very catchy ? statement: ?If you measure a lot, you measure nothing!? What’s meant by this is: It is possible to measure a lot. However the values are only useful if you can validate them. In everyday activity, for example, you can be surprised once the scales at home show a big deviation from those at the doctor?s or the bicycle speedometer deviates many hundreds of metres from the GPS instrument. The saying also often alludes to your tendency to generate progressively more data inside our modern world, without considering 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 best accuracy might not be important. In industrial applications, however, it really 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 whether the values are correct.
Traceability to the national standard
The keyword here’s thus the traceability to the national standard. Realizing that the respective measuring instrument measures the right value can be of great importance for many applications. For instance, 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 perhaps a recall ? and thus reduces stress, time and costs. The expenditure on the calibration has thus quickly covered itself. Beauty are happy.
Besides meeting the audit requirements, traceability may 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 is the feeling of security: The measuring instruments will continue to supply the correct values!
Certification relative to the German accreditation body
The illustration shows how the four calibration sequences in accordance with DKD-R 3-3 differ.
The highest standard because of this is 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 some time. Because the beginning of 2022, tecsis has been accredited in accordance with 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 used in calibration machines. Within their case, the test sequence follows the EN ISO 376 standard. At the very least eight measuring stages are approached, with a complete 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.
In the case of 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 for this.
An additional option for regular calibration may be 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 punches, pneumatic presses, sealing presses, spindle presses, tablet presses and toggle lever presses. Here, calibration provides a contribution to ensuring safe working conditions.
Bona Fide may be the instrumentation for checking the contact forces of welding tongs. Ideally, these 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 mobile phone displays, for example, both the measuring instruments and their calibration can quickly pay back: If one in such a process isn’t noticed immediately (for instance, if only the travel is controlled), several thousand euros in material value can be destroyed within minutes.
Adjustment before calibration can be useful
Based on the instrument, application and regulation, it may be worthwhile to have an adjustment completed before calibration. In this manner, the user ensures that their measuring instrument achieves the corresponding accuracy during calibration. For the calibration itself, the user gets the option of choosing the sort and procedure, both for the own and for third-party products.
Note
On the WIKA website you will see further information on the average person calibration services in addition to 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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