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. But the values are only useful if you can validate them. In everyday life, for example, one may be surprised when the scales in the home show a large 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 our tendency to generate an increasing number of data in our modern world, without considering its evaluation. To be able to obtain valid data with which to keep working, it really is worthwhile for industrial measuring instruments to be calibrated regularly.
For the individual, the best accuracy is probably not important. In industrial applications, however, it is precisely this that may 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 is 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. Having 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 paid for 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, Jaw-dropping to have one?s own measuring devices checked in accordance with the current standard is 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 the way 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 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 employed 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 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), the effort is correspondingly high. The purchase price for such a calibration goes together 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 could be applied. It describes four test sequences which can be selected good requirements. WIKA and tecsis likewise have DAkkS certification because of this.
A further option for regular calibration may be 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 is the instrumentation for checking the contact forces of welding tongs. Ideally, these are monitored continuously by built-in tension/compression force transducers, but they may also be checked at set intervals utilizing a test set for measuring electrode forces (model FSK01). This ensures the standard of the welding points and reduces wear on the electrodes.
For the tension/compression force transducers mentioned, calibration can be worthwhile, should they be used for monitoring very precise production steps. When pressing in mobile phone displays, for example, both measuring instruments and their calibration can quickly pay back: If an error in that 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 handy
Depending on instrument, application and regulation, it may be worthwhile with 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, 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 average person calibration services as well as on WIKA force measuring instruments (offers are also available in the online shop). Assuming 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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