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 whole lot, you measure nothing!? What is meant by that is: You can measure a lot. However the values are only useful if you can validate them. In everyday life, 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 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. So as 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 will not be 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 complement the measuring device with the national standard ? in short: to check if the values are correct.
Traceability to the national standard
The keyword here is thus the traceability to the national standard. Realizing that the respective measuring instrument measures the proper value can be of great importance for most applications. For instance, 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 therefore reduces stress, time and costs. The expenditure on the calibration has thus quickly paid for itself. Many people are 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 in accordance with the current standard may be the feeling of security: The measuring instruments will continue steadily to supply 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 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 some time. Since the beginning of 2022, tecsis has been accredited in accordance with DIN EN ISO / IEC 17025 for the measurand force.
Just 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 Behind The Scenes , 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. In addition, 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 this type of calibration goes hand in hand with this.
In the case of industrial devices, the question arises as to 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 in line with the requirements. WIKA and tecsis also 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 exemplory case of the usefulness of regular calibration may be the checking of hydraulic compression force transducers. These instruments gauge 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.
Another example is the instrumentation for checking the contact forces of welding tongs. Ideally, they are monitored continuously by built-in tension/compression force transducers, but they may also be checked at set intervals using 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 cellular phone displays, for example, both the measuring instruments and their calibration can quickly pay off: If an error in such a process isn’t noticed immediately (for example, only if the travel is controlled), several thousand euros in material value could be destroyed within minutes.
Adjustment before calibration can be useful
According to the instrument, application and regulation, it can be worthwhile to have an adjustment carried out 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 sort and procedure, both for our 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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