Everyone involved in measurement technology knows the somewhat flippant ? but very catchy ? statement: ?If you measure a whole lot, you measure nothing!? What’s meant by this is: You can measure a lot. But the values are just useful when 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 an increasing number of data in our modern world, without considering its evaluation. To be able 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 best quality ? hence the calibration of the measuring instruments. It serves to match 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 is thus the traceability to the national standard. Understanding that the respective measuring instrument measures the proper value could be of great importance for many applications. For instance, ISO 9000 requires that the deviations of the test equipment used should be monitored. Having an up-to-date calibration, passing the audit is not any problem. This avoids the repetition of the audit, production downtime or even a recall ? and therefore reduces stress, time and costs. Mischievous on the calibration has thus quickly covered 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 is the feeling of security: The measuring instruments will continue to provide 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 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 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 used 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), the effort is correspondingly high. The purchase price for this type of calibration goes hand in hand 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 that can be selected good 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 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, however they can 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 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
Depending on the 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, 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 will discover further information on the average person calibration services as well as on WIKA force measuring instruments (offers are also available in the online shop). In case you have any questions, your contact will gladly assist you to.
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Calibration or adjustment ? Where?s the difference?g