Everyone involved in measurement technology knows the somewhat flippant ? but very catchy ? statement: ?If you measure a whole lot, you measure nothing!? What is meant by Hero 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 large deviation from those at the doctor?s or the bicycle speedometer deviates many a huge selection 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 thinking about 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 really is precisely this that may make the crucial 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 short: to check whether the values are correct.
Traceability to the national standard
The keyword here’s thus the traceability to the national standard. Understanding 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 should be monitored. With 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. The expenditure on the calibration has thus quickly paid for itself. Everyone is happy.
Besides meeting the audit requirements, traceability can also be required 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 to supply the correct values!
Certification relative to 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 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 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 employed 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. In addition, 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 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 can be applied. It describes four test sequences which might be selected based on the requirements. WIKA and tecsis likewise have DAkkS certification because of this.
An additional 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 gauge 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 provides 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 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 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 easily pay off: If an error in that process isn’t noticed immediately (for instance, if only the travel is controlled), several thousand euros in material value could be destroyed within minutes.
Adjustment before calibration can be useful
With regards to the instrument, application and regulation, it might be worthwhile to have an adjustment completed before calibration. In this manner, the user means that their measuring instrument achieves the corresponding accuracy during calibration. For the calibration itself, an individual gets 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 average person calibration services as well as on WIKA force measuring instruments (offers are also available in the online shop). Should you have any questions, your contact will gladly help you.
Also read our post
Calibration or adjustment ? Where?s the difference?