Everyone involved in measurement technology knows the somewhat flippant ? but very catchy ? statement: ?In Suck that you measure a whole lot, you measure nothing!? What is meant by that is: It is possible to measure a lot. However the values are only useful when you can validate them. In everyday life, for example, one may be surprised when the scales at home show a large 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 a growing number of data in our modern world, without thinking about 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 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 whether the values are correct.
Traceability to the national standard
The keyword here’s thus the traceability to the national standard. Knowing that the respective measuring instrument measures the right 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. With an up-to-date calibration, passing the audit is not any 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 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 in accordance with the German accreditation body
The illustration shows how 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 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 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 this type of calibration goes together with this.
Regarding 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 that can be selected in line with the 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 exemplory case of the usefulness of regular calibration may be 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 offers a contribution to ensuring safe working conditions.
Another example may be the instrumentation for checking the contact forces of welding tongs. Ideally, these are monitored continuously by built-in tension/compression force transducers, but they can 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 is also 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 off: If one in that process is not noticed immediately (for instance, only if 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 could 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, an individual gets the option of choosing the type and procedure, both for our own and for third-party products.
Note
On the WIKA website you will discover further information on the individual 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 help you.
Also read our post
Calibration or adjustment ? Where?s the difference?g