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’s meant by that is: You can measure a lot. However the values are only useful when you can validate them. In everyday life, for example, one may be surprised once the scales in the home show a large deviation from those at the physician?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 increasingly more data inside our modern world, without thinking about its evaluation. As a way 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 is precisely this that can 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 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. 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. 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 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 relative to the current standard may be the feeling of security: The measuring instruments will continue to provide the correct values!
Certification relative to the German accreditation body
The illustration shows the way the four calibration sequences in accordance with 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. 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 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), 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 as to whether this type of 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.
Affordable for regular calibration is the non-standardised 3.1 inspection certificate.
Practical examples
An illustrative exemplory case 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 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, however 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 the measuring instruments and their calibration can quickly pay off: If an error in such a process is not noticed immediately (for example, only if the travel is controlled), thousands of euros in material value can be destroyed within minutes.
Adjustment before calibration can be useful
According 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, the user gets the option of choosing the type and procedure, both for our own and for third-party products.
Note
On the WIKA website you can find further information on the individual calibration services in addition to on WIKA force measuring instruments (offers may also be 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?