Everyone involved in measurement technology knows the somewhat flippant ? but very catchy ? statement: ?If you measure a lot, you measure nothing!? What’s meant by that is: It is possible to measure a lot. But the values are just useful when you can validate them. In everyday life, for example, one may be surprised when the scales in the 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 word also often alludes to your tendency to generate an increasing number of data in our modern world, without thinking about its evaluation. So that you can obtain valid data with which to continue working, it really is worthwhile for industrial measuring instruments to be calibrated regularly.
For the individual, the highest accuracy is probably not important. In industrial applications, however, it is precisely this that may make the key 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 if the values are correct.
Traceability to the national standard
The keyword here’s thus the traceability to the national standard. Realizing that the respective measuring instrument measures the proper value could 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 even a recall ? and thus 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 can also be necessary 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 supply the correct values!
Certification in accordance with the German accreditation body
The illustration shows the way the four calibration sequences in accordance with DKD-R 3-3 differ.
The highest standard because of 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 some time. Because 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 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), your time and effort is correspondingly high. The purchase price for such a calibration goes together with this.
In the case of industrial devices, the question arises concerning whether this type of procedure is worthwhile. Alternatively, the DKD-R 3-3 directive can be applied. It describes four test sequences which can be selected in line with the requirements. WIKA and tecsis also 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 measure 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 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 can also be checked at set intervals utilizing 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 mobile phone displays, for example, both measuring instruments and their calibration can easily pay back: If an error in such a process isn’t noticed immediately (for example, if only the travel is controlled), thousands of euros in material value could be destroyed within minutes.
Adjustment before calibration can be handy
Depending on instrument, application and regulation, it may be worthwhile to have an adjustment completed before calibration. In this way, the user ensures 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 can find further information on the average person calibration services in addition to on WIKA force measuring instruments (offers may also be available in the online shop). Should Hope have any questions, your contact will gladly assist you to.
Also read our post
Calibration or adjustment ? Where?s the difference?