Extrusion International 4-2017

33 Extrusion International 4/2017 Unlike for legal verification, where the validity of a marking or certificate is defined by law, the valid- ity of a calibration interval follows practical require- ments such as manufacturer indications, require- ments of the applied quality standards, or company internal and customer specific regulations. Traceability and calibration hierarchy In order for measurement results to be compared, they must be traced back to a national or interna- tional measurement standard To this purpose, the display of the measuring must be compared with the measurement standards in one or more stages. On each of these stages a calibration is carried out with a measurement standard, which has been pre- viously calibrated with a higher-level measurement standard. According to the ranking of the mea- surement standard – from a working or company reference measurement standard to a national or international measurement standard –there is a cali- bration hierarchy to be respected by the organiza- tion performing the calibration. This stretches from the in-house laboratory through accredited labora- tories up to the national metrological institute. Correct Calibrations Different standards, regulations and directive must be respected when carrying out calibrations. A mea- surement unit must satisfy basic requirements be- fore it can be calibrated. One must also know and consider the physical conditions under which a cali- bration is carried out. Regulations are essentially applicable when a com- pany decides to respect a standard or directive or when it delivers products that are subject to legal requirements (like in the medical or transportation markets). Standards for Quality Control – Statutory Regulations Standards and directives, such as the ISO 9000 se- ries, are becoming increasingly important for qual- ity assurance in all industrial nations. This standard explicitly requires, among other things, to calibrate all test equipment that directly or indirectly influ- ences the quality of the product. This includes, for example, test equipment that is used as reference measurement standard during the production pro- cess. Zumbach Electronic AG adheres to different direc- tives and standards. The regulations of the FDA (American Food and Drug Administration), for ex- ample, are important worldwide with respect to international trading relations. The CFR (Code of Federal Regulation) requires « the calibration of instruments, apparatus, gauges, and recording de- vices at suitable intervals in accordance with an es- tablished written program containing specific direc- tions, schedules, limits for accuracy and precision, and provisions for remedial action in the event accu- racy and/or precision limits are not met». European legislation has similar requirements. Example of a Zumbach measuring unit: Calibration and self-compensation functions of ODAC ® Measuring Heads Our measuring units are calibrated using reference and also working measurement standards which are certified by the federal office for metrology (www. metas.ch) or by accredited laboratories. Each unit is supplied with a detailed calibration protocol. A regular check for measuring errors along with the corresponding protocol can be carried out accord- ing to the customer requirements. The regularity of these calibrations depends on the customer spe- cific requirements (internal regulations). We recom- mend a verification of the measurement error every 12 to 24 months. All the measuring heads of the ODAC ® series have a self-compensation function (Patent DE3111356), which makes a regular calibration superfluous, ex- cept when components had to be replaced. All the relevant parameters for accuracy are con- tinuously monitored by the measuring electronics and automatically compensated. This is particularly important for counteracting possible ageing effects of the scanner motor or possible long-term drifts of the measuring electronics. Documentation A calibration protocol presents the results of the calibration and documents the traceability to a na- tional measurement standard for the considered physical units in accordance with the International System of Units (SI). ZUMBACH Electronics www.zumbach.com