Extrusion 7-2017

84 kompakt Extrusion 7/2017 ➠ ZUMBACH Electronic AG www.zumbach.com n Calibration in measurement technology means characteriz- ing the measurement behaviour of a measuring unit by compa- ring the indications provided by the unit with a known “mea- surement standard” (a physical object) used in the calibration procedure. During the calibration, the measuring instrument is not subject to changes, as opposed to adjustment where a measuring unit is tuned or modified in order to minimize the measurement er- rors or to guarantee that the measurement errors do not ex- ceed predetermined bounds. Verification in legal metrology, however, pertains to the examination and marking and/or is- suing of a verification certificate for a measuring system. The examining authority thus verifies whether the measuring unit satisfies the corresponding legal prerequisites. Unlike for legal verification, where the validity of a marking or certificate is defined by law, the validity of a calibration interval follows practical requirements such as manufacturer indicati- ons, requirements of the applied quality standards, or company internal and customer specific regulations. Traceability and calibration hierarchy : In order for measure- ment results to be compared, they must be traced back to a na- tional or international measurement standard to this purpose, the display of the measuring must be compared with the mea- surement standards in one or more stages. On each of these stages a calibration is carried out with a measurement stan- dard, which has been previously 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 measure- ment standard – there is a calibration hierarchy to be respected by the organization performing the calibration. This stretches from the in-house laboratory through accredited laboratories up to the national metrological institute. Correct Calibrations : Different standards, regulations and di- rective must be respected when carrying out calibrations. A measurement unit must satisfy basic requirements before it can be calibrated. One must also know and consider the physical conditions under which a calibration is carried out. (Self)compensation of Measuring Units Increases Accuracy of Measurements Regulations are essentially applicable when a company 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 series, are be- coming increasingly important for quality assurance in all indu- strial nations. This standard explicitly requires, among other things, to calibrate all test equipment that directly or indirectly influences the quality of the product. This includes, for exam- ple, test equipment that is used as reference measurement standard during the production process. Zumbach Electronic adheres to different directives and stan- dards. The regulations of the FDA (American Food and Drug Administration), for example, are important worldwide with respect to international trading relations. The CFR (Code of Fe- deral Regulation) requires “the calibration of instruments, ap- paratus, gauges, and recording devices at suitable intervals in accordance with an established written program containing specific directions, schedules, limits for accuracy and precision, and provisions for remedial action in the event accuracy 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 : Zumbach’s 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 correspon- ding protocol can be carried out according to the customer re- quirements. The regularity of these calibrations depends on the customer specific requirements (internal regulations). The com- pany recommend a verification of the measurement error every 12 to 24 months. All the measuring heads of the ODAC ® series have a self-com- pensation function (Patent DE3111356), which makes a regular calibration superfluous, except when components had to be re- placed. All the relevant parameters for accuracy are continuously moni- tored by the measuring electronics and automatically compen- sated. 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 national measurement standard for the considered physical units in ac- cordance with the International System of Units (SI). Picture: Typical ODAC ® laser diameter measuring gauge with a certified measurement standard used to calibrate the device