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Standards, Accreditation, and Traceability
Standards are codified requirements for a process such as calibration or compliance. Promulgated by cooperative industry bodies and/or governmental entities, standards are the cornerstone of calibration.
Three key industry standards govern the way calibration is done around the world today:
- ISO/IEC/EN 17025 (compliant): the most rigorous globally-accepted standard. Prescribes "General Requirements for the Competence of Calibration and Testing Laboratories". The service organization providing this calibration meets the requirements of ISO17025.
- ISO/IEC/EN 17025 (accredited): the most rigorous globally-accepted standard. Prescribes "General Requirements for the Competence of Calibration and Testing Laboratories". This is verified by an independent accrediting body operating under ISO17011.
- ANSI/NCSL Z540-1-1994 (R2002): known as "Z540". A U.S. standard that sets compliance guidelines for "Calibration Laboratories and Measuring and Test Equipment".
- ISO 9001: a set of quality management process standards that confirms adherence to quality guidelines, including calibration and maintenance.
Every compliant calibration will be accompanied by a calibration certificate and other documentation attesting to the standards that have been followed.
Accreditation is a rigorous certification process that ensures compliance with applicable standards. It enforces traceability and consistency across an entire calibration process. Accreditation is all about the capability and competence of a calibration process, as confirmed by an accreditation body. In the language of standards and metrology, the terms "competent" and "competence" denote the verified ability to carry out calibration procedures in compliance with applicable standards.
An accredited laboratory that performs ISO 17025 calibrations, for example, will have proven facilities and equipment and competent personnel—specific individuals empowered to do the ISO 17025 calibrations. Traceability is a requirement in accreditation.
Tektronix service facilities are ISO 9001-registered and/or ISO17025 accredited. All sites that offer calibration can deliver Z540 traceable calibration (in the U.S.) or the local equivalent.
- Every accredited lab has a "scope of measurements," documented on its accreditation certificate, defining the types of measurements the lab is certified for: DC voltage, resistance, etc.
- ISO 17025 accreditation requires review and approval of every single measurement step in the calibration procedure—sometimes thousands of measurements.
- Procedures submitted for accreditation by third-party calibration vendors may not be the same as those recommended by the instrument manufacturer.
Traceability is the thread that connects your calibrated tools to established references and standards. It confirms that your instruments will measure accepted units (whether electronic, optical, or dimensional) to agreed levels of accuracy. Traceability is key to meeting worldwide measurement, trade and regulatory requirements.
Certified measurement products sold by Tektronix are traceable to national metrology institutes and the SI (International System of Units). Tektronix measurement products are shipped with Certificates of Traceable Calibration.
Traceability begins with standards maintained in national metrology institutes as shown in Figure 1. These standards, understood to have the highest accuracy available, are used to calibrate instruments in independent or corporate laboratories. These in turn confer traceability to instruments in calibration departments within individual companies such as Tektronix.
- Tektronix measurement instruments built in the United States are compliant with ANSI/NCSL Z540.1-1994(R2002) requirements, traceable to one or more of the following national metrology institutes: NIST, NPL and PTB. The facility is ISO 9001 registered.
- Tektronix measurement instruments built in China comply with ANSI/NCSL Z540.1-1994(R2002) requirements, traceable to one or more of the following national metrology institutes: NIM, NIST, NPL and PTB. The facility is ISO 9001 registered.
- The NIST website lists more than 100 national metrology laboratories worldwide
- The national metrology institutes throughout the world regularly compare their standards with one another, ensuring consistency across national borders
- Standards encompass electrical, optical, dimensional, and other measurements. All are traceable to national metrology laboratories
- ISO 9001 quality standards require traceability. Compliant facilities must "calibrate... against certified equipment having a known valid relationship to internationally or nationally recognized standards."
Traceability follows a hierarchy of standards, each referencing the one above it and conferring its traceability to those below it. In this example, two schemes for voltage calibration are shown. The left branch derives some standards from external laboratories.