The calibration of measuring instruments is necessary to maintain accuracy, but does not necessarily increase precision. Precision most generally stays constant over the working range of the instrument.
Introduction to ISO 10012 Standards:
ISO 10012-1 :2003. Quality assurance requirements for measuring equipment – Part 1: Metrological confirmation system for measuring equipment contains quality assurance requirements to ensure that measurements are made with intended accuracy. It contains guidance on the implementation of the requirements and specifies the main features of the confirmation system. It applies to measurement equipment used in the demonstration of conformance with a specification, not to other measuring equipment, records of measurement, or competence of personnel. ISO 10012 applies to testing laboratories, including those providing a calibration service. It includes laboratories operating a quality system in accordance with ISO/IEC 10725. It also covers those who must meet the requirements of ISO 9001. An integral part of the quality system is the documentation of the control of inspection, measurement, and test equipment. It must be specific in terms of which items of equipment are subject to the provisions of ISO 10012, in terms of the allocation of responsibilities, and in terms of the actions to be taken. Objective evidence must be available to validate that the required accuracy is achieved. The following are basic summaries of what must be accomplished to meet the requirements for a measurement quality system by ISO (and many other) standards.
All measuring equipment must be identified, controlled, and calibrated and records of the calibration and traceability to national standards must be kept.
The system for evaluating measuring equipment to meet the required sensitivity, accuracy, and reliability must be defined in written procedures.
The calibration system must be evaluated on a periodic basis by internal audits and by management reviews.
The actions involved with the entire calibration system must be planned. This planning must consider management system analysis.
The uncertainty of measurement must be determined, which generally involves gage repeatability and reproducibility and other statistical methods.
The methods and actions used to confirm the measuring equipment and devices must be documented.
Records must be kept on the methods used to calibrate measuring and test equipment and the retention time for these records must be specified.
Suitable procedures must be in place to ensure that nonconforming measuring equipment is not used.
A labeling system must be in place that shows the unique identification of each piece of measuring equipment or device and its status.
The frequency of recalibration for each measuring device must be established, documented, and be based upon the type of equipment and severity of wear.
Where adjustments may be made that may logically go undetected, sealing of the adjusting devices or case is required.
Procedures must define controls that will be followed when any outside source is used regarding the calibration or supply of measuring equipment.
Calibrations must be traceable to national standards. If no national standard is available, the method of establishing and maintaining the standard must be documented.
Measuring equipment will be handled, transported and stored according to established procedures in order to prevent misuse, damage and changes in functional characteristics.
Where uncertainties accumulate, the method of calculation of the uncertainty must be specified in procedures for each case.
Gages, measuring equipment, and test equipment will be used, calibrated, and stored in conditions that ensure the stability of the equipment. Ambient environmental conditions must be maintained.
Documented procedures are required for the qualifications and training of personnel that make measurement or test determinations.
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