Calibration of Measuring Devices

determination of the error of measuring devices and establishment of the devices’ fitness for use. Calibration is carried out by agencies of the metrological service, using reference standards and base standards. Governmental calibration is obligatory for measuring devices used in reporting material value, for government tests and expert examinations, and for recording national and international sports records, and also for calibration of the original base standards. All other measuring devices are calibrated by the appropriate departments.

There are four types of calibration: (1) primary calibration, which is performed when a measuring device is put into circulation from production or returned from repair; (2) periodic calibration, which is conducted during use or storage of a device; (3) special calibration, which results from the need for immediate verification of the good condition of a device; and (4) inspection calibration, which is performed during metrological inspections of enterprises, supply centers, warehouses, and commercial organizations. Calibration may be done in various ways, including (1) comparison of the measuring device being calibrated with a base standard of the same type (that is, comparison of a gauge with a gauge or one measuring instrument with another); (2) comparison of measuring devices of the same type by means of a comparator (for example, comparison of weights on scales); (3) direct measurement by the instrument being calibrated of a quantity that is displayed by a reference gauge; (4) direct measurement by a reference instrument of a quantity displayed by the gauge being tested; or (5) indirect measurement of a quantity that is measured by the measuring device under test. Independent calibration—that is, testing of measuring devices for relative (dimensionless) quantities, which does not require transfer of the dimensions of units of measurement from standards—is also possible.

A description of the methods and technical procedures for calibration of specific measuring devices is contained in the corresponding governmental standards or procedural instructions. The calibration methods and the corresponding comparison instruments are frequently shown in calibration diagrams, which establish the order and accuracy for the transfer of units from reference standards to base standards and from the latter to working measuring devices. If the results of calibration are positive, a verification stamp is placed on the measuring device and, where required, a certificate is issued.