Calibration Certificate
Introduction
Calibration is the process of comparing the values obtained by a measuring instrument with the corresponding measurement of a reference standard (or standard). According to the International Bureau of Weights and Measures, calibration is "an operation that, under specific conditions, establishes in a first step a relationship between the values and measurement uncertainties provided by standards and corresponding indications with the associated measurement uncertainties and, in a second step, uses this information to establish a relationship to obtain a measurement result from an indication."[1].
From this definition it can be deduced that to calibrate an instrument or a standard it is necessary to have one of greater precision (standard) that provides the conventionally verifiable value, which will be used to compare it with the indication of the instrument that is being subjected to calibration. This is done through an uninterrupted and fully documented chain of comparisons until reaching the primary standard, which constitutes what is known as traceability.[2] The objective of calibration is to maintain and verify the proper functioning of the equipment, respond to the requirements established in the quality standards and guarantee the reliability and traceability of the measurements. Measuring instruments require calibration more frequently the more exact their samples are, that is, the smaller the error tolerances. In general, calibration intervals depend on factors such as the requirements given by a client or a regulation and the stability over time of the instrument to be calibrated.[3].
The calibration of any measuring instrument must be carried out under controlled humidity and temperature conditions by an accredited calibration laboratory; there are various accrediting bodies depending on each country.
In Mexico there is the Mexican Accreditation Entity, EMA, an entity that accredits the quality and technical competence of a calibration laboratory to offer metrology and instrument calibration services.
During the calibration process, the output value of the instrument to be calibrated is contrasted against a standard at different points in the calibration range. If the calibration error—an error that is revealed during calibration—is less than the rejection limit determined, either by standards, the company or the manufacturer's recommendation, the calibration will be accepted.[4] Otherwise, an adjustment of the instrument with a subsequent contrast is required. These last two steps are repeated as many times as necessary until the error obtained is less than the established limit. In equipment in which adjustment is not available, such as thermocouples, etc.; If the marked tolerances are not met, the devices will have to be replaced with others that have been previously calibrated.