Under the procedure of metrological certification should be understood as checking the conformity of the device indicators obtained as a result of testing with the established metrological values, which are recorded in GOST 8.326-89. This event is carried out in order to legitimize the use of measuring instruments and confirm the reliability of the results of studies conducted with its use.
Why is this procedure necessary?
Carrying out metrological certification of measurement methods and special instruments is caused by the need to determine how the actual performance of the equipment complies with the requirements of standards and regulations. Verification may be subject to certain devices. But also those that are not subject to mandatory state examination in the territorial bodies of the State Metrological Service. Also, tests are periodically carried out with experimental samples of the developed measuring instruments, as well as imported equipment, imported into the territory of the Russian Federation in a single copy or in a limited batch.
Verification and metrological certification of measuring instruments pursues the following objectives:
determination of priority qualities and properties of devices subject to regular verification and control;
establishing a list of metrological characteristics and identifying inconsistencies with parameters approved by official documents;
approbation of new research and calibration methods.
Certification is carried out by state bodies subordinate to the HMS and conducting their activities according to a special developed program. The results of equipment testing after metrological certification are drawn up in the form of protocols of an established form. If the verification results are positive, a Certificate of passing the appropriate control and certification is issued. This document indicates all the characteristics that devices manufactured on the basis of GOST should have.
Measuring instruments and testing equipment. What is the difference?
In contrast to the verification of measuring instruments, metrological certification of test equipment is assigned to confirm the possibility of creating testing conditions within the framework of minor errors and to establish the suitability of using the devices for their intended purpose. Both verification and certification can be primary or repeated (periodic). During the primary test procedure:
the degree of influence of external factors or circumstances on the choice of the mode of operation of the device is determined;
threshold values are recorded and documented when testing specific types of products;
deviations from averaged normalized values are determined;
the possibility of guaranteeing the safety of personnel is being established;
confirmed the absence of harmful effects on the environment;
a list of important equipment indicators that need to be regularly inspected is identified.
Repeated metrological certification and verification is carried out during the operational operation of the testing equipment. The devices are tested in the volume that is necessary to confirm the parameters of compliance of the operating characteristics with the requirements of regulatory and operational documents. The results of the metrological research and certification are entered into the protocol. If the results of the test turn out to be positive, a certificate of a standard form is issued for the equipment and an appropriate entry is made in the operational documents.
About reproducing units of standard values
An important condition during the metrological certification is to ensure the unity of the physical characteristics of the device with its minimum and maximum operation. Speaking about the unity of measurements, they understand the characteristic of qualitative criteria, which consists in translating the results of the verification into legal units. The exact dimensions of these criteria are set within the obtained values. At the same time, inaccuracies in testing and obtaining results are taken into account with a given probability, therefore, they are within clearly established frameworks.
The term "unity of measurement" has a wide meaning, since it involves solving the paramount tasks of metrological research. The unification of the physical quantities necessary when developing a system for reproducing and transmitting data with absolute accuracy. Metrological certification of measurement methods allows for their unity with minimal accuracy. Necessary for scientific and technical analysis.
To achieve and maintain a high level of measurement uniformity, the activities of many subordinate metrological services in the regions are carried out. They conduct research in accordance with applicable rules, requirements and standards. The functioning of the system of government bodies ensuring the uniformity of measurements is regulated by regulatory legal acts of the metrological service and territorial structures subordinate to them.
To guarantee the uniformity of measurements, a prerequisite is the presence of identical units with a gradation of all existing measurement systems of a fixed value. This can be achieved due to the maximum accuracy during reproduction and storage in specialized institutions of the established standards of physical quantities, as well as the transfer of their sizes by the used control device.
Derivative and basic units
Metrological certification is applied to measuring instruments requiring the reproduction of units of a physical quantity. This indicator is the next sequence of operations to derive a unit of physical quantity at the highest accuracy. This happens by comparing with the state standard or the original model measuring instrument.
Reproduction of a basic unit is the execution of a unit through the formation of a fixed value. The basic unit can be reproduced only with the help of the state primary standard. As an example, we give a unit of mass equal to one kilogram. The state standard is made in the form of a platinoiridium weight, which is stored in the International Bureau of Weights and Measures as a world standard for a kilogram. All other countries that use the standard measurement system are given a copy of this kilogram weight in a nominal value of 1 kg. Taking into account the latest international comparisons that were carried out 40 years ago, the mass of the platinoiridium weight, which is part of the state standard of the Russian Federation, amounted to 1.000000087 kg.
Unlike the main one, reproduction of a derived unit involves the establishment of a physical quantity in strictly defined units based on indirect measurements and other quantities that are functionally related to the measured parameter. So, for example, the reproduction of a unit of force, according to Newton’s law, takes place on the basis of the formula known to all students: P = mg, where m is body weight; g - its acceleration during free fall.
Storage and transfer
Metrological certification is applied to measuring instruments capable of not only reproducing, but also transmitting units in exact sizes, that is, bringing the values of stored calibrated devices into conformity with the sizes of standard units during verification or calibration. In this case, the transfer of the size of the unit occurs from top to bottom, that is, first they receive more accurate means, then less accurate.
When storing a unit, a set of several simultaneous actions is meant, which are designed to ensure the stability of the unit's dimensions in time with the performance of a particular measuring device. Saving the reference unit in parallel entails the implementation of several interrelated operations that would allow to maintain the metrological criteria of the standard in a strictly established framework. When storing the primary standard, regular research can be avoided, including comparison with national standards of foreign countries to increase the accuracy of reproduction and increase the efficiency of transmission methods.
More about the standard
This is a set of measuring instruments designed to reproduce or save a unit. As already noted, during the certification of metrological equipment, the transfer of sizes to lower competent is carried out in the prescribed manner. Moreover, GOST 8.057-80 defines an acceptable classification, assigns general requirements for the formation, conservation and use of the standard.
The number of standards does not match the number of existing physical quantities. For some units, a standard is not created, because sometimes it is impossible to directly compare and make sure that physical quantities are consistent. For example, during the metrological certification of measuring devices, the area standard is not used, since in principle it cannot exist, it is also impossible to develop it. Sometimes standards are not developed if units of physical quantities are reproduced with minimal error against the background of primitive devices for measurements.
Reference Properties
The standard may have its own calibration. Metrological certification involves the mandatory consideration of the design of the sample, its physical properties and the method of reproducing the main and derived units. In this case, the standard should be unchanged, compare, easily reproducible.
By invariance is meant the property of the measuring instrument to maintain stable values of reproducible units over a certain time interval. In addition, all changes that depend on external conditions should be strictly determined by the functions of the quantities that are available for accurate measurement. High results of metrological certification of measuring channels can serve as an idea for the development of "natural" standards of various sizes, based on physical and constant indicators.
Reproducibility is the ability to reproduce a unit of a physical quantity based on a theoretical definition with a minimum probability of error for the current level of development of the measuring instrument. It is achieved through the constant study of the standard to identify the percentage of systematic errors and their exclusion by making appropriate adjustments.
When conducting metrological certification, the comparability of the standard plays a huge role, which allows us to achieve full comparison with the standard of other measuring instruments that are lower in the verification scheme, including secondary standards. This allows you to achieve maximum accuracy with any applicable measurement technique. Comparability implies that the reference samples do not introduce any distortion into the result of the comparison.
The main types of standards
The first classification of standards used in the metrological certification of methods and means of measurement is based on the reproduction of units. Thus, the standards are divided into primary and secondary. Primary guarantees the conservation and reproduction of a physical quantity with maximum accuracy. Such a standard will show the most reliable result in the country, in comparison with other standards. They are unique measuring devices that have a complex measuring structure. Primary standards are created taking into account the latest achievements of scientific and technological progress; therefore, they form the basis of the state system for using the instruments of measurement uniformity.
The secondary standard stores the unit parameters that were obtained after comparison with the primary standard in the same physical quantity. Such samples are always included in the complex of subordinate means of saving units and distributing their sizes; they are used only when there is a real need for organizing the metrological certification. According to GOST, the safety standards and minimum wear of the state standard are provided by bodies related to the HMS system.
The composition of the secondary standards includes measuring instruments with which a unit of physical quantity is stored and conditions for the transfer of dimensions are controlled. The secondary standard, which is the starting point for the State Metrological Service, is often called a worker or departmental. In aggregate, state primary or secondary standards, which serve as the basis for ensuring the unity of indicators, make up the state’s standard base.
National and International Model Values
It is easy to guess that the international standard is a sample of a physical quantity, which is accepted as a sample under an international treaty. Such a standard takes precedence over domestic models. When passing the procedure of metrological certification of measuring channels, mandatory coordination with the parameters of the international standard of physical quantity is required.
Domestic standards, which are also called national, are more often primary samples that are officially approved as the main source. State standards are made, stored and used in the central metrological scientific institutes of the country. The error in the reproduction of a unit shall not exceed the minimum permissible deviations. Since the national standard is considered to be fully consistent with the international one, it is used in various scientific and technical projects. The composition of domestic standards also includes measuring instruments that allow you to store and reproduce a unit of physical quantity. National standards sometimes undergo a comparison procedure with sovereign samples from other countries.
By the number of measuring instruments that are included in the standard, distinguish:
group standards containing a combination of the same type of measuring instruments for the range and nominal value;
single samples, in the composition of which there is only one measuring system (instrument or reference installation) for the execution and saving of a unit.
If the sample measure is intended to be transported to the place of metrological certification according to the measurement methodology, it is called transported or mobile.
Inaccuracies
Permissible error limits of standards are established by GOST 8.381–80. Deviations in primary samples of the state level are unstable. Such an error can be systematically excluded, which can be understood by the boundaries at which it is found. Random deviation is determined by the mean square multiplication. As a result of measurements, when the unit is executed, the number of independent measurements is indicated. Instability of the standard defines changes in the size of the unit when reproducing or storing the standard for a certain time interval.
The degree of error of the secondary standard can be estimated by the degree of deviation of the sizes of the saved units from the size of the derived unit obtained from the primary sample. In this case, the total error is necessarily indicated and random deviations are taken into account when comparing, transferring unit sizes or instability of the secondary sample. In total, the error can be characterized as the result of measurements taken when comparing with the primary or secondary standard, which is higher in the measuring scheme. Also, the resulting number can be the extreme limit of the deviation with a probability of not more than 0.99.
In the certification of metrological channels, the transfer of parameters of units of physical quantities from secondary reference measuring devices is carried out using working standards. By the way, this term was introduced in Russia not so long ago. Instead, the phrase “exemplary measuring instruments” was used, however, it was necessary to abandon it in order to bring the terminology in line with international.
Working standards are divided into categories. Each of them is used in a specific order and rules of subordination according to the verification scheme. Different types of measurements require a different discharge of the sample, which also depends on the standards of calibration schemes. The correct transfer of units of physical quantity in the existing links of the metrological chain can be done right up to the installation of calibration schemes, which is a normative document. The verification scheme establishes the subordination of the measuring instruments involved in the transfer of the dimensions of the sample to the working devices, indicating the errors and the measurement method.