Questions for self-verification.

To guarantee the MIs uniformity, it's necessary to gauge them and systematically check their errors by comparison with the higher accuracy MI, which in its turn must be compared with the else higher accuracy MI, etc.

Finally, MI of the highest accuracy must be compared against the single MI, which in accordance with the definition, reproduces a physical quantity unit and is called as standard.

Thus, according to a metrological duty, all the MIs can be divided onto two groups.

1. Working MIs - are used for measurements that are not related with a unit size transfer .

2. MIs, which provide transfer of a unit size to all the working MIs.

The standards and the reference MIs, definitions of which in accordance with ДСТУ 2681-94 were represented earlier, belong to the second group. According to subordination the standards are divided into primary and secondary.

Primary standard reproduces the unit with the highest accuracy (in contrast with other standards of the same unit).

The special standards, that are intended for the units reproduction under special conditions (super frequencies, pressures, temperatures, etc.) are the primary standards varieties.

Secondary standards are subordinated to the primary ones, their values are traceable to the primary ones. Standard-copies, transfer standards, and working standards are belonged to the secondary ones.

Standard-copies are appointed to transfer a unit-size to the working standards, which serve for verification of the reference and the highest accuracy working MIs.

Transfer standard is appointed for mutual comparison of standards, which, taking into account the different reasons, can not be directly compared one against another.

This is because the standards are enough complicated stationary installations, which are not subjected to transportation. The transfer standards have considerably more simple design; only the stability of a PQ reproducing during the standards transportation and comparing are required.

The standards on their composition  are divided into individual and collective ones.

Individual standard contains only one material measure                 (instrument or installation).

Collective standard contains the same type material measures (measurement devices) that reproduce a unit-size as arithmetic mean of the reproduction results made by every element from that assemblage.

 As an example of the inividual standard the primary mass standard can serve. Its assembladge concludes: the international prototype copy of the kilogram-platinum-iridium prototype № 12, which represents by itself a weight in a form of cylinder with rounded ribs by diameter and high of 39 millimeters and the standard balances № 1 and № 2 of 1 kg range with remote control that are appointed for the mass unit-size transfer from the prototype № 12 to the standard-copies and from the standard-copies to the working standards according to the procedure which is standardized by the specification.

As an example of a collective standard the primary standard of electric resistance can be. It includes 10 manganin coils of electric resistance with the nominal resistance of l ohm and a bridge measurement installation.

Herewith they suppose that the electric resistance values arithmetic mean is less liable to variations than the resistance of each coil.

Duplicate-standard consists of six 1 ohm coils. The transfer standards and the working standards are the 1 ohm material measures of electric resistance.

To transfer a unit size from the standard to the working MIs the intermediate reference MIs are introduced in such a way that in the issue a hierarchical structure, on the top of which a State standard is located, appears.

To guarantee the necessary accuracy of the working MIs it is necessary to specify an amount of stages for the unit-size transfer from the standard and a transfer error for the every step. These errors are conditioned by the unit-size transfer method as well as by the reference MIs own metrological characteristics.

Thereby for every physical quantity the appropriate hierarchy scheme must be specified.

                                      11.2 Hierarchy scheme