2.1 Classification of reproducing physical quantities units and systems for transferring their sizes (RUTS)and systems for transferring their sizes (RUTS)
2.1.3 Varieties of the elements of a particular RUTS system
2.1.3.1 Reference metrological measuring instruments (RMMI)
Within the framework of the state system of measurements being considered, it is pos- sible to refer to reference MMIs for a particular RUTS system, the following categories of MMIs:
state measurement standards (SMS) defined in GOST 16263; among them are distinguished (see also GOST 8.057 [195]) state primary measurement standards (SPMS) and state special measurement standards (SSMS);
verification setups for reproducing the units by the indirect method. In practice these setups obtained the name “verification setups of the highest accuracy” (VSHA);
complex of working measurement standards (WMS) borrowed from other verifica- tion schemes (is admitted too by GOST 8.057–80).
However the definitions of each category are fuzzy to such an extent that they do not permit the MMI given to refer specifically to one of them.
In fact, all PQ units (except the basic ones) can be reproduced by the method of indirect measurements (through the direct measurements of other PQs, the units of which are known). Therefore, if a verification setup of a high accuracy means a com- plex fixed MIs necessary for indirect measurements, then there will be no principle distinctions from the national measurement standard.
On the other hand if one assumes that in the third category, too (of borrowed metro- logical measurement means: measuring instruments or working measurement stan- dards), all standards included into the complex are fixed within the framework of one setup, then the latter will not differ at all from the first two categories (since MIs of other PQs can doubtlessly reproduce the PQ given only by an indirect method.
Since the assumptions made are not regulated by anything, then there seems to be some difficulty in referring MMI to some category.
Evidently the nomenclature of the varieties of reference MMIs has to follow from the distinction of the RUTS systems types on the basis of different essential signs of their reproduction, i.e., it has to be based on the classification of RUTS systems, which will be considered in Section 2.1.4.
Here we will only notice that this issue requires an independent terminology devel- opment taking into account the matter stated in this item, as well as in Section 2.1.4.
Section 2.1 Classification of RUTS systems 75 2.1.3.2 Subordinate MMI
The category of subordinate metrological measuring instruments intended for metro- logical application includes
standards-copies (S-C);
varieties of secondary measurement standards;
working measurement standards which can be related to some grade of standards;
verification setups (VS).
All of these varieties are indicated in GOST 16263 and included into GOST 8.057 [195]. Here, too, the interpretation of these varieties requires further improvement.
Thus, the working standard is for some reason defined not generally by a measuring instrument (it would be more logical to ascribe to it the corresponding metrological functions), but by three concrete varieties of measuring instruments (measures, instru- ments, transducers), and as a result it is necessary to artificially introduce the concept
“verification setup” (VS).
No distinctions (including those of metrological kind) are seen between the cate- gories of secondary standards intended for transferring the unit size: S-C and WMS.
In accordance with Section 2.1.2.8 (and the definitions in GOST 16263–70) they all can serve only in transferring the unit size; and the introduction of the S-C as an addi- tional transfer link with a new name but the same functions filled by the VS and WMS appears even less convincing.
Moreover, the name S-C is itself not really adequate. The idea springs to mind that it would be better to use this term for a measuring instrument which really fulfils func- tions of the copy (as a reserve version, see Section 2.1.3.3). It should be noted that because of this a number of real verification schemes and standard-copies have been introduced with various functions.
In our opinion, from a metrological point of view for subordinate metrological mea- suring instruments, it would be quite enough to have only one category of working standards of various grades.
2.1.3.3 Auxiliary MMI
This class of metrological measuring instruments, as mentioned above, was formed historically on the basis of experience gained in applying reference and subordinate metrological measuring instruments. This experience has shown that in some cases it is useful and necessary to have, together with reference and subordinate metrolog- ical measuring instruments, a number of metrological measuring instruments of an auxiliary destination, which fulfill one of thefunctionsindicated below, which result from themetrological applicationof reference and subordinate metrological measur- ing instruments:
performing comparisonof reference and subordinate metrological measuring in- struments of a given particular RUTS system, or corresponding basic (as a rule, the reference ones) metrological measuring instruments of the RUTS systems of one and the same physical quantity but for various measurement systems (national and international ones);
checking of thesafety(invariability) of metrological characteristics of a reference metrological measuring instrument;
replacement of a reference metrological measuring instrument in case of its failure.
To perform thefirstfunction the following varieties of measuring instruments are re- quired:reference measurement standards(according GOST 16263–70 and 8.057–80 [195]) andcomparators(they are not regulated anywhere, but provided for in GOST 8.061–80 [194]). To perform thesecondandthirdfunctions only one category is pro- vided for. It is astandard–witness(according to GOST 16263–70).
According to GOST 8.057–80 the measuring instruments which control the invari- ability of the size of a unit reproduced by a state measurement standard have to be in- cluded into it, i.e., to perform the second function there is no any independent category of metrological measuring instruments. Thus, it turns out that the standard-witness serves only for replacing the state measurement standard.
Taking this into account it is possible to say that the term “standard-witness” used for the function of replacing the state measurement standard cannot be considered to be very accurate. For this purpose the name “standard-copy” seems more appropriate.
It is also not satisfactory that until now the important category of comparators has not been regulated though any transfer of the unit size performed through comparison (see Section 2.1.2.7); and if it is necessary for this purpose to use additional measuring instruments, which undoubtedly influence the accuracy and method of transferring the unit size, then they are worthy of the same attention as is the case with other metro- logical measuring instruments.
This “nonsense” is mostly observable in the case of a verification scheme for mass measuring instruments (weights and balances). Only weights are the metrological mea- suring instruments, whereas the balances, although they have grades, are not regulated by the national verification scheme, i.e., they are considered to be versions of working measuring instruments.
2.1.3.4 Methods of transferring a measurement unit size
In accordance with GOST 8.061–80 [194], four categories are provided for methods of transferring the unit sizes (in the GOST they are called “verification methods”, which, in our opinion, is not entirely correct):
(1) direct collation (without comparison means, i.e., not using auxiliary MMM);
(2) collation with a comparator or other comparison means;
Section 2.1 Classification of RUTS systems 77 (3) the method of direct measurements;
(4) the method of indirect measurements.
Disregarding the first three varieties, which are interpreted more or less distinctly (see, for example [394, p. 179]), let us dwell only on the method of indirect measurements.
In indirect measurements, as is known, the value of a physical quantity (a PQ being sought)being measured is determined on the basis of direct measurements ofother physical quantities, i.e.,
'i.meas/0 Da
'1.meas/0 '2.meas/0,: : :,'j.meas/0,: : :,'i.meas/0,Ck
, (2.11)
wherei ¤j, andCkis the totality of some constants which appear when determining units in a certain system of units.
Taking into account the equation of direct measurements (2.8a), as well as equation (2.11), it is possible to see that when carrying out such measurementsa priori infor- mationconcerns only the units ofotherphysical quantities, Therefore, in view of the aforesaid (Section 2.1.2.7), equation (2.11) can be only the equation of thereproduc- tionof the unit given.
However, if the value 'i.meas/0 of the quantity sought is known from some other more accurate measurements (perhaps also obtained by an indirect method), then the transfer of the unit size becomes possible:
'i.meas2 /D'i.meas1 / and ạ'i2ºŒ'i02 D ạ'i1ºŒ'i01 , hence
Œ'i02 D ạ'i1º
ạ'i2ºŒ'i01 .
But such a comparison is possible when either a more accurate measuring instru- ment is the measure, or both measuring instruments measure one and the same concrete realization of the physical quantity by an indirect method, i.e., they are transportable.