2.1 Classification of reproducing physical quantities units and systems for transferring their sizes (RUTS)and systems for transferring their sizes (RUTS)
2.1.2 Analysis of the RUTS systems
2.1.2.7 Analysis of the concepts “reproduction of a unit of a physical quantity”
and “transfer of the size of a physical quantity unit”
The concept “RUTS system” is usually determined with its full name, i.e., with enu- meration of the main functions and their objects. In this connection it is important to analyze what is meant by the concepts “reproduction of a unit size” and “transfer of the unit size” of a physical quantity. Unfortunately, there is no clarity on this issue, especially with regard to the interpretation of the concept “reproduction of the unit”
(compare with [323, 390, 437, p. 12]).
SMU RUTS
system SSSRD SCMM
SND of SEMU
RUTS systems in particular kinds of measurement System of RUTS
means (MMI) RMMI
system
SMS VSHA
system
SMMI system
SSMS RWMS system SSS
AMMI system
System of RUTS methods
SRM STM
SEMU
Figure 2.2.Interrelation of subsystems of the system of ensuring the measurement uniformity.
Here: SEMU is the system of ensuring the measurements uniformity; SND is the subsystem of normative documents of SEMU; SMU is the subsystem of measurement units; RUTS sys- tem is the subsystem of reproducing PQ units and transferring their sizes; SSSRD is the state system of standard reference data; SCMM is the subsystem for certifying methods of measure- ments; RUTS subsystems are the subsystems of reproducing PQ units and transferring their sizes in particular kinds of measurement; Subsystem of RUTS means is variety of metrological measurement instruments (MMI); Subsystem of RUTS methods is variety of methods of repro- ducing PQ units and transferring their sizes; RMMI subsystem is variety of reference MMIs;
SMMI subsystem is variety of subordinate MMIs; AMMI subsystem is variety of auxiliary MMIs; SMS is the subsystem of the state measurement standards; VSHA is the subsystem of the verification setups of the highest accuracy; SSMS is the subsystem of the secondary mea- surement standards; WMS is the subsystem of the working measurement standards; SSS is the subsystem of the standard samples; SRM is the subsystem of the reproducing methods; STM is the subsystem of the transfer methods.
In the Reference Supplement to GOST 8.057–80 (a documentary standard) the re- production of a physical quantity unit is defined as the “totality of metrological op- erations aimed at determination of a PQ value reproduced by astate measurement standardat an accuracy at the level of recent achievements of metrology”.
Thus, here the reproduction of the unit is connected with a measuring instrument which is the most accurate in the given system of measurements. However “reproduc-
Section 2.1 Classification of RUTS systems 69 tion of a unit” is defined in terms of “reproduction of physical quantity” and does not expose the concept essence (let us note that a unit is one of the realizations of the same physical quantity).
However such a point of view does not conflict with another official document [195], according to whichany measureby its own definition reproduces the physical quantity of dimensions given (including the unit size). In this connection let us note that the largest part of measurement standards (also including national ones) reproduce not strictly the unit, but frequently the dimensions of the physical quantity which are too far from the unit. That is one of the difficulties in interpreting the term “reproduction of a unit”.
From the above it is obvious that there is a need to study more deeply the essence of this concept as one of the fundamental concepts of practical metrology, in particular of the problem of measurement uniformity assurance.
A single work specially devoted to this problem is the paper “Definition and re- production of physical quantity units” by Prof. S. V. Gorbatcevich1. In that work the author analyses the essence of the concept “reproduction of the units” and gives a more or less successful definition: “reproduction of the unit is the creation of a such an ob- ject (body or instrument), the properties or parameters of which are expressed by the quantity in terms of units corresponding their definition”.
A deep understanding is examined (unfortunately without giving an unambiguous formulation) in a monograph by M. F. Malikov [323, pp. 315–325]. The author also connects the “reproduction of the unit” with the practical realization of its theoretical definition. However, here, as distinct from the previous work, the author applies “re- production of the unit” not only to all measurement standards (including secondary ones) but also to working measurement standards, though on p. 285 he ascribes this property only to measures.
However there is onecommonthing which joins various points of view at the con- cept “reproduction of the unit”. This is the relation of the unit to a concrete measuring instrument, itsmaterialization(realization, embodiment).
It was shown above (Section 2.1.2.6) that a certain realization of the PQ unit in a concrete measuring instrument (a real content of measurement information about the unit size) with the help of which the measurement is carried out, is, according to expression (2.8a), a necessary condition of any measurement. In other words:any MI has to realize(actualize, materialize)in itself the unit size.
The vailability of a numerical factor for converting the unit size into its multiple or submultiple part does not play any principle role.
From this it follows that to apply the concept “reproduction of the unit size” in the sense of its materialization (realization) only to measurement standards is meaningless.
It is also applicable to working measuring instruments in this sense.
1 Metrologiya12(1972), 3.
Let us note, however, that information about the unit size really contained in every particular measuring instruments is a priori measurement information (in any mea- surement with the help of the given measuring instrument) obtained by an earlier experiment (as a posteriori measurement information in measurements with another measuring instrument).
A uniqueexception, obviously, isthe most accuratemeasuring instrument in the given system, for which there is no a priori information about the PQ dimension.
The unique a priori information about the unit of the given PQ for such a measuring instrument isformal information contained in the unit definition.
Thus, aunique possible versionof separating the concept “reproduction of the unit size” simply from its “materialization” can be the correlation of the first concept only with the most accurate measuring instrument in the given system of measurements.
So, the reproduction of the unit is its materialization (realization) of such a type, that the unique a priori information about the unit is its theoretical definition.
Such a definition in addition to its logical strictness allows us for the first time to approach theclassification of RUTS systems, as well as tounify their type structures.
Formalization of the concept “reproduction” needs to be made in further studies. In the simplest case of one measuring instrument used for the purpose of reproducing, which corresponds to measurement equation (2.8), then taking into account (2.9) and believing that according to the definition for this measuring instrumentạ' º D1, we obtain the equation of unit reproduction
'(meas)’st DNstŒ' . (C)
“Reproduction means” is also a measuring means, only without experimental a pri- ori information about the unit.
The concept “transfer of the unit size” is less disputable, since it contains in its name (term) rather full information about its essence.
In GOST 8.057–80 [195] the following definition of “transfer of the unit size” is given: the totality of metrological procedures aimed at defining on the basis of cali- bration or verification the PQ value which has to be ascribed to a secondary or work- ing standard at the time of either their calibration or metrological certification, or to a working measuring instrument in the process of its verification.
In [390, p. 173] the “transfer of the unit size” (under which the transfer of the unit size as a particular case of PQ realization can be understood) is defined as “founding (confirmation, ascription) metrological characteristics of a verified or certified mea- suring instrument with the help of a more accurate measuring instrument”.
In all other cases (without definitions) the “transfer of the unit size” is understood to be simply the totality of hierarchy comparison (within the limits of the given ver- ification scheme) of unit sizes “embedded” in subordinate measuring instruments by their verification or calibration (see, e.g., [437, p. 83]).
We think that further detailing is unnecessary (in the same way as in the preceding case), since a nongraduated measuring instrument, strictly speaking, is not a measur-
Section 2.1 Classification of RUTS systems 71 ing instrument (nothing can be measured with it). Moreover, the concepts “verifica- tion”, “certification”, “comparison”, “calibration”, and “graduation” reflect varieties of metrological procedures on transferring the unit size and are secondary with regard to the concept “transfer of the unit size “ presently being considered.
From this it follows that the main content of the concept “transfer of the unit size” is constituted bycomparison of unit sizes, “frozen”(embedded in the form of a priori measurement information)in(subordinate)measuring instruments varying in accuracy.
To make this concept formal, let us use the same equation (2.8). Since in transferring (comparison) they try to reach the situation when'2.meas/0 D'1.meas/0, where'1.meas/0 is the PQ value obtained with a more accurate measuring instrument, and'2.meas/0 is the value of the same PQ obtained with a subordinate measuring instrument, there we haveN2Œ'02 DN1Œ'10 , from which we get theequation of unit size transfer:
Œ'20 D N1 N2
Œ'10 . (D)
This case covers all the basic methods of transfer. Methods of indirect measurements which are frequently included into varieties of transfer methods, strictly speaking, can- not be related to the transfer methods (see Section 2.1.3.4).
An analysis of the main concepts of RUTS systems would not be complete without considering concept “maintaining the PQ unit”, which necessarily enters the legal definition of the concept “standard” [195].
For the concept “maintaining the PQ unit” there is only one explanation given in the reference supplement to GOST 8.057–80 [195]: “unit storage is the totality of metrological procedures aimed to keep the PQ, the value of which has been ascribed to the primary or working measurement standards at their metrological certification, invariable with time.
However such a definition should rather be referred to the concept “maintaining the measurement standard” (compare with [323, p. 326] and [331]). Needless to say, at proper maintenance (which is absolutely mandatory, according to GOST 8.057–80) of the measurement standard, the latter, as well as the size of the unit it reproduces, will be kept. But generally speaking, theunit is maintained by any measuring instrument since the latter materializes (memorizes) it.
Therefore,maintaining the unitis simplyits realizationwith a given measuring in- strumentat any time. In particular, undermaintaining the unit with the measurement standardone should understandits reproduction at any time. However long the mea- surement standard reproduces the unit, so long will it maintains this unit (certainly, the longer the better).
In this connection it should be noted that the reproduction of the unit with the mea- surement standard (with the state measurement standard as the most accurate one in the SSM) in a definite time can be performed by two methods:
(1) thediscretemethod, according to which the unit is reproduced only at any time interval where the standard setup is “switched on”; in the remaining time the stan- dard is the reproducer of the unit onlypotentially;
(2) theanalogousmethod, according to which the standard reproduces the unit at any moment of time until it exists as the standard.
From this, inter alia, a very important requirement becomes obvious which concerns the nomenclature of the metrological characteristics of national measurement stan- dards connected with their ability to maintain corresponding units. Whereas accord- ing to the analogous method of reproduction it is sufficient to characterize the error of maintaining the unit byinstability(with a stability index), when using the discrete method of reproduction (as will be seen in Section 2.1.4.2, this method is the most widespread one of the national measurement standards in force) it is also necessary to indicate together with the stability index the reproducibility of this standard (as an error of the standard due to its different “inclusions”.