Questions for self – verification

1. What are metrological assurance and standardization?

2. How did the systems of the PQ units appear? How were they developed?

3. Which international organizations are involved inthe improvement of the metrological assurance? What are their functions?

4. What are the tasks of the Interstate Council on Standardization?

5. What is the structure of the State standardization system of Ukraine? How does this system work?

6. How is the metrological assurance performed in Ukraine? List the most important organizations.

METROLOGY. BASIC TERMS AND DEFINITIONS

Metrology is the science about measurement. Metrology is not a narrow- specialized science. It includes a wide range of theoretical and practical problems:

- general theory of measurements;

- PQ units and their systems;

- measurement methods and measurement instruments;

- methods of determination of measurements accuracy;

- bases of assurance of measurements traceability and standardization of MI;

- standards and reference MI;

- methods of unit-size transfer from standards or reference MIs to working MIs.

Reference (standard) measurement instrument^* is a measurement instrument, which is used for verification and gauging of other measurement instruments and confirmed as a reference (standard).

^* Comment: in accordance with the Law of Ukraine "About

               metrology and metrological activity" from

              13.03.99 those measurement instruments are referred           to as WORKING STANDARDS.

Standard (of physical quantity unit) (reference standard) is a measurement instrument officially confirmed as a standard, that provides reproducing and (or) retention of the PQ unit and transfers its dimension to the due instruments which stand under it in the hierarchy scheme.

 Metrology is concerned even with juridical and legislative problems, being the base of both standardization and production quality system.

2.1. Physical quantities

The physical quantity (PQ) is the property common to a class of material objects qualitatively and individual for each one quantitatively.

For example, all physical objects have weight, that characterizes their inertial properties, but quantitatively this property for one object is bigger, and for another one it is smaller.

Generally, the PQ concept is based on two more general concepts, namely, the quantity and the quality, so PQ is characterized in two relations- quantitative and qualitative. That is why a formal object representing a PQ consists of two symbols- the number and the name of a unit.

The magnitude of physical quantity is a quantitative component of physical quantity in the given object.

One shouldn’t use the term "quantity" to represent only quantitative characteristic of the given property, for example, in expressions "voltage quantity ", "mass quantity ", etc. In such cases one should use the terms "voltage value ", "mass value".

There are three levels of PQ value in measurment theory and practice:

- the true value (of PQ) ;

- the conventional true (actual) value (of PQ) ;         

- the measurement result .

The true value (of physical quantity) is the value of physical quantity, which could represent ideally the definite property of an object.

      The word “ideally” indicates the theoretical and philosophical nature of this concept. Nobody has ever known, nobody knows and nobody will know the true value of a PQ. Metrology progress is an endless way to define the true value of a physical quantity. Quite comprehensible, grounded conception was adopted for the practical usage instead of this “ideal” one.

The conventional true value (of a physical quantity); actual value (of a physical quantity) is a physical quantity value, determined by an experiment. It is close enough to the true value, and it can be used instead of the true value for given purpose.

For example, during the verification of working MI (we shall it consider below) readings of reference MIs are taken as the actual PQ values.

While the true value of the given PQ is single, though unachievable, a lot of actual values can correspond to it. For example, during verification measurements of the same PQ value with different reference MIs, one obtains their different readings, i.e. different actual PQ values.

Result of a measurement is a value of a physical quantity, determined by means of its measurement.

Result of a measurement is obtained in everyday practice of production and research works by means of the so-called working MIs, which are not intended to trace the PQ unit magnitude.

Sometimes it is thought by mistake, that all reference MIs have higher accuracy than working MIs. In fact, this is not true. In the definition of the reference MIs there is nothing about their accuracy, and it is a question of their purpose to trace a PQ unit magnitude and confirmation by service of legal metrology.

Though certainly, during the process of verification or gauging of some MI a used reference MI must be more accurate than MI under erificating or gauging.

System of physical units

Unit is a physical quantity of a certain dimension, accepted by agreement for the quantitative representation of the uniform quantities.

System of units is a complex of units of a certain system of physical quantities.

In Ukraine the international system of units SI is adopted.

SI system consists of seven base units and two supplementary units.

Here are the base SI system units and their Ukrainian and international designations:

- length - meter (м, m);

- mass - kilogram (кг, kg);

- time - second (c, s);

- lectric current - ampere (A, A);

- thermodynamic temperature - Kelvin (K, К);

- luminous intensity - candela (кд, cd);

- amount of matter - mol (моль, mol);

- supplementary units:

- flat angle - radian (рад, rad);

- solid angle - steradian (ctep, sr);

and 113 derived units, including:

- space and time - 6;

- mechanical - 14;

- electric and magnetic - 40;

- thermal - 11;

- light - 15;

- acoustic -14;

- ionizing radiations - 2;

- molecular physics and physical chemistry - 11,

which are the coherent  (concordant) units.

Definitions of the base, supplementary and the most widely used electric and magnetic units of SI system should be reviewed (you have learned them in the course of physics) on the recommended literature.