V.
Isaiev
State
Development Stages of State Standard
of Alternating Current Unit
INTRODUCTION
The electric meters which
must have verified acuracy are widely
used in the
field of energy. The reference measuring instruments are used for verification
of metrological characteristics. The most
accurate of such
devices are the state
primary standards.
The State Enterprise
"Ukrmetrteststandart" carries
out research and development work "Development of
the state primary standard of the unit
of alternating current" at the request of the
Ministry of Economic Development and Trade of
Ukraine within the
framework of the budget program
"Preservation and functioning of the national standards base,
applied scientific and technical developments,
working
in the branch of standardization,
metrology and standards base".
According to the national standard DSTU 3231 [1], the basis for the
development of a state
standard is the evidence of
a large park of precision and
other measuring instruments in Ukraine and
the technical ability to disseminate the
unit of alternating
current. The number of precision
measuring instruments exploited in Ukraine
is more than
200 units, and the total amount
of AC measuring devices is about 100,000 units. The analysis
of the calibration and
measurment
capabilities of the national metrological
institutes of the world shows
the vast majority of the
realization method of national
standards using thermoelectric transformation which allows to
achieve measurement uncertainty in
units or tens of μA / A.
The measuring
instruments which should be calibrated by mean of
the state primary standard have large area
of application: electricity (accounting for energy resources); instrument
making (production of measuring and testing equipment); scientific research
(measuring alternating current during physical experiments), etc.
The
availability of the state primary standard will allow to create a system of
metrological support wich will be independent from the national standards of
other countries.
Purpose of
the work is
- Establishment of
a metrological support system for the
production and operation of alternating
current measuring instruments
in the range
from 0.01 to
- Ensuring
unity and metrological traceability of
measurement results in Ukraine in this
industry.
-
Development,
research and meteorological attestation of the state primary standard of the
unit of alternating current [2].
- Ensuring
the required accuracy, unchanging the unit size of
alternating current, stability of the metrological characteristics of the state
standard.
METHODS AND STAGES
The state primary standard will
reproduce the unit size of alternating current by the indirect method:
comparing it with the equivalent value of direct current using a high resolution nanovoltmeter, precision
thermo-converter
and precision shunts [3]. World level of technical development
and production of measuring equipment
allows to reproduce alternating
current with high accuracy with
help of Ohm's
law. This fact binds the
aforementioned standard to the state
primary standard of AC electric
voltage unit in the range
from 0.1 to 1000 volts, which
is stored in SE "Ukrmetrteststandart".
The resistance unit size will be
obtained from the state primary
standard of the electric resistance
unit (stored in National Scientific Center "Institute
of Metrology")
[4].
Research
and development work stages are
-
Implementation
theoretical research and analysis of methods for reproduction of alternating current. Determination of
requirements to the working conditions
of the state standard. Acting
a comparison with foreign analogues.
-
Development of the bases of construction
and the structural scheme of the state standard. Establishing of technical,
including metrological, requirements for elements of the structural scheme of
the state standard.
-
Development of a program for investigating
technical, including metrological, characteristics of a set of reference
shunts, reference thermo-converter,
source
of alternatig current, source of direct current, measures of
electrical resistance. Carrying out researches of mentioned elements.
-
Development of methodical document and
design documentation.
-
Experimental investigation of the standard complement and drawing up a
scientific and technical report on the research and
development work.
RESULTS OF
THE RESEARCH AND DEVELOPMENT WORK
During the
first stage of research and development, theoretical studies, comparisons with
foreign analogues and analysis of methods for measuring and reproducing alternating current are
carried out. The method of comparing alternating current with an equivalent direct current using a precision thermoelectric converter and
shunts is chosen to construct the developing standard (see schematic diagram on Fig. 1). The standard complement is established and the requirements for the
operation conditions are specified.
Direct current from Source 1 proceeds
through investigated current thermoconverter TCC, precision shunt R2
and
precision measure of electrical resistance
R1. The voltage at
the output terminals of R1 enters
the input of a direct voltage meter V1. The equivalent value of the current
strength is determined by the
measurements of V1 and
the value of R1. Voltage meter
V3 is required to control the
reference value of the output
voltage of the precision thermo-comparator
792A which receives the output voltage
of the precision
shunt R2.
It is necessary to record the meter V3 reading when
the alternating current flows from Source
Fig. 1 Schematic diagram of dissemination of alternatig current unit to
thermoelectric current converters
The next step is
technical
analysis of elements of the structural scheme of the standard. Determination of
the influence of each structural element on the general metrological
characteristics of the standard
is executed.
It
is obvious that the main source of measurement uncertainty
during the dissemination of this unit is the combination of
measurement uncertainties
of the thermoelectric comparator Fluke 792A, precision shunts A40, a set of
measures of electric resistance.
These
factors should be accompanied by the short-term instability of DC and AC
sources which causes fluctuations in the measurements as well as the scattering of DC voltage measurements.
At the third stage the research program of reference shunts set, reference thermo-converter, AC source, DC source, measures of electrical
resistance is
prepared as well as the analysis of sources of uncertainty is carried out. Theoretical and experimental
investigations of mantioned elements
are implemented.
At the fourth stage the methodical
document on the transfer of
the alternating current unit size
to other laboratory standards
and precise measurement instuments is worked out. The
elaboration of design documentation, methodology
for attestation of the state
standard and other documents in accordance with
DSTU 3231 is yielded.
The final step of research and development work
is experimental study of the main elements of the standard, metrological attestation
of the standard, revision of its design documentation. Preparation of the
scientific and technical report according to the results and reviewing it by
the scientific and technical council of SE"Ukrmetrteststandart"
and interdepartmental commission is an important part of national standard
developing. Submitting documents to the Ministry of Economic Development and
Trade of Ukraine for approval is the last portion of official registration.
CONCLUSION
The results of research and development
work will be used to ensure the unity and
traceability of measurements of electrical quantities that are carried out in
the field of power engineering and instrumentation. Implementation of research and
development work
results must be carried out by putting into operation the state primary
standard at the State Enterprise "Ukrmetrteststandart".
Further dissemenation of the AC unit size to
laboratory standards and high precision means of measuring alternating current
will be realized.
REEFERENCES
[1] DSTU 2681. Metrology. Terms and Definitions, 1994.
[2] DSTU 3231. Metrology. Standards of Phisical
Quantities Units. General Principles, 2007.
[3] Website of Bureau
International de Ponds et Measures: www.bipm.org.
[4] Website of National
Scientific Center "Institute of Metrology": www.metrology.kharkov.ua.