1) The document discusses various standards and units of measurement including fundamental and derived units. 2) It describes different types of standards including international, primary, secondary, working, current, voltage, resistance, capacitance, and time/frequency standards. 3) The key points are that standards define units of measurement and are classified based on their level of accuracy and use from international to working standards used in laboratories.

1. Standards & Units
M. Afnan Habibi

2. Lesson Summary
• Introduction Concept Measurement
• Fundamental and Derived Units
• Standards Classification

3. Introduction
• Measurement is the result of a quantitative comparison between a
given quantity and a quantity of the same kind chosen as a unit.
• The result of the measurement is expressed by a number representing
the ratio between the unknown quantity and the standard.
• A standard is defined as the physical personification of the unit of
measurement.
• The device or instrument used for comparing the unknown quantity
with the unit of measurement or a standard quantity is called a
measuring instrument

4. Introduction
• In direct measurement methods, the unknown quantity is measured
directly instead of comparing it with a standard. Examples: current by
ammeter, voltage by voltmeter, resistance by ohmmeter, power by
wattmeter, etc.
• In indirect measurement methods, the value of the unknown quantity
is determined by measuring the functionally related quantity and
calculating the desired quantity rather than measuring it directly.
Example: R=V/I

5. Fundamental and Derived Units
• The fundamental units in mechanics are measures of length, mass and
time. Because they are fundamental to most other physical quantities.
• Measures of certain physical quantities in the thermal, electrical and
illumination disciplines are also represented by auxiliary fundamental
units.
• All other units which can be expressed in terms of the fundamental
units are called derived units.
• Every derived unit originates from some physical law defining that unit.

6. Dimensions
• A derived unit is recognized by its dimensions, which can be defined as
the complete algebraic formula for the derived unit.
• The dimensional symbols for the fundamental units of length, mass and
time are L, M and T respectively.
• The dimensional formulas of the derived units are particularly useful for
converting units from one system to another. Example: Newton

7. Standards
• A standard of measurement is a physical representation of a unit of
measurement.
• A unit is realized by reference to an arbitrary material standard or to
natural phenomena including physical and atomic constants.
• The term ‘standard’ is applied to a piece of equipment having a known
measure of physical quantity.

8. The Classifications of Standards
1) International standards
2) Primary standards
3) Secondary standards
4) Working standards
5) Current standards
6) Voltage standards
7) Resistance standards
8) Capacitance standards
9) Time and frequency standards

9. International Standards
• The international standards represent
certain units of measurement to the
closest possible accuracy that production
and measurement technology allow.
• These standards are maintained at the
International Bureau of Weights and
Measures and are not available to the
ordinary user of measuring instruments
for purposes of comparison or calibration
Symbol Name Quantity
A ampere electric current
K kelvin temperature
s second time
m metre length
kg kilogram mass
cd candela luminous intensity
mol mole amount of substance

10. Primary Standards
• The primary standards are maintained by national standards
laboratories in different places of the world.
• The National Bureau of Standards (NBS) in Washington is responsible
for maintenance of the primary standards in North America.
• Other national laboratories include the National Physical Laboratory
(NPL) in Great Britain and the oldest in the world, the Physikalisch
Technische Reichsanstalt in Germany.
• Primary standards are not available for use outside the national
laboratories.

11. Secondary Standards
• Secondary standards are the basic reference standards used in the
industrial measurement laboratories.
• These standards are maintained by the particular involved industry and
are checked locally against other reference standards in the area.

12. Working Standards
• Working standards are the principle tools of a measurement laboratory.
• They are used to check and calibrate general laboratory instruments for
accuracy and performance or to perform comparison measurements in
industrial applications.

13. Current Standard
• The fundamental unit of electric current (Ampere) is defined by the
International System of Units (SI) as the constant current
• Which maintained in two straight parallel conductors of infinite length
and negligible circular cross section placed 1 meter apart in vacuum, will
produce between these conductors a force equal to 2 × 10-7 newton per
meter length

14. Voltage Standard
• In early times, the standard volt was
based on an electrochemical cell
called the saturated standard cell or
simply standard cell.
Standard cell of emf of 1.0183 volt at 20°C (Courtesy, physics.kenyon.edu)

15. Voltage Standard
• In 1962, based on the work of Brian Josephson, a new standard for the
volt was introduced. A thin-film junction is cooled to nearly absolute
zero and irradiated with microwave energy.
• A voltage is developed across the junction, which is related to the
irradiating frequency by the following relationship: V=hf/2e
• h= 6.63 x 10-34 Js
• e= 1.602 x 10-19 C
• f= frequency of microwave irradiation.

16. Resistance Standard
• The standard resistor is a coil
of wire of some alloy like
manganin which has a high
electrical resistivity and a low
temperature coefficient of
resistance.
• The resistance coil is mounted
in a double walled sealed
container to prevent changes in
resistance due to moisture
conditions in the atmosphere.
Resistance standard

17. Capacitance Standard
• The unit of capacitance (the farad)
can be measured with a Maxwell dc
commutated bridge, where the
capacitance is computed from
the resistive bridge arms and the
frequency of the dc commutation.
• Standard capacitors are usually
constructed from interleaved metal
plates with air as the dielectric
material. Commutated dc method for measuring capacitance

18. Time Standard and Frequency Standard
• A mean solar second is then equal to 1/86400 of the mean solar day.
• In the year 1956, the ephemeris second has been defined by the
International Bureau of Weights and Measures as the fraction
1/31556925.99747 of the tropical year for 1900 January 01 at 12 h ET
(Ephemeris Time), and adopted as the fundamental invariable unit
of time.
• The International Committee of Weights and Measures has now defined the
second in terms of frequency of the cesium transition, assigning a value of
9192631770 Hz to the hyperfine transition of the cesium atom unperturbed
by external fields.