ch2 standards

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Chapter 2 STANDARDS Standard is a physical representation of a unit of measurement. A known accurate measure of physical quantity is termed as a standard. Dr. Mohd Ridzuan bin Ahmad Faculty of Electrical Engineering Universiti Teknologi Malaysia 81310 Skudai, Johor.

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Page 1: Ch2 Standards

Chapter 2STANDARDS

Standard is a physical representation of a unit of measurement. A known accurate

measure of physical quantity is termed as a standard.

Dr. Mohd Ridzuan bin AhmadFaculty of Electrical Engineering

Universiti Teknologi Malaysia81310 Skudai, Johor.

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• Classification of Standards

• Standards of Fundamental Quantities

• Standards of Derived Quantities

Standards

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Standard of Paper Size

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Classification of Standards

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Consists of 4;

• international standard• primary standard• secondary standard• working standard

International Standards (ISs)

• ISs are devices designed and constructed to specifications of an international forum

• i.e. BSI, IEC, EU

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Classification of Standards

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

International Standards (ISs) cont…

• ISs represents unit of measurement of various physical quantities to the highest possible accuracy that is attainable by use of advanced technique of production and measurement technology

Power Transformer comply toBS EN 60076-3:2001

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Classification of Standards

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

International Standards (ISs) cont…

• ISs maintained systematically by actual measurement in physic definition such as mass, length, time, current etc…

• i.e the standard maintained by the inter. Bureau of weight & measure in Paris

• ISs not available to ordinary user for purpose of day-to-day comparisons and calibration

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Classification of Standards

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Primary Standards (PSs)

• PSs are devices maintained by organizations/national laboratories in different part of the world or countries

• PSs devices represent the fundamental, derive quantities and calibrated independently by absolute measurement

• Main function of PS is to calibrate/check & certify secondary reference standards

• PSs are not easily available to an ordinary user of instruments for verification/calibration or working standards

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Classification of Standards

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Secondary Standards (SSs)

• Basic reference standards employed by industrial measurement laboratories

• main function is the maintenance & periodic calibration of secondary standards against primary standards of the national standards laboratory/organization

• SSs are freely available to the ordinary user of instruments for checking & calibrations of working standards

ESD protection area

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Classification of Standards

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Working Standards (WSs)

• high accuracy devices that commercially available, checked & certified against either the primary or secondary standard

• i.e safety equipment in industry

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Classification of Standards

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Relationship between standard and accuracy

PS

IS

SS

WS

Diagram Traceability

Accu

racy

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Consists of;

• Mass

• Time

• Length

• Absolute Ampere

• Temperature

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Mass;

• standard for mass is the International Prototype Kilogram (platinum-iridium cylinder)

• kept at the Inter. Bureau of Weights & Measure in France

• kilogram was originally defined as the mass of one liter of pure water at a temperature of 3.98 oC & standard atmospheric pressure (101 325 Pa).

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Mass; ……cont.

• since 1998, the SI system defines the unit to be equal to the mass of the international prototype of the kilogram,

• made from alloy of platinum & iridium of 39 mm height & diameter

• official copies of the prototype kilogram are made available as national prototype (made in 1880s) & compared to Paris prototype (“Le Grand Kilo”) roughly every 10 years

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Time;

• 60 seconds = 1 minute

• 3600 seconds = 1 hour

• 86.4 kilo seconds (86 400 seconds) = 1 day (in SI)

• the factor of 60 may have influenced by Babylonians based on their 60 in counting system

• the hour defined by Egyptians in term of rotation of earth as 1/24 of a mean of solar, 1/86400 of a mean solar day

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Time; ….cont…

• the second was defined in terms of the period of revolution of the Earth around the sun for a particular moment

• the earth’s motion was describe in Newcomb’s Table of the sun that provides a formula for the motion of the sun at the epoch 1900 based on astronomical observations made during the 18 & 19 centuries

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Time; ….cont…

• the second thus defined as a fraction 1/35 556 925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time (ET)

• ET was defined as the measure of time that brings the observed positions of the celestial bodies into accord with the Newtonian dynamical theory of motion

• the second was ratified by 11th General Conference on Weight & Measures in 1960

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Time; ….cont…

• 2 astronomers at United States Naval Observatory (USNO) & National Physical Laboratory England determined the relationship between the hyperfine transition freq of the caesium atom & the ephemeris second

• in 1967 the 13th General Conference on Weight & Measures defined the second of atomic time in SI as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom (at 0 K)

Caesium atomic clock, 1955

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A walk through time

Ancient calendar depends on celestial bodies.

First clock at Egypt

Mechanical clock

Caesium – Atomic clock

World Time Zone. GMT20000 years ago

1656

3500 BC 1967

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Greenwich Mean Time (GMT)

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Length: ……..”meter” • The meter is the unit of length in the International System of Units (SI)

• It is one of the seven SI base units

m

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Length: ……..”meter”

SI multiples of meter

Multiple Name Symbol Multiple Name Symbol

100 meter m      

101 decameter dam 10–1 decimeter dm

102 hectometer hm 10–2 centimeter cm

103 kilometer km 10–3 millimeter mm

106 megameter Mm 10–6 micrometer µm

109 gigameter Gm 10–9 nanometer nm

1012 terameter Tm 10–12 picometer pm

1015 petameter Pm 10–15 femtometer fm

1018 exameter Em 10–18 attometer am

1021 zettameter Zm 10–21 zeptometer zm

1024 yottameter Ym 10–24 yoctometer ym

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Length: ……..”meter” • The origins of the meter go back to at least the 18th century

• Some suggested defining the meter as the length of a pendulum having a half-period of one second;

• others suggested defining the meter as one ten-millionth of the length of the Earth's meridian along a quadrant (one-fourth the circumference of the Earth).

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Length: ……..”meter”

• In 1791, soon after the French Revolution, the French Academy of Sciences chose the meridian definition over the pendulum definition because the force of gravity varies slightly over the surface of the Earth, affecting the period of the pendulum.

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Length: ……..”meter”

• in 1889, the 1st general conference on weights & measures (CGPM- Conférence Générale des Poids et Mesures) defined ‘meter’ as a length of the International Prototype Meter, the distances between two finely scribed lines of platinum iridium bar when subject to certain specified conditions.

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Length: ……..”meter” • definition of the meter was then replaced by CGPM in 1960 using a definition based upon a wavelength of krypton-86 radiation.

• this definition was adopted in order to reduce the uncertainty with which the meter may be realized

• to further reduce the uncertainty, in 1983 the CGPM replaced this latter definition by the following definition:

• “The meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second”

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Temperature

• is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature

• is one of the principal parameters of thermodynamics

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Temperature

• On the microscopic scale, temperature is defined as the average energy of microscopic motions of a single particle in the system per degree of Freedom

• If no heat flow occurs, the two objects have the same temperature; otherwise heat flows from the hotter object to the colder object.

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Temperature

• the above basic principles are stated in the zeroth law (equilibrium) and second law (entropy) of thermodynamics, respectively

• For a solid, these microscopic motions are principally the vibrations of its atoms about their sites in the solid

• For an ideal monatomic gas, the microscopic motions are the translational motions of the constituent gas particles.

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Temperature

• The International Temperature Scale of 1990 (ITS-90) is an equipment calibration standard for making measurements on the Kelvin and Celsius temperature scales

Figure: Long-stem platinum resistance thermometers are sometimes used at temperatures as low as 83 K (-190 °C). The apparatus in the photo is used to calibrate the thermometer at the triple point of argon (83.8058 K).

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Temperature

• ITS–90 is an approximation of the thermodynamic temperature scale that facilitates the comparability and compatibility of temperature measurements internationally • ITS–90 offers defined calibration points ranging from 0.65 K to approximately 1358 K (−272.5 °C to 1085 °C) and is subdivided into multiple temperature ranges which overlap in some instances.

The new PTB (Physikalisch-Technische Bundesanstalt) scale for the temperature interval from 0.65 K to 3.2 K (in short: PTB-2006 shows how the two scales can be combined in future to form one improved International Temperature Scale.

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Temperature

• ITS-90 is designed to represent the thermodynamic (absolute) temperature scale (referencing absolute zero) as closely as possible throughout its range

• thermometer designs include helium vapor pressure thermometers, helium gas thermometers, standard platinum resistance thermometers (known as SPRTs or RTD) and monochromatic radiation thermometers

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Temperature

• Although the Kelvin and Celsius scales are defined using absolute zero (0 K) and the triple point of water (273.16 K and 0.01 °C), it is impractical to use this definition at temperatures that are very different from the triple point of water

• Accordingly, ITS–90 uses numerous defined points, all of which are based on various thermodynamic equilibrium states of fourteen pure chemical elements and one compound (water)

The triple point of a substance is the temperature & pressure at

which three phases (liquid, gas & solid) of that substance may coexist

in thermodynamic equilibrium. [273.16 K and 611.73 Pa]

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Temperature

• ITS–90 also draws a distinction between “freezing” and “melting” points

• The distinction depends on whether heat is going into (melting) or out of (freezing) the sample when the measurement is made

• Only gallium is measured while melting, all the other metals are measured while the samples are freezing.

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Temperature

• at the triple point is defined to be exactly 0.0100C or 273.16K

• when the triple point is realized all three phases of matter coexist; liquid, vapor & solid

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Standards of Fundamental Quantities

Absolute Ampere: • the ampere, (symbol: A) is a unit of electric current, or amount of electric charge per second

•1 coulomb is approx. to 6.24 × 1018 e, where e is theelementary charge, 1.602176487×10−19 C. • the ampere is an SI base unit, and is named after André-Marie Ampère, one of the main discoverers of electromagnetism.

t

QitiQ ;

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Absolute Ampere:

• the ampere is a constant current which, if maintained in two straightparallel conductors of infinite length, of negligible circular cross section, and placed 1 metre apart in a vacuum, would produce between these conductors a force equal to 2×10-7 newton per metre of length

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Absolute Ampere: • the unit of charge, the coulomb, is defined, as a derived unit, to be the amount of charge displaced by a one ampere current in the time of one second

As a result, electric current is also the time rate of change or displacement of electric charge. One ampere represents the rate of 1 coulomb of charge per second.

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Absolute Ampere: • Because it is a base unit, the definition of the ampere is not tied to any other electrical unit. The definition for the ampere is equivalent to fixing a value of the permeability of vacuum to

• Prior to 1948, the so-called "international ampere" was used, defined in terms of the electrolytic deposition rate of silver. The older unit is equal to 0.999 85 A.

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Absolute Ampere: • The unit of electric charge, the coulomb, is defined in terms of the ampere: one coulomb is the amount of electric charge (formerly quantity of electricity) carried in a current of one ampere flowing for one second

• Current, then, is the rate at which charge flows through a wire or surface. One ampere of current (I) is equal to a flow of one coulomb of charge (Q) per second of time (t):

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Absolute Ampere:

• Since a coulomb is approximately equal to 6.24150948×1018 elementary charges(e), one ampere is approximately equivalent to 6.24150948×1018 e, such as electrons, moving past a boundary in one second

• More precisely using the SI definitions for the conventional values of the Josephson and Von Klitzing constants, the ampere can be defined as exactly 6.241 509 629 152 65 x 1018 elementary charges per second

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Absolute Ampere: • The ampere is most accurately realized using a watt balance, but is in practice maintained via Ohm's Law from the units of EMF and resistance, the volt and the ohm, since the latter two can be tied to physical phenomena that are relatively easy to reproduce, the Josephson junction and the quantum Hall effect, respectively

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Standards of Fundamental Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Absolute Ampere:

• The definition of the ampere, involves the kilogram, but an alternative link is the Josephson-effect constant (KJ-90) and von Klitzing's quantum-Hall resistance (RJ-90), both of which were given fixed, conventional values in 1990

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Standards of Derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Voltage Standards

• The volt (symbol: V) is the SI derived unit of electric potential difference or electromotive force

• It is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, the first modern chemical battery.

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Standards of derived Quantities

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Voltage Standards

• The volt is defined as the potential difference across a conductor when a current of one ampere dissipates one watt of power

• Hence, it is the base SI representation m2 · kg · s-3 · A-1, which can be equally represented as one joule of energy per coulomb of charge, J/C.

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Standards of derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Voltage Standards

• Since 1990 the volt is maintained internationally for practical measurement using the Josephson effect, where a conventional value is used for the Josephson constant, fixed by the 18th General Conference on Weights and Measures as K {J-90} = 0.4835979 GHz/µV.

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Standards of derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Voltage Standards • Electrical potential difference can be thought of as the ability to move electrical charge through a resistance

• Voltage is a property of an electric field, not individual electrons

• An electron moving across a voltage difference experiences a net change in energy, often measured in electron-volts

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Standards of derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Voltage Standards • In essence, the volt measures how much kinetic energy each electron carries

• The no. of electrons is measured by the charge, in coulombs

• thus, the volt is multiplied by the current flow, in amperes which are one coulomb per second to yield the total electrical power in the current, in watts

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Standards of derived Quantities

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Voltage Standards • When using the term 'potential difference' or voltage, one must be clear about the two points between which the voltage is specified or measured. There are two ways in which the term is used.

• Voltage with respect to a common point

• Voltage between two stated points

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Standards of derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Voltage Standards based on Josephson Junction • The Josephson effect is the phenomenon of current flow across two weakly coupled superconductors, separated by a very thin insulating barrier

• This arrangement—two superconductors linked by a non-conducting barrier known as a Josephson junction; the current that crosses the barrier is the Josephson current

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Standards of derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Voltage Standards based on Josephson Junction

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Standards of derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Voltage Standards based on Josephson Junction

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Standards of derived Quantities

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Voltage Standards based on Josephson Junction

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Standards of derived Quantities

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Voltage Standards based on Weston Cell

• The Weston cell, invented by Edward Weston in 1893, is a wet-chemical cell that produces a highly stable voltage suitable as a laboratory standard for calibration of voltmeters

• It was adopted as the International Standard for EMF in 1911

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Standards of derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Voltage Standards based on Weston Cell

• The original design was a saturated cadmium cell producing a convenient 1.0183 Volt reference and had the advantage of having a lower temperature coefficient than the previously used Clark cell. (Reference cells must be applied in such a way that no current is drawn from them.)

• The temperature coefficient can be reduced by shifting to an unsaturated design, the predominant type today.

• However, an unsaturated cell's output decreases by some 80 microvolts per year, which is compensated by periodical calibration against a saturated cell.

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Standards of derived Quantities

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Resistance Standards based on Quantum Hall effect

• the primary standard for resistance is based on the Hall Effect

• recall the principle a thin semiconductor. bar carries a DC current

• the bar is subjected to a magnetic field perpendicular to it

• a voltage developed across the bar perpendicular to the direction of the current flow, this is Hall Voltage

• the ratio of the Hall Voltage to the DC current is called Hall Resistance, RH of the bar

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Standards of derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Resistance Standards based on Quantum Hall effect

• For a simple metal where there is only one type of charge carrier (electrons) the Hall voltage VH is given by

• The Hall coefficient is defined as

• where I is the current across the plate length, B is the magnetic flux density, d is the depth of the plate, e is the electron charge, and n is the charge carrier density of the carrier electrons.

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Standards of derived Quantities

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Resistance Standards based on Quantum Hall effect

• in 1980, it was discovered that by;

• cooling the bar in liquid helium, semiconductor becomes a superconductor

• greatly increasing the magnetic, the Hall resistance increased in discrete steps

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Standards of derived Quantities

INSTRUMENT & ELECTRICAL MEASUREMENT - Standards

Resistance Standards based on Quantum Hall effect

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Standards of derived Quantities

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Capacitive Standards

• A capacitor is an electrical/electronic device that can store energy in the electric field between a pair of conductors (called "plates")

• The process of storing energy in the capacitor is known as "charging", and involves electric charges of equal magnitude, but opposite polarity, building up on each plate

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Standards of derived Quantities

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Capacitive Standards

• Capacitors are often used in electrical circuit and electronic circuits as energy-storage devices

• They can also be used to differentiate between high-frequency and low-frequency signals as electronic filters

• Capacitors are occasionally referred to as condensers

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Standards of derived Quantities

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Capacitive Standards

• A capacitor consists of two conductive •electrodes, or plates, separated by adielectric

• capacitor's capacitance (C) is a measure of the amount of charge (Q) stored on each plate for a given potential difference or voltage (V) which appears between the plates

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Standards of derived Quantities

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Capacitive Standards

• In SI units, a capacitor has a capacitance of one farad when one coulomb of charge is stored due to one volt applied potential difference across the plates

• Since the farad is a very large unit, values of capacitors are usually expressed in microfarads (µF), nanofarads (nF), or picofarads (pF)

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Standards of derived Quantities

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Capacitive Standards

• When there is a difference in electric charge between the plates, an electric field is created in the region between the plates that is proportional to the amount of charge that has been moved from one plate to the other

•This electric field creates a potential difference V = E·d between the plates of this simple parallel-plate capacitor.

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Standards of derived Quantities

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Inductance Standards

• An inductor is a passive electrical device employed in electrical circuits for its property of inductance

• Inductors are used extensively in analog circuits and signal Processing for rectifiers.

• Inductors in conjunction with capacitors and other components form tuned circuits or filter out specific signal frequencies

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Standards of derived Quantities

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Inductance Standards

• This can range from the use of large inductors as chokes in power supplies, which in conjunction with filter capacitors remove residual hum or other fluctuations from the direct current output, to such small inductances as generated by a ferrite bead or torus around a cable to prevent radio frequency interference from being transmitted down the wire

• Smaller inductor/capacitor combinations provide tuned circuits used in radio reception and broadcasting, for instance.

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Standards of derived Quantities

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Inductance Standards

•Inductance (measured in henries) is an effect which results from the magnetic field that forms around a current-carrying conductor

•Electrical current through the conductor creates a magnetic flux proportional to the current

• A change in this current creates a change in magnetic flux that, in turn, generates an electromotive force (emf) that acts to oppose this change in current

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Standards of derived Quantities

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Inductance Standards

• Inductance is a meas. of the generated •emf for a unit change in current

• an inductor with an inductance of 1H produces an emf of 1V when the currentthrough the inductor changes at the rate of 1A

• The number of turns, the area of each loop/turn, and what it is wrapped around all affect the inductance.

• i.e the magnetic flux linking these turns can be increased by using a high permeability material

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Standards of derived Quantities

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Inductance Standards

• inductance is a measure of the amount of magnetic flux produced for a given electric current

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Standards of derived Quantities

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Inductance Standards

• An inductor is usually constructed as a coil of conducting material, typically copper wire, wrapped around a core either of air or of ferromagnetic material

• Core materials with a higher permeability than air confine the magnetic field closely to the inductor, thereby increasing the inductance

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Tutorial

1. What is standards?2. Discuss the difference between primary and

secondary standards.3. What is the latest standard to define length.

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What is standard?

• Standards is a physical devices that have stable characteristics and accurately defined. It is used as a reference for measurement units.

• A known accurate measure of physical quantity is termed as a standard

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Primary vs secondary standard

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Latest length standard

• The length of the path travelled by light in a vacuum during a time of 1/229,792,458 of a second.