measurements and instrumentation
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DESCRIPTIONMEASUREMENTS AND INSTRUMENTATION. Units and standards of measurements. BY:- ANJAN P.SELVAM R.V.GANAPATHY. SYSTEMS OF MEASURMENT. - PowerPoint PPT Presentation
MEASUREMENTS AND INSTRUMENTATION
UNITS AND STANDARDS OF MEASUREMENTSBY:-ANJAN P.SELVAMR.V.GANAPATHY
SYSTEMS OF MEASURMENTA system of measurement is a set of units which can be used to specify anything which can be measured and were historically important, regulated and defined because of trade and internal commerce. Scientifically, when later analyzed, some quantities are designated as fundamental units meaning all other needed units can be derived from them, whereas in the early and most historic eras, the units were given by the ruling entities and were not necessarily well inter-related or self-consistent.
HISTORY OF SCIENTIFIC SYSTEMThe French revolution scientific system steady significant pressure convert to a scientific basis so called customary units of measure. Most systems length (distance) weight time fundamental quantities . Some systems changed to recognize improved relationship notably 1824 legal changes imperial system.Later science developments added electric current complete minimum set of fundamental quantities by which all other metrological units may be defined. Other quantities power speed, etc. derived from fundamental set for example, speed is distance divided by time. Historically wide range of units same quantity; for example, in several cultural settings, length was measured in inches, feet, yards, fathoms, rods, stadia, leagues, with conversion factors which are not simple powers of ten or even always simple fractions within a given customary system.
DIFFERENT SYSTEMS OF MEASUREMENTS
METRIC SYSTEMMetric systems of units evolved since adoption first well-defined system in France 1791. During this use of these systems spread throughout first to the non-English-speaking countries more recently to the English speaking countries.Multiples and submultiples of metric units are related by powers of ten; the names for these are formed with prefixes. This relationship is compatible with the decimal system of numbers and it contributes greatly to the convenience of metric units.In the early metric system there were two fundamental or base units, the metre and the gram, for length and mass. The other units of length and mass, and all units of area, volume, and compound units such as density were derived from these two fundamental units.
IMPERIAL AND U.S.CUSTOMARY UNITSBoth the Imperial units and U.S. customary units derive from earlier English units. Imperial units were mostly used in the British Commonwealth and the former British Empire. They are still used in common household applications to some extent and so are also sometimes called common units, but have now been mostly replaced by the metric system in commercial, scientific, and industrial applications.Contrarily, however, U.S. customary units are still the main system of measurement in the United States. The customary units have a strong hold due to the vast industrial infrastructure and commercial development. The metric system is preferred in certain fields such as science, medicine and technology. These two systems are closely related, however they differ between them. Units of length and area are identical except for surveying purposes. The Avoirdupois units of mass and weight differ for units larger than a pound (lb.).
NATURAL UNITSNatural units are physical units of measurement defined in terms of universal physical constants in such a manner that some chosen physical constants take on the numerical value of one when expressed in terms of a particular set of natural units. Natural units are natural because the origin of their definition comes only from properties of nature and not from any human construct. Various systems of natural units are possible. Some examples:Geometric unit systemsPlanck unitsStoney units Schrdinger units Atomic units(au) Electronic unitsQuantum electrodynamical units
NON STANDARD UNITSNon-standard measurement units found in books, newspapers etc., include:AreaEnergyMassVertical distanceVolume
ELECTROSTATIC UNITSThe electrostatic system of units is a system of units used to measure electrical quantities of electric charge, current, and voltage, within the centimeter gram second (or "CGS") metric system of units. In electrostatic units, electrical charge is defined via the force it exerts on other charges. Although CGS units have mostly been supplanted by the MKS or "International System of Units" (SI) units, electrostatic units are still in use in some applications, most notably physics.The main electrostatic units are:Statcoulomb or "esu" for chargeStatvolt for voltageGauss for magnetic induction
DimensionUnitDefinitionSIcharge electrostatic unit of charge, Franklin, statcoulomb1 esu = 1 statC = 1 Fr = (gcm/s)= 3.33564 1010 Celectric current Biot1 esu/s= 3.33564 1010 C/selectric potential Statvolt1 statV = 1 erg/esu= 299.792458 Velectric field1 statV/cm = 1 dyn/esu= 2.99792458 104 V/mmagnetic field strength (H) Oersted1 Oe= 1000/(4) A/m = 79.577 A/mmagnetic flux Maxwell1 Mw = 1 Gcm= 108 Wbmagnetic induction (B) Gauss1 G = 1 Mw/cm= 104 Tresistance1 s/cm= 8.988 1011 resistivity1 s= 8.988 109 mcapacitance1 cm= 1.113 1012 FInductaNcestatH= 8.988 1011 Hwave number kayser1 /cm= 100 /m
CGS AND MKS UNITSScientists have adopted the metric system to simplify their calculations and promote communication across national boundaries. The result was two clusterings of metric units in science and engineering. One cluster, based on the centimeter, the gram, and the second, is called the CGS system. The other, based on the meter, kilogram, and second, is called the MKS system.The CGS system was introduced formally by the British Association for the Advancement of Science in 1874. It found almost immediate favor with working scientists, and it was the system most commonly used in scientific work for many years. During the 20th century, metric units based on the meter and kilogram--the MKS units--were used more and more in commercial transactions, engineering, and other practical areas. By 1950 there was some discomfort among users of metric units, because the need to translate between CGS and MKS units went against the metric ideal of a universal measuring system.In 1960 the Eleventh General Conference adopted the name International System of Units (SI) for this collection of units.
CGS unitmeasuringSI equivalentbarye (ba) pressure0.1 pascal (Pa)biot (Bi) electric current10 amperes (A)calorie (cal) heat energy4.1868 joule (J)darcy permeability0.98692 x 10-12 square meter (m2)debye (D)electric dipole moment3.33564 x 10-30 coulomb meter (Cm)dyne (dyn)force10-5 newton (N)emumagnetic dipole moment0.001 ampere square meter (Am2)ergwork, energy10-7 joule (J)franklin (Fr)electric charge3.3356 x 10-10 coulomb (C)galileo (Gal)acceleration0.01 meter per second squared (ms-2)gauss (G)magnetic flux density10-4 tesla (T)gilbert (Gi)magnetomotive force0.795 775 ampere-turns (A)kayser (K)wave number100 per meter (m-1)lambert (Lb)luminance3183.099 candelas per square meter (cdm-2)langleyheat transmission41.84 kilojoules per square meter (kJm-2)line (li)magnetic flux10-8 weber (Wb)maxwell (Mx)magnetic flux10-8 weber (Wb)oersted (Oe)magnetic field strength79.577 472 ampere-turns per meter (Am-1) phot (ph)illumination104 lux (lx)poise (P)dynamic viscosity0.1 pascal second (Pas)stilb (sb)luminance104 candelas per square meter (cdm-2)stokes (St)kinematic viscosity10-4 square meters per second (m2s-1)unit polemagnetic flux1.256 637 x 10-7 weber (Wb)
DIFFERENT STANDARDS OF MEASUREMENTS
THE INTERNATIONAL SYSTEM OF UNITS (SI)All systems of weights and measures, metric and non-metric, are linked through a network of international agreements supporting the International System of Units. The International System is called the SI, using the first two initials of its French name Systme International d'Units. The key agreement is the Treaty of the Meter (Convention du Mtre), signed in Paris on May 20, 1875. 48 nations have now signed this treaty, including all the major industrialized countries. The United States is a charter member of this metric club, having signed the original document back in 1875.
The SI is maintained by a small agency in Paris, the International Bureau of Weights and Measures (BIPM, for Bureau International des Poids et Mesures), and it is updated every few years by an international conference, the General Conference on Weights and Measures (CGPM, for Confrence Gnrale des Poids et Mesures), attended by representatives of all the industrial countries and international scientific and engineering organizations. The 22nd CGPM met in October 2003; the next meeting will be in 2007. As BIPM states on its web site, "The SI is not static but evolves to match the world's increasingly demanding requirements for measurement."
At the heart of the SI is a short list of base units defined in an absolute way without referring to any other units. The base units are consistent with the part of the metric system called the MKS system. In all there are seven SI base units:the meter for distance, the kilogram for mass, the second for time, the ampere for electric current, the kelvin for temperature, the mole for amount of substance, and the candela for intensity of light.
SI derived units, are defined algebraically in terms of these fundamental units.Currently there are 22 SI derived units. They include:the radian and steradian for plane and solid angles, respectively; the newton for force and the pascal fo