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Electrical Units Electrical Units Ratio of SI unit Magnitude of Quantity Symbol Equation SI unit symbol CGS unit SI to cgs unit Z Current I, i I=E/R; I = E/Z; I = Q/t Ampere A Abampere 10-1 Quantity Q, q Q = it; Q = CE Coulomb C Abcoulomb 10-1 Electromotive force E, e E = IR; E = W/Q Volt V Abvolt 108 Resistance R, r R=E/I; R = rl /A Ohm Ω Abohm 109 Resistivity rr= RA / I Ohm-metre Ω•m Abohm-cm 1011 Conductance G, g G =g A / l G = A/rl Siemens S Abmho 10-9 Conductivity gg = 1/r; g = I/ RA Siemens/meter S/m Abmho/cm 10-11 Capacitance C C = Q/E Farad F Abfarad* 10-9 Permittivity e Farads/meter F/m Stat farad*/cm 8.85 X 10-12 Relative permittivity er er = e/eo Numerical Numerical I Self-inductance L L = - N(df/dt) Henry H Abhenry 109 1/2 9 Mutual inductance M M = K(L1L2) Henry H Abhenry 10 Energy J J = eit Joule J Erg 107 kwh kwh = kw/3600; 3.6 MJ Kilowatthour kWh 36 X 1012 Active power W W = J/t; W = EI cos U Watt W Abwatt 107 Reactive power jQ Q = El sin U Var var Abvar 107 Apparent power VA VA = El Volt-ampere VA Power factor pf pf = W/VA; pf = W/(W + jQ) 1 p Ω 9 Reactance, inductive XL XL = 2 fL Ohm Abohm 10 p Ω 9 Reactance, capacitive XC XC = 1/(2 fC) Ohm Abohm 10 Ω 9 Impedance Z Z = E/I Z = R + j(XL - XC) Ohm Abohm 10 Conductance G G = R/Z2 Siemens S Abmho 10-9 Susceptance B B = X/Z2 Siemens S Abmho 10-9 Admittance Y Y =I/E; Y = G + jB Siemens S Abmho 10-9 Frequency f f = 1/T Hertz Hz Cps Hz 1 Period T T = 1/f Second s Second 1 Time constant T L/R; RC Second s Second 1 Angular velocity ωω= 2πf Radians/second rad/s Radians/second 1 *1 Abfarad (EMU Units) = 9 X 10-20 stat farads (ESU units). Reproduced with Permission from McGraw-Hill, Marks’ Standard Handbook for Mechanical Engineers, 8th ed. Authors: Baumeister, et al. Copyright 1987 Z-264 One Omega Drive | Stamford, CT 06907 | 1-888-TC-OMEGA (1-888-826-6342) | [email protected] www.omega.com UNITED KINGDOM www. omega.co.uk Manchester, England 0800-488-488 UNITED STATES FRANCE www.omega.com www.omega.fr 1-800-TC-OMEGA Guyancourt, France Stamford, CT. 088-466-342 CANADA CZECH REPUBLIC www.omega.ca www.omegaeng.cz Laval(Quebec) Karviná, Czech Republic 1-800-TC-OMEGA 596-311-899 GERMANY BENELUX www.omega.de www.omega.nl Deckenpfronn, Germany Amstelveen, NL 0800-8266342 0800-099-33-44 More than 100,000 Products Available! Temperature Data Acquisition Calibrators, Connectors, General Test and Measurement Auto-Dialers and Alarm Monitoring Systems, Instruments, Glass Bulb Thermometers, Handheld Instruments Communication Products and Converters, Data for Temperature Measurement, Ice Point References, Acquisition and Analysis Software, Data Loggers Indicating Labels, Crayons, Cements and Lacquers, Infrared Plug-in Cards, Signal Conditioners, USB, RS232, RS485 Temperature Measurement Instruments, Recorders Relative and Parallel Port Data Acquisition Systems, Wireless Humidity Measurement Instruments, RTD Probes, Elements Transmitters and Receivers and Assemblies, Temperature & Process Meters, Timers and Counters, Temperature and Process Controllers and Power Pressure, Strain and Force Switching Devices, Thermistor Elements, Probes and Displacement Transducers, Dynamic Measurement Assemblies,Thermocouples Thermowells and Head and Well Force Sensors, Instrumentation for Pressure and Strain Assemblies, Transmitters, Wire Measurements, Load Cells, Pressure Gauges, Pressure Flow and Level Reference Section, Pressure Switches, Pressure Transducers, Air Velocity Indicators, Doppler Flowmeters, Level Proximity Transducers, Regulators, Measurement, Magnetic Flowmeters, Mass Flowmeters, Strain Gages, Torque Transducers, Valves Pitot Tubes, Pumps, Rotameters, Turbine and Paddle Wheel Flowmeters, Ultrasonic Flowmeters, Valves, Variable Area Heaters Flowmeters, Vortex Shedding Flowmeters Band Heaters, Cartridge Heaters, Circulation Heaters, Comfort Heaters, Controllers, Meters and Switching pH and Conductivity Devices, Flexible Heaters, General Test and Measurement Conductivity Instrumentation, Dissolved Oxygen Instruments, Heater Hook-up Wire, Heating Cable Instrumentation, Environmental Instrumentation, pH Systems, Immersion Heaters, Process Air and Duct, Electrodes and Instruments, Water and Soil Analysis Heaters, Radiant Heaters, Strip Heaters, Tubular Heaters Instrumentation click here to go to the omega.com home page.
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