DOCSLIB.ORG

A Guide to Low Resistance Measurement Contents

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Guide to Low Resistance Measurement Contents Tried. Tested. Trusted. A Guide to Low Resistance Measurement Contents 02-03 Introduction 04-05 Applications 06 Resistance 06-09 Principles of Resistance Measurement 09-10 Methods of 4 Terminal Connections 10-19 Possible Measurement Errors 14-18 Choosing the Right Instrument 18-24 Application Examples 25-33 Useful Formulas and Charts 34 Find out more Tried. Tested. Trusted. With resistance measurement, precision is everything. This guide is what we know about achieving the highest quality measurements possible. The measurement of very large or very small cable characteristics, temperature coefficients quantities is always difficult, and resistance and various formulas to ensure you make the best measurement is no exception. Values above 1G possible choice when selecting your measuring Ω and values below 1 both present measurement instrument and measurement technique. Ω problems. We hope you will find this booklet a valuable Cropico is a world leader in low resistance addition to your toolkit. measurement; we produce a comprehensive range of low resistance ohmmeters and accessories which cover most measurement applications. This handbook gives an overview of low resistance measurement techniques, explains common causes of errors and how to avoid them. We have also included useful tables of wire and 2 Tried. Tested. Trusted. 3 Applications There are many reasons why the resistance of material is measured. Here are a few. Manufacturers of components thus avoiding the joint or contact from Resistors, inductors and chokes all have to becoming excessively hot, a poor cable joint or verify that their product meets the specified switch contact will soon fail due to this heating resistance tolerance, end of production line and effect. Routine preventative maintenance with quality control testing. regular resistance checks ensures the best possible life performances. Manufacturers of switches, relays & connectors Electric motor & generator manufacturers Verification that the contact resistance is below There is a requirement to determine the pre specified limits is required. This can be maximum temperature reached under full load. achieved at end of production line testing, To determine this temperature, the temperature ensuring quality control. coefficient of the copper winding is used. The resistance is first measured with the motor or Cable manufacturers generator cold i.e. at ambient temperature, the Must measure the resistance of the copper unit is then run at full load for a specified period wires they produce, resistance too high means and the resistance measured again. From the that the current carrying capability of the cable change in resistance value, the internal is reduced; resistance too low means that the motor/generator temperature can be manufacturer is being too generous on the determined. Our ohmmeters are also used to cable diameter using more copper than he measure the individual coils of a motor winding, needs to, which can be very expensive. to ensure there are no short or open circuit turns and that each coil is balanced. Installation & maintenance of power cables, switchgear & voltage tap changers The automotive industry These require the cable joints and switch Requirement to measure the resistance of robot contacts to be of the lowest possible resistance welding cables to ensure that the weld quality 4 Tried. Tested. Trusted. does not deteriorate, i.e. battery lead crimp connectors, air bag detonator resistance, resistance of wiring harness, and quality of crimp connectors on components. Fuse manufacturers For quality control, resistance bonding measurements on aircraft and military vehicles, it is necessary to ensure that all equipment installed in aircraft is electrically connected to the air frame, including galley equipment. Tanks and other military vehicles have the same requirements. Producers and users of large electrical currents all need to measure distribution of joint resistance, busbars, and connectors to electrodes for electroplating. Railway utilities Including trams and underground railways (Metro) - for the measurement of power distribution cable joints, including the resistance of rail track joints, because the rails are often used for signalling information. 5 RESISTANCE Resistance Ohm’s Law V = I x R (Volts = Current x Resistance). The Ohm ( ) is a unit of electrical resistance equal to that oΩf a conductor in which a Volt Amp current of one ampere is produced by a potential of one volt across its terminals. Ohm's law, named after its discoverer the German Volt physicist Georg Ohm, is one of the most important, Resistance = Current basic laws of electricity. It defines the relationship between the three fundamental electrical quantities: current, voltage and resistance. When a voltage is There exists a variety of resistance measuring applied to a circuit containing only resistive instruments that will calculate and display the elements, current flows according to Ohm's Law, resistance reading without the need for which is shown below. calculations by the user. These measuring instruments will employ either a two wire or a Current I fouRr wire measurement technique. Where: Kelvin Double Bridge I = Electrical Current (Amperes) The Kelvin Bridge is a variation of the V = Voltage (Voltage) Wheatstone bridge which enables low R = Resistance (Ohms) V resistances to be measured. The R measurement range would typically be 1m to 1k with the smallest resolution of 1µ Ω. The limΩitations of the Kelvin bridge are:- Ω PRINCIPLES OF RESISTANCE 1. requires manual balancing MEASUREMENT 2. sensitive null detector or galvanometer is required to detect balance condition Ammeter Voltmeter method 3. measurement current needs to be This method goes right back to basics. If we use reasonably high to achieve sufficient R a battery as our voltage source, a voltmeter to sensitivity measure the voltage and an ammeter to measure the current in the circuit, we can calculate the The Kelvin Double Bridge has generally been resistance with reasonable accuracy. replaced by digital ohmmeters. Whilst this method can provide good measurement results, it is not a practical DMM - Two-wire Connection solution to everyday measurement needs. A simple digital multimeter can be used for R 6 Tried. Tested. Trusted. higher values of resistance. They employ the 2 wire method of measurement and are only DMM suitable for measuring values above 100 and Test meter Terminals where high accuracy is not required. Ω Resistance of test leads 0.02 R1 R2 When measuring the resistance of a each 1 metre lead component (Rx) a test current is forced through the component and the test meter R3 Connection resistance R4 measures the voltage at its terminals. The meter then calculates and displays the resulting resistance and is known as a two- RX wire measurement. It should be noted that the DMM measures:- Rx + R1 + R2 + R3 + R4 meter measures the voltage at its terminals and not across the component. As a result of When measuring larger resistance values this this, the voltage drop across the connection additional lead resistance error can be leads is also included in the resistance ignored, but as you can see from the chart calculation. Good quality test leads will have a below, the error becomes significantly higher resistance of approximately 0.02 per meter. as the measured value decreases, and totally In addition to the resistance of thΩe leads, the inappropriate below 10 . resistance of the lead connection will also be Ω included in the measurement and this can be as high as or even higher in value than the leads themselves. TABLE 1 Examples of possible measurement errors Test lead Connection Rx measured at DMM Error Error % RX resistance R1 + R2 resistance R3 + R4 terminals = Rx + R1 + R2 + R3 + R4 1000 0.04 0.04 1000.08 0.08 0.008 Ω 100 Ω 0.04 0.04 Ω 100.08 Ω 0.08 Ω 0.08 Ω 10 Ω 0.04 0.04 Ω 10.08 Ω 0.08 Ω 0.8 Ω 1 Ω 0.04 0.04 Ω 1.08 Ω 0.08 Ω 8 Ω 100 Ωm 0.04 0.04 Ω 180 m Ω 0.08 Ω 80 Ω 10 m Ω 0.04 0.04 Ω 90 m Ω 0.08 Ω 800 Ω 1 m Ω 0.04 0.04 Ω 81 m Ω 0.08 Ω 8000 Ω Ω Ω Ω Ω 100 µ 0.04 0.04 Digital80o.1hm mmeters – 4 wire0.0c8onnection 8000 Ω Ω Ω Ω Ω 7 T P C To measure true DC, resistance ohmmeters Voltage measured across Rx typically use 4 wire measurement. DC current is passed through the Rx and through the RX ohmmeter’s internal standard. The voltage across Constant the Rx and the internal standard is then measured current source and the ratio of the two readings is used to calculate the resistance. With this method the current only needs to be steady for the few milliseconds required for the ohmmeter to make both readings, but it requires two measurement Four wire connection circuits. The voltage measured is very small and a The four wire (Kelvin) method of measurement is µV measurement sensitivity is usually required. preferred for resistance values below 100 , and all Cropico milliohmmeters and microhmmeΩters use this method. These measurements are made using 4 separate wires. 2 wires carry the current, known I I Voltage measured Voltage measured t t as the source or current leads and pass current n n across Rx across ohmmeter e e r r r r internal standard through the Rx. The other 2 wires known as the u u C C RX Rstd sense or potential leads, are used to sense the voltage drop across Rx. Whilst some small current Alternatively a constant current source is used to will flow in the sense leads, it is negligible and can pass a current through the Rx. The volt drop be ignored. The volt drop across the ohmmeter’s across the Rx is then measured and the resistance sense terminals is therefore virtually the same as the calculated.
Load more

Recommended publications
  • Laboratory Manual Physics 166, 167, 168, 169
    Laboratory Manual Physics 166, 167, 168, 169 Lab manual, part 2 For PHY 167 and 169 students Department of Physics and Astronomy HERBERT LEHMAN COLLEGE Spring 2018 TABLE OF CONTENTS Writing a laboratory report ............................................................................................................................... 1 Introduction: Measurement and uncertainty ................................................................................................. 3 Introduction: Units and conversions ............................................................................................................ 11 Experiment 1: Density .................................................................................................................................... 12 Experiment 2: Acceleration of a Freely Falling Object .............................................................................. 17 Experiment 3: Static Equilibrium .................................................................................................................. 22 Experiment 4: Newton’s Second Law .......................................................................................................... 27 Experiment 5: Conservation Laws in Collisions ......................................................................................... 33 Experiment 6: The Ballistic Pendulum ......................................................................................................... 41 Experiment 7: Rotational Equilibrium ........................................................................................................
    [Show full text]
  • GEORG OHM - Ω Physicist and Mathematician
    GEORG OHM - Ω Physicist and Mathematician The start Georg Simon Ohm was born on 16th of March 1789 in Erlangen in Germany and died on 6th of July 1854 in Munich, Germany. He was born into a Protestant family and was the son of Johann Wolfgang Ohm and Maria Elizabeth Beck. The family had seven children, but only three survived: Georg, his younger brother Martin and his sister Elizabeth Barbara. His mother died when Georg was only 10 years old. Education Georg and Martin were taught by their father who brought them to a high standard in mathematics, physics, chemistry and philosophy. Georg Simon attended Erlangen Gymnasium from age eleven to fifteen where he hardly received any scientific education. After the Gymnasium, he was sent to Switzerland as his father was concerned that his son was wasting his educational opportunity. In September 1806 Ohm accepted a position as a mathematics teacher in a school in Gottstadt. Ohm restarted his mathematical studies, left his teaching post in March 1809 and became a private tutor in Neuchâtel. For two years he carried out his duties as a tutor while he followed private studies of mathematics. Then in April 1811 he returned to the University of Erlangen. Teaching Ohm received his doctorate from the University of Erlangen on October 25, 1811. He immediately joined the faculty there as a lecturer in mathematics but left after three semesters because of unpromising prospects. He could not survive on his salary as a lecturer. He had a few more teaching jobs after that and unhappy with his job, Georg began writing an elementary textbook on geometry as a way to prove his abilities.
    [Show full text]
  • Lord Kelvin and the Age of the Earth.Pdf
    ME201/MTH281/ME400/CHE400 Lord Kelvin and the Age of the Earth Lord Kelvin (1824 - 1907) 1. About Lord Kelvin Lord Kelvin was born William Thomson in Belfast Ireland in 1824. He attended Glasgow University from the age of 10, and later took his BA at Cambridge. He was appointed Professor of Natural Philosophy at Glasgow in 1846, a position he retained the rest of his life. He worked on a broad range of topics in physics, including thermody- namics, electricity and magnetism, hydrodynamics, atomic physics, and earth science. He also had a strong interest in practical problems, and in 1866 he was knighted for his work on the transtlantic cable. In 1892 he became Baron Kelvin, and this name survives as the name of the absolute temperature scale which he proposed in 1848. During his long career, Kelvin published more than 600 papers. He was elected to the Royal Society in 1851, and served as president of that organization from 1890 to 1895. The information in this section and the picture above were taken from a very useful web site called the MacTu- tor History of Mathematics Archive, sponsored by St. Andrews University. The web address is http://www-history.mcs.st-and.ac.uk/~history/ 2 kelvin.nb 2. The Age of the Earth The earth shows it age in many ways. Some techniques for estimating this age require us to observe the present state of a time-dependent process, and from that observation infer the time at which the process started. If we believe that the process started when the earth was formed, we get an estimate of the earth's age.
    [Show full text]
  • Guide for the Use of the International System of Units (SI)
    Guide for the Use of the International System of Units (SI) m kg s cd SI mol K A NIST Special Publication 811 2008 Edition Ambler Thompson and Barry N. Taylor NIST Special Publication 811 2008 Edition Guide for the Use of the International System of Units (SI) Ambler Thompson Technology Services and Barry N. Taylor Physics Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 (Supersedes NIST Special Publication 811, 1995 Edition, April 1995) March 2008 U.S. Department of Commerce Carlos M. Gutierrez, Secretary National Institute of Standards and Technology James M. Turner, Acting Director National Institute of Standards and Technology Special Publication 811, 2008 Edition (Supersedes NIST Special Publication 811, April 1995 Edition) Natl. Inst. Stand. Technol. Spec. Publ. 811, 2008 Ed., 85 pages (March 2008; 2nd printing November 2008) CODEN: NSPUE3 Note on 2nd printing: This 2nd printing dated November 2008 of NIST SP811 corrects a number of minor typographical errors present in the 1st printing dated March 2008. Guide for the Use of the International System of Units (SI) Preface The International System of Units, universally abbreviated SI (from the French Le Système International d’Unités), is the modern metric system of measurement. Long the dominant measurement system used in science, the SI is becoming the dominant measurement system used in international commerce. The Omnibus Trade and Competitiveness Act of August 1988 [Public Law (PL) 100-418] changed the name of the National Bureau of Standards (NBS) to the National Institute of Standards and Technology (NIST) and gave to NIST the added task of helping U.S.
    [Show full text]
  • Student Pages Part B 3C P2
    Fat: Who Says? Measuring Obesity by Bioelectrical Impedance Analysis Circuitous Adventures-Measuring Electrical Values Student Information Page 3C Part B Activity Introduction: Surge ahead and learn how to use a multimeter device to measure voltage, amps, and resistance. Resistance is futile! Activity Background: Whenever charged particles are taken from one object and given to another object, an imbalance of charge occurs. This imbalance of charge is called voltage (or potential difference). Voltage is measured in units called Volts (V), named after Alessandro Volta. An electric current is nothing more than the flow of electric charges from one location to another. The measure of how much flow is occurring at any given point is called the amperage and is measured in units called amps (A), named after André-Marie Ampère. Electric charges can only flow through certain materials, called conductors. Materials that resist the flow of current are called insulators. Materials offer resistance to the flow of current. This resistance is measured in units called ohms (Ω), named after its discovered Georg Ohm. Ohm’s law states that the amount of current (I) flowing through a conductor times the resistance (R) of the conductor is equal to voltage (V) of the source of power (i.e. batteries). This law is often expressed in the following form: V = I X R Note: V = voltage, I = current, and R = resistance Activity Materials: • 2 batteries • 1 battery holder • Several electrical wires (stripped) or with alligator clips • 1 buzzer • 1 switch • 1 Analog multimeter • 1 Copy Student Information Page • 1 Copy Student Data Page • Transparency of Figure 3 Part B LESSON 3 ® Positively Aging /M.O.R.E.
    [Show full text]
  • UNITS This Appendix Explains Some of the Abbreviations1•2 Used For
    APPENDIX: UNITS This appendix explains some of the abbreviations1•2 used for units in this book and gives conversion factors to SI units and atomic units: length 1 a0 = 1 bohr = 0.5291771 X 10-10 m 1 A= 1 Angstrom= lo-10 m = 1.889727 ao mass 1 me = 1 atomic unit of mass = mass of an electron 9.109534 X 10-31 kg = 5.485803 X 10-4 U 1 u 1 universal atomic mass unit = one twelfth the mass of a 12c atom 1.6605655 x lo-27 kg = 1822.887 me time 1 t Eh 1 = 1 atomic unit of time = 2.418884 x l0-17 s 1 s = 1 second = 4.134137 x 1016 t/Eh temperature 1 K = 1 Kelvin amount of substance 1 mol = 1 mole 6.022045 x 1023 atoms, molecules, or formula units energy 1 cm-1 = 1 wavenumber 1 kayser 1.986477 x lo-23 J 4.556335 x 10-6 Eh 857 858 APPENDIX: UNITS 1 kcal/mol = 1 kilocalorie per mole 4.184 kJ/mol = 1.593601 x 10-3 Eh 1 eV 1 electron volt = 1.602189 x lo-19 J 3.674902 X 10-2 Eh 1 Eh 1 hartree = 4.359814 x lo-18 J Since so many different energy units are used in the book, it is helpful to have a conversion table. Such a table was calculated from the recommended values of Cohen and Taylor3 for the physical censtants and is given in Table 1. REFERENCES 1. "Standard for Metric Practice", American Society for Testing and Materials, Philadelphia (1976).
    [Show full text]
  • The Kelvin and Temperature Measurements
    Volume 106, Number 1, January–February 2001 Journal of Research of the National Institute of Standards and Technology [J. Res. Natl. Inst. Stand. Technol. 106, 105–149 (2001)] The Kelvin and Temperature Measurements Volume 106 Number 1 January–February 2001 B. W. Mangum, G. T. Furukawa, The International Temperature Scale of are available to the thermometry commu- K. G. Kreider, C. W. Meyer, D. C. 1990 (ITS-90) is defined from 0.65 K nity are described. Part II of the paper Ripple, G. F. Strouse, W. L. Tew, upwards to the highest temperature measur- describes the realization of temperature able by spectral radiation thermometry, above 1234.93 K for which the ITS-90 is M. R. Moldover, B. Carol Johnson, the radiation thermometry being based on defined in terms of the calibration of spec- H. W. Yoon, C. E. Gibson, and the Planck radiation law. When it was troradiometers using reference blackbody R. D. Saunders developed, the ITS-90 represented thermo- sources that are at the temperature of the dynamic temperatures as closely as pos- equilibrium liquid-solid phase transition National Institute of Standards and sible. Part I of this paper describes the real- of pure silver, gold, or copper. The realiza- Technology, ization of contact thermometry up to tion of temperature from absolute spec- 1234.93 K, the temperature range in which tral or total radiometry over the tempera- Gaithersburg, MD 20899-0001 the ITS-90 is defined in terms of calibra- ture range from about 60 K to 3000 K is [email protected] tion of thermometers at 15 fixed points and also described.
    [Show full text]
  • Kelvin Color Temperature
    KELVIN COLOR TEMPERATURE William Thompson Kelvin was a 19th century physicist and mathematician who invented a temperature scale that had absolute zero as its low endpoint. In physics, absolute zero is a very cold temperature, the coldest possible, at which no heat exists and kinetic energy (movement) ceases. On the Celsius scale absolute zero is -273 degrees, and on the Fahrenheit scale it is -459 degrees. The Kelvin temperature scale is often used for scientific measurements. Kelvins, as the degrees are now called, are derived from the actual temperature of a black body radiator, which means a black material heated to that temperature. An incandescent filament is very dark, and approaches being a black body radiator, so the actual temperature of an incandescent filament is somewhat close to its color temperature in Kelvins. The color temperature of a lamp is very important in the television industry where the camera must be calibrated for white balance. This is often done by focusing the camera on a white card in the available lighting and tweaking it so that the card reads as true white. All other colors will automatically adjust so that they read properly. This is especially important to reproduce “normal” looking skin tones. In theatre applications, where it is only important for colors to read properly to the human eye, the exact color temperature of lamps is not so important. Incandescent lamps tend to have a color temperature around 3200 K, but this is true only if they are operating with full voltage. Remember that dimmers work by varying the voltage pressure supplied to the lamp.
    [Show full text]
  • Energy Pioneers
    Providing energy education to students in the communities we serve. That’s our Promise to Michigan. Energy Pioneers The following pages will give an overview about famous people in history who studied energy and invented useful things we still use today. Read about these people then complete the matching activity on the last page. For more great energy resources visit: www.ConsumersEnergy.com/kids © 2015 Consumers Energy. All rights reserved. Providing energy education to students in the communities we serve. That’s our Promise to Michigan. Thomas Edison (1847) Information comes from the Department of Energy, including sourced pictures. Source: Wikimedia Commons (Public Domain) Born in 1847. Not a very good student. Created many inventions including the phonograph (similar to a record player), the light bulb, the first power plant and the first movie camera. One of his most famous quotes is, “Invention is one percent inspiration and ninety-nine percent perspiration.” For more great energy resources visit: www.ConsumersEnergy.com/kids © 2015 Consumers Energy. All rights reserved. Providing energy education to students in the communities we serve. That’s our Promise to Michigan. Marie Curie (1867) Information comes from the Department of Energy, including sourced pictures. Source: Nobel Foundation, Wikimedia Commons (Public Domain) Born in 1867. Learned to read at 4. There were no universities in her native Poland that accepted women, so she had to move to France to attend college. She, along with her husband, discovered the first radioactive element. In 1903, she was awarded the Nobel Prize in Physics for the discovery of radium. Marie Curie was the first woman to win a Nobel Prize in Physics.
    [Show full text]
  • Electrical Basics
    Electrical Basics Power & Ohm’s Law Group 1 • Work together to understand the informaon in your secon. • You will have 10 minutes to review the material and present it to the class. • With some applied force, electrons will move from a negatively charged atom to a positively charged atom. This flow of electrons between atoms is called current. • Current is represented by the symbol I 3 • When there is a lack of electrons at one end of a conductor and an abundance at the other end, current will flow through the conductor. This difference in “pressure” is referred to as voltage. • This “pressure” is sometimes referred to as “electromotive force” or EMF. • Voltage is represented by the symbol E 4 • Resistance is the opposition to the flow of electrons (aka “current”). • Every material offers some resistance. • Conductors offer very low resistance. • Insulators offer high resistance. • Resistance is represented by the Symbol R • Resistance is measured in Ohms Ω 5 • Current is measured by literally counting the number of electrons that pass a given point. • Current will be the same at any point of a wire. • The basic unit for counting electrons is the "coulomb“. (French physicist Charles Augustin de Coulomb in 1780’s) 6 • 1 coulomb = 6.24 x 1018 electrons = 6,240,000,000,000,000,000 = more than 6 billion billion electrons! If 1 coulomb of electrons go by each second, then we say that the current is 1 "ampere" or 1 amp (Named after André-Marie Ampère, 1826) 7 • Voltage is measured in volts. • A voltage of 1 volt means that 1 "Joule" of energy is being delivered for each coulomb of charge that flows through the circuit.
    [Show full text]
  • The International System of Units (SI) - Conversion Factors For
    NIST Special Publication 1038 The International System of Units (SI) – Conversion Factors for General Use Kenneth Butcher Linda Crown Elizabeth J. Gentry Weights and Measures Division Technology Services NIST Special Publication 1038 The International System of Units (SI) - Conversion Factors for General Use Editors: Kenneth S. Butcher Linda D. Crown Elizabeth J. Gentry Weights and Measures Division Carol Hockert, Chief Weights and Measures Division Technology Services National Institute of Standards and Technology May 2006 U.S. Department of Commerce Carlo M. Gutierrez, Secretary Technology Administration Robert Cresanti, Under Secretary of Commerce for Technology National Institute of Standards and Technology William Jeffrey, Director Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose. National Institute of Standards and Technology Special Publications 1038 Natl. Inst. Stand. Technol. Spec. Pub. 1038, 24 pages (May 2006) Available through NIST Weights and Measures Division STOP 2600 Gaithersburg, MD 20899-2600 Phone: (301) 975-4004 — Fax: (301) 926-0647 Internet: www.nist.gov/owm or www.nist.gov/metric TABLE OF CONTENTS FOREWORD.................................................................................................................................................................v
    [Show full text]
  • SI Base Units
    463 Appendix I SI base units 1 THE SEVEN BASE UNITS IN THE INTERNatioNAL SYSTEM OF UNITS (SI) Quantity Name of Symbol base SI Unit Length metre m Mass kilogram kg Time second s Electric current ampere A Thermodynamic temperature kelvin K Amount of substance mole mol Luminous intensity candela cd 2 SOME DERIVED SI UNITS WITH THEIR SYMBOL/DerivatioN Quantity Common Unit Symbol Derivation symbol Term Term Length a, b, c metre m SI base unit Area A square metre m² Volume V cubic metre m³ Mass m kilogram kg SI base unit Density r (rho) kilogram per cubic metre kg/m³ Force F newton N 1 N = 1 kgm/s2 Weight force W newton N 9.80665 N = 1 kgf Time t second s SI base unit Velocity v metre per second m/s Acceleration a metre per second per second m/s2 Frequency (cycles per second) f hertz Hz 1 Hz = 1 c/s Bending moment (torque) M newton metre Nm Pressure P, F newton per square metre Pa (N/m²) 1 MN/m² = 1 N/mm² Stress σ (sigma) newton per square metre Pa (N/m²) Work, energy W joule J 1 J = 1 Nm Power P watt W 1 W = 1 J/s Quantity of heat Q joule J Thermodynamic temperature T kelvin K SI base unit Specific heat capacity c joule per kilogram degree kelvin J/ kg × K Thermal conductivity k watt per metre degree kelvin W/m × K Coefficient of heat U watt per square metre kelvin w/ m² × K 464 Rural structures in the tropics: design and development 3 MUltiples AND SUB MUltiples OF SI–UNITS COMMONLY USED IN CONSTRUCTION THEORY Factor Prefix Symbol 106 mega M 103 kilo k (102 hecto h) (10 deca da) (10-1 deci d) (10-2 centi c) 10-3 milli m 10-6 micro u Prefix in brackets should be avoided.
    [Show full text]