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Anglicky v odborných předmětech "Support of teaching technical subjects in English “

Anglicky v odborných předmětech "Support of teaching technical subjects in English “. Tutorial : Mechanic - electrician Topic : Basics of electrical engineering the 2nd. y ear Measurement of current and voltage Prepared by: Ing. Jiří Smílek.

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Anglicky v odborných předmětech "Support of teaching technical subjects in English “

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  1. Anglicky v odborných předmětech"Support ofteachingtechnicalsubjects in English“ Tutorial: Mechanic - electrician Topic: Basicsofelectricalengineering the 2nd. year Measurementofcurrentand voltage Prepared by: Ing. Jiří Smílek Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

  2. Change the current and voltage of electric measurements Resistance - joined in series rheostat - large current consumption potentiometer – small current consumption • Change AC and DC current and voltage: • Change AC current and voltage: • Transformer – more economical than resistance • used transformer – Autotransformer

  3. Measuring current Deflection method - voltage is measured by Ammeters to show the value of the measured current deflection or figure. • Used method: • Involvement of the measuring device: Ammeters are connected in series to the measured circuit • Properties of the meter: • Power consumption is negligible - Ammeter does not affect the circuit, • Internal impedance (resistance) - infinitely small, at least significantly smaller than the impedance through which the current is measured. • does not have a rise in voltage drop across the A- meter

  4. Measuring current • Shunt • constant device • kA = n x range/number of scale intervals • Measuring transformer current– MTP - only AC • nominal secondary voltage MTP • I2 = 5 A (1A – for energy - billing metering) • transfer MTP • pP = I1/ I2=I1/ 5 • Constant device with MTP • kp = kApP • Magnification range ammeter:

  5. Measuring current • Calculation of the shunt • voltage on the A-meter - RA and shunt Rb is the same • Substituting according to Ohm's law • Expression RPafter adjustment • We designate for the number, how many times we want to extend the range of the ammeter, the letter n • passes through the shunt a current (n - 1) times larger than the ammeter and the shunt must have a resistance (n - 1) times smaller than the resistance of the voltmeter. • Magnification range of the ammeter:

  6. Measuring voltage Deflection method - the voltage is measured by voltmeters showing the value of the measured voltage deviation or figure. • Used method: • Involvement of the measuring device: Voltmeters are connected in parallel to the measured circuit • Properties of the measuring device: • Power consumption is negligible - a voltmeter does not have an affect on the circuit being measured,, • Internal impedance (resistance) - infinitely large - at least substantially larger than the impedance at which the voltage is measured.

  7. Measuring voltage • Series resistance - series • connection via terminals - one series • more series • by using the ranges • Constant device • kU = n x range/ number of scale intervals • Measuring transformer voltage– MTN - only AC • nominal secondary voltage MTN • U2 = 100 V • transfer MTU • pN = U1/ U2= U1/ 100 • Constant device with MTN • kp = kVpN • Magnification range of the voltmeter:

  8. Measuring voltage • Calculation of series • Current in the circuit RP - RV is the same • Substituting according to Ohm's law • or • Expression of RP • after adjustment • If we need the range of the voltmeter to increase n-times, it must have a ballast resistor (n - 1) times larger, • Magnification range of the voltmeter:

  9. Activities for students – questions • Name the ways of changing the current and voltage AC and DC circuit measurements • current - • voltage - • Describe the method of measuring current and voltage • Draw and write the name of the methods involved in the measuring device for measuring current and voltage • current • voltage

  10. Activities for students – questions • List and describe the characteristics of measuring devices for measuring voltage and current • voltage - • current - • Derive equations for a ballast device to enlarge the measuring range of the device voltage • Derive equations for a ballast device for increasing the extent of current meter

  11. Bibliography • Mužík, J. Management ve vzdělávání dospělých. Praha: EUROLEX BOHEMIA, 2000. ISBN 80-7361-269-7. • Operační program Vzdělávání pro konkurenceschopnost, ESF 2007 – 2013. • Dostupné na: http://www.msmt.cz/eu/provadeci-dokument-k-op-vzdelavani-pro-konkurenceschopnost • Učebnice Elektrická měření – Ing. Pavel Vylegala, SŠE Ostrava, 2006 • Učebnice Elektrické měření – SNTL, 1981 • Elektrotechnika - Laboratorní cvičení pro bakalářské studium - Doc. Ing. Miloš Hammer, CSc.

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