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ZveřejnilRůžena Dušková
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Tutorial: Mechanic - electrician Topic: Basics of electrical engineering the 2nd. year Measuring the capacity 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.
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Definition of units of capacity The basic unit - 1 F (farad) 1 farad is the capacity of an electric capacitor, which has a voltage of 1V and holds a charge of 1C. Capacitance is: Directly proportional to: the active area S permittivity ε Inversely proportional to: the distance between the plates d C= ε S/d
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The used method: Volt-ampere (Ohm’s) method – applied to the measurements of large impedances Supply voltage must have a known and constant frequency a)Involvement of a small C b)Involvement of a large C
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We must know: current voltage When we don’t know the value of the capacity C X we calculate it from basic data from an A-metre and a V-metre Capacitive reactance Of which we don’t know the capacity, the angular frequency – ω will help Or the help of frequency f Calculation 1 – when an AC current:
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When measuring it is important that there is an AC current flowing through the circuit If not, you should make a re-count on a replacement scheme Phasor diagram Calculation 2:
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The used method: Measuring capacity distribution of an electric charge The measurement procedure: The capacity of the capacitor C is known and the position I of switch p is charged with a voltage U and a charge Q. Switch the switch to position 2; by an unknown capacity C X connected in parallel to capacity C. The charge is divided into two capacitors and the voltage U is subtracted again from the voltmeter. For the switch applies In position 1 - Q = U.C In position 2 - Q = U.Cx + U x C x. Unknown capacity of a capacitor
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Describe how to define a unit of capacity ◦ Name for what is the proportional capacity of the capacitor ◦ Write what are the requirements for power voltage ◦ Draw a circuit for measuring ◦ small C ◦ large C
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Calculate an example: A block capacitor has an unreadable data capacity; we can find out about the circuit with an ammeter. The ammeter showed a current I = 2.76A at a voltage of 230V, 50 Hz Capacitive reactance ◦ X C = Capacitance ◦ C X =
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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- konkurenceschopnosthttp://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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