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Tutorial: Mechanic - electrician Topic: Electric measurement the 2nd. Year Measuring devices 3 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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Types of system ◦ Resonance Uses frequency measurement - especially industrial frequency ◦ Inductance Uses measurement of electricity 1 Phase 3 Phase active reactive
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The system of resonance Construction: The measuring system comprises: an electromagnet, yoke steel springs (tongues), tuned to the mechanical resonance vibrations of certain frequencies of measured currents.
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Principle of operation: the most vibrated tongue, whose own mechanical frequency is in resonance with the frequency strength, which vibrated the tongue – ie double the frequency of the current coils Describe the function: tongues are put into electromechanical resonance alternating magnetic field to excite immobile coils.
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Properties: Measured frequency 16 – 1500 Hz Accuracy to 0,2 % (currently 0,5%) Need to observe the approximate nominal voltage Dependence on temperature - change in flexibility of tongues vibration pads Uses: Measurement of industrial frequencies (50 Hz) Tachometers, with a narrow speed range Symbol:
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Induction system – with a gradual field Construction: 2 electromagnets small air gap voltage coil a lot of thread, thin wire large air gap current coil few turns, strong wire aluminium wheel, revolution counter Properties: Large overload, large private consumption, low accuracy, a large influence of temperature and frequency. measures only AC electrical energy. Symbol:
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Principle of operation: currents in the electromagnet coils are phase shifted influence of spatial distribution of nuclei produces a gradual magnetic field. This field raises in the wheel eddy currents that cause torque Principle function: the measurement of energy consumption is a current coil associated with a network in series with the appliance, ◦ in a 3 phase meter there are 3 current coils voltage coil is connected to the network in parallel counter records the consumption of electrical energy usually in kilowatt-hours - kWh
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Name the known measuring systems ◦ Describe the design of some of the systems Describe principle functions 1. system Draw a symbol of the measuring device 1. system Name the uses of the system 1. system
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Fill in the missing words : currents in the coils of the electromagnet are …………………….. ……………………. influence ……………… ………………cores produces ………………. magnetic field. the field raises in the wheel……….. ……….., that ……….. torque.
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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
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