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

1. Anglicky v odborných předmětech"Support ofteachingtechnicalsubjects in English“ Tutorial: Mechanic - electrician Topic: Electric measurement the 2nd. Year Measuringdevices 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.

2. Measuring systems • Types of system • Resonance • Uses • frequency measurement - especially industrial frequency • Inductance • Uses • measurement of electricity • 1 Phase • 3 Phase • active • reactive

3. Measuring systems The measuring system is the physical nature of the conversion of electrical values to torque • 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.

4. The system of resonance • Describe the function: • tongues are put into electromechanical resonance alternating magnetic field to excite immobile coils. • 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

5. The system of resonance • 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:

6. Measuring systems The measuring system is the physical nature of the conversion of electrical values to torque • 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:

7. Induction system • 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

8. Activities for students – questions • Name the known measuring systems • Describe the design of some of the systems • Describe principle functions1. system • Draw a symbol of the measuring device 1. system • Name the uses of the system 1. system

9. Activities for students – questions • Fill in the missing words : • currents in the coils of the electromagnet are …………………….. ……………………. • influence ……………… ………………coresproduces ………………. magnetic field. • the field raises in the wheel……….. ……….. , that……….. torque.

10. 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