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Lab1-SupplementNotes

# Lab1-SupplementNotes - Electrical Measurement Laboratory...

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1 Electrical Measurement Laboratory Laboratory #1 Objective To introduce the basic principles of DC meters and their use in measurement of voltage, current and resistance. Æ To study loading effects.

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2 Loading Effects: Voltmeter E 1M Ω - + 1M Ω a b E R R R I R V ab 2 1 2 2 + = = 2 1 1 1 E E V ab = + = R 1 R 2 I Without voltmeter With non ideal voltmeter E 1M Ω - + 1M Ω a b R 1 R 2 I R v If R v =1M Ω Ω = + × = M R ab 2 1 1 1 1 1 3 2 1 1 2 1 E E V ab = + = Loading Effects: Ammeter E 500 Ω - + 1k Ω a b 2 1 R R E I + = R 1 R 2 I Without Ammeter With non ideal ammeter E 500 Ω - + 1k Ω a b R 1 R 2 I R A If R A =300 Ω 1500 500 1000 E E I = + = 1800 E I =
3 Galvanometer – D’Arsonval Meter Electro-mechanical device based on magnetic force on current. Deflection is proportional to current in device. Æ Permanent-Magnet Moving-Coil Mechanism (PPMC) Simpson microammeter I FS = Full scale deflection current R m = Internal resistance Current is proportional to voltage (ohm’s law) Î voltmeter

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