20-11-2012, 04:41 PM
FAMILIARIZATION OF VARIOUS ELECTRICAL INSTRUMENTS
FAMILIARIZATION OF VARIOUS.docx (Size: 226.69 KB / Downloads: 32)
THEORY OF EXPERIMENT:
• AMMETER
Ammeters are employed for measuring current in a circuit and connected in series with the circuit. As ammeter is connected in series, the voltage drop across ammeter terminals should be as low as possible. This requires that the resistance of the ammeter should be as low as possible.
• VOLTMETER
Voltmeters are employed to measure the potential difference across any two points of the circuit these are connected in the parallel to the circuit. The resistance of voltmeter is kept very high by connecting a high resistance in series of the voltmeter with the current coil of the instrument.
• WATTMETER
The measurement of real power in AC circuits is done by using an instrument using Wattmeter. The real power in AC circuits is given by expression VI cosø where, cosø is power factor. A wattmeter is comprises of two coils namely current coil and pressure coil. The current coil is connected in series with the load and the pressure coil is connected across the load.
• ENERGYMETER
Energy meter is an instrument which is used o measure he consumption of electric energy in an AC circuits. It measures energy in KWH. The principle of operation of an energy meter is just like wattmeter except that due to power through the meter ,a disc rotates. The number of revolution made by the disc is counted.
• TACHOMETER
Tachometer is an instrument to measure the speed in r.p.m..The speed of a rotating shaft is measured by inserting he tapered projected of the tachometer into the tapered hole in a rotating shaft of which speed is to be measured.
• RHEOSTAT
Rheostats are made up of high resistivity material like nickel-chromium iron alloy closely wound over a circular tube.These are available both in single tube and double tube.Inter-turn insulation is provided to avoid short circuiting of turns. The tube of rheostat are made of insulating material like asbestos.