measurement of resistance
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MEASUREMENT OF RESISTANCE
Prepared by,
Madhumitha Jayaraj
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WHY resistance of material is measured ???
Cable manufacturers
Electric motor & generator manufacturers
Installation & maintenance of power cables, switchgear & voltage tap changers
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CLASSIFICATION
< 1 Ω
LOW RESISTANCE
1Ω < R < 100kΩ
MEDIUM RESISTANCE
> 100kΩ
HIGH RESISTANCE
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MEDIUM RESISTANCE MEASUREMENT
Wheat stone Bridge
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Substitution method
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Ammeter-Voltmeter method
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LOW RESISTANCE MEASUREMENT
• AMMETER VOLTMETER METHOD
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KELVIN DOUBLE BRIDGE
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COMMERCIAL KELVIN DOUBLE BRIDGE
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MEASUREMENT OF HIGH RESISTANCEDIRECT DEFLECTION METHOD
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Measurement of high resistance having metallic sheath
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LOSS OF CHARGE METHOD
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R’ = t/(C loge V1/V2 )
While measuring insulation resistance of a cable ora capacitor the test need not be repeated. In thiscase C will be the capacitance of the cable undertest, which must be known and R1 will be theinsulation resistance to be measured. NO externalresistance is to be inserted in the circuit. The valueof R1 then can be obtained directly from theexpression.
R = t/(C log V2/V1 )
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MEGOHM BRIDGE METHOD
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Modified Wheatstone Bridge
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QUERIES..?