Classification of Resistance
Resistance that are required to be measured may have any value from a few micro ohms to mega ohms.From the point of view of measurement, resistances are classified as three main groups.
1. Low Resistances: resistance of the order of 1Ω or less than 1Ω.
2. Medium Resistance: This class includes the resistance from 1Ω upwards to about 0.1MΩ.
3. High Resistance: Resistances of the order of 0.1 MΩ and above are classified as high resistance.
Note: The classification given above is not rigid, but forms a basis for techniques, followed or measurement. Which may be different for different classes.
Different Methods used for Measurement of Resistance are:
1. For low Resistance Measurement:
(a) Ammeter-Voltmeter method
(b) Kelvin’s double bridge method
(c) Potentiometer method.
2. For Medium Resistance Measurement:
(a) Ammeter-Voltmeter method
(b) Substitution method
(c) Whetstone bridge method
(d) Ohmmeter method
3. For High Resistance Measurement:
(a) Direct deflection method
(b) Loss of charge method
(c) Mega Ohm bridge method
(d) Megger.
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