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A measuring instrument invented by William Thomson, 1st Baron Kelvin.
Used to measuring very low resistances (typically less than 1/10 of an ohm).
The operation is like Wheatstone bridge except for the presence of additional resistors.
Modification of Wheatstone Bridge
r - the resistance of the contacts that connect the unknown resistance R to the standards resistance, S.
‘m’ @ ‘n’ – the range between each galvanometer is connected for obtaining a null point.
Fundamental
Fundamental
Balance equation of this bridge
Balance equation of this bridge
The equation shows that if the galvanometer connects at point ‘d’ then the resistance of lead will not affect their results.
For obtaining the desired result, the actual resistance of exact ratio connects between the point ‘m’ and ‘n’ and the galvanometer connects at the junction of the resistor.
Limitations of Kelvin Bridge
The sensitive galvanometer is used for detecting the balance condition.
The high measurement current is required for obtaining the good sensitivity.
EXAMPLE
EXAMPLE
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