Chapter 5 DC Bridges.ppt

# Cross sectional as the faulty cable so that l a l b

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cross sectional as the faulty cable, so that L a =L b . Therefore, ) 2 ( 2 1 1 L R R R L x

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modified version of the wheatstone bridge purpose of the modification is to eliminate the effect of constant and lead resistance when measuring unknown low resistance. The resistance in the range of 1 Ω to approximately 1µ Ω may be measured with a high degree of accuracy using Kelvin’s Bridge. 12/07/18 17 5.7 Kelvin Bridge R 2 G R 1 R x R 3 a b c R y E Chapter 5 : DC & AC Brigdes
When galvanometer is connected to point a , Ry is added to Rx resulting high indication for Rx When galvanometer is connected to point c , Ry is added to R3 resulting measurement of Rx is lower than the actual value If the galvanometer is connected to point b , in between point b in such a way that the ratio of the resistance from c to b and that from a to b equals the ratio of resistances R1 and R2, then Cont’d… 2 1 R R R R ab cb Chapter 5 : DC & AC Brigdes

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Cont’d… and the usual balance equations for the bridge give the relationship 12/07/18 19 2 1 3 2 1 ) ( R R R R and R R R but R R R R R R ab cb y cb ab ab cb x 2 2 1 2 2 1 2 1 1 1 R R R R R R R R R R R R R R R ab y ab ab cb ab cb Chapter 5 : DC & AC Brigdes
Therefore 12/07/18 20 Cont’d… Chapter 5 : DC & AC Brigdes 2 1 1 2 1 2 2 1 2 1 2 2 1 2 R R R R R R R R R R R R R R R R R R R R R R R R as and R R R R R y y y y cb y y ab y cb y cb ab y ab Substituting for R ab and R cb in equation

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12/07/18 21 Cont’d… Chapter 5 : DC & AC Brigdes 2 3 1 2 1 2 3 2 1 2 1 1 R R R R R R R R R R R R R R R R x y y x
• Fall '17
• puan nor azilah binti ahmad
• Voltage divider, Thévenin's theorem, I1R1

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