EE101 EE CIRCUITS 1

1T SY 2014-2015

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Circuit Theorems

Bridge Circuits

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LEARNING OUTCOME

Solve parameters involved in a basic bridge circuit.

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BRIDGE CIRCUITS

Bridge circuits are used in electronic measuring

equipment to precisely measure resistance in dc

circuits and similar quantities in ac circuits

Wheatstone bridge: used to measure resistance (more

accurate measurement)

Maxwell bridge: used to determine the inductance and series

resistance of an inductor having relatively large series

resistance

Hay bridge: used to measure the inductance and series

resistance of an inductor having a small series resistance

Schering bridge: used to determine the value of unknown

capacitance

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BRIDGE CIRCUITS

Various configurations of bridge circuits

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BRIDGE CIRCUITS

A balanced bridge is one in which the current through the

resistance R5 is equal to zero

An unbalanced bridge is one in which the current through R5 is

not zero

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WHEATSTONE BRIDGE CIRCUIT

The unknown resistance 𝑅𝑋 is connected to the bridge.

The variable resistance is adjusted until no current flows through

the galvanometer (which is essentially a d’Arsonval movement

operating as a sensitive current-indicating device like an ammeter

in the microampere range).

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WHEATSTONE BRIDGE CIRCUIT

Under this condition, 𝑣1 = 𝑣2 and the bridge is said to be

balanced.

Since no current flows through the galvanometer, 𝑅1 and

𝑅2 behave as though they were in series; so do 𝑅3 and 𝑅𝑋.

The fact that no current flows through the galvanometer also

implies that 𝑣1 = 𝑣2.

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WHEATSTONE BRIDGE CIRCUIT

Applying the voltage division principle

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BRIDGE CIRCUITS

To analyze the operation of these networks,

use the techniques developed earlier such as:

Resistor 𝑅5 may be removed and replaced with

either a short (since 𝑉𝑅5 = 0) or an open (since

𝐼𝑅5 = 0)

May use mesh or nodal analysis

May use Thevenin’s theorem

May use delta and wye transformation

And other applicable techniques

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ILLUSTRATION 1: BRIDGE CIRCUITS

Solve for the currents through R1 and R4 in the

circuit below:

𝐼𝑅1 = 2 A 𝐼𝑅4 = 1 A MCBLOYOLA

ILLUSTRATION 2: BRIDGE CIRCUITS

a) For the circuit shown, what value of R4 will ensure

that the bridge is balanced?

b) Determine the current I through R5 in the figure

below when R4 = 0 Ω and when R4 = 50 Ω.

20 Ω , 286 mA, -52.6 mA MCBLOYOLA

REFERENCES

Please refer to course syllabus.

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