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AC BRIDGE An ac bridge consist of four arms of impedances, a source of excitation and a balance detector. Used for measurement of unknown impedances like inductance, capacitance, for storage factor, dissipation factor, phase shifting etc. All the ac bridges are based on the Wheatstone bridge.

AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

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An ac bridge consist of four arms of impedances, a source of excitation and a balance detector.

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Page 1: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

AC BRIDGEAn ac bridge consist of four arms of impedances, a

source of excitation and a balance detector.Used for measurement of unknown impedances like

inductance, capacitance, for storage factor, dissipation factor, phase shifting etc.

All the ac bridges are based on the Wheatstone bridge.

Page 2: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

MAXWELL’S INDUCTANCE CAPACITANCE BRIDGE

In this bridge, an inductance is measured by comparison with a standard variable capacitance.

Balance equation –(R3 + j3)=R2R4 Separating real and imaginary-

= and L3=R2R4C

Q factor - Q=R1=C4R4

Page 3: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

ADVANTAGES

The two balance equation are independent if we choose R4 and C4 as variable element.

The frequency does no appear in any of the two equations.

It very useful in measurement of wide range of inductance at power and audio frequency.

Page 4: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

DISADVANTAGESThis bridge requires a variable standard

capacitor which may be expensive if calibrated to high degree of accuracy.

The bridge is limited to measurement of low Q coils. (Q>10)

Page 5: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

DE SAUTY’S BRIDGEThe De Sauty’s bridge is an A.C Bridge works on the

principle of Wheat stone’s bridge . This bridge is used to determine the capacity of an

unknown capacitor C1 in terms of a standard known capacitor C2.

R1 and R2 are non - inductive resistors . R1, R2 ,C1 and C2 are connected in a Wheat stone’s bridge.

Headphone is used as a detector.

Page 6: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

When the bridge is balanced, the ratios of impedances are equal as given below-

= = =

= C

Page 7: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

ADVANTAGES

The advantage of this bridge is its simplicity to obtain a perfect balance.

DISADVANTAGESA perfect balance can be obtained, only if both the capacitors are free from dielectric losses i.e. when air capacitors are used .

Page 8: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

WEIN’S BRIDGE

Wien bridge is primarily known as a frequency determining bridge and find its application as harmonic distortion analyzer, audio and HF oscillators etc.

At balance- R3 = R4 Equating real and imaginary parts-= + , = When R1=R2=R and C1=C2=C=2 and =1/2RC

Page 9: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

ADVANTAGES

This may be used for measurement of capacitance also

DISADVANTAGESBecause of frequency sensitivity, the Wien's bridge may be difficult to balance unless the waveform of the applied voltage is sinosuidal.

Page 10: AC bridges ( Weins bridge, Desauty bridge, Maxwell's inductance bridge)

THANK YOU