A Schering Bridge is a bridge circuit used for measuring an unknown electrical capacitance and its dissipation factor. The dissipation factor of a capacitor is the the ratio of its resistance to its capacitive reactance. The Schering Bridge is basically a four-arm alternating-current (AC) bridge circuit whose measurement depends on balancing the loads on its arms .

1. Schering bridge
E.KAROLINEKERSIN
ASSISTANT PROFESSOR

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The Schering bridge is one type of AC bridge, which is
used to measure the unknown capacitance, relative
permeability, dissipation factor, and dielectric loss of a
capacitor.
The high voltage in this bridge is obtained by using the
step-up transformer.
Schering bridge

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• The main objective of this bridge is to find
capacitance value.
• The main apparatus required for connection are
trainer kit, decade capacitance box, multimeter, CRO,
and patch chords.
• The formula used to get the capacitance value is the
CX=C2(R4/R3).

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• It is also capable of measuring the
dielectric loss of the capacitor in addition
to its capacitance value.
• It compares the capacitance of an
imperfect capacitor in term of the
capacitance of a standard capacitor.

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• This is essentially an ac bridge
with four arms, AB, BC, CD,
and DA.
• AB consists of a standard
capacitor of capacitance C1.
• The arm BC consists of the
capacitor under measurement
of capacitance C2 with
resistance r in series .

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• The arm CD consists of a
resistor of known resistance
R3.
• The arm AD consists of the
parallel of a resistance R4
and a capacitance C4.
• The alternating voltage is
applied between node B
and D,

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At balanced condition, there would not be
any voltage difference across the detector
of the bridge. And at that condition,

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Now by comparing, find out the impedance of the
ac bridge in terms of impedances of the Schering
Bridge.

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The Schering bridge is able to determine the
quality of the capacitor in terms of its
dissipation factor.
Pure capacitor leads the current by 90°.
But an imperfect capacitor leads the current
with a phase angle less than 90°.
The difference of the angle from 90° is referred
to as defect angle of the capacitor.
The tangent of the defect angle is called the
dissipation factor of the capacitor.
In other words, the ratio of the resistive
component and the reactive component of a
capacitor is the dissipation factor.
Hence, for this capacitor under measurement
By equating real and imaginary
part separately with zero, we get

10. Advantages
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• The balance equation is
independent of frequency.
• It is used for measuring the
insulating properties of
electrical cables and
equipment's.
• It can measure small
capacitors at low voltages
precisely.

11. Disadvatages
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There is a difficulty in obtaining
balance as R3

12. Applications
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This bridge is used for the relative
permittivity of the dielectric materials