EE202
Please Do Not Use This
Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
Title: Measurement of Capacitance Using
Schering Bridge
Aim: To Measure the value of an unknown
resistance and to determine the characteristics of a resistor.
Apparatus:
1. A.F Signal Generator
2. Two Decade Resistance
Boxes
3. Two Decade Capacitance
Boxes
4. Capacitor of Unknown
Value
5. Head Phones
Please Do Not Use This
Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
THEORY:
Schering bridge is one of the very important and
useful methods of measuring the capacitance and dielectric loss of a capacitor.
In fact, it is a device for comparing an imperfect capacitor C2 in term of
a loss-free standard capacitor C1 [figure 1]. The imperfect capacitor is
represented by its equivalent loss-free capacitor C2 in series with
resistance r [figure 2].
For high voltage
application, the voltage is applied at the junction shown in the figure. The
junction between arms 3 and 4 is earthed. Since capacitor impedances at lower
frequencies are much higher than resistances, most of the voltage will appear
across capacitors. Grounding of the junction affords safety to the operator
from the high-voltage hazards while making balancing adjustment in arm 3 and 4.
For balance,
Z1Z3 =
Z2Z4
Or,
Separating the reals and imaginaries, we
have C2 = C1(R4/R3) and r = R3.(C4/C1).
The quality of a capacitor is usually
expressed in term of its phase defect angle or dielectric loss angle which is
defined as the angle by which current departs from exact quadrature from the
applied voltage i.e. the complement of the phase angle. If ɸ is the actual
phase angle and δ the defect angle, then ɸ+δ=900. For smaller values
of δ, tan δ = sin δ = cos ɸ (approximately). Tan δ is usually called
the dissipation factor of the R-C circuit. For low power factors, therefore,
dissipation factor is approximately equal to the power factor.
Advantages
of Schering Bridge:
·
1)
The balance equation is independent of frequency.
·
2)
It is used for measuring the insulating properties of electrical cables and
equipments.
For
Procedure and Circuit Diagram, See your Electrical Laboratory Manual on page
3.
Fill Up
Tables in Your Manual and Continue To….
PRECAUTIONS:
Answers
to Questions:
No Questions in this experiment.
Please Do Not Use This
Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
Blogger Comment
Facebook Comment