ESI 250-DA - Understanding Series and Parallel Capacitance

2.
4.
2
SERIES
AND
PARALLEL
CAPACITANCE
The
bridge
measures a
simple
equivalent
circuit for the
impedance
connected
to
its
terminals.
This
equivalent
circuit
consists
of
a capacitance and
a
resistance
connected in
series. An
alternate representation
of the same
impedance
is an
equivalent
circuit
consisting of a
different
capacitance and
resistance
connected
in parallel.
The
phase and magnitude of the measured
impedance
are identical
for
both
circuits.
For values of
D
greater
than 0.01
the
series and
parallel
capacitances
differ
measurably
(by
more
than
0.01%),
Although
the
bridge
measures
only the
equivalent series circuit
of a capacitor,
the
values
of the
equivalent
parallel
circuit may be easily calculated.
WHEN
THE
BRIDGE
MEASURES
SERIES
CAPACITANCE,
C
:
s
r
V
D
^
Cg
=
(MULTIPLIER
SWITCH
setting)
x
(MAIN
DIAL reading)
D =
(CIRCUIT
SELECTOR
reading)
x (D-Q DIAL reading) x
(fj^^)
Q
R
J.
D
D
2irfC,
D
-
j
2irfC
D
and
Q
in per unit
R
in kilohms
s
f in
kc
C
in
microfarads
s
j
=
Z
in
kilohms
TO
CALCULATE
THE
EQUIVALENT
PARALLEL CIRCUIT:
The D of
the
equivalent
parallel
circuit
always equals the D of the equivalent
series
circuit.
The
same
is
true
of
Q.
C
C
=
P
(1
+
R
P
L
D
1
^
2ir
fC
P
lefsTI 250-DA
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