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Q or Figure of Merit
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Impedance (cont.)
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of a simple reactor
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In series circuits where phase
angle and any two of the
Z, R and X components
are known, the unknown
component may be
determined from the expressions:
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of a single capacitor
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where
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Q =
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a ratio expressing the figure of
merit,
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where
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Z =
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magnitude of impedance in ohms,
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XL =
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inductive reactance in ohms,
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R =
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resistance in ohms,
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XC =
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capacitive reactance in ohms,
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X =
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reactance (inductive or
capacitive) in ohms,
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RL =
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resistance in ohms acting in series
with inductance,
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Nomenclature
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RC =
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resistance in ohms acting in series
with capacitance,
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Z =
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absolute or numerical value of
impedance magnitude in ohms,
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Impedance
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R =
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resistance in ohms,
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In any a-c circuit where
resistance and reactance
values of the
R, L and C components
are given, the
absolute or numerical
magnitude of impedance and
phase angle
can be computed from the formulas
which
follow:
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XL =
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inductive reactance in ohms,
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XC =
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capacitive reactance in ohms,
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L =
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inductance in henrys,
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C =
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capacitance in farads,
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In general the basic formulas
expressing total
impedance are:
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RL =
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resistance in ohms acting in
series with inductance,
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for series circuits,
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RC =
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resistance in ohms acting in
series with capacitance,
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 =
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phase angle in degrees by which
current leads voltage in a capacitive
circuit, or lags voltage in an inductive
circuit. In a resonant circuit ,
where
XL equals
XC,
equals 0o.
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for parallel circuits,
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Degrees X 0.0175 = radians.
1 radian = 57.3o
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See page 17
for formulas involving impedance, conductance,
susceptance and admittance.
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Numerical Magnitude of Impedance . . .
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of resistance alone
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Z = R
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= 0o
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