Nonlinear
Distortion Conversion Scales
N I
.
d'
. d
ya22
+
a32
+
a42
+
....
an2
X
100
o/
ya22
+
a32
+
a42
+
....
an2 X 100
oJ
on
mear
1stort1on: =
1
o =
1
o
va1
2
+
a2
2
+
a3
2
+
....
an2
RMS
value
of
complete
signal
The
harmonic
distortion
d in
percent
for
sine-waves
can
be
calculated
from
the
number
of
dB
the
individual
harmonics
lie
below
the
r.m.s.
value
of
the
complete
signal
containing
the
fundamental
and
all
harmonics.
Example: The harmonics
of
a signal
are
found
to
lie
the
following
number
of
dB
below
the
r.m.s.
value
of
the
complete
signal.
From scale A:
the
value X for
the
individual harmonics
is
found
to,
C:
A
A
8
8
2.
harmonic
a
2
= - 68 dB
3.
harmonic
a
3
= -
62
dB
4.
harmonic
a
4
= - 76 dB
2.
harmonic
xl
= 0.0016
3.
harmonic
x2 = 0.0064
4.
harmonic
x3 = 0.00025
.I;x = o.00825
From scale B it
is
now
found
that
for .};X = o.00825
the
distortion
d
in
% will
be,
d = o.
09%
-80d8
-70
-60
-50
-.40dB
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