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Section II
3 - 1 9 .
WAV E F O R M ERRORS.
3-20. In
o r d e r t o m a i n t a i n accuracy
must remember that
y o u
device,
responding
but the
terms
in
of the r m s voltage of a p u r e sine wave. If
the waveform of the voltage being measured contains
harmonic
appreciable
voltages or other
ages, the meter indication w i l l deviate f r o m the
value on the o r d e r indicated by Table 3-1.
r m s
Table
3-1.
Effect
of Harmonics on Model
Measurements
Voltage
True
Input Voltage
Characteristics
Fundamental = 100
Fundamental +
10%
2nd harmonic
Fundamental +20%
2nd harmonic
Fundamental +
50%
2nd harmonic
Fundamental + 10%
3 r d harmonic
Fundamental + 20%
3 r d harmonic
Fundamental +
50%
3 r d harmonic
3 - 2 2 .
MEASUREMENTS.
DECIBEL
3-23. Measurements
i n t e r m s
the
as
measurements
same way
voltage
indication is read on the dbscale (-12 to +2 decibels).
The decibel l e v e l is the algebraic sum of the meter db
scale indication and DB VOLTS
3 - 2 4 , To r e a d p o w e r directly i n d b m ( 0 dbm=1
i n t o 600 ohms) the
measurement must be
600 ohms.
Comparative
db measurements (without
spect to reference level) may be obtained by direct
r e a d i n g provided
each measurement is made across
the same impedance value. The difference in decibels
or
measurements
between two
m o r e
by
reading d i r e c t l y f r o m
(For
of db measurements
examples
3 - 2 5 .
IMPEDANCE CORRECTION GRAPH.
3-26.
To obtain
the l e v e l
other than 600
pedances
shown
3-2
graph
i n fi g u r e
dbm w i l l be the algebraic sum of the levelas indicated
the meter and the
o n
c o r r e c t i o n
F o r example, if the
r a n g e
tion, the measurement made across 90 ohms,
3-2
of measurement,
t h i s i n s t r u m e n t i s a n average
meter scale
is calibrated
s p u r i o u s v o l t ‑
true
403A
| Value Indicated
RMS
by
Value
403A
100
100
100 - 102
110
100 -
96 - 104
94 - 108
90 - 116
of decibels
made in
a r e
except that the
(RANGE)
p o s i t i o n
milliwatt
across
made
r e ‑
be obtained
may
the db-scale indications.
to Table 3-2).
r e f e r
in dbm w i t h respect to i m ‑
ohms,
the meter
c o r r e c t i o n
used. The level
m a y b e
shown
the
graph.
o n
switch is at the +30 db
p o s i ‑
and the
indication on the DB scale
tained as follows:
+ 1
(db scale indication)
(range
+30
(level in db as indicated by meter)
+31
+ 8
(correction
+39
dbm
3-27.
F o r the same
ment made across
(db scale indication)
+ 1
+30
(range
+31
(level
-12.5
(correction
+18.5
dbm
3-2.
Table
Meter
Range
Scale
Switch
Measurements:
Voltage
* NOTE: In caseswhere a meter scale
below -8 db is obtained, it is best to switch
next
to the
l o w e r range on the instrument so
.
a
reading
w i l l be obtained in the
tion of the scale where highest accuracy
be obtained.
The same situation exists
urements. When a
1/3
scale, the
lower
switched to the next lower
the upper
reading in
3-30.
SHUNT RESISTORS.
Model
i n
'3-31. The @
Shunt Resistors
Model
403A
y o u r
These r e s i s t o r s make possible current readings o f
f r o m
1 a m p to 3 amps f u l l scale.
s
o
.
+1,
the level in dbm is ob‑
switch position)
90 ohms impedance)
f o r
conditions,
w i t h the measure‑
10,000
ohms:
switch position)
in db as indicated by
meter)
10,000
ohms impedance)
f o r
Examples of Voltage and DB
Measurements
Meter
Indicates
r e a d i n g
u p p e r p o r ‑
f o r
voltage m e a s ‑
is obtained in the
reading
switch should
range
to obtain a
range
2/3
scale.
11029A
through Model
(Table 1-2)
a r e available to
into a
current
measuring
Model 403A
=
Actual
Level
m a y
be
11034A
convert
device.
00125-3
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