HP 339A - Page 20

Section
III
Model
339A
3-13.
Turn-On
and
Warm-Up.
3-14.
Before
connecting
ac
power
to
the
339 A,
be
certain
the
rear
panel
voltage
selector
switches
are set
to
correspond
to
the
voltage
of the
available
power
line and
that
the
proper
fuse
is
installed
for
the
voltage
selected.
For
rated
measurement
accuracy,
the
339A
should
be
allowed
to
“warm-up”
for
at
least 15
minutes.
3-15.
DISTORTION
MEASUREMENT.
3-16. Distortion
Measurement Using
the
339A
Internal
Oscillator.
3-17.
The
Model
339A Distortion
Measurment Set
is
designed
to
provide
complete
capability
for measuring
Total
Harmonic
Distortion by
combining an
automatic,
high
resolution
distortion
analyzer and a
low
distortion
signal
source.
Figure
3-2 illustrates the
fundamental
application of
the
Model 339A.
The figure
shows
the
equipment
configuration and
includes
an
operating
procedure
for
making THD
measurements.
339A
DISTORTION
MEASUREMENT
SET
DEVICE
BEING
TESTED
ANALYZER
INPUT
PRELIMINARY
ADJUSTMENTS.
a.
Set
the
OSCILLATOR
LEVEL
control
to
OFF.
b.
Set
the
METER
RESPONSE
switch
to
NORMal.
c
Set
the
ANALYZER
INPUT/GND
SELECT
switch
to
Distortion
ANalyzer.
(Low
input
connected to
chassis
ground
or floated as
desired.)
d.
Set
FILTER
switches as
desired.
e.
Connect
the
339A
DISTORTION
MEASUREMENT
SET
and
the
device to
be
tested as
shown.
OSCILLATOR
ADJUSTMENT.
f Set
the
FUNCTION
switch to
OSCillator
LEVEL
and
adjust the
OSCILLATOR
LEVEL
and
LEVEL
vernier
controls
for the
desired
signal
level
as
indicated
on
the
meter
(Change
the
METER
INPUT
RANGE
switch
as
necesary to
obtain the
proper
meter
range.)
g.
Set
the
FREQUENCY
controls
and
FREQUENCY
VERNIER
for the
desired
output
frequency.
(Use a
frequency
counter
if
frequency
is
critical.)
ANALYZER
ADJUSTMENT
h. Set
the
FUNCTION
switch to
DISTORTION.
i.
Select
the
proper
input range by
turning the
METER
INPUT
RANGE
control
in
the
direction
indicated by
the
INPUT
RANGE
indicator
lights.
The
proper input
range
has been
selected
when the
INPUT
RANGE
control
is
set to
the
lowest
range
w
ic
extinguishes
both
indicator
lights.
j
Adjust
the
DISTORTION
RANGE
control to
obtain
an
"on-scale"
meter
indication as
near
full-scale
as
possible.
k
Read
the
amount
of total
harmonic
distortion
(THD)
in dB by
adding
the dB
figure
on the
DISTORTION
RANGE
control
and
the
dB
reading
of the
meter,
or
the
amount
of
THD
in
per-cent
is
indicated by
the
meter
reading
(second
or
third
scale)
relative to
t
e
full-scale
per-cent
figure on
the
DISTORTION
RANGE
control.
Figure
3-2. Distortion
Measurement
Using
339A
Internal
Oscillator.