7.1.2. Graphical Recording
from
the
DC
OUTPUT
For discontinuous noise (typewriters, teleprinters etc.)
the
DC
OUTPUT
should
be used, since
the
level recorder may have
too
slow a response
or
be
too
unsteady
for
recordings from
the
AC OUTPUT.
The
"Impulse"
response
position
of
the
METER SWITCH should
be
selected.
The
recorder should be adjusted so
that
the
deflection
on
the
paper
is
equivalent
to
the
reading
on
the
meter
of
the
2209.
For
this
purpose it
is
suggested
that
a
25
dB Range
Potentiometer
is
used in
the
Level Recorder.
The
adjustment
is
made
by
first calibrating
the
2209
by
one
of
the
methods described in section 2.2. With
the
reference signal still operating
(whether internal reference voltage
or
external sound source), adjust
the
INPUT ATTENUATOR and INPUT POTENTIOMETER
of
the
recorder
until
the
pen
of
the
recorder indicates
the
same number
of
dB below
the
20
dB
chart
line
(25
dB range) as
the
meter
indicates below full scale de-
flection.
The
extra 5 dB
of
chart
deflection can
be
used with accuracy
provided overload
is
not
indicated. An example
is
shown in Fig.7.2, where
the
various meter responses
to
a sample
of
teletype
noise are compared.
JOOOOOOOOOOOOOODOOOODODOOOOOODODDOOOOOOOOOOO
Brilol
&
Ki-
Brilol
&
Ki-
110
Sound Pressure
100
-
Level
(dB)
90
BO
70
60
30
sec.
OP
0102
~62529
Fig.7.2. Recordings from
DC
OUTPUT
with
various meter
responses
The
most
suitable settings
of
the
Recorder controls are:
92
POTENTIOMETER RANGE
RECTIFIER
LOWER LIMITING
FREQUENCY
WRITING SPEED
25
dB
DC
50
Hz
315
mm/sec
To Next Page
Loading...
