Feedback Instruments
Limited
Sweep Facility
Control
Slide switch enables internal
or
external sweep (VCF)
to
be selected
External
Gives normal unswept operation,
but
a voltage applied
to
the
'VCF'
socket modifies the frequency
of
operation
as
follows:
Linear mode: Voltage applied
to
the VCF
input
in-
creases
frequency at
the
rate
of
about
+0.3V
per 1 major
scaledivison (negative voltages decrease frequency).
Logarithmic mode: Voltage applied
to
the VCF
input
decreases
frequency at
the
rate
of
about 5V per factor
of
10.
Internal
Provides a triangular waveform
from
the socket
'TB
out
/''
and a corresponding square waveform
from
the
'TB
out
U ' socket. Sweep frequency rate adjustable
by
sinQie
logarithmic
control
from
50Hz
to
0.001 Hz.
Triangle amplitude:
5V
pk-pk
(OV
to
+5V)
from
1
k.O.
Square waveform
TTL:
(OV
to
+5V)
to
drive
two
standard loads available
from
'TB
out
U
'.
Operating Modes
Lever switch
'run/S-S/trig'
gives
continuous operation
in
'run'
position. When moved
from
'run'
to
'S-S'
(single shot) the triangle
output
goes
to
zero
and
then
executes a half cycle
(OV
to
+5V) when the switch
is
moved
to
the
'trig'
position. When operated in the
'S-S'
8
condition
the
'TB
out
lf
· may
be
used
as
a 'pen
lift'
control
for
X-Y
recorders. The 'set
max-min'
spring
return lever switch over-rides the sweep triangle generator
to
hold the waveform at its maximum (5V)
or
minimum
(OV) excursion. In the run condition this maximum
or
minimum
is
held
only
during the operation
of
the
'set
max-min'
switch.
In
'single-shot' the conditon
of
maximum
or
minimum
is
held until some other con-
dition
is
initiated.
Frequency Marker
An effective bright-up marker
for
use
with
oscilloscope
displays
of
frequency
responses
is
available
as
ahesitation
in
the
sweep triangle voltage. The position
of
this
is
controlled
by
a 'marker' control. The triangular voltage
and frequency at which this occurs
can
be
held
by
an
associated 'marker' pushbutton.
Sweep Width
This control
gives
the
proportion
of
the sweep triangle
voltage
used
to
control the frequency
of
the internal
sweep generator. The
scale
is
calibrated
from
0%
to
80%
for
linear sweep,
and
from
0
to
3
decades
for
logarithmic
sweep. In both conditions
('lin'
and
'log') the maximum
frequency
is
set
by
the main dial
and
occurs when the
triangle
output
voltage from
'TB'
is
maximum (+5V).
The calibration on the
sweep
width
control indicates the
sweep
width
as
a
proportion
of
the main frequency
setting.
e.g.
linear mode, main dial 50kHz, sweep-width
80%,
gives
sweep
from
10kHz
to
50kHz, sweep-width
two
decades,
gives
sweep from 500Hz
to
50kHz.
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