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Model 5245L
e.
Switches +1?0
volts as
first
step
in
generating
lamp control voltages
(distinguishes
between CHECK
and
not-CHECK
positions). Further
srvitching
is
done
by
A3, final svitching
by
A2.
2-53.
The
level control
designated
-LEVEL+ on
the
front
panel adjusts
the
dc
input
trigger level
from
-0.
3
volts dc to +0.3 volts
dc.
Refer
to
schematic
diagram
Figure
7-3 and 7-4 for
circuit
details.
This control allows the trigger level for input
signals
to be adjusted
above
or
below ground
potential.
The
level control
range
is
increased to
t3 volts
dc
when
the input sensitivity switch
is
set
at
1
volt
rms,
and
is
increased to
+30
volts
dc
for
the
10
volt
rms
setting.
The murimum countercloclsvise position
(PRESET)
closes a switch which automatically sets
the trigger
level
at
ground
potential for
all
attenuator positions.
2.54.
TIME-BASE SwITCH ASSEMBLY A2.
2-55. The time-base switch
assembly
(designated
TIME-BASE on
front
panel)
is
a lO-position
switch
(EXT,
10s,
ls,
.
1s, 10ms,
lms,
.
1ms,
10ps,
1ps,
.
1ps).
Refer to the schematic diagram,
Figure 7-4, for
cir-
cuit
details.
Srpitch
functions are listed
belorv.
a.
Produces gate
controls
4, 2tr
22r 23r 24r 25r26,
27, 28,
and 29
using
switched
-15 volts from
A1
(SENSITIVITY switch).
b.
Produces
all decimal point control voltages using
switched +1?0
volts
from A3
(FUNCTION switch).
Decimal point control voltages are
connected
to appro-
priate
input terminals
on
decimal point assembly
A8.
c.
Produces
aII
measurement units control voltages
using switched +1?0volts from
A3.
Measurement
unit
control
voltages
are
connected
to
appropriate
input
terminals
on
measurement
units assembly
A9.
d.
Generates
resetpulsesby momentarily supplying
-15
volts
while switch
is between
detent
positions. This
resets
all
counter
circuits
if
time-base selection is
changed
during a measurement operation. Reset out-
put
is
connected
to
manual
reset input of
sampling
control assembly (pin
9
of
A23).
e.
Connects
time-base selected frequency from
A21
(function
control
assembly)
to EXT
connector
on
front
panel when
switch
is
not
in
EXT position. Disconnects
selected frequency
from
EXT connector when switch
is in
EXT position.
2.56.
FUNCTION
SWTTCH
ASSEMBLY
A3.
2-57. The
function switch
assembly
(designated
FIJNCTION
on
the
front
panel)
is
a 1O-position switch
(MANUAL STOP; MANUAL START;
FREQUENCY;
PERIOD A\TERAGE
for
1, 10, 100,
lK,
10K, and
100K
periods;
and REMOTE OR TIME
II.{T).
Refer to
the
schematic
diagram, Figure
7-5, for
circuit
details.
Switch
functions are listed
belorv.
02349-1
Section
II
Paragraphs 2-53 to 2-bg
a.
Produces gate
controls
?
through
13
by
switch-
ing -15 volts from po\r/er
supply.
b.
Contributes
to generationof
gate
controls
1
thru
6
and
21
thru
29.
c.
Contributes
to
generation
of decimal
point
and
measurement
units controls from
switched
+170
volts
from A1
(SENSITIVITY switch).
d.
Produces
start
and
stop
input
voltages
(-
15
volts)
to gate flip-flop in the
gate
control assembly (pins
13
and
14
of
A23)
when switched
to MANUAL START
and
MAI.{UAL
STOP.
e.
Shorts sample-rate
trigger
pulse
to
ground
at
pin
4
of
A23
when switched
to either MANUAL
START
or
MANUAL
STOP.
This inhibits
operation
of
the
sample rate
and
holdoff
multivibrators,
thereby pre-
ventingthe
reset amplifier from operating
in
MANUAL
functions. This arrangement allows the
accumulation
of
counts
in the DCA's over
several gate
openings
during MANUAL
operation.
Reset
is still
possible
in
the
MANUAL function
by
use
of the
RESET push
button
on
the
front
panel.
f.
Opens
thetransfer-pulse
linebetween
the
STOR-
AGE switch
on
the rear panel
and
the
decimal counters
when switched
to either MANUAL
START or MANUAL
STOP.
This prevents display storage operation.
g.
Opens
inhibit-signal line
between
the DIGITAL
RECORDER
connector on
the rear
panel and pin
12
of
A23
when switched
to
either
MANUAL START or
MANUAL
STOP.
This prevents
undesired
triggering
of the holdoff multivibrator which
could
inhibit
the
gate
flip-flop.
h.
Generates
reset pulses by momentarily supply-
ing
-l5volts
while switch is
between
detent
positions.
This resets
all
counter circuits
if
function selection
is
changed
during
a
measurement
operation.
Reset
output
is
connected
to
manual
reset input of sampling
control assembly (pin
9
of
A23).
2.58.
MODE
S\MITCH
ASSEMBLY
A4.
2-59.
The
mode switch assembly
(designated MODE
on
rear
panel)
is
a three-position
switch (EXT
STD
FREQ
1
MHz,
INT
STD FREQ, SCALER). Refer to
the
schematic
diagram, Figure
7-6,
for circuit
de-
tails.
Switch
functions are listed below:
a.
Connects external 1-MHz standard
to trigger-
circuit
of
the oscillator assembly
(A26)
when
in
EXT
STD
FREQ
1
MHz
position.
b.
Connects
output
ofinternal oscillator to trigger-
circuit
of
oscillator
assemblywhen
in INT
STD FREQ
position.
2-13
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