Racal Instruments 9901 Maintenance Manual page 31

Pulse/Contacf
Switch:
OPERATE/CHECK
Switch:
START/STOP
Push-Button:
NORMAl/HOLD
Switch:
RESET Push-Button:
POWER ON/OFF
Switch:
This
switch
selects the input
timing
mode
for
the
'A'
and
'B'
channel d.c.
amplifiers.
(a)
Pulse (-IT.) position.
The
position
is
for
operating with electronically derived
signals.
(b)
Contact
(
n
)
position.
This position
is
used for
measurement where
the timing
signals
are
obtained from contacts.
The
Start/Stop switches
must be
set
so that
is
used
for
contact
closing
and
.S'
for
contact opening.
A
capacitor
is
introduced
internally to
reduce
the
effects
of contact
bounce.
OPERATE
is
normal setting.
CHECK
provides
a
1
MHz
readout of
the internal
reference
frequency
for
self-check of
counting
and
display circuits.
Segment
Check
To check
all
LED segments
in
the display,
press
the
RESET button
while
in
CHECK
mode.
This will
produce an
"all
8" display.
Provides
manual
start/stop
on Time
Interval
and
Totalize
modes.
In
the
NORMAL
position the instrument
provides continuous updating of the display.
In
the
HOLD
position the display
is
held but
a single shot
update can be obtained by
depressing the
adjacent RESET button.
When
the
RESET button
is
depressed
and
released the instrument will
clear
down
to
zero
and
initiate
a
new measurement.
The
RESET button
is
also
used
in
the
segment check.
Switches
off
the Internal
d.c. supplies.
2-8
9901 Vol. 2