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START
Slope Switch:
A
slide
switch
which
selects either positive-
going
or
negative-going
trigger
edge
for
start
of
time
interval,
time
interval
average,
and
totalize
measurements.
Applies
to
the
'
B'
channel only.
STOP
Slope Switch:
Selects the required
'stop'
trigger
edge
polarity
on
time
interval,
time
interval
average, and
totalize.
DELAY
IN(/OUT
Switch
When
measuring
time
intervals
with
external
start
and
stop
contacts, contact
bounce
effects
can be
suppressed
by
setting
the
DELAY
switch
to
IN.
This
holds
off
any
stop signal
for
approximately 10ms.
The
control
is
operative with the
a.c. and
d.c.
amplifiers of
channel
'B'
and
the
d.c.
amplifier of
channel
'A'.
B-B/B-A
Switch
Position
B-B
selects single line
'start/stop'
for
time
interval
measurement (Channel
'B').
Position
B-A
selects
'start'
Channel
'B'
and
'stop'
Channel
'A'
on time
interval
measure-
ments.
AQ/DC
Switches
These
switches
select either
a.c.
or
d.c.
coupling
in
the input amplifiers.
Operation on
DC Mode
The
use of
d.c.
mode
is
recommended
in
the
following circumstances:-
(a)
For signals
having
a
slow
rate
of
rise
and
fall
(e.g. sinusoidal signals of
frequency lower
than 10
Hz).
(b)
For signals of
rectangular
waveform
which have
a
mark/space
ratio
other than
1
:1
,
provided
the
frequency
is
less
than
10
MHz.
9902
&9906
Vol.l
3-3
CHECIVOPERAT^HOLD
Switch:
OPERATE
is
normal
setting.
CHECK
provides a
1
MHz
readout
of
the
internal
reference
frequency
(on
Frequency and
Period)
for
self-check
of
counting and
display
circuits.
In
the
HOLD
position the
display
is
held, but a single shot
update
can be obtained by
depressing
and
releasing
the
adjacent
RESET
button.
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.
START/STOP
Push-Button:
Provides
manual
start/stop
on Time
Interval
and
Totalize
modes.
RESET
Push-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.
AC
SENSITIVITY
Control:
This
is
a
potentiometer providing
manual
variation of
sensitivity
in
the
'A'
input
when
the
AC/DC
switch
is
set to
AC.
The
most
sensitive position
is
fully
anticlockwise.
The
control
is
also useful
in
filtering
out
h.f. interference
on lower
frequency
measurements
.
POWER
ON/OFF
Switch:
Switches
off
the
a.c.
supply
to the line
power
transformer.
INDICATORS
OVERFLOW:
The
OVERFLOW
indicator
will
illuminate
when
the
count
exceeds
the
capacity
of the
display.
GATE:
The
GATE
indicator illuminates
when
the
counter gate
is
'open'.
Thus the
illumination
period
is
related
to
gate time selected.
9902&9906
Vol.l
3-4
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