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CHAPTER
3
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PA
S
Function Push-Button Switch
Bonk;
This
bank
of
seven
push button switches,
located near
the centre of the front
panel,
select the
following
measurement modes:-
(i)
-Lh
Provides time
interval
measurement between
two
successive events.
The
events
may
be
on one
line
(B-B)
or
separate
lines
(B-A),
with
start
and
stop slopes of the
same
or
opposite
polarity.
(ii)
T.
I.Avg.
This
mode
is
suitable
for
the
measurement
of
short repetitive
events, with
start/stop controls
as
in T.
I.
By averaging
over a
number
of
events
the resolution
is
increased.
(iii)
FREQ.
'A'
Provides
frequency
measurement
of
the
'A'
channel
input with
readout
in
kHz.
9902
AUTO
ond
MANUAL
Modes
With
the
MAN
(manual) switch depressed,
the required
gate time
can be
selected from the
Range
('n')
buttons.
With
the
AUTO
switch
depressed, the instrument
will
automatically
select the
gate time (.01, 0.1
or
1
second)
which
gives
optimum
resolution
on
the display.
9902
&
9906
Vol
.
1
3-1
Function Push-Button
Switch
Bank
(Cont'd.);
9906
VHF
and
HF
Modes
The
AUTO/
manual
facility
is
not
fitted.
Instead, these
switches are
marked
VHF
and
HF, and
serve
as
frequency range
selectors.
With
HF
selected the
'A'
input
range
is
lOHz
to
30MHz,
directly
gated.
With
VHF
selected
the
'A'
range
is
30MHz
to
200MHz,
prescaled by
4, but
with
direct
readout
of the
measured frequency.
(iv)
PERIOD
'A'
Provides period
measurement
on
'A'
channel
signal
with readout
in
microseconds.
(v)
RATIO
n_A
B
Refer
to
Chapter
4,
para.
4.9.
(vi)
TOTAL
A_
n
Provides
accumulated
total
of
events
applied
to
Channel
'A',
with
prescaling
by
the factor
'n'
according
to
the switch
selected
in
the
Timebase
switch
bank.
Timebase Range
Push-Buttons
;
This
bank
of six
'n'
switches
offer
a
choice
of gate times.
The
multiplier
'n'
associated
with each switch
may
also
be
defined
as
follows;-
(a)
The
number
of
periods
averaged on
'period
average' measurement.
(b)
The
'A'
input prescale factor
on
'totalise'
.
(c)
The
'B'
input prescale factor
on
'ratio'.
(d)
The number
of
intervals
averaged on
'time Interval
average'.
(e)
The
switch
bank
also
is
used
to
select
the
clock
unit
on
'time interval'.
9902
&9906
Vol.l
3-2
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