Time Interval - Racal Instruments 9901 Maintenance Manual

TIME INTERVAL
(T.l.
and
T.l.
Average)
2.5
In fhis
mode
fhe
instrumenl-
is
effecMvely
serving os a
sfop waf-ch by counting clock
pulses derived from
the
frequency
standard. The
time
interval
may
be
controlled by
successive events
on a single
line (such as
pulse widths)
in
which
case
Input
'B'
is
used with
the
B-B/B-A
switch
set to
B-B.
2.6
For timing events
on separate
lines the
B-B/B-A
switch must be
set to
B-A. The
start' signal applied
to
the
'B'
Input
and
the
'stop' signal to the
'A' input. Trigger
slopes can be
selected
by
the
START/STOP
slope switches,
The
T.l.
mode
is
most
suited
to the
measurement
of single
intervals such
as pulse
widths.
A
range
of widths from
100
ns to several hours
may
be measured by
select-
ing the appropriate
clock
unit.
The
maximum
clock
rate
is
100
ns, therefore resolution
on
short
duration
pulses
is
likely to
be
unsatisfactory,
but can be improved by
the use of
T.l.
Average mode, which
increases resolution by
the
averaging
of the inherent ±
1
count
'gate
uncertainty'
factor over a
number
of time
intervals
(1
to
10^).
It
should be noted, when
time averaging,
that the repetition rate
of the
pulses under measurement must
not be
synchronous with
the
frequency standard
in
use.
Time
Interval Operation
2.8
(1)
Set the
POWER
switch
to
ON.
(2)
Set the
following
controls:-
(a) Function:
depress the T.l. or T.l. Avg.
button, as required.
(b)
Pulse/Contact
switch:
as
required.
(c)
B-B/B-A
switch:
for
single
line select B-B.
For
double
line
select
B-A
ond
AC/DC
switch
to
DC.
(d)
*START
and
STOP
slope switches: select required triggering
polarities
(not required
for
manual
timing),
(e)
HOLD/NORMAL
switch: select
NORMAL.
(3)
Connect
the
input(s) for
electronic timing.
For single
line
timing
connect
the external signals to Input
'B'. For
double
line
connect
the
'start'
line
to
'B'
and
the
'stop' line to 'A',
(4)
Press the
Range
(n)
button
which
provides the appropriate readout.
The guide
lines from the
T.l, buttons indicate the
time
units of the display.
(5)
For
manual
timing
press the
START/STOP
push-button,
as required.
(6) If
operating
on
HOLD
press
and
release the RESET
button
to initiate
a
new
(non-manual)
timing process.
*NOTE:
On
Time
Interval
Average
(single
line) the
T
to
X
and T_
to
"L
measurement
is
effectively
equivalent
to
Period
mode.
Therefore
the user
is
recommended
to
use Period
for
this particular type
of
measurement
as
the accuracy
is
greater
and
the
measurement
time
reduced.
9901 Vol.2
2-3