Time Interval (Single And Double Line); Time Interval Average; Time Interval Average Measurement - Racal Instruments 9901 Maintenance Manual

TIME
INTERVAL
AVERAGE
3.11
The
reference frequency
is
10
MHz,
thus the
shortest available clock
unit
is
100
ns,
which
places
a
limit
on
the resolution
available
for
such measurements
such
as
narrow
pulse widths. Greater
resolution
is
achieved by
the 'averaging'
technique,
which
functions
as follows:-
3.12
Referring
to
Figure
3.4
the
clock
input
to
the counter has
to pass through two
gates
in series (gates 'A'
and
'B'
in
the
diagram). The
successive
Start
and
Stop
pulses
open and
close
Gate
'A'
allowing 10
MHz
clock pulses
to pass to
Gate
'B'
during
each
'gate open' period.
Gate
'B'
is
held
open by
the
time base
for
the selected time (10*^)
and
the
clock
pulses are totalled
in
the counter.
At
the
end
of the selected time base period
Gate
'B'
closes
and
the
count
is
displayed
as
the average time
interval
.
NOTE:
To
obtain
the
improved
resolution from time
interval averaging,
the
recurrence
frequency
of the timing input signal must
not
be harmonically
related
to the
frequency
standard of the counter.
Time
Interval
Average
Measurement
Fig.
3.
4
9901 Vol. 2
3-5