Period Measurement - Racal Instruments 9901 Maintenance Manual

CHAPTER
2
9
=
Jillliy
Ji
s
POWER
SUPPLY
2.1
Before operating a
new
instrument,
or at
a
new
location, check
that the mains
voltage
selection
is
correct (check
rear panel
label)
and
that the
fuse has the
specified rating.
FREQUENCY MEASUREMENT
2.2
In this
mode
the
unknown
frequency
is
gated
to the counter decades
for the
gating
period selected by
the chosen
Range
push-button
(n).
For
frequencies
below
1
0
kHz
the use of period mode
will
give greater
resolution.
(1)
Set the
POWER
switch
to
ON,
(2)
Set the following controls:-
(a)
Function switch
to
FREQUENCY -
'A'
MAN.
(b)
AC/DC
switch
to
AC
or
DC,
as required.
(c)
If
using
AC
mode
set the
SENSITIVITY
control
initially to the
maximum
clockwise
position.
(d)
CHECK/OPERATE
switch
to
OPERATE
.
(e)
HOLD/NORMAL
switch
to
NORMAL.
(f)
Pulse/Contact switch
to Pulse
(_n_).
(3)
Connect
the
unknown
signal to the
'A'
input socket.
(4)
If
counting
is
not
satisfactory adjust the SENSITIVITY
control anti-clockwise
towards the 10
mV
setting
until
a
stable
reading
is
obtained.
(5)
Select the
'n'
push-button which
fills
the display, or
switch
to
AUTO
for
optimum
resolution. The frequency
readout
is
in
kHz.
(6)
If
operating
on
HOLD,
press
and
release the
RESET
button
to
obtain a
new
reading.
PERIOD MEASUREMENT
2.3
This
mode
is
recommended
for
measuring low frequencies
in
the
range
1
Hz
to
10
kHz
with improved
resolution. The incoming
unknown
signal
is
taken
to
the
time-base
decade
dividers, the output of which
(selected
by
the
Range
push-buttons)
is
used
to
gate the
internal frequency standard
to the counter decades.
The
display indicates the
actual value
of the period of the
incoming
signal
in
microseconds. Greater
accuracy
is
obtained by
selecting a longer
gate time,
thus
taking the
measurement
over a
greater number
of periods.
9901 Vol.2
2-1