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5.3.2
CHANNEL
C
BLOCK
5.
3.2.1
Functional Description
5. 3.
2.
1.1
Refer
to
the
block
diagram
given
in
Figure
5.3.
Channel
C
processes the
signal applied
at
the
Channel
C
input
and
feeds
it
to
the
measurement
block.
5. 3. 2.
1.2
Channel
C's
input
is
protected by
a fuse,
mounted
in
the input connector,
and by
a signal-limiting
circuit.
Next
is
an
automatic
level
control
circuit
which reduces
the range
of the signal level
applied
to the amplifier.
5. 3.
2.
1.3
After amplification, the
signal
is
prescaled
by
64 before being passed
via
a
buffer and a
signal
gate
to
the
measurement
block.
Figure
5.3
-
Channel
C
Block
Diagram
5. 3.
2.
1.4
The
amplitude
of
the
signal at the
amplifier
output
is
monitored by
a
detector and comparator.
The comparator
output controls the low-signal
latch.
If
the
detector output
is
below the
threshold, the latch
is
set
and
the
channel output
is
inhibited
by
the signal gate.
When
the detector output goes
above
the threshold, the low-signal
latch
is
armed
and opens
the
signal
gate
on
the next
signal
edge from
the prescaler. This
enables
the
instrument
to
make
measurements
on
signal bursts.
5.
3. 2.
1.5
The
detector output
is
also
applied
to
the
continuous
signal latch.
This
latch
is
reset at the
beginning of each gate period
and
is
set
if
the
detector output
falls
below
the threshold
level.
The
microprocessor samples the
latch
output throughout the
gate
period.
If
the
measured
signal
falls
below
the
threshold
level
during
this
period, the
measured
result
is
set to zero.
5. 3. 2.
1.6
If
Channel
C
is
not selected, the low-signal latch
is
held
in
reset
by
a
control
signal
from
the
microprocessor and
the
output
to the
measurement
block
is
inhibited.
The
same
control signal
is
used
to
enable
Channel
A
so
that the
two
channels
cannot
be
enabled
at
the
same
time.
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