Fluke PM6681 - Page 32

Input
Amplifier B
Input
channel B
is the
same as input channel A
with
the fol-
lowing exceptions:
—
The Common B via A switches,
that connect the B-chan-
nel comparator
to
the input signal on
channel
A.
-
The B-channel delay line.
-
The
B-channel
has no iowpass filter.
—
The
B-channei
has a
special event-delay signal
output
to
OQ0504, U56.
•
Delay
Line
A line of
approximately 65 cm is
placed between the
"B-
channel
comparator output"
pins
15 and 16 and the
buffer
stage V33 and V4, (see
Figure
4-9). This delay line
is
a
part of the circuit board,
it
should
compensate
for delays in
OQ0502, U58.
•
Event Delay
Also
for
use
in
the arming
function,
the
inverse output
from
the buffer
stage
V4
of
channel
B
is
used, (see Figure
4-
10).
This
signal called
EVENT-DELAY,
is
connected to the
OQ0504 circuit U56
via the
transistor
V12 and the 1C, U47
which works as a
multiplexer.
The EVENT-DELAY signal
is
also used by
the HOLD-OFF
logic when the
input
puises
should
be counted, (see Coun-
ter circuits on
page
11).
VI 2 U56
Figure
4-10
Event delay.
Calibration
Circuits
U93 and a delay line on the
PCA generates a
xx
ns
long
pulse,
and feed
it to channel
B
input on
the counter IC,
U56. This pulse is
initiated by the
p-controller
pulse CAL-
TEST-PULSE.
4~8
Hardware
Functional
Description