Data Output Unit (Dou); Circuit Description; Input Signal Conditioners - Fluke 8600A Instruction Manual

8600A
INTEGRATE PERIOD
SLOPE
is
proportional to
the instrument
input
signal
A/D
INTEGRATOR
OUTPUT VOLTAGE
CLOCK
OSCILLATOR
SIGNAL
100ms
READ
PERIOD
TIME
is
proportional to the
instrument
input
signal
ZERO
LEVEL
Figure
3-2.
TIMING DIAGRAM FOR
DUAL-SLOPE
A/D
CONVERSION
3-17.
The
clock
oscillator pulse count,
accumulated
during the read period,
is
applied to the
LED
display to
produce
the
digital
readout of
the instrument input
sig-
nal.
The
range information from
the selected range switch
positions the
decimal point
and
illuminates the proper
display
annunciator.
3-18. Data Output Unit
(DOU)
3-19.
The
DOU
provides the
display
data
as a rear
panel card-edge output. The bed
information presented
to the instrument
display
(polarity,
overload, range code,
and
digit)
is
also applied to the
DOU
input.
A
busy
flag
is
provided
so that the
output
data
may
not be used while
the
8600A
is
feeding
a
new
input measurement
to the
DOU.
A
register pulse
train
plus
one of
the data strobe
signals
time the data
transfer to insure that
all
the data supplied to
the
DOU
output
is
stable
and not taken
during
transition
periods.
For
detailed
information
refer
to Section
6.
3-20.
CIRCUIT DESCRIPTION
3-21
.
The
following
circuit descriptions are keyed
to the
functional blocks defined
in
the
overall functional block
diagram of Figure
3-1
.
Corresponding
functional blocks
are
defined
in
more
detail using either simplified block
dia-
grams
or
by
referring to the schematics.
Schematics
for
the
8600
A
circuits are provided
in Section
8.
3-22. Input
Signal Conditioners
3-23.
INPUT DIVIDER
3-24.
The
Input Divider comprises
a series
connected
resistor
network
(R3, R4, R5, R6, R7, and R8)
totaling
approximately
ten
megohms.
This
network
is
tapped
at
three points to provided
division ratios
of 10:
1
,
100:
1
,
and
1000:
1
.
Relays K2, K3, and
K4
each
select
one
of the
division
ratios; as directed
by
the range switches.
3-25.
OHMS CONVERTER
3-26 The
Ohms
Converter produces
a
known
amount
of
current
that,
when
applied to an
unknown
resistance
(Rx)
connected
across the
VJ2
terminals, will
develop
a voltage
(Vx)
proportional to the value of Rx. Producing
the
known
amount
of current
is
accomplished with
a current follower,
Ul, two
feedback
loops,
and
a current source
(U3 and
Q3).
One
feedback loop
is
from
the
Vf2 HI
terminal to the non-
inverting input of
Ul
(Pin
3).
The
voltage of
this
loop
is
applied to the
A/D
Converter.
The
other
feedback loop
is
from
the output of
Ul
through
R20
and
R90
to the
inver-
ting
input of
Ul
(Pin
2).
The
current source (U3 and Q3)
1/77
3-3