Fluke 8600A - A;D Converter; AC Converter

8600A
Table 3-1.
OHMS
CONVERTER
OPERATING
CONDITIONS
8600A
RANGE
Ro
Ro
+
10KO
lx
Rx
Max.
RANGE
RELAY
A-D
RANGE
K2
K3
K4
K5
20MO
9990KO
10,000KO
O.lpA
20MO
~——-
—
X
2000
KO
9990KO
1
0,000
KO
1mA
2000KO
200
990KO
I.OOOKO
lOpA
200KO
X
2V
20
90KO
100KO
100m
a
20KO
X
2V
2
OO
10KO
1000m
A
2KO
X
2V
2000
OO
10KO
1000m
A
2000
X
0.2V
Table 3-2.
AC CONVERTER
RELAY
OPERATION
8600A
RANGE
K4
K6
K7
K8
A-D
RANGE
1200VAC
X
X
2V
200VAC
X
X
2V
20VAC
X X
2V
2
VAC
X
2V
200mVAC
X
0.2V
3-30.
AC
CONVERTER
3-3
1 .
The
AC
Converter
produces
a dc output voltage
proportional
to the
ac input voltage.
Table
3-2 presents
the relay
conditions
for each
ac volts range;
relay
K4
is
located on
the Input
Divider
pcb and
closes
to apply
the
AC Converter
output
to
the
A-D Converter
. Figure
3-4
is
a
simplified
circuit
diagram
of
the AC Converter.
3-32
With
no ac
signal
applied to
the VO terminals,
Ql,
Ul,
and
Q7
are biased
on
such that
the current
flowing
through
CL1 and
Q7
produces
OV at
the collector of
Q7.
An
ac signal
is coupled
by
Cl from
the VO terminals
to
input
impedance
resistor,
R1 7. The
ac signal
is then applied
to
the inverting
input
of Ql
and
U2. The network
composed
of
Ql
,
U2,
CR5
,
Q7,
CR1
1 ,
CR1
2,
and R46 (or
R37, R47,
and
R38 depending
on
the range
selected)
is
a
form
of
logarithmic
amplifier.
The net
result
is that
the
dc
level
detected
by
CR1 2 and
filtered
by
the low pass (L.P.)
filter
is proportional
to the
RMS
equivalent of the
ac voltage
applied
to the VO
terminals.
The
dc level from the
L.P.
filter
is
applied
to the A/D
Converter. The degree
of loga-
rithmic response
is determined
by
the
feedback
resistance
1/77
3-5