A/D Converter; Ac Converter - Fluke 8600A Instruction Manual

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
990
KO
I.OOOKO
lOpA
200
KO
X
2V
20
90KO
100KO
100m
a
20
KO
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
1200V
AC
X
X
2V
200
VAC
X
X
2V
20V
AC
X X
2V
2
VAC
X
2V
200m
VAC
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