Theory
of
Op
OHMS
FI
REFERENCE
CURRENT
I
R416 R401
100
M.F.
54SK
-7v
FROM PRECISION
VOLTAGE REFERENCE
SWITCH STATE TABLE
Figure
W.
Ohms
Current
Source
is turned off to isolate the SENSE HI terminal from the
UMlC
and
U301D during the hold period. This
INPUT
HI
terminal.
effect
of measuring
the
SENSE
HI
terminal with
re
INPUT
M
terminal rather than SENSE
LO.
Althol
Additional input switching occurs during the hold period
resistance of the
INPUT
LO
lead
is
in series
w
of the trackhold cycle. (Refer to
the
hold period in the
unknown resistance, accuracy
is
not
affected
as
lonl
switch table in Figure
5-8.)
In ranges rl through 14, the
resistance of the
lead
is
less than
lW
in
the
2C
SENSE
LO
ferminal is switched into the
dc
input
path
by
range and less than
1WQ
in the 20 MP range.
U301D, and the INPUT
LO
terminal is switched out of the
dc input path by U301C. This
has
the effect of measuring
5-20-
WD
the SENSE
HI
terminal with respect to the SENSE
LO
The Analog-toDigital
(AID)
Converter (Figwe
5-1
terminal.
Fluke's patented recirculating remainder techniq
input volttige (Vin) is compared to the output
In ranges r5 and r6, the SENSE
LO
and
INPUT
LO
precision Digital-to-Analog Converter (DAC). The
terminals
are
both switched into
the
dc input path
by
of the
AD
Amplifiery connected
as
a
comparz
RANGE
2wn
2kR
20
kQ
200
kR
2000
kQ
20
Mn
I
ration
CTlONS
-
s
the
ect
to
$
the
h
the
is
the
D
kP
0
=
Switch closed
U402A
0
0
uses
.
An
E
the
utput
)ry is
5-9
U402B
0
0
U402C
0
0
U402D
0
0
0
0
0
U403A
0
U403B
0
U403C
0
0
0
0
0
U403D
0
0
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