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Operation
TF-1
TF-2
Figure
4-4
Thick
film
resistor
network
testing
Foyr-terminal
ohms
measurements
For general
purpose
testing,
the Keithley
Model
196
can
be used
to
make
four-terminal resistance
measure-
ments
of
each
thick
film.
As shown
in
Figure
4-5,
OHMS
HI
and
OHMS
SENSE
HI
are
connected
to
one
matrix row,
and
OHMS
LO
and
OHMS
SENSE
LO
are
connected
to
another matrix row.
With
this
configura-
tion,
the
resistance of
each
resistor
element
and/or
combined
elemente can
be measured
by
closing the
ap-
propriate
crosspoints.
In Figure
4-5,
crosspoints
111
(Row
1,
Column
1)
and
213
(Row
2,
Column
3)
are
closed
to
measure
the
combined
resistance of
R1 and
R2.
The
effects
of
thermal
EMFs
generated
by
relay
con-
tacts
and
connectiorts
can be
cancelled
by
using
the
off-
set
compensated
ohms
feature of the
Model
196.
(The
Model
7012
has been designed
to
keep
relay
EMF
at
a
minimal
level.)
To compensate
for
thermal
EMFs,
close
two
crosspoints (such as
1!1!1
and
11211),
this will
short
the input
of
the
Model
196,
enable zero
to
cancel
inter-
nal
offset,
and
then enable
offset
compensated ohms.
4-6
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