HP 3468A - Page 83

MS
The
extended
ohms
feature
is
available
only
via
the
HP-IL
F7
commands.
With
ex-
tended
ohms
you
can
measure
resistances
above
30
Mohms.
When
in
the
Extend-
ed
Ohms
mode,
the
3468A
goes
to
the
30
Mohm
range,
2-wire
mode.
An
internal
resistance
of
approximately
10
Mohms
is
placed
in
parallel
with
the
inputs.
If
this
resistance
is
measured
first
and
then
the
unknown
resistor
connected
to
the
in-
puts,
the
parallel
combination
can
be
measured
and
a
calculation
performed
to
determine
the
approximate
value
of
the
unknown
resistance.
The
formula
for
the
calculation
is:
Ri * Rt
Ri — Rt
Rx =
Rx
is
the
unknown
resistance,
Ri
is
the
measured
value
of
the
internal
10
Mohm
resistor
and
Rt
is
the
measured
value
of
the
parallel
combination.
The
test
leads
should
be
a
very
short
shielded
twisted
pair
to
not
pick
up
radiated
noise.
A
program
that
will
make
the
necessary
measurements,
perform
the
calculations,
and
display
the
value
for
the
unknown
resistor,
is
given
in
the
following
figure.
Lines
Description
16)
EXTEMOEO
OHMS
EXAMPLE
‘
20
'
-hre-
85
VERSION
40-50
Line
40
sets
the
interface
at
select
code
9
2@
CLEAR
to
the
REMOTE
state.
This
ensures
that
all
4@
RENOTE
9
instruments
in
the
loop
have
been
autoad-
oe
Bese
ss
Ha
OREN
TEaHe
dressed.
Line
50
sets
variable
A1
equal
to
Al
i"o2
0
:
:
i
76
DYSP"
EXTENDED
OHMS
Exam
the
select
code
of
the
3468A,
i.e.,
901.
PLE"
@
CISP
60-130
These
lines
display
messages
to
open
the
86
DISP
“Extended
ohms
is
a
2-uy
input
terminals
on
the
3468A.
Line
60
ire
ohms"
displays
the
message
on
the
3468A
34
DISP
“measurement
tor
resist
display.
anc
144
OISP
“above
34
Mohms.“
@
DIS
140-150
The
3468A
is
set
up
for
the
extended
F
ohms
function
(F7),
5%
digit
display
(N5),
116
OISP
eee
eee
input
t
autozero
on
(Z1),
and
single
trigger
(T2)
in
Sena
aad
‘
=
line
140.
Line
150
enters
the
readings
of
126
OIsp
PRESS
CCONTI]
TO
BEGIN
the
internal
10
Mohm
resistor
into
variable
138
PRUSE
Ris
ed
PR
eR
ae
agen
ee
160-210
These
lines
display
messages
to
connect
168
QUTPUT
Al
;"OZAD0
RESISTOR“
Baouer
inp
wane
measured
tor
the:
i?
CLEAR
@
DISP
"Connect
resist
3
_
ance
to
be"
220-230
These
two
lines
are
identical
to
lines
198
DISP
"measured
to
the
3478A
140-150.
The
resistance
of
the
parallel
138
Rhee.
i
seorminats™
combination
is
entered
into
variable
R2.
206
DISP
#
DISF
"
PRESS
CoO
240
Line
240
performs
the
calculation
describ-
13
Base
ed
above
to
determine
the
value
of
the
229
QUTPHT
Al
i
"E7NSZIT2«
unknown
resistence.
2236
ENTER
Al
;
RZ
250
The
calculated
resistance
value
is
246
RI=R1¢R2-(R1-R2>
displayed
on
the
3468A
display.
25
OUTPUT
AL
i
"oe
;R341
8°65
,
64
CLEAR
@
DISP
"THE
RESISTANCE
260
The
calculated
resistance
value
is
IS:
“;R2-16°63
"MOHME.
*
displayed
on
the
-hp-
Model
85
screen.
ENB
79