HP 3468A - Resistance Measurement Techniques

The 3468A is capable of measuring resistance from .1 milli-ohm to 30 Megohms
in six ranges. Resistance measurements may be made in either 2- or 4-wire ohms
configuration. The illustrations in Figure 2-4 show how resistance measurements
are
made.
A
known
current
is
supplied
by
the
3468A
and
flows
through
the
unknown resistance. The DC voltmeter measures the attendant voltage across the
resistor
and
calculates
the
resistance.
Table
2-5
shows
the
nominal
current
through
the
unknown
resistance
for
the
individual
ohms
ranges.
Resistances
in
ex-
cess
of
30
Megohms
may
be
measured
using
the
extended
ohms
mode.
LEAD
RESISTANCE
LEAD
RESISTANCE
INPUT
2
SENSE
INPUT
(4 wine) (2 wine)
26148
(TYPE 4404
THERMISTOR
AT 20°C)
ALL TERM
*500Vpk
MAX
MEASURED
RESISTANCE
/
IS
2816.049
AN
ERROR
d
3A/250V
OF
.07%.
FUSE
"intemal to the 3468A
2-WIRE
OHMS
MEASUREMENT
4-WIRE
OHMS
MEASUREMENT
Figure 2-4. Resistance Measurements
Table
2-5.
Nominal
Currents
through
Unknown
Resistance
2-Wire Ohms
The
two
wire
ohms
mode
is
used
most
commonly
when
the
resistance
of
the
test
4
leads
is
not
critical.
Inaccurate
results
may
occur
when
using
the
2-wire
ohms
\
mode
if
the
resistance
of
the
test
leads
is
very
high,
i.e.,
long
test
leads.
Suppose
22