Resistance Measurements
The Agilent 34401A offers two methods for measuring resistance:
2-wire and 4-wire ohms. For both methods, the test current flows from
the input HI terminal and then through the resistor being measured. For
2-wire ohms, the voltage drop across the resistor being mea sur ed is
sensed internal to the multimeter. Therefore, test lead r es ista n c e is als o
measured. For 4-wire ohms, separate “sense” connections are required.
Since no current flows in the sense leads, the resistance in these leads
does not give a measurement error.
The errors mentioned earlier in this chapter for dc voltage me asurements
also apply to resistance meas urements. Additional error source s unique
to resistance measurements are discussed on the follo wing pages.
4-Wire Ohms Measurements
The 4-wire ohms method provides the most accurate way to measure
small resistances. Test lead resistances and contac t resistances are
automatically reduced using this method. Four-wire ohms is often used
in automated test applications where long cable lengths, numerous
connections, or switches exist between the multimeter and the device-
under-test. The recommended connections for 4-wire ohms
measurements are shown below. See also “To Measure Resistance,”
on page 17.
I test
Ideal
Meter
HI
LO
LO-Sense
HI-Sense
R = Vmeter
Itest
7
Chapter 7 Measurement Tutorial
Resistance Measurements
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