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negative screw terminals and sensed via 1B positive and negative screw 
terminals.

OUT0± and OUT2± are also referred to as COM0± in a 4-wire configuration.

The primary advantage of using a 4-wire configuration is that it has greater 
accuracy than a 2-wire configuration while making resistance 
measurements. Figure 2-8 shows signal connections for a 2-wire resistance 
measurement of a resistor R

1

.

Figure 2-8.  Signal Connections for a 2-Wire Resistance Measurement

When measuring R

1

 in a 2-wire configuration, the voltmeter measures not 

only voltage across R

1

 due to the excitation current (of the voltmeter) but 

also the voltages developed across the parasitic resistance of the voltmeter 
cables. When the resistance is finally calculated, these parasitic voltages 
make the measurement inaccurate:

Therefore, in a 2-wire resistance measurement, the voltmeter ends up 
measuring a resistance that includes the parasitic resistance of the cables 
and switches.

To overcome this problem—to eliminate the parasitic resistance of the 
connecting cables—a voltmeter uses two sets of cables, one for excitation 

V

SENSE

+

2-Wire

Measurement

V

parasitic

V

parasitic

V

R

1

R

1

I

EX

I

EX

V

SENSE

–

Parasitic resistance of
the cables connecting
the resistance to the 
measurement device

1measured

2V

1

+

---------------------------------------

2R

1

+

=

=