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HP E1312A/E1412A Multimeter Application Information 29Chapter 2
Resistance Measurements
The HP E1312A and HP E1412A offer 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 measured is sensed
internal to the multimeter. Therefore, input cable resistance is also
measured. For 4-wire ohms, separate “sense” connections are required.
Since no current flows in the HI-LO “Sense” terminal cables, the resistances
in these cables do not give a measurement error.
The errors discussed previously for dc voltage measurements also apply to
resistance measurements. Additional error sources unique to resistance
measurements are discussed in the following sections.
4-Wire Ohms
Measurements
The 4-wire ohms method provides the most accurate way to measure small
resistances. Errors due to test cable resistances and contact resistances are
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.