User`s guide

52 U2741A User’s Guide
3 Measurement Tutorial
Resistance Measurement Considerations
When measuring resistance, the test current flows from the
input HI terminal through the resistor being measured. The
voltage drop across the resistor being measured is sensed
internally in the digital multimeter. Therefore, the test lead
resistance is also measured.
The errors mentioned earlier in this chapter for DC voltage
measurements also apply to resistance measurements.
Additional error sources unique to resistance measurements
are discussed here.
Resistance Measurements
The Agilent U2741A 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 measured is sensed internal to the
digital multimeter. Therefore, test lead resistance is also
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
measurements also apply to resistance measurements.
Additional error sources unique to resistance measurements
are discussed on the following pages.
4-Wire Ohms Measurements
The 4- wire ohms method provides the most accurate way to
measure small resistances. Test lead resistances and contact
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 digital multimeter and the
device- under- test. The recommended connections for 4- wire
ohms measurements are shown below.
User's Guide.book Page 52 Friday, August 8, 2008 9:11 AM