Keithley 6430 Instruction Manual page 72

2-8 Connections
2-wire sensing
When using 2-wire sensing to source and/or measure voltage, the error associated with IR
drops in the test leads could be significant. The ratio between the test lead resistance and DUT
resistance determines the error that is introduced. If the error introduced by the IR drop of the
test leads is not acceptable, use 4-wire sensing.
For example, assume test lead resistance (R
10kΩ. The error is calculated as follows:
Error = R
Notice that as the resistance of the DUT increases, the error decreases. For DUT above
1GΩ, guarding should also be used. See Cable guard.
Since current in a series circuit is the same at all points in the loop, remote sensing does not
improve I-Source or I-Measure accuracy. Thus, if sourcing current and measuring current, you
can use local sensing.
NOTE
4-wire sensing
Voltage source and measure accuracy are optimized by using 4-wire sense connections.
When sourcing voltage, 4-wire sensing ensures that the programmed voltage is delivered to the
DUT. When measuring voltage, only the voltage drop across the DUT is measured.
Use 4-wire sensing for the following source-measure conditions:
•
•
4-wire sensing specification clarifications
•
•
•
/ R
L DUT
= 1Ω / 10kΩ
= 0.0001
= 0.01%
For Measure Only (V or I) operation, 2-wire sensing must be used.
The error contributed by test lead resistance for local sensing is not acceptable.
Optimum Ohms, V-Source, and/or V-Measure accuracy are required.
There is no hardware configurations needed to enable 4-wire sense. Simply hook up the
sense wires; otherwise, the Model 6430 will sense the voltage locally through resistors.
Specified accuracies for both source and measure are only achieved using 4-wire
sensing.
Sense wires must be no more than 10Ω per lead.
) is 1Ω and the DUT resistance (R
L
) is
DUT