User manual

2400 Series SourceMeter

User’s Manual Connections 2-7

sensing must be selected. The 2-wire sense mode is the BENCH and

GPIB default. See

“Sense selection,” page 2-12, for details.

4-wire remote sensing

When sourcing and/or measuring voltage, there can be errors associated with IR

drops in the test leads. Voltage source and measure accuracy are optimized by

using 4-wire remote sense connections. When sourcing voltage, 4-wire remote

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

remote sensing for the following source-measure conditions:

• Test circuit impedance is <1kΩ.

• Optimum Ohms, V-Source, and/or V-Measure accuracy are required.

NOTE Specified accuracies for both source and measure are only achieved using

4-wire remote sensing.

WARNING When sourcing voltage in remote sense, make sure the sense

leads are connected to the DUT. If a sense lead becomes dis

connected, 0V will be sensed, and the SourceMeter will

increase the output voltage (to possibly hazardous levels) to

compensate. For increased safety, you can limit the voltage

output by the SourceMeter. See

Section 3, “V-source protec-

tion,” to limit the output voltage level.

NOTE When the output is turned off in the 4-wire sense mode, the sense lines

are internally disconnected for safety reasons. The sense lines are auto

matically reconnected when the output is turned on, and 4-wire sensing is

restored.

2-wire local sensing

2-wire local sense connections can only be used if the error contributed by test

lead IR drop is acceptable to the user. At current levels below 100mA, the errors

are usually not significant (assuming test lead resistance is not greater than 1Ω).

Since current in a series circuit is the same at all points in the loop, remote sens-

ing does not improve I-Source or I-Measure accuracy. Thus, if sourcing current

and measuring current, you can use local sensing. Other conditions that allow the

use of 2-wire local sensing include:

• Test circuit impedance is 1kΩ. Above 1GΩ, guarding should also be used

(“Cable guard”).

• Measure Only (V or I) operation.