Two-Wire Compared To Four-Wire Measurements - Keithley 2450 Reference Manual

Section 2: General operation

Two-wire compared to four-wire measurements

You can use 2-wire or 4-wire measurement techniques with the Model 2450.
You can use 2-wire, or local sensing, measurement techniques for the following source-measure
conditions:
•
Sourcing and measuring low current.
•
Sourcing and measuring voltage in high impedance (more than 1 kΩ) test circuits.
•
Measure-only operation (voltage or current).
When you use 2-wire sensing, voltage is sensed at the output connectors.
You should only use 2-wire connections if the error contributed by test-lead IR drop is acceptable.
You should use 4-wire, or remote sense, measurement techniques for the following source-measure
conditions:
•
Low impedance applications
•
When sourcing high current
•
When sourcing low voltage
•
When sourcing higher current and measuring low voltages
•
When enforcing voltage limits directly at the DUT
•
When sourcing or measuring voltage in low impedance (less than 100 Ω) test circuits
•
When optimizing the accuracy for low resistance, voltage source, or voltage measurements
Use 4-wire connections when you are concerned about voltage drops because of lead or contact
resistance that could affect measurement accuracy. This can occur on low impedance devices when
you are sourcing or measuring voltage, especially in semiconductor device testing. For example,
when testing low impedance devices (less than 100 ohms), usually a higher current is sourced and
small voltages are measured.
Sourcing current and measuring voltage drops in a 4-wire configuration is used when measuring
resistivity of a material using a 4-point collinear probe.
It is sometimes necessary to use a 4-wire configuration when sourcing small voltages (less than 1 V)
and measuring current. This is true when performing I-V tests on semiconductor devices such as
diodes.
When you source or measure voltage in a low-impedance test circuit, there can be errors because of
lead resistance. Use 4-wire remote sensing to eliminate these errors. If you use 4-wire remote
sensing when you source voltage, the programmed voltage is delivered to the device under test
(DUT). If you use 4-wire remote sending when you measure voltage, only the voltage drop across the
DUT is measured.
The maximum voltage drop between the force and sense leads is 5 V.
When the output is off, the remote sense lines are disconnected and 4-wire sensing is disabled.
When the output is off, the instrument uses 2-wire sense, regardless of the sense setting. When the
output is on, the selected sense setting is used.
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Model 2450 Interactive SourceMeter® Instrument Reference Manual
2450-901-01 Rev. B/September 2013