Contact check measurements
The Models 2604B, 2614B, and 2634B do not perform contact check measurements.
The contact check function prevents measurements that may be in error due to excessive resistance
in the force or sense leads when making remotely sensed (Kelvin) measurements. Potential sources
for this resistance include poor contact at the device under test (DUT), failing relay contacts on a
switching card, and wires that are too long or thin. To use contact check, the current limit must be at
least 1 mA (this allows enough current to flow when performing the test), and the source-measure unit
(SMU) must not be in High-Z output-off mode.
The contact check function also detects an open circuit that may occur when a four-point probe is
misplaced or misaligned. This relationship is shown schematically in the figure below, where R
C
is the
resistance of the mechanical contact at the DUT, and R
S
is the series resistance of relays and cables.
Figure 11: Contact check measurements
When the source is off, smuX.source.offmode is set to smuX.OUTPUT_ZERO, and the effective
current limit is less than 1 mA, contact check operations result in error code 5066,
source.offlimiti too low for contact check. In the zero off mode,
smuX.source.offlimiti is ignored and the effective current limit depends on what the channel is
sourcing when it is turned off. If the channel is sourcing:
• Voltage: The current limit is determined by smuX.source.limiti.
• Current: The current limit is determined by the greater of smuX.source.leveli or 10 percent
of smuX.source.rangei.
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