Model 2657A High Power System SourceMeter® Instrument Reference Manual
Section 2: General operation
2657A-901-01 Rev. B/December 2012
2-37
Contact check measurements
Overview
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 will also detect an open circuit that may occur when a four-point probe is
misplaced or misaligned. This relationship is shown schematically in the figure titled "Contact check
measurements," , where R
Cxx
is the resistance of the mechanical contact at the DUT, and R
Sxx
is the
series resistance of relays and cables.
Figure 10: Contact check measurements
Sense HI
Sense LO
HI
DUT
R
SH2
R
SL2
LO
R
SH1
R
SL1
R
CH2
R
CL2
R
CH1
R
CL1
Model 2657A
Cable/Relay
Resistance
Contact
Resistance
Aggregate contact resistance HI
Measured resistance = R
SH1
+ R
SH2
+ R
CH1
+ R
CH2
1
1
2
Aggregate contact resistance LO
Measured resistance = R
SL1
+ R
SL2
+ R
CL1
+ R
CL2
2
Summary of Contents for 2657A
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