Tektronix KEITHLEY SourceMeter 2606B Reference Manual page 227

Section 8: Theory of operation Model 2606B System SourceMeter® Instrument Reference Manual
Figure 97: Current source sweep operation in voltage and power compliance
Guard
GUARD is at the same potential as output HI. If hazardous voltages are present at output HI,
they are also present at the GUARD terminal.
The rear-panel GUARD terminals are always enabled and provide a buffered voltage that is at the
same level as the HI (or SENSE HI for remote sense) voltage. The purpose of guarding is to eliminate
the effects of leakage current (and capacitance) that can exist between HI and LO. In the absence of
a driven guard, leakage in the external test circuit could be high enough to adversely affect the
performance of the SMU.
Leakage current can occur through parasitic or nonparasitic leakage paths. An example of parasitic
resistance is the leakage path across the insulator in a coaxial or triaxial cable. An example of
nonparasitic resistance is the leakage path through a resistor that is connected in parallel to the
device-under-test (DUT).
8-12 2606B-901-01 Rev. C November 2021