Section 7: Theory of operation Model 2601B-PULSE System SourceMeter Instrument Reference Manual
7-24 2601B-PULSE-901-01A April 2020
Figure 122: Contact check circuit
Guard
GUARD is at the same potential as output HI. Thus, 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 System SourceMeter
®
Instrument.
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).
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