Guard Overview - Keithley 2601 Reference Manual

Series 2600 System SourceMeter® Instruments Reference Manual
Figure 8-14
Contact check circuit configuration
Guard
WARNING

Guard overview

The driven guard (available at the rear panel GUARD terminals) is always enabled and provides a
buffered voltage that is at the same level as the Input/Output 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 input/output high and low. In the absence of a driven guard, leakage in the
external test circuit could be high enough to adversely affect the performance of the SourceMeter.
Leakage current can occur through parasitic or non-parasitic leakage paths. An example of
parasitic resistance is the leakage path across the insulator in a coax or triax cable. An example of
non-parasitic resistance is the leakage path through a resistor that is connected in parallel to the
DUT.
2600S-901-01 Rev. C / January 2008
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.
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Section 8: Source-Measure Concepts
8-19