Keithley 2601B Reference Manual page 90

Section 2: General operation Series 2600B System SourceMeter® Instrument Reference Manual
Figure 30: Model 2634B/2635B/2636B safety shield for hazardous voltage test circuit
connections
Guarding
A driven guard is always enabled and provides a buffered voltage that is at the same level as the
input/output HI voltage. The purpose of guarding is to eliminate the effects of leakage current (and
capacitance) that can exist between HI and LO. Without guarding, leakage and capacitance in the
external high-impedance test circuit could be high enough to adversely effect the performance of the
Series 2600B.
Guarding (shown below) should be used when test circuit impedance is >1 GΩ.
2-66 2600BS-901-01 Rev. B / May 2013