Tektronix Keithley 2651A Reference Manual page 243

Model 2651A High Power System SourceMeter® Instrument Reference Manual Section 4: Theory of operation
Also in the figures below, the driven guard is connected to the cable shield and extended to the metal
guard plate for the insulators. Since the voltage on either end of R is the same (0 V drop), no
L1
current can flow through the leakage resistance path. Thus, the SourceMeter instrument only
measures the current through the DUT.
Figure 92: Unguarded measurements
Figure 93: Guarded measurements
2651A-901-01 Rev. C October 2021 4-25