Tektronix Keithley 2651A Reference Manual page 88

Model 2651A High Power System SourceMeter® Instrument Reference Manual Section 2: General operation
The digital I/O port of the Model 2651A is not suitable for control of safety circuits and should
not be used to control a safety interlock.
See Digital I/O (on page 3-92) for information on the digital I/O port.
Floating a SMU
Using an external source in the test system may require that a Model 2651A source-measure unit
(SMU) float off chassis earth ground. An example of such a test system is shown below, which
includes an external voltage source. Notice that output LO of the external voltage source is connected
to chassis earth ground.
For the test circuit shown below, the Model 2651A must float off chassis earth ground. As shown, LO
of the Model 2651A is floating +10 V above chassis earth ground. If LO of the Model 2651A was
instead connected to chassis ground, the external voltage source would be shorted to the chassis
ground.
Figure 23: Floating the Model 2651A schematic
The Model 2651A connections for the floating configuration are shown below. In order to float the
SMU, input/output LO must be isolated from chassis ground. This is accomplished by not connecting
input/output LO to chassis ground.
2651A-901-01 Rev. C October 2021 2-63