Floating A Smu - Keithley 2601B Reference Manual

Series 2600B System SourceMeter® Instrument Reference Manual Section 2: General operation
Construction material: A metal test fixture must be connected to a known protective earth (safety
ground) as described in the above WARNING. A nonconductive test fixture must be constructed of
materials that are suitable for flammability, voltage, and temperature conditions that may exist in the
test circuit. The construction requirements for a nonconductive enclosure are also described in the
WARNING above.
Test circuit isolation: With the lid closed, the test fixture must completely surround the test circuit. A
metal test fixture must be electrically isolated from the test circuit. Input/output connectors mounted
on a metal test fixture must be isolated from the test fixture. Internally, Teflon standoffs are typically
used to insulate the internal printed circuit board or guard plate for the test circuit from a metal test
fixture.
Interlock switch: The test fixture must have a normally-open interlock switch. The interlock switch
must be installed so that when the lid of the test fixture is opened, the switch will open, and when the
lid is closed, the switch will close.
The Series 2600B digital I/O port provides an output enable line or an interlock line (dependent on the
model number). When properly used with a test fixture, the output of the Series 2600B will turn off
when the lid of the test fixture is opened. The output enable (OE) is found on Models
2601B/2602B/2604B while the Models 2611B/2612B/2614B/2634B/2635B/2636B have an interlock.
The digital I/O port of the Model 2601B/2602B/2604B is not suitable for control of safety
circuits and should not be used to control a safety interlock. The interlock pin on the digital
I/O port for the Model 2611B/2612B/2614B/2634B/2635B/2636B can be used to control a
safety interlock.
See the topic titled Digital I/O (on page 3-83) for information on the digital I/O port.

Floating a SMU

Using an external source in the test system may require that a Series 2600B 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 low of the external voltage source is
connected to chassis earth ground.
For the test circuit shown below, the Series 2600B must float off chassis earth ground. As shown, LO
of the Series 2600B is floating +10 V above chassis earth ground. If LO of the Series 2600B was
instead connected to chassis ground, the external voltage source would be shorted to the chassis
ground.
2600BS-901-01 Rev. B / May 2013 2-73