Floating A Smu - Keithley 2601 Reference Manual

Section 3: DUT Test Connections
Construction material – A metal test fixture must be connected to a known safety Earth Ground
as described in the above WARNING. A nonmetallic 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 nonmetallic 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 also be isolated from the test fixture. Internally,
Teflon standoffs are typically used to insulate the internal pc-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.
WARNING

Floating a SMU

Using an external source in the test system may require that a Series 2600 SMU float off chassis
earth ground. An example of such a test system is shown in
external voltage source. Notice that output low of the voltage source is connected to chassis earth
ground.
For the test circuit shown in
shown, SMU LO of the Model 26xx is floating +10V above chassis earth ground. If SMU LO of the
Model 26xx was instead connected to chassis ground, the external voltage source would be
shorted through chassis ground.
The Series 2600 connections for the floating configuration
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.
The external voltage source in
Series 2600 instrument. Keep in mind that if the combined outputs of the sources exceeds 42V,
then a safety shield will be required for the DUT (see the following WARNINGS).
3-20
When an interlock is required for safety, a separate circuit should
be provided that meets the requirements of the application to
reliably protect the operator from exposed voltages.
The output enable pin on the digital I/O port on the Models 2601
and2602 SourceMeter 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 Models 2611, 2612, 2635, and 2636 can be used
to control a safety interlock.
Figure 3-23, the Series 2600 must float off chassis earth ground. As
Figure 3-23
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Series 2600 System SourceMeter® Instruments Reference Manual
Figure
(Figure
and Figure 3-24 can instead be a SMU of a second
3-23, which includes an
3-23) are shown in Figure
2600S-901-01 Rev. C / January 2008
3-24.