Model 2657A High Power System SourceMeter® Instrument Reference Manual
Section 2: General operation
2657A-901-01 Rev. B/December 2012
2-63
When hazardous voltages (>30 V RMS, 42 V peak) will be present, the test fixture must meet the
following safety requirements:
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. Although the outer layer on a high
voltage triaxial cable must be connected to the test fixture's metal chassis, the inner two layers of the
cable (input/output connectors) 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 Model 2657A digital I/O port provides an interlock line. When properly used with a test fixture, the
output of the Model 2657A turns off when the lid of the test fixture is opened.
See the topic titled
(on page 3-80) for information on the digital I/O port and the safety
interlock.
The Keithley Instruments Model 8010 is a test fixture that has been specifically designed for use with
the Model 2657A as well as other Keithley Instruments products. Refer to the Model 8010
documentation for specific connection information.
Floating a SMU
You can use an external source in the test system to bias the Model 2657A source-measure unit
(SMU) above protective earth (safety ground). An example of such a test system is shown below. The
external source is used to bias the Model 2657A +10 V above protective earth (safety ground).
Figure 21: Floating the Model 2657A schematic
V-source
HI
LO
10 V
LO
HI
+ –
Safety shield
External Source*
* Maximum voltage for external
source is 250 VDC.
+
–
Model 2657A LO
not connected to
chassis ground (floating)
Model
2657A
SMU
DUT
Connected to
protective earth
(safety ground)
Summary of Contents for 2657A
Page 3: ......