Test Fixture - Keithley 2651A Reference Manual

Model 2651A High Power System SourceMeter® Instrument Reference Manual

Test fixture

The Model 2651A digital I/O port provides an output enable line for use with a test fixture switch.
When properly used, the output of the Model 2651A will turn off when the lid of the test fixture is
opened.
A test fixture can be used for an external test circuit. The test fixture can be a metal or nonmetallic
enclosure, and is typically equipped with a lid. The test circuit is mounted inside the test fixture. When
hazardous voltages (>30 V RMS, 42 V peak) will be present, the test fixture must have the following
safety requirements:
To provide protection from shock hazards, an enclosure should be provided which surrounds
all live parts.
Nonmetallic enclosures must be constructed of materials suitably rated for flammability and
the voltage and temperature requirements of the test circuit.
For metallic enclosures, the test fixture chassis must be properly connected to safety earth
ground. A grounding wire (#16 AWG or larger) must be attached securely to the test fixture at
a screw terminal designed for safety grounding. The other end of the ground wire must be
attached to a known safety earth ground.
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.
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
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 the topic titled
2651A-901-01 Rev. A / March 2011
Digital I/O (on page 3-83) for information on the digital I/O port.
WARNING
WARNING
Section 2: General operation
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