Keithley 6220 Reference Manual page 77

Model 6220/6221 Reference Manual
Noise Shield or Guard plate
A metal plate will provide noise shielding or guarding for the DUT or test circuit. It
will also serve as a mounting panel for DUT or test circuits. The guard plate must
be insulated with appropriate spacing from the chassis of the test fixture.
When the triax inner shield is connected to Output Low, the metal plate serves as
a noise shield. When triax inner shield is connected to Cable Guard, the metal
plate servers a guard plate.
Terminals and internal wiring
DUT and test circuits are to be mounted on the guard plate using insulated termi-
nals. To minimize leakage, select terminals that use Teflon insulators.
Inside the test fixture, use insulated wires for connections to DUT. Use silver sol-
der for all connections. Silver solder minimizes thermal EMFs.
Handling and cleaning test fixtures
Dust, body oil, solder flux, and other contaminants on connector and terminal
insulators can significantly decrease the insulation resistance resulting in exces-
sive leakage currents. Contaminants on DUT and test circuit components can cre-
ate a leakage path. The leakage currents may be large enough to corrupt
low-level measurements.
Handling tips:
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Cleaning tips:
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Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - TestEquipmentDepot.com
Do not touch the bodies of DUT or test circuit components. If you cannot
handle them by their leads, use clean cotton gloves to install them in the
test fixture.
Do not touch any connector or terminal insulator.
If installing a test circuit that is on a PC board, handle the board by the
edges. Do not touch any board traces or components.
Use dry nitrogen gas to clean dust off connector and terminal insulators,
DUT, and other test circuit components.
If you have just built the test fixture, remove any solder flux using methanol
along with clean foam-tipped swabs or a clean soft brush. Clean the areas
as explained in the next tip.
To clean contaminated areas, use methanol and clean foam-tipped swabs.
After cleaning a large area, you may want to flush the area with methanol.
Blow dry with dry nitrogen gas.
After cleaning, the test fixture (and any other cleaned devices or test
circuits) should be allowed to dry in a 122° F (50° C) low-humidity environ-
ment for several hours.
Return to Section 2 topics
Output Connections 2-23