Table of Contents
Advertisement
2-10
Measurement Concepts
Connectors, terminals and internal wiring
Basic connector requirements include a 3-lug female triax connector, and three banana jacks.
One banana jack is used to make the COMMON connection to the electrometer for guarded
measurements. The other two banana jacks will accommodate connection to an external power
supply. The banana jacks must be insulated from the chassis of the test fixture. The outer shell
of the triax connector must be referenced to chassis ground. Therefore, DO NOT insulate the
outer shell of the triax connector from the metal chassis of the test fixture.
DUT and test circuits are to be mounted on the guard plate using insulated terminals. To min-
imize leakage, select terminals that use virgin Teflon insulators.
Inside the test fixture, use an insulated wire to connect the inner shell of the triax connector
to the guard plate. For unguarded measurements, the guard plate will serve as a noise shield. For
the volts and ohms functions, turning GRD on will connect guard to the guard plate.
Handling and cleaning test fixtures
Dust, body oil, solder flux, and other contaminants on connector and terminal insulators can
significantly decrease the leakage resistance resulting in excessive leakage currents. Contami-
nants on DUT and test circuit components can create a leakage path. The leakage currents may
be large enough to corrupt low-level measurements.
Handling tips:
•
•
•
Cleaning tips:
•
•
•
•
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
o
allowed to dry in a 50
C low-humidity environment for several hours.
Advertisement
Table of Contents
