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4.4.3
Offset Current Verification
Recommended Equipment
• Model 707 Switching Matrix
• Model 617 Electrometer
• Model 7078-TRX-3 Triax Cable
• Model 6172 2-slot male to 3-lug female triaxial
adapter
Test Connections
Figure 4-3 shows the test connections for offset current
veriÞcation. The Model 7172 row being tested is to be
connected to the Model 617 Electrometer input through
the triaxial cable and the triaxial adapter. Note that the
electrometer ground strap is to be removed, and the
electrometer should be operated in the unguarded
mode.
Procedure
NOTE
The following procedure should be performed
at an ambient temperature of 23°C and at a
relative humidity of less than 50%.
1. Turn on the Model 617 power and allow it to warm
up for two hours before beginning the veriÞcation
procedure.
2. With the power off, install the Model 7172 in the
desired slot of the Model 707 Switching Matrix.
Remove all other cards from the instrument, and
install the slot covers.
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3. After the prescribed warm up period, select the
amps function and the 2pA range on the Model 617.
Zero correct the instrument, and then select
autoranging.
4. Connect the Model 617 to row A of the Model 7172,
as shown in Figure 4-3.
5. Close crosspoint A1 by using the Model 707 front
panel controls.
6. Disable zero check on the Model 617, and allow the
reading to settle.
7. Verify that the offset current reading is <500fA.
8. Enable zero check on the Model 617, and open
crosspoint A1.
9. Repeat steps 5 through 8 for crosspoints A2 through
A12. Only one crosspoint at a time should be closed.
10. Disconnect the triax cable from row A, and connect
it instead to row B.
11. Repeat steps 5 through 8 for crosspoints B1 through
B12. Only one crosspoint at a time should be closed.
12. Connect the triax cable to each succeeding row and
repeat steps 5 through 8 for each of the row's cross-
points.
4.4.4
Path Isolation Verification
The procedure for verifying path isolation is discussed
below. Should the card fail any of the tests, clean it using
the procedures outlined in paragraph 4.2.
SECTION 4
Service Information
4-5
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