Contact Potential Tests; Common Mode Offset Current Testing - Keithley 7071 Instruction Manual

SERVICE INFORMATION
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Model 7071
Figure 4-4. Common Mode Offset Current Testing
4.4.5 Contact Potential Tests
These tests check the EMF generated by each relay con-
tact pair (H and L) for each pathway. The tests simply con-
sist of using a nanovoltmeter (Model l81) to measure the
contact potential.
Perform the following procedure to check contact poten-
tial of each path:
1. Turn the Model 707 off if it is on.
2. Set the Model 181 to the 2mV range, short the input
leads and press ZERO to null out internal offset. Leave
ZERO enabled for the entire procedure.
3. Connect the Model 181 to a quick-disconnect terminal
block as shown in the illustration caption of Figure 45.
Do not connect the terminal block to the matrix card
at this time.
4. Place the matrix card in slot 1 of the Model 707. but
do not slide it all the way into the mainframe.
5. Connect the pre-wired terminal block to ROW A of the
matrix card.
6. Feed the test leads through the cable clamp of the
matrix card and push the card all the way into the
mainframe. lighten the two spring loaded screws to
completely mate the card with the backplane.
7. Turn on the Model 707
8. Program the Model 707 to close crosspoint Al.
9. Verify that the reading on the Model X31 is < 5~v. This
measurement is the contact potential of the pathway.
10. From the Model 707, open crosspoint Al.
11. Repeat the basic procedure in steps 8 through 10 to
check the rest of the pathways (crosspoints A2 through
Al2) of the row.
12. Turn off the Model 7CV and slide out the matrix card
far enough to gain access to the pre-wired terminal
block.
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