SECTION 3
Front Panel Operation
Model 487
Figure 3-9. Basic V-Source Connections
3.7 V/I OHMS MEASUREMENTS
(Model 487)
By using the V-Source in conjunction with its picoam-
meter, the Model 487 can make resistance measurements
as high as 50.5 x lO”9.. With V/I ohms selected, the resis-
tance is automatically calculated from the applied volt-
age and measured Current (R = V/D and displayed (in
ohms) on the Model 487. A& resolution of the resis-
tance measurement depends on the s&&d current
Rage.
The V/I ohms function is enabled by pressing SHIFT and
then OHMS. The display will toggle to the resistance (.Q)
measurement state. To disable V/I ohms, again press
Sm and then OHMS. The display will return to the
normal amps measurement state.
Perform the following steps to make V/I ohms measure
mentsz
1. Turn on the Model 487 and allow it to warm up for
two hours to achieve rated accuracy.
2. Disable the V/I ohms function, if it is currently se-
lected.
3. With zero check enabled and the V-Source in
standby, connect the circuit shown in Figure 3-10.
The Keithley Model 8002A test fixture is shown be-
cause it is ideally suited for V/I ohms measurements
of Z-terminal devices.
4. Select a current range that gives the nearest full scale
reading or autorange, and perform zero correction
by pressing SHBT and then CORRECT.
5. Set the V-Source to the desired voltage level.
6. Press OPERATE to tom on the source output, and
disable zero check. The current measurement willbe
displayed.
7. Enable V/I ohms by pressing Sm and then
OHMS. The resistance measurement will be dis-
played in ohms (Q).
8. To measure from a baseline resistance, enable rel
while in V/I ohms.
3-14
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