Keithley 6485, User Manual, Page: 62 / 115

3-6 Measurements and Sourcing Voltage Model 6485 and 6487 User’s Manual
Procedure
Perform the following steps to measure current:
Step 1. Select current function
For the Model 6487, press the I|
Ω
key to make sure the current function is selected.
Step 2. Enable zero check
Zero check should always be enabled before making connection changes. The ZCHK key
toggles zero check on and off.
Step 3. Perform zero correction
To achieve optimum accuracy for low current measurements, it is recommended that you
zero correct the picoammeter. To do so, make sure the 2nA range is selected, then press
the ZCOR key (Model 6485) or REL key (Model 6487) to perform zero correction
(“ZZ” indicated for Model 6485; MON indicator on for Model 6487).
Step 4. Select a manual measurement range or enable auto range
Use the manual RANGE keys to select a manual measurement range or press AUTO to
enable auto range. With auto range enabled, the instrument will automatically go to the
most sensitive range to make the measurement. See
Section 4 for details on range.
Step 5. Connect the current to be measured to the picoammeter
Basic connections for measurements are shown in Figure 3-1 and Figure 3-2 .
WARNING A safety shield is advisable whenever floating measurements are being
made. Connections for the safety shield are shown in
Figure 3-1 and
Figure 3-2 . The metal safety shield must completely surround the
noise shield or floating test circuit, and it must be connected to safety
earth ground using #18 AWG or larger wire.
NOTE When not making floating measurements, it is recommended that you ground
measurement LO at only one place in the circuit, such as with the ground link
connection on the rear panel of the 6485/6487. (See
“Ground loops,”
page B-2 .)
Fundamental information on making connections to the picoammeter input is
provided in
Section 2 .