3-8 Measurements and Sourcing Voltage Model 6487 Reference Manual
klqb After overloading with high voltage, it may take several minutes for the input
current to drop to within specified limits. Input current can be verified by plac-
ing the protection cap on the input connector and then use the ground link to
connect COMMON and CHASSIS ground. With the instrument on the 2nA range
and zero check disabled, allow the reading to settle until the input bias current is
within specifications. The specifications for input bias current are included in
the offset portion of the accuracy specification listed in Appendix A.
Perform the following steps to measure current:
Step 1. Select current function
Press the I | ¾ 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. When on, the “ZEROCHK” message is displayed.
Step 3. Perform zero correction
To achieve optimum accuracy for low current measurements, it is recommended that you
zero correct the picoammeter:
• Select the 2nA range (which is the lowest range).
• Press the REL key so that the MON annunciator is on.
Step 4. Select a manual measurement range or enable auto range
Use the RANGE and 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 3-2.
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