Coulombs Measurements 5-3
Coulombs measurement procedure
CAUTION The maximum input voltage and current to Model 6514 is 250V peak and
21mA. Exceeding either of these values may cause damage to the instru-
ment that is not covered by the warranty.
WARNING The maximum common-mode input voltage, which is the voltage between
the input (HI or LO) and chassis ground, is 500V peak. Exceeding this value
may create a shock hazard.
NOTE After measuring high voltage in the volts function, it may take several minutes for
input current to drop to within specified limits. Input current can be verified by plac-
ing the protection cap on the input triax connector, and then installing the ground link
between COMMON and CHASSIS ground. With the instrument on the 20pA 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 listed in
Appendix A.
Perform the following steps to measure charge:
Step 1 Enable zero check and select the coulombs (Q) function
Zero check should always be enabled before making function or connection changes. The
ZCHK key toggles zero check on and off. When on, the “ZC” or “ZZ” message is displayed. See
Section 2 for details on zero check.
The coulombs function is selected by pressing the Q key.
Step 2 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 auto range between the HIGH
range group (2µC and 20µC) or the LOW range group (20nC and 200nC). To select the HIGH
range group, press SHIFT and then the RANGE key. To select the LOW range group, press
SHIFT and then the RANGE key. See Section 6 for details on range.
Step 3 If desired, set and enable auto discharge
See “Auto Discharge” to set an auto discharge level and enable it.
Step 4 Connect the input cable to Model 6514 (open input)
Make sure that the test circuit is not connected to the input.
Step 5 Disable zero check and press the REL key
When zero check is turned off, a charge may be induced on the input. Pressing the REL key
zeroes the display. See “Zero Check Hop” in “Coulombs Measurement Considerations” (in this
section). Details on Relative are provided in Section 7.
NOTE If the zeroed reading drifts significantly after REL is enabled, disable REL and toggle
zero check on and off until drift is minimized. Enable zero check and repeat Step 5.
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