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Keithley 6514 User Manual

Keithley 6514
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5-6 Coulombs Measurements
NOTES The format that the reading string is returned in is set by commands in the FORMat
Subsystem (see Section 16).
If there is no reading available when :DATA? is sent, an error (-230) will occur.
The READ? command can be used to return “fresh” readings. This command triggers
and returns the readings. See Section 15 for details.
Programming example
The following command sequence will perform one coulombs measurement:
*RST ‘ Return 6514 to RST defaults.
SYST:ZCH ON ‘ Enable zero check.
FUNC ‘CHAR’ ‘ Select the Coulombs function.
CHAR:RANG:AUTO ON ‘ Enable auto range.
‘ Connect input cable.
SYST:ZCH OFF ‘ Disable zero check.
CALC2:NULL:STAT ON ‘ Enable Rel to zero the display.
‘ Connect charge circuit to DUT.
READ? ‘ Trigger and return one reading.
Coulombs measurement considerations
Some considerations for making accurate Coulombs measurements are summarized as fol-
lows. Additional measurement considerations are covered in Appendix C. For comprehensive
information on precision measurements, refer to the Low Level Measurements handbook, which
is available from Keithley Instruments.
Input bias current
A primary consideration when making charge measurements is the input bias (offset) current
of the integrating amplifier. Any such current is integrated along with the input signal and
reflected in the final reading. Model 6514 has a maximum input bias of 4fA for charge at T
CAL
(temperature at time of calibration). This input offset translates into a charge of 4fC per second
at the T
CAL
temperature. This value must be subtracted from the final reading to obtain the cor-
rect value.
Input bias current may be reduced by performing the offset correction procedure explained
in Section 19.
External voltage source
When using an external voltage source, the input current should be limited to less than 1mA
by placing a resistor in series with the high input lead. The value of this resistor should be at
least:
R = 1000 × V (ohms)
where; V is the voltage across the resistor, or the compliance of the current being integrated.

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Keithley 6514 Specifications

General IconGeneral
BrandKeithley
Model6514
CategoryMeasuring Instruments
LanguageEnglish

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