Keithley 6485 User Manual

2-16 Measurement Concepts Model 6485 Picoammeter Instruction Manual
B) SYSTem:ZCORrect[:STATe] <b>
This method to perform zero correction is consistent with the way it is performed from the
front panel. That is, zero correction is performed while zero check is enabled. The zero
correct state can be turned on and off repeatedly without requiring. If no ACQ has not been
performed since the most recent reset, zero is used for the ACQ value.
Measurement considerations
There are a variety of factors to consider when making low level measurements. These
considerations are listed and summarized in Table 2-5 and are detailed in Section 3 and
Section C. For comprehensive information on all measurement considerations, refer to the
Low Level Measurements handbook, which is available from Keithley Instruments.
Table 2-5
Summary of measurement considerations
Considerations Description
See Section 3 for details
Input bias current Offset current of Model 6485 could affect low current measurements.
Voltage burden Offset voltage of Model 6485 could cause errors if it is high in
relation to the voltage of the measured circuit.
Noise Noise generated by source resistance and source capacitance.
See Section C for details
Ground loops Multiple ground points can create error signals.
Triboelectric effects Charge currents generated in a cable by friction between a conductor
and the surrounding insulator (i.e. bending a triax cable).
Piezoelectric and stored
charge effects
Currents generated by mechanical stress on certain insulating
materials.
Electrochemical effects Currents generated by the formation of chemical batteries on a
circuit board caused by ionic contamination.
Humidity Reduces insulation resistance on PC boards and test connection
insulators.
Light Light sensitive components must be tested in a light-free
environment.
Electrostatic interference Charge induced by bringing a charged object near your test circuit.
Magnetic fields The presence of magnetic fields can generate EMF (voltage).
Electromagnetic interference
(EMI)
EMI from external sources (i.e. radio and TV transmitters) can
affect sensitive measurements.

Keithley 6485 Specifications

General

Model	Keithley 6485
Category	Picoammeter
Input Impedance	>10^14 Ohms
Voltage Burden	<200µV
Accuracy	0.4% of reading
Voltage Source Range	Not Applicable
Voltage Source Resolution	Not Applicable
Voltage Source Accuracy	Not Applicable
Interface	IEEE-488
Power Requirements	100V to 240V AC, 50/60Hz
Dimensions	89 mm high x 214 mm wide x 369 mm deep (3.5 in x 8.4 in x 14.5 in)