Keithley 6485 User Manual

Model 6485 Picoammeter Instruction Manual Applications Guide I-11
As shown in Figure I-8, this will cause a current (i) to flow through the low to ground
capacitance of the picoammeter (A). Picoammeter HI is connected to the highest resis-
tance side of the circuit being measured, the “R” side of this current source. This circuit is
connected properly, so this current does not flow through the picoammeter and, therefore,
does not cause any measurement errors.
Figure I-8
Proper connection
However, when the HI of the picoammeter is connected to the low impedance power sup-
ply, this AC current (i) flows through the picoammeter (A) as illustrated in Figure I-9. This
current may affect the measurement accuracy, especially at low signal levels.
Current Source
6485
Picoammeter
+
-
i
HI
LO
R
A

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)