I-10
Applications Guide
Model 6485 Picoammeter Instruction Manual
•
Keep all charged objects (including people) and conductors away from sensitive
areas of the test circuit.
•
Avoid movement and vibration near the test area.
•
When measuring currents <1nA, shield the device under test by surrounding it with
a metal enclosure and connect the enclosure electrically to the test circuit common
terminal.
Shielding vs. Guarding
Shielding usually implies the use of a metallic enclosure to prevent electrostatic interfer-
ence from affecting a high impedance circuit. Guarding implies the use of an added low
impedance conductor, maintained at the same potential as the high impedance circuit,
which will intercept any interfering voltage or current. A guard does not necessarily pro-
vide shielding. (
“Leakage currents and guarding,” page I-2
.)
Making connections
To avoid measurement errors, it is critical to make proper connections from the picoam-
meter to the device under test. To make a proper connection,
always connect the high
resistance terminal of the meter to the highest resistance point of the circuit under
test.
shows a picoammeter connected to a current source that consists of a voltage
source in series with a resistor. An AC powered voltage source usually has a significant
level (often several volts) of line frequency common mode voltage.
Figure I-7
Connecting the HI terminal (picoammeter) to high resistance
+
-
6485
Picoammeter
Current Source
R
HI
LO
A
Summary of Contents for 6485
Page 20: ......
Page 24: ......
Page 44: ...1 20 Getting Started Model 6485 Picoammeter Instruction Manual ...
Page 66: ...3 6 Measurements Model 6485 Picoammeter Instruction Manual ...
Page 138: ...9 20 Remote Operation Model 6485 Picoammeter Instruction Manual ...
Page 159: ...11 CommonCommands ...
Page 164: ...11 6 Common Commands Model 6485 Picoammeter Instruction Manual ...
Page 165: ...12 SCPISignalOriented MeasurementCommands ...
Page 190: ...14 12 SCPI Reference Tables Model 6485 Picoammeter Instruction Manual ...
Page 214: ...16 14 Calibration Model 6485 Instruction Manual ...
Page 219: ...A Specifications ...
Page 221: ...B StatusandErrorMessages ...
Page 227: ...C GeneralMeasurement Considerations ...
Page 233: ...D DDCEmulationCommands ...
Page 247: ...E ExamplePrograms ...
Page 250: ...E 4 Example Programs Model 6485 Picoammeter Instruction Manual ...
Page 251: ...F IEEE 488BusOverview ...
Page 266: ...F 16 IEEE 488 Bus Overview Model 6485 Picoammeter Instruction Manual ...
Page 267: ...G IEEE 488andSCPI ConformanceInformation ...
Page 311: ......