Keithley 6487 Reference Manual page 315

Model 6487 Reference Manual
The cabling in the circuit also requires shielding. Capacitive coupling between an electro-
static noise source and the signal conductors or cables can be greatly reduced by surround-
ing those conductors with a grounded metal shield
the noise current generated by the electrostatic voltage source and the coupling capaci-
tance flows through the shield to ground rather than through the signal conductors.
Figure G-6
Electrostatic shielding
Figure G-5
Shielding a high impedance device
+
HI
6487
V-Source
-
LO
Equivalent Circuit
Ground
Noise
current
High Impedance
DUT
HI
Measured
Current
(I)
LO
Shield
Shield-to-cable
capacitance
Source-to-shield
capacitance
V
Electrostatic
voltage source
Applications Guide
Metal
Shield
6487
A
Picoammeter
(Figure G-6). With this shield in place,
Ground-referenced
signal conductor
G-9