Guarding Methods - Keithley 6430 Instruction Manual

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Guarding methods

Cable guard
Use the high-impedance (cable) guard connection scheme shown in Figure 2-4 for the fol-
lowing source-measure condition:
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Figure 2-4
High-impedance
guarding
DUT
Connect to earth
safety ground using
#18 AWG wire or
larger
Cable guard is always available at the Remote PreAmp. If not using the Remote PreAmp,
use the V, Ω GUARD banana jack on the mainframe with CABLE guard selected. See Guard
selection to select cable guard.
A test fixture is typically used when testing high-impedance devices. The test fixture reduces
noise and protects the user from a potentially hazardous voltage on the guard shield (or plate).
See Section 5, Guard for details on using guard.
Note that the test fixture chassis is connected to In/Out LO to reduce noise.
The Model 6430 will perform to rated specification with up to 1V drop per source lead
on the 100µA through 100mA ranges. On the 10µA range and belo w (when using the
Remote PreAmp), the allowable voltage drop in each source lead is limited as follows:
Maximum allowable resistance
Current range per source lead
10µA
1µA
100nA
10nA
1nA
100pA
10pA
1pA
Test circuit impedance is >1GΩ.
Test Fixture
HI
Triax Cable
Guard
LO
Guard
Shield
WARNING Guard is at the same voltage level as
10Ω
50Ω
500Ω
5kΩ
50kΩ
1MΩ
50MΩ
1GΩ
KEITHLEY
6430
REMOTE
PreAmp
input/output high. Therefore, if a
hazardous voltage (≥42V peak) is
present on input/output high, it is also
present on the guard terminals of the
Remote PreAmp and mainframe.
Connections
*Keithley part number: CA-176-1D.
Preamp Cable*
Connect to
REMOTE PreAmp
connector on rear
panel of mainframe
2-9