Keithley 6430 Quick Results Guide

Quick Results Guide 9
Guarding
Cable guard
When testing high-impedance DUT (>1G), cable guard is used to drive the shields of
cables and test fixtures to minimize leakage currents and input capacitance. A typical
connection scheme using cable guard is shown in Figure 8. The following menu sequence
selects cable guard:
Press CONFIG > press SOURCE V (or SOURCE I or MEAS ) > select GUARD >
select CABLE
WARNING To prevent injury from electric shock, the guard shield must be enclosed in a
safety shield (i.e., test fixture) that is connected to safety earth ground (as
shown in Figure 8).
Ohms guard
Ohms guard allows in-circuit resistance measurements on DUT where other parasitic
leakage devices are present. Basic connections with ohms guard are shown in Figure 9.
The following menu sequence selects ohms guard:
Press CONFIG > press MEAS  (or SOURCE V or SOURCE I) > select GUARD >
select OHMS
Guard
Shield
Triax Cable
Test Fixture
HI
LO
Connect to earth
safety ground using
#18 AWG wire or
larger
DUT
WARNING
Guard is at the same voltage level as
input/output high. Therefore, if a
hazardous voltage (³42V peak) is
present on input/output high, it is also
present on the guard terminals of the
Remote PreAmp and mainframe.
6430
REMOTE
PreAmp
SENSE
MAINFRAME
Connect to
REMOTE PreAmp
connector on rear
panel of mainframe
Guard
IN/OUT
HIGH
Preamp Cable*
KEITHLEY
*Keithley part number: CA-176-1D.
Figure 8
Cable guard

Keithley 6430 Specifications

General

Brand	Keithley
Model	6430
Category	Measuring Instruments
Language	English