Cable Guard; Ohms Guard; Figure 5 Cable Guard Connections - Keithley SourceMeter 2400 Series Quick Results Manual

8 Quick Results Guide

Cable guard

When testing high-impedance DUT (>1GΩ), cable guard is used to drive the shields of
cables and test fixtures to minimize leakage currents and input capacitance. A typical connec-
tion scheme using cable guard is shown in Figure 5. The following menu sequence selects
cable guard:
Press CONFIG > press SOURCE V (or SOURCE I or MEAS Ω) > select GUARD > select
CABLE
The guard terminal of the SourceMeter is at virtually the same potential as input/output HI.
Therefore, if there is hazardous voltage at input/output HI, it is also present on the guard shield
for the test circuit.
WARNING
Figure 5
Cable guard connections

Ohms guard

Ohms guard allows in-circuit resistance measurements on DUT where other parasitic leak-
age devices are present. Connection schemes for a Delta DUT configuration is shown in
Figure 6.
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 5).
Guard Shield
Test Fixture
DUT
HI
LO
4-WIRE INPUT/
SENSE OUTPUT
IEEE-488
(ENTER IEEE ADDRESS
WITH FRONT PANEL MENU)
CAUTION:
Connect to earth safety ground
using #18 AWG wire or larger.
WARNING:
NO INTERNAL OPERATOR SERVICAB
V, Ω
GUARD
GUARD
SENSE
RS232
FOR CONTINUED PROTECTION AGAINST FIR