Cable Guard - Keithley SourceMeter 2400 Quick Start Manual

Section 1: Introduction
NOTE Specified accuracies for both source and measure are achieved only

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 connection 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 1
Cable guard connections
1-8
using 4-wire remote sensing.
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:
Return to
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
Section Topics
Series 2400 SourceMeter® Quick Start Guide
2400S-903-01 Rev. E / September 2011