Keithley 2600B User Manual

Series 2600B
System SourceMeter® Instrument Reference Manual Section 4:
Theory of operation
2600BS-901-01 Rev. C / August 2016 4-25
Inside the test fixture, a triaxial cable can be used to extend guard to the device under test (DUT).
The center conductor of the cable is used for HI, and the inner shield is used for guard.
The figures below show how cable guard can eliminate leakage current through the insulators in a
test fixture. In this figure, leakage current (I
L
) flows through the insulators (R
L1
and R
L2
) to LO,
adversely affecting the low-current (or high-resistance) measurement of the DUT.
Also in the figures below, the driven guard is connected to the cable shield and extended to the metal
guard plate for the insulators. Since the voltage on either end of R
L1
is the same (0 V drop), no
current can flow through the leakage resistance path. Thus, the SourceMeter instrument only
measures the current through the DUT.
Figure 105: Unguarded measurements
Figure 106: Guarded measurements

Keithley 2600B Specifications

General

Brand	Keithley
Model	2600B
Category	Measuring Instruments
Language	English