Section 2: General operation
Model 2657A High Power System SourceMeter® Instrument Reference Manual
2-56
2657A-901-01 Rev. B/December 2012
The safety shield can be metallic or nonconductive, and must completely surround the DUT test
circuit. A metal safety shield must be connected to a known protective earth (safety ground). See
(on page 2-62) for important safety information on the use of a metal or a nonconductive
enclosure.
Guarding
A driven guard is always enabled and provides a buffered voltage that is at the same level as the
input/output HI voltage. The purpose of guarding is to eliminate the effects of leakage current (and
capacitance) that can exist between HI and LO. Without guarding, leakage and capacitance in the
external high-impedance test circuit could be high enough to adversely effect the performance of the
Model 2657A.
Guarding (shown below) should be used when test circuit impedance is >1 G
Ω
.
See
(on page 4-23) for details on the principles of guarding.
Guard voltage can be hazardous. With an unguarded device under test (DUT) connection, terminate
the guard before the end of the cable. Refer to
High-voltage triaxial cable termination
(on page 2-
44) for details.
Connect the enclosure of all metal test fixtures to protective earth (safety ground). See your specific
test fixture for information. Nonconductive test fixtures must be rated to double the maximum
capability of the test equipment in the system.
NOTE
WARNING
Summary of Contents for 2657A
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