Agilent Technologies N3280A manual Coaxial Guard Connections, Guard Connections for Test Fixtures

2 - Installation

NOTE: Any voltage drop in the load leads must be subtracted from the full-scale voltage available at the output terminals.

Coaxial Guard Connections

An active guard connection is available at the output connector. When the guard connection is extended to a test fixture for example, it can be used to eliminate the effects of leakage current that can exist between the Hi and Lo output terminals when testing high-impedance devices. In particular, the Hi output terminal and the Hi sense terminal may benefit from guarding. In this way, any leakage current that is not load current will be collected by the circuit and not be included in the output current measurement.

The guard connection is always enabled and provides a buffered voltage that is at approximately the same potential as the Hi output terminal. The output impedance of the guard is approximately 2.1K ohms.

If you are using tri-axial cables to extend the guard connection to the test fixture, use the center connector for the Hi connection, the inner shield for the guard connection, and the outer shield as the Lo connection (see figure 2-5).

OUTPUT 1

MATING PLUG

SHOWN

TIGHTEN SCREWS

LOCKING SCREW Hsen Hi Lo Lsen

INSERT WIRES

TRIAXIAL CABLE

TEST FIXTURE

_

+

GUARD SHIELD

Figure 2-5. Guard Connections for Test Fixtures

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