5: Source-measure considerations 2470 High Voltage SourceMeter Instrument
5-16 2470-901-01 Rev. A / May 2019
Using guard with a test fixture
A test fixture is typically used when testing high-impedance devices. The test fixture reduces noise
and protects users from a potentially hazardous voltage on the guard shield.
Inside the test fixture, the guard can be connected to a guard plate or shield that surrounds the device
under test (DUT).
Connect the test fixture chassis to LO to reduce noise.
A safety shield must be used whenever hazardous voltages (>30 V
RMS
, 42 V
PEAK
) will be
present in the test circuit. To prevent electrical shock that could cause injury or death, never
use the 2470 in a test circuit that may contain hazardous voltages without a properly installed
and configured safety shield.
Inside the test fixture, a triaxial cable can be used to extend guard to the DUT. See the connection
diagrams on the rear panel of the instrument for the triaxial guard to conductor connections.
Guard circuit drawing
In the following schematic, note that guarding eliminates resistance leakage current (R
L1
). The current
flowing in resistance leakage 2 (R
L2
) is supplied by the guard and does not affect the DUT current
(I
DUT
).
Figure 100: Guarded configuration
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