8508A
Users Manual
SENSE HI
SENSE HI
SENSE LO
SENSE LO
INPUT HI
INPUT HI
INPUT LO
INPUT LO
Rx
Ra
Rb
Rg
Metal
Screen
GUARD
GUARD
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Figure 3-9. Ω Guard Measurements
Internal Guard Connections
External Guard
not selected: In the Ohms or PRT Functions the Guard terminals on the
front and rear panels are isolated from each other and from any internal connection. The
internal guard shields and tracks are connected directly to the internal 0 V.
External Guard selected: In the Ohms or PRT Functions selecting the External Guard
provides an Ohms Guard function. The internal guard shields, tracks, and the selected
front or rear Guard terminal are connected to the internal 0 V.
Guard terminal front Guard terminal rear
Front
Rear
External Guard
Internal Guard
Internal Guard and External Guard External Guard
(OHMS and PRT) (DCV & I, ACV & I)
0 V
Internal Guard
Shield and Tracks
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Figure 3-10. Internal Guard Connections
Selecting External Guard (ExGd)
See Figure 3-9 for connections when using the Ω Guard feature.
To select
External Guard:
1. Press
Input key to enter the INPUT menu.
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INPUT Menu
2. Press the menu key ExGd to toggle the Multimeter’s Guarding options.
The ExGd annunciator on the left-hand display indicates that External Guarding is
selected.
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