Calibrator
Connect the Calibrator to a DUT
29
When to Use EARTH and GUARD
Figure
shows the internal connections made by the Guard setting.
Figure 2. EARTH and GUARD Internal Connections
Earth
The Calibrator front-panel OUTPUT LO terminal is normally isolated from earth (chassis) ground. To
make a connection between the OUTPUT LO terminal and earth ground, an external connection must
be made to the chassis ground terminals.
To avoid ground loops and noise, you must have only one earth ground-to-LO terminal connection in
the system. Usually you make all signal ground connections at the DUT. Generally, a connection to
Earth ground is only used for ac and dc volts where the DUT is isolated from earth ground. There must,
however, be a safety ground for the Calibrator. See
.
External Guard
The guard is an electrical shield, isolated from the chassis, that protects the analog circuitry. The guard
provides a low-impedance path for common-mode noise and ground loop currents. The internal guard
is connected to OUTPUT LO through approximately 30
Ω
. There is normally an internal connection
between the guard and the OUTPUT LO terminal. When you select the external guard setting, you
break this internal connection, which allows you to connect a lead from the GUARD terminal to earth
ground on another instrument in an interconnected system. Use this external guard connection
whenever you test a DUT that has a grounded LO terminal. Remember to always maintain only one
earth ground tie point in a system.
Chassis ground
Internal guard shield
OUTPUT LO
signal ground
GUARD
Safety ground
through
ac line cord
Chassis Ground
binding post
OUTPUT LO
binding post
GUARD
binding post
