-6-
Figure 3.
ISOLATED BALANCED/UNBALANCED LINES:
The audio signals for the 310 are transmitted over a wire pair
using balanced line technology. This means each wire carries a signal
that is opposite in polarity of the other. At the input of the intercom is
an isolated balanced line transformer. This transformer subtracts the
two signals from each other providing an output free of noise generat-
ed onto the wires by some other noise source such as a motor or light
fixture near the wires.
The isolation provided by the transformer means that the grounds
of the units are not connected by the audio lines. Therefore, ground
loops and other problems caused by non-isolated systems are avoided.
The polarity of the audio lines between the + and - signal terminals
need not be maintained.
A shielded cable can be used in installations where extreme
problems from interference are suspected. The shield should always
be connected to the ground of only one of the intercoms. Connecting
the shield to ground at both ends will cause ground currents to travel
through the shield which could cause hum in the system.
There are several diagrams in the back of the manual to aid in
wiring intercoms together. The wiring diagram section illustrates bal-
anced and unbalanced line interconnection along with how a shielded
audio cable can be used. (See figures 5 through 12.) It also illustrates
multiple intercom interconnections.
290A3078
24VDC IN/OUT
GROUND
GROUND
CLASS I WIRING
CLASS II WIRING
REMOTE CONTROL
REMOTE SPEAKER
EXT CALL
CONTACT
+
-
COMMON
J2
J7
PHASE
Summary of Contents for 310LD-MV
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