Atkinson Dynamics AD-28LD-MV Handleiding voor installatie- en service-instructies - Pagina 6

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CLASS I WIRING

ISOLATED BALANCED/UNBALANCED LINES:

The audio signals 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 generated 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

COMMON

PHASE

GROUND

24VDC IN/OUT

REMOTE CONTROL

REMOTE SPEAKER

CLASS II WIRING

Figure 3.

-6-

GROUND

EXT CALL

CONTACT

290A3078