5. Attach the conduit to the enclosure. Feed the wiring through the conduit, and bring it into
the enclosure.
6 Connect an 18 AWG twisted pair wire between SelectFone station L1 PAGE L2 and Line
Balance L1 PAGE-L2 terminals. Similarly connect the 18 AWG twisted pair wire for
each channel line between terminals of LINE-BALANCE assembly and corresponding
SelectFone station terminals as shown in Figures 1, 4, 5, and 6.
IV. ADJUSTMENTS AND OPERATION.
After all of the stations, the line balance assembly, and paging speakers have been installed and the
wiring is complete, the system should be evaluated and adjustments made to ensure proper operation.
Before beginning, verify that all station handsets are on hook.
Turn on AC power to the system and begin the evaluation at the SelectFone station closest to the line
balance assembly. Lift the handset off hook; the off-hook indicator should turn on. Press the push-to-
page switch on the handset and speak firmly and directly into the handset microphone, verifying that
the message is audible over all speakers except those associated with that station. When paging, if the
line balance assembly is connected properly and the page line is loaded properly, very little or no mes-
sage should be heard on the handset receiver. If necessary, open the cover of the line balance assembly
and adjust the page line loading by turning the control to the point where little or no page is audible
in the handset receiver. In the future, if 10 or more units are added to the system, this adjustment may
again be necessary.
After line balance adjustments are completed for the page line, the paging speaker volume level can
be adjusted on the associated speaker/amplifier module. To access the speaker/amplifier volume level
control, remove the station cover. The station is pre-set at the factory to produce 1/2 the maximum
output level with moderate page line input.
Check the operation of all channels by holding a conversation between two or more SelectFone stations
on each channel. If the line balance assembly is properly connected, the speaker should hear little or
none of his own voice in the handset receiver. No channel line load adjustment is provided.
The handset transmitter signal is amplified by the handset/amplifier. The handset amplifier has a
transmitter volume control and receiver level control. To access these controls remove the front cover
of the station. These controls are located on the printed circuit board mounted to the back of the front
cover and can be adjusted with a small screwdriver. These controls are pre-set at the factory to produce
optimum results in the industrial environment. Before attempting to adjust these controls, check for
a missing or improperly connected line balance assembly, crossed wires, or grounded wires. Stations
located far (3000 feet or more) from the line balance assembly may require that the receiver level control
be adjusted to compensate for cable resistance.
V. TROUBLESHOOTING
In an SelectFone system, AC power circuit conductors are in the same cable with communication con-
ductors. Even if the system is properly installed, there is an AC voltage between page line or channel
line conductors and ground. This is a result of the induced voltage that is due to the capacitance of the
AC power circuit conductors running in parallel with the communication circuit conductors. At times
this voltage can read 50 volts or more. This voltage is of no consequence because the page and channel
lines are balanced twisted pair audio circuits.
In an SelectFone system, the audio voltage across page line conductors or across any channel line con-
ductors (L1 and L2) is of the order of 0.5 to 0.75 volts peak when someone is speaking into the handset
microphone. The voltage will be proportional to the person’s voice speaking into the handset.
Hum or Buzz
When one of the two conductors in the page or channel lines short circuits to ground, the audio cir-
cuit becomes unbalanced. If there is leakage to ground from one of the conductors, the audio circuit
becomes unbalanced.
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