GAI-Tronics 495-001 Mine Dial / Page Phone Interface Cabinet - Manual (Page 14)

Pub. 42004-198D
Model 495-001 Mine Dial/Page Phone Interface Cabinet Page: 14 of 22
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Adjustment of the Switchboard Monitor Circuit
Current to operate the switchboard monitor relay within the All-Call/Merge assembly is controlled by an
adjustable resistor attached to terminal block TB401 on the enclosure for the All-Call/Merge assembly.
See Figure 7. Because the current also varies with the resistance of the telephone switchboard cable, this
resistor is adjusted to compensate for this cable loss.
In normal operation, the switchboard monitor relay is continuously energized and the green indicator light
on the front panel of the All-Call/Merge assembly is illuminated. To set the adjustable resistor properly,
it is first necessary to find the critical point; if the light is on, increase resistance until it goes off. Or, if
the light is not lit, decrease resistance until it does light. Then, as a safety factor, decrease the resistance
by about 25%.
The monitor relay current can be measured by temporarily replacing the “test link” between terminals 11
and 12 on TB401 with an ammeter. See Figure 7. The current should be between 20 and 40 mA when
properly adjusted. The monitor relay contacts are rated for 2 amps, 28 V dc/120 V ac.
Check-Out of Optional Alarm Circuit
Relay contact outputs are provided for ac power failure alarm (TB404-9, 10 and 11) and PABX failure
alarm (TB402-22, 23 and 24). These relay contacts can be used to activate audible/visual alarms such as
bells or strobe lights as required. See Figure 7 for wiring details. These relay contacts are rated for 2 A,
28 V dc/120 V ac.
Check-Out of Operation and Adjustment of All-Call Mode
1. Activate the All-Call page by following the instructions outlined in Operation section on page 15.
2. Observe that the red P AGE M ODE indicator on the All-Call/Merge assembly is lit during operation in
this mode.
3. Adjust the A LL -C ALL P AGE L EVEL control on the front panel of the All-Call/Merge assembly so that
the speaker level at a 491 Series Mine Dial/Page Phone is the same in this model as in the normal
individual station call mode.