Studio Technologies 45A - Manual (Page 16)

Issue 2, November 2011 Model 45A User Guide
Page 16 Studio Technologies, Inc.
the supplied voltage must be 24 volts or
greater as measured directly at the Model
45A’s 2-wire (PL) connectors. Whether the
connected party-line intercom circuit can
provide this much energy will depend on
the characteristics of a specific installation.
The relevant factors include the capacity
of the intercom power supply, the number
and type of connected user devices, and
the length and type of the interconnecting
cables.
The capacity of the intercom power sup-
ply must meet or exceed the needs of the
connected user devices, including the
Model 45A. It’s a good idea to perform a
calculation of the total maximum current
draw prior to attempting to install and use
the unit. As a real-time confirmation often
these power supplies have status indica-
tors that can provide a direct indication of
their ability to supply the connected loads.
In many cases the length and type
(gauge) of the interconnecting cable will
be the limiting factor as to whether the
intercom circuit can provide adequate
power for a Model 45A. This is because
the intercom circuit’s DC voltage will drop
in direct relation to the length of the in-
terconnecting cable. And with the Model
45A’s relatively large current draw this
voltage drop can become appreciable
in situations where belt pack operation
wouldn’t normally be impacted. Perform-
ing accurate calculations in this scenario
is a bit more difficult but might be required
to ensure a reliable installation.
Initial Operation
As soon as a source of power is applied
the Model 45A will begin its power-up
sequence. As a “boot-up” indication the
input power, status, and meter LEDs will
light, one at a time, in a “walk-through”
sequence. After the sequence has com-
pleted, one of the input power LEDs will
light indicating which power source is
actively powering the unit. The Model 45A
is now fully functional.
Configuration
To support the needs of various applica-
tions the Model 45A allows a number of
operating parameters to be configured.
A 5-position DIP switch assembly, located
on the front panel, is used to establish the
desired configuration. Refer to Figure 6
for a view of the DIP switch and to Appen-
dix D for a list of the configuration choices.
Using the Connected 2-Wire
Party-Line Circuit as the
Model 45A’s Power Source
Configuration DIP switch 1 is used to
select whether or not the connected 2-wire
intercom circuit can be used to provide
power for the Model 45A. When the switch
is in its off (down) position the intercom
circuit cannot be used to power the Model
45A. This ensures that no current will be
drawn from the intercom circuit, some-
thing that can be important if the circuit is
limited in available current, or if the length
of the interconnecting cable is excessive.
When switch 1 is in its on (up) position the
2-wire party-line circuit can serve as the
power source for the Model 45A.
It’s important to remember that if an ex-
ternal source of 24 volts DC is connected
it will always be used as the Model 45A’s
power source. Even if switch 1 is in its
on (up) position, power will be drawn
from the connected intercom circuit only