Manual

Issue 3, August 2015 Model 45A User Guide
Page 16 Studio Technologies, Inc.
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 beltpack 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
completed, 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. The following para-
graphs provide detailed information on se-
lecting the configuration. Refer to Appendix
D for a list of all the configuration settings.
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 inter-
com circuit can be used to provide power
for the Model 45A. When the switch is in its
off (down) position the intercom circuit can-
not be used to power the Model 45A. This
ensures that no current will be drawn from
the intercom circuit, something that can be
important if the circuit is limited in available
current, or if the length of the interconnect-
ing 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.
Figure 6. 2-wire (PL) input power switch settings