Studio Technologies 45A - Manual (Page 21)

Model 45A User Guide Issue 2, November 2011
Studio Technologies, Inc. Page 21
application would be to use RTS BP325
belt packs. Select the connected devices
so that their total current doesn’t exceed
300 milliamperes. That’s not always the
easiest figure to calculate but a web
search will generally find specifications for
all commonly used devices. For example,
a search finds that the original version of
the BP325 consumes a maximum of 85
milliamperes of current. According to this
figure up to three of these units can be
connected to each Model 45A Interface.
Newer versions of the BP325 use surface
mount component technology and have
a lower maximum current draw of 65 mil-
liamperes. Four of these “modern” BP325
units can easily be supported.
The Model 45A’s intercom power supply
circuit operates under software control.
This allows detection of fault conditions
and protection of both the Model 45A’s
circuitry and connected intercom user
devices. Upon initial Model 45A 2-wire
intercom power up no monitoring of the
intercom power output takes place for
a period of five seconds. This allows the
Model 45A’s circuitry and the connected
intercom user devices to stabilize. The
LED associated with pin 2 will light to
indicate that the output is active. After
this initial 5-second period monitoring
becomes active. A fault condition is
detected if the power on pin 2 falls be-
low 24 volts for a continuous 1-second
interval. The hardware and software re-
sponds to this condition by turning off the
power source to pin 2 and flashing the
pin 2 LED as a warning. After a 5-second
“cool-down” interval the output returns to
the same condition as upon initial power
up. Power is again applied to pin 2, the
pin 2 status LED will light, and monitor-
ing won’t begin for another five seconds.
A full short-circuit condition applied to the
Model 45A’s 2-wire connectors will result in
a continuous cycle of six seconds on (five
seconds for start up and one second for
detection) and five seconds off.
As a diagnostic aid the 2-wire (PL) power
status LED associated with pin 3 always
remains active, even when the Model 45A
is supplying power to the 2-wire party-line
intercom circuit. Whenever DC in excess
of approximately 18 volts is present on
pin 3 the LED will light. This condition will
typically not exist but could prove useful
in special circumstances.
2-Wire Circuit Serves as the
Unit’s Power Source
If no external source of 24 volts DC is
connected and configuration DIP switch 1
is in its on (up) position, the connected
2-wire party-line circuit can provide power
for the Model 45A. If this condition is active
the 2-wire (PL) input power LED will light.
The 2-wire (PL) power status LED will also
be lit, indicating that power in excess of 18
volts is detected on pin 2. The pin 3 LED
will also light if the same condition is pres-
ent on pin 3.
Level Meters
The Model 45A contains four 5-segment
LED level meters. These meters are pro-
vided as a support aid during installation,
configuration, operation, and troubleshoot-
ing. The meters represent the strength of
the signals coming in from, and going out
to, the 4-wire connections. The meters are
organized in two groups each representing
one input and one output. They are cali-
brated to reflect the level in dB relative to
+4 dBu. This is similar to the way in which
now-legacy VU meters functioned. As an