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5. SM40 SURVEILLANCE CENTRE MODULES
5.6
Amplifier Surveillance Board - ASB
P.C.B. of 6.5 x 7.2 cm with solder-pin connection points. Used for sensing the presence of the 20kHz
pilot tone signal at amplifier outputs and in loudspeaker lines (100V system). Can be mounted using
Phoenix interconnection modules or normal set-screws.
The Amplifier Surveillance Board is the device which constantly checks the 100V loudspeaker lines for the
presence of the 20kHz pilot tone signal. It is possible to adapt the ASB for 70V and 50V loudspeaker lines
by changing a resistor (see fig.4).
The unit, a small circuit board, can easily be mounted in the back of a 19-inch rack unit, near to the
amplifiers, to monitor the amplifier output.
It may also be mounted in a small enclosure on a loudspeaker cabinet, or in a junction box, to monitor the
100V loudspeaker lines.
The signal is tapped off the loudspeaker line or amplifier output (in parallel with the loudspeaker line), and
enters the ASB via the LINE IN contacts.
It is possible to add amplifier monitoring and spare amplifier switching to a public address system, because
the ASB is fitted with a relay with one make/break contact,which can be used to activate warning devices or
switch in spare amplifiers (see Figs. 2 & 4). A jumper (S2) is provided to allow this relay to be active or non-
active (see Fig.4). If no errors are detected, this relay is activated and provides a contact closure between
points 6 and 7 (see relay output fig.1).
In spare amplifier switching, external relays are used for switching the audio input and output signals of the
defective amplifier to the spare amplifier. These external relays must be wired to the OUT contacts on the
ASB (see Fig.4). The corresponding Pilot Tone Generator Card (PGC) should be mounted in the SM40
Routing and Switching frame, a separate 15V power supply must be used to power both the ASB's and the
spare amplifier signal switching relays (see Fig. 2).
As well as switching in the spare amplifier, error information can be communicated to an SM40 Surveillance
Centre via the DATA contacts on the ASB (see Fig.3)
If the unit senses that no pilot tone signal is present, the built in relay is de-activated and a message is sent
(via the system's communication line) to the CPC, which would give visual, or printed, information about
the error.
This communication function may also be used alone, where a quantity of ASB's are placed at strategic
points throughout the distribution system, monitoring the loudspeaker lines, and sending error information
back to the Central Processor.
The unit is also provided with an external contact input, marked EXT IN. Any external device (smoke
detector, micro switch, etc,.) which provides a 'break' contact, for use as an alarm/error may be used to
activate the ASB, giving the system an error warning. A jumper (S3) is provided to allow either the 20kHz
LINE IN or external (EXT IN) contacts to be used (see Fig.1).
In order for the Central Processor to "recognise" which ASB is giving the error indication, and in which
sequence the ASB is to receive its data communications, each unit is given an "address". This address setting
is accomplished by setting the DIP switches on the board itself (see settings list at the end of this chapter).
Up to 128 ASB's, and/or Loudspeaker Surveillance Boards (LSB's), may be linked to the same
communications bus.
A single, standard 2 core, 0.75mm
(and LSB's), linked via the same communications bus, to the Central Surveillance Centre.
The DATA, and + solder pins are duplicated in order to simplify wiring of the communications line and the
power supply to the following ASB, or LSB (see Fig.4).
2
screened microphone cable may be used for connection of all the ASB's
LBB 1368/00
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