Operating Principles - Philips SM40 Instructions For Use Manual

1. GENERAL INTRODUCTION AND OPERATING PRINCIPLES
1.2 OPERATION PRINCIPLES
The SM40 Public Address Distribution Centre is easy to use and logical in its operation, it is helpful
however to understand, in principle, how the system works.
Herewith a typical series of actions, initiated by the operator, and carried out by the system:
1. User Key on Call Station (CST) is pushed (see Chapter 5.12).
2. Central Processor Card (CPC), which is continuously scanning the system, monitors which User Key
on which CST is being pressed. It then puts into effect a list of orders it was given at its programming
stage (see Chapter 4.1).
3. First it looks to see which amplifier input, or inputs, our User Key is routed to (see Chapters 4.3.1, 5.3
and 5.12)
4. Then it makes sure that no other Call Station is currently calling that same input (see Chapter 5.12).
If the requested loudspeaker zone is already being called, the CPC checks which priority rating each
User Key has been given, and if the original caller has a lower priority than the Key being pushed, its
call will be muted and overridden by the new caller.
If the Key being pushed has the same, or a lower priority than the original Key, its call will be ignored,
and a 'BUSY' LED mounted on the Call station illuminates to advise that the call has not gone
through.
5. If all is clear the CPC checks which attention tone and/or pre-recorded message has been programmed
to precede an announcement originating from our User Key, then it switches on the Signal Generator
Card; selects a tone; activates message(s) from the Digital Message Card(s) (DMC's) and feeds it to the
designated amplifier inputs (see Chapters 5.4 and 5.11).
6. Meanwhile it sends an electrical signal, via the IPC, back to the CST which energises a flashing green
LED in order to tell the user that the call is going through, but that they will have to wait until the
attention signal has finished (see Chapter 5.12).
7. If our key was given an alarm tone it will, dependent on the type of tone, be broadcast either for
1 minute, or until the user key is released.
8. The CPC checks, not only to see where the User Key has been routed to, but whether it has been
given any special orders regarding what it is to do when it gets there. Normally the CPC will mute any
music signal being transmitted to a loudspeaker zone, when an announcement is being broadcast in it.
9. In order to allow the announcement and/or signal to come through at full volume, regardless of the
volume settings of amplifiers or individual loudspeakers, the CPC switches in a series of corresponding
relays mounted on the Control Relay Card(CRC). These in turn activate the volume control override
circuits of the SQ45 amplifiers and/or individual volume controls in loudspeakers, or loudspeaker
groups (see Chapter 5.6).
10. When the CPC is certain that all is in order, it proceeds to give the message to the Input Card (IPC),
which in turn initiates the Call Station (CST) microphone.
11. The amplifier built into the CST amplifies the audio signal to line level, after which it runs through
the Input Card (IPC); via the Matrix Cards (MC)s; through Tone Control Cards (TCC)s if fitted; via
the Interconnection Board (IB); to the Termination Board (TB); and out to the inputs of the
amplifiers; which in turn feed loudspeakers located in geographical or functional zones.
12. When the announcement is completed and the User Key is released, the system returns to its idle
mode, with the CPC continually scanning, until another call is made. This whole operation is carried
out in less than
clear and efficient manner.
1 th
/ of a second, giving the user the speed and power necessary to communicate in a
10
1
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