Table of Contents
Advertisement
5. SM40 SURVEILLANCE CENTRE MODULES
5.3
Pilot tone generator card (PGC)
Eurocard 10 x 22 cm with an 'ab' connector (2 x 32) containing a 20 kHz
tone oscillator and 16 independent electronically balanced outputs. These
are connected to amplifier test inputs.
The SM40 Surveillance Centre uses an ultrasonic (20kHz) pilot tone, inserted at the specially developed test
input of the Philips SQ45 amplifier. This tone is then relayed to all the loudspeakers throughout the
corresponding zone. The Surveillance Centre checks for the presence of this tone at various strategic points
in the zone. If the tone is not present at a particular point, it is obvious that the normal audio signal is not
going to be broadcast at that point either.
In each card a single oscillator is used to drive 16 electronically balanced outputs, which are floating free of
earth (ground). One PGC therefore can feed 16 amplifiers/loudspeaker zones with pilot tone signals.
The Central Processor Card (CPC) does not control, and has no infuence upon, the Pilot Tone Generator
Card (PGC). Neither is the PGC connected to any other card in the system.
The only dependence that the card has on the system is the fact that it requires +/- 15 Volt powering, which
is normally supplied from either the Basic System or an Extension Frame. Because of this, the amount of
PGC's used in a system is unlimited.
Two green leds, mounted on the front edge of the card, advise that adequate supply voltages are present.
In order for the system to operate correctly, it is essential that the Volume Adjust control (see board layout
illustration) is set so that 10V is measured at the 100V output tap of the SQ45 amplifiers. All SQ45
amplifier Input Sensitivity Switches should be in the 1000 mV position. One master switch on the Pilot
tone generator card then sets the sensitivity level for all SQ45 amplifiers.
5.3.1 Reduction of power dissipation in amplifiers
To reduce the power dissipation in amplifiers when surveillance is used, the Amplifier Surveillance Board
(LBB 1368/00), the Loudspeaker Surveillance Board (LBB 1367/00) and the Pilot Generator Card (LBB
1369/00) have been modified. The modification enables a 20kHz 'burst-pilot-tone' to be used instead of a
continuous 20 kHz 'pilot-tone'. This feature can be selected by a jumper located on the Pilot Generator
Card. The modified type number versions are compatible with previous versions and can be used all together
in a single system.
Selecting 'continuous mode' or 'burst-mode'
Using jumper X2 the following mode can be selected:
Continiuous mode:
Burst-mode:
Note: When the modified PGC is used in a system where LSBs and/or ASBs are NOT CAPABLE of
working with the 20kHz 'burst-tone', jumper X2 must ALWAYS be placed in the continuous mode to
prevent malfunction of the Surveillance Centre. Where possible, it is advisable to set X2 in the 20kHz
'burst-tone' position in systems where only NEW (modified) LSBs and/or ASBs are installed. This will
greatly reduce the dissipation of the SQ45 amplifier. The modification to the PGC is implemented from
serial number 431 onwards. The modified PGC (LBB 1369/00) has been installed as standard in the LBB
1370/30 surveillance basic frame from serial number 734 onwards.
For modification details to the ASB and LSB refer to the relevant sections.
X2 in position 2-3 (output frequency 20kHz ±1kHz).
X2 in position 1-2 (output frequency 20kHz ±1kHz).
-
20kHz present:
35 ±5msecs.
-
20kHz absent:
260 ±30msecs.
LBB 1369
5
31
Advertisement
Table of Contents
