Fire Fighting Enterprises FIRERAY 2000 EExd - Manual (Page 3)

Page 3 of 12
WARNING
The area into which the Fireray parts are to be fitted must be made safe before attempting any work
on the system. It must also be checked thoroughly prior/during/after commissioning, to ensure it
cannot compromise the safety of the area in which it is fitted. Note that only the Transmitter and
Receiver parts may be installed in the hazardous area, NOT the Controller Unit.
If the flamepath of the enclosure is damaged in any way, the unit must be returned to the
manufacturer and a new unit purchased.
PRINCIPLE OF OPERATION
General
The Fireray system operates by passing an infra-red beam between a Transmitter and Receiver, through
the protected area. The received signal strength will be attenuated if smoke is present in the beam. The
beam strength is measured continuously and, should any attenuation be present which exceeds presets
thresholds, fire or fault alarms are generated as appropriate. Each installed Fireray can cover an area 7.5
metres either side of the beam, giving a maximum coverage of up to 1500
2
m with a 100m beam path
length.
Transmitter and Receiver Units
A modulated Infra-Red light beam is projected from the Tx (Transmitter ) via it’s optical system. The
projected beam has a circular footprint, with a useable spread of approx 3m @ 100m range. The Rx
(Receiver) has a corresponding filtered optical system which collects and focuses the beam onto a
photo-detector. During installation, the Rx has a maximum beam acceptance angle of up to 5

(dependant on gain and threshold settings). The wide Tx beam, in conjunction with the large Rx
acceptance angle simplifies alignment and gives good tolerance to beam mis-alignments after
installation.
Controller Unit And Alarm Thresholds
The signal received at the Rx is amplified and filtered to reject sunlight and other unwanted optical
noise such as may be caused by ambient lighting,. The signal is then passed to the Controller Unit,
where it undergoes further filtering and validity checking, before finally being analysed for signal
strength. The signal is then compared to a reference level (determined by the user’s threshold setting),
and should the signal be reduced below the set threshold, the FIRE ALARM relay will be activated
within approx 12 seconds. Three user selectable threshold setting are available **. Note that only one
threshold switch must be closed to select the required threshold. A red lamp on the Controller Unit
front panel also indicates a FIRE ALARM condition.
Controller Unit -Fault Thresholds
If the signal is reduced suddenly by more than 93% in 8 to 10 seconds, perhaps due to total beam
blockage, a cable break, or the Tx or Rx becoming unserviceable, the controller interprets this as a fault
situation. Loss of power to any of the system parts will also cause a fault signal to be generated. In any
of these events, the controller will activate the FAULT ALARM relay continuously. The system will
return to normal operation immediately, once the correct signals are restored, except in the event of a
power loss to the controller, in which case normal operation is resumed after 50 seconds from
restoration of power. A yellow lamp (LED4) in the Controller Unit also indicates when the system is in
a FAULT or RESET condition.
Controller Unit - Compensation (AGC) Operation And Action At Compensation Limit
The Controller Unit also incorporates an AGC (Automatic Gain Control) system , which monitors very
slow changes in the received signal due to contamination of the optical system (EG: build up of dust on
the lenses) and any changes due to system ageing. If the signal is reduced by more than approx 11%, the
AGC system is activated. Then if the signal is still low after 1.5 hours, a 7% increase is made to the
system gain, to bring the signal strength back into the nominal range. Additionally, should the signal
strength increase, perhaps due to improved alignment following building movement, the system can
reduce its gain in 7% steps. From an initial nominal setting, up to 11 increasing and 3 decreasing
correction steps are possible.