The SFA-4 Alarm system is a multiplexed system using
the MEDCON A data transmission standard, a pulse width modulated signal, on 2
core inter-panel wiring, capable of displaying up to 60 alarm conditions. Each
SFA-4 alarm displays four alarm conditions, with a normal lamp for each, using
long-life 5 x 20 mm block LEDs..
Signals from plant or other monitored
equipment are connected into the SFA-4. As an alarm condition occurs, the
appropriate alarm condition will flash and the audible alarm will sound.
Operating the Mute switch will silence the audible on that panel and convert
the flashing lights to steady (the audible on any other panels is not
affected). If the condition remains, the audible can be selected to re-trigger,
requiring re-muting. In this case, if a condition is to be in an alarm
condition for a prolonged period, e.g. for maintenance, the re-trigger can be
prevented by silencing the audible with the Lockout button within the panel.
The audible will not then sound for that condition of that service until it has
returned to normal and then back to alarm condition. A volume control is fitted
within the panel. A loud speaker is used for the audible rather than a buzzer,
to give a mellow sound which, whilst drawing attention to the alarm condition,
can be tolerated by staff otherwise occupied.
Operation of the test button
on the front of the panel will cause the normal lamps to illuminate, the alarm
conditions to flash and the audible to sound.
The alarm is housed in a
steel enclosure with a plastic bezel. Within the enclosure are mounted the
power supply with battery reserve, control board with lamps, selector switches
etc. . The battery reserve enables the system to remain in operation for up to
4 hours .