FB-AP Detector Features
Response setting
Each detector in the FB-AP Series range can operate in one of five response modes, any of which can be selected from the control panel. Each mode corresponds to a unique response behavior, which can be broadly related to sensitivity to fire. Whatever the type of detector, Mode 1 will give a higher sensitivity to fire than Mode 5. The selection of the most suitable mode depends on the application.
For ionization and optical smoke detectors, the modes relate to different combinations of smoke response threshold and response time. For the heat detector, the mode relates to the fixed temperature setting and the sensitivity to rate-of-rise of temperature. For the multi-sensor, the mode relates to the levels of smoke and heat sensitivity and to the way in which the responses of the two sensors are combined.
The response characteristics of the detectors have been carefully set so that detectors will comply with the requirements of the relevant part of the fire codes in all response modes. The mathematic algorithms embedded in the detectors are used to carry out changes in characteristics between modes. Since the response characteristics are defined within the detectors, Firebus takes responsibility for compliance with standards in different response modes.
The internal signal processing of the detectors is designed so that the analog value reported is always close to 25 for a normal condition. The alarm threshold is 55, irrespective of the response mode selected.
Similarly, the alarm flag in the protocol is always set when the analog value exceeds 55, irrespective of mode. This simplifies the switching between response modes since the alarm threshold in the control panel can remain fixed at 55 and the alarm flag is valid in all modes.
The response mode, which is selected through the protocol, is stored in non-volatile memory and will therefore be retained when the detector is powered down. All FB-AP Series detectors are factory set to mode 3 before shipping.
Response modes are defined more fully in the individual detector descriptions.
User bytes and other stored data
All FB-AP Series devices contain non-volatile memory, in the form of Electrically Erasable Programmable Read Only Memory (EEPROM), which is included primarily to store data needed for the correct operation of the device. However, four bytes of this EEPROM are available to the user and can be accessed by the control panel through the protocol. This block of non-volatile memory can be used, for example, to store the installation date, the site code or date of last service. The only restriction on use is that the maximum number of write cycles should not exceed 20,000 over the life of the device.
Conventional alarm facility
FB-AP Series devices are polled at regular intervals to maintain communication with the control panel and therefore enable correct monitoring of the protected premises. However, if the polling mechanism fails, for example because of a processor failure in the panel, the internal operation of the FB-AP Series device will be unaffected as long as a DC supply is maintained. After 108± 4 seconds without protocol, the device will automatically switch to its conventional alarm mode. In this mode it will operate as if it were a conventional detector (or manual call point) and will impose an alarm signal on the loop if an alarm condition is detected by the internal processing.
The alarm signal takes the form of periodic current pulses, which can be detected by simple hardware in the control panel.
Flashing LED
All FB-AP Series detectors have two integral LED indicators, which can be illuminated at any time by the control panel to indicate devices in alarm. When activated, the LEDs will draw an extra 3mA from the loop. In addition to this mode of operation it is possible to enable a flashing LED mode by writing to one of the memory locations. In this mode the LEDs will flash each time the device is polled. The device does not draw extra current in this mode since the LED current is part of the normal current pulse reply from the device.
This facility is available on all FB-AP Series detectors and the manual call point. FB-AP Series detectors and call points are factory set to non-flashing mode.
Remote test feature
This feature, available on all FB-AP Series detectors and the call point, is enabled from the Fire Alarm Control Panel (FACP) by changing the state of a forward command bit. On receipt of the command the detector is forced by electrical means into an alarm condition. After a delay of approximately 10 seconds due to signal processing, an analogue value of between 54 and 120 – nominally 85 – is returned, provided that the detector is functioning correctly. This value is sustained until the forward command bit is changed back to its original state, after which a period of 40 seconds is required for the detector to return to its normal analog value.
The manual call point is different in that the receipt of the command bit will cause the call point to generate the interrupt sequence, followed by a sustained value of 64. The call point resets when the forward command bit is changed back to its original state.
Rejection of transient signals
All FB-AP Series detector algorithms are designed to give low sensitivity to very rapid changes in the sensor output, since these are unlikely to be caused by real fire conditions.
This is achieved by digital low-pass filtering of the sensor values which optimises the rejection of false alarm sources while maintaining the response to fire. The filter parameters depend on the mode selected and for some modes the filtering is minimal. The filtering has no significant effect on the response to fires but does affect the way in which detectors respond to transients and to step changes of smoke or heat. This is seen in the “minimum time to alarm” given in individual detector specifications. These times represent the time taken by the detector to reach the alarm condition when responding to a large step change in input.