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Analog Addressable Fire Alarm System


Main Panel Block Diagram

  • The fire alarm system continuously monitors the detectors.
  • Detectors are divided into zones. (Using Software configuration file in the base board).
  • Detectors are connected to the system through loops. (physically)
  • The Loops are connected to the loop boards. Each Board can have 3 loops. Each loop can have 254 detectors. (Depending on the address size)
  • Each Loop has an address and each device has an address given using DIP switches. (These are stored in the Software config file)
  • Devices send digital data packets containing the Addresses and the Data.
  • The digital data packets are sent digitally using analog signals through the twisted pair cables. (Analog Addressable Signals)


ID address on DIP switches

All addressable loop units must be given an address between
1-254 to be operational. The loop units located on the same
physical loop must all have unique addresses. The address is
set by a 8 pole DIP switch located on each addressable
unit.
The DIP switch values follow the binary system.

  • The value of the address is set according to the switches set
    to ON position. For example:
  • The switches numbered 1,2,3,4 and 6 are set to ON position.
    The values for these switches are 1+2+4+8+32=47.

Procedure for Replacing fire detectors
  1. Disconnect the faulty detector and remove it from the base plate.
  2. Check the ID settings on the address switch for the faulty detector.
  3. Set the corresponding ID on the address switch for the new detector.
  4. Seal the address switch on the detectors with the attached label after the address has been set.
  5. Connect and mount the new detector.
  6. Check and reset any fault codes generated by the replaced faulty detector.
  7. Perform a function test of the detector.
Signaling
  • The digital data is transferred through the twisted pair cables as an analog signal.
  • The Frequency Shift Keying principle is used to add Digital data to the Analog signal.

Eg:
  • 2200Hz represents 0
  • 1200Hz represents 1

Data Packet Structure
  • Preamble: Introduction of the device(sender), let the receiver know data transfer is about to start.
  • Start byte: This contains the sender’s address and specifies the communication packet is starting.
  • Address: Specifies the destination address.
  • Command: Numerical Value for the command to be executed
  • Number of data bytes: Specifies the number of communication data bytes to follow.
  • Data: Data associated with the command.
 Courtesy: Consilium

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