Fire system with current response calibration

1. A fire system for a building, the fire system comprising:

a fire panel for monitoring the building and activating an alarm; and

a plurality of remote units electrically connected to the fire panel in a circuit having a loop configuration, at least some of the plurality of remote units comprising an indicating device for modulating a current in the circuit;

wherein the plurality of remote units are in communication with the fire panel in a master-slave relationship;

wherein the fire panel comprises a calibration module for polling each indicating device to obtain a current response value and for storing said current response values, the current response value of an indicating device being based on the amplitude of the current when modulated by that indicating device; and

the calibration module is configured to adjust a current threshold value based on an input from a user and the current response values, the current threshold value being the current response value at which the fire panel triggers an alarm, and the adjusted current threshold value being determined to be equal to the lowest current response value plus or minus a predetermined error threshold.

2. The fire system as claimed in claim 1 , wherein the fire panel comprises a memory device for storing the current response values.

3. The fire system as claimed in claim 2 , wherein the fire panel comprises a loop card, and the loop card comprises the memory device.

4. The fire system as claimed in claim 1 , wherein the fire panel is configured to trigger a maintenance mode of operation for measuring the current response value of each indicating device and/or a calibration mode of operation for measuring and storing the current response value of each indicating device in the fire system.

5. The fire system as claimed in claim 4 , wherein the maintenance mode is automatically triggered in response to changes to the fire system and/or in response to passage of a time period.

6. The fire system as claimed in claim 4 , wherein the maintenance mode and/or the calibration mode is triggered in response to an input from an operator.

7. The fire system as claimed in claim 4 , wherein the maintenance mode is triggered as part of a maintenance routine.

8. The fire system as claimed in claim 4 , wherein the calibration module is configured to produce a maintenance report in the maintenance mode.

9. The fire system as claimed in claim 1 , wherein the calibration module is configured to poll the indicating devices by transmitting a polling signal through the loop.

10. The fire system as claimed in claim 9 , wherein the polling signal is a modulation of a voltage in the loop, and/or wherein the indicating devices are configured to respond to the polling signal by modulating the current in the loop.

11. The fire system as claimed in claim 1 , wherein the calibration module is configured to indicate a warning if a current response value is within a predetermined margin from a current threshold value, the current threshold value being the current response value at which the fire panel triggers an alarm.

12. The fire system as claimed in claim 1 comprising a plurality of isolators for electrically isolating at least some of the remote units from the rest of the loop during calibration.

13. The fire system as claimed in claim 1 , wherein the fire panel is configured to determine which indicating device a detected modulation in current has originated from based on the current response values.

14. A method of operating a fire system as claimed in claim 1 , wherein the method comprises polling each indicating device for its current response value, and then reporting said current response values to a user and/or storing said current response values.

15. The fire system as claimed in claim 4 , wherein the calibration module is configured to trigger the maintenance mode and/or calibration mode.