| 摘要 |
A 2-wire fire alarm system has at least one fire detector and at least one manual call point connecting the wires in parallel and the voltage on one of the wires is altered by different amounts by a circuit fault, operation of a fire detector and operation of a call point. Removal of a detector causes alteration of the voltage by yet a different amount. A detector circuit generates different alarm signals according to the different changes in voltage. <IMAGE> |
