Abstract: A power supply control device is provided in a fire alarm system having terminals such as fire detectors and/or repeaters with comparators to detect abnormalities such as fire or an operating status of controlled apparatus, and is equipped with a reference voltage supply a source to supply reference voltage to the comparators, and a power supply control to allow the reference voltage to be supplied to the comparators only during the detecting time.

Abstract: A line interruption supervisory device for a fire alarm system is capable of reliably carrying out the line supervision even if the line length is long and/or there is a large number of connected fire detectors. To this end, a terminating capacitor is connected across the terminal of a pair of power/signal lines to which fire detectors are connected. A memory first stores the voltage available on the power/signal lines when the line supervision is requested, immediately followed by the interruption by a cut-off circuit of the power supply to a pair of power/signal lines, and further followed by a comparison of the voltage available on the power/signal lines before the power supply interruption with a line voltage available after a lapse of a predetermined time from the power supply interruption by a line interruption discriminating circuit to determine, according to any difference between these voltages, whether there is an open power/signal line.

Abstract: A fire alarm system includes a receiver unit such as a fire control panel or a repeater having zone lines connected thereto, with various types of fire detectors being connected to the zone line. Supervising power is normally supplied to the zone lines. When the receiver unit receives a fire signal via a zone line from a fire detector, the receiver unit decides from what type of detector the fire signal was transmitted. Types of fire detectors include, for example, a type having as switching means only a mechanical contact for causing said zone line to be in a short-circuited condition, a type having as switching means a switching circuit with a self-holding function, or a type having a response lamp.

Abstract: A fire alarm system includes a receiver unit connected to a plurality of terminal unit groupings, each of the terminal unit groupings made up of a plurality of terminal units. The fire alarm system operates in one of a system polling mode, a point polling mode and a selecting mode. In the system polling mode, the receiver units polls all of the terminal units and provides a grouping response period in which each of the terminal unit groupings is permitted to respond to the receiver unit polling. If one of the terminal units of a particular grouping undergoes a status change, such a terminal unit transmits to the receiver unit a group response signal during the corresponding group response period. Then, the system enters the point polling mode, in which the terminal units of the terminal unit grouping corresponding to the group response period in which a group response signal was received are polled.