| 摘要 |
A signalling system is provided including a central controller, and one or more remote devices electrically connected to the central controller. The central controller supplies an operating current OL to each remote device, and is adapted to transmit signals to each device. Each remote device has a first state Vlo in which it draws the operating current from the central controller, and a second state Vhi in which it draws a current lower than the operating current from the central controller. Each remote device is adapted to transmit a response signal in the form of one or more current pulses when the, or each device is in its second state. When in its second state Vhi, each remote device may draw power from an auxiliary power source such as a capacitor or battery arrangement. The central controller may include a voltage modulator adapted to modulate the voltage supplied to each remote device in order to alter the state of the, or each remote device. The signalling system is particularly suited for use in a fire alarm system, intruder alarm system, plant monitoring system and the like.
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