Two-wire fire sensing and receiving system

DETAILED DESCRIPTION An object of the present, invention therefore, is to provide a two-wire fire sensing and receiving system which works on a feeding current of a relatively small level used for charging a capacitor coupled to a sensing device that will be operated by the discharging current of said capacitor, and a sensing current of a relatively large current level which actuates a switching element for energizing a fire alarming device, wherein an overcurrent at the time of closing the power supply that tends to increase with the increased number of capacitors as a result of the employment of an increased number of sensing devices, is restrained to be sufficiently smaller than said sensing current of high level, and the electric current fed to the capacitors that decreases with the increased number of capacitors is maintained to be greater than a value necessary for reliably charging said capacitors within a limited period of charging time, so that the upper limit and the lower limit of the currents are controlled.
Another object of the present invention is to provide a two-wire fire sensing and receiving system in which the upper limit of the feeding current is effectively determined by a resistor having a resistance 1/10 to 1/20 that of the high resistance that was previously used to limit the feeding current, and the drop of the power supply voltage to the detector circuit for energizing the sensing devices is substantially avoided.
A further object of the present invention is to provide a two-wire fire sensing and receiving system having increased number of fire sensing devices composed of said detector circuit, that are connected in parallel with the two-wire circuit for feeding electric current and receiving signals, said two-wire circuit being drawn from a d-c power supply, by minimizing the voltage drop that would develop over the circuit from the d-c power supply to the detector circuits which include a capacitor to actuate the sinsing devices, and permitting the charging current to the capacitor to be increased as compared to prior art circuits