Transmission line-monitoring apparatus for use in a fire alarm system
First Claim
1. A transmission line-monitoring apparatus for use in a fire alarm system which includes a fire control panel, a pair of main transmission lines extending from said fire control panel and doubling as power supply lines and signal lines, at least one pair of branched transmission lines branched off from said main transmission lines, said transmission line-monitoring apparatus connected between said pair of branched transmission lines, a pair of branched transmission lines on the output side of said monitoring apparatus, and a plurality of terminal devices connected in parallel to each other between said pair of branched output transmission lines, said monitoring apparatus comprising:
- a transistor inserted in at least one of said pair of branched transmission lines, the emitter and the collector of said transistor being connected in series between said at least one of said pair of branched transmission lines and a corresponding one of said pair of branched output transmission lines;
a constant current circuit connected to the base of said transistor so as to supply a constant base current;
a short-circuit detection circuit connected between the emitter and the collector of said transistor so as to generate a short-circuit detection signal representing that a short circuit has occurred in said pair of branched output transmission lines when the emitter-collector voltage of said transistor exceeds a predetermined value; and
a line-disconnecting control circuit connected to said short-circuit detection circuit so as to cause said transistor to be switched off via said constant current circuit when said line-disconnecting control circuit is operated by said short-circuit detection signal, thereby disconnecting said pair of branched output transmission lines.
1 Assignment
0 Petitions
Accused Products
Abstract
A transmission line-monitoring apparatus which is able to detect the occurrence of a short circuit even when a line has a large resistance and also to speedily disconnect the short-circuited transmission line upon detection of a short circuit. When a short circuit occurs between branched transmission lines on the output side of the apparatus, a short-circuit detection circuit contained in the transmission-line monitoring apparatus detects this short circuit so as to send a short-circuit detection signal to a line-disconnecting control circuit. Then, the control circuit is operated so as to cause a constant current circuit to interrupt the supply of a base current to a transistor, thereby disconnecting a short-circuited output branched transmission line from a corresponding input branched transmission line.
32 Citations
24 Claims
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1. A transmission line-monitoring apparatus for use in a fire alarm system which includes a fire control panel, a pair of main transmission lines extending from said fire control panel and doubling as power supply lines and signal lines, at least one pair of branched transmission lines branched off from said main transmission lines, said transmission line-monitoring apparatus connected between said pair of branched transmission lines, a pair of branched transmission lines on the output side of said monitoring apparatus, and a plurality of terminal devices connected in parallel to each other between said pair of branched output transmission lines, said monitoring apparatus comprising:
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a transistor inserted in at least one of said pair of branched transmission lines, the emitter and the collector of said transistor being connected in series between said at least one of said pair of branched transmission lines and a corresponding one of said pair of branched output transmission lines; a constant current circuit connected to the base of said transistor so as to supply a constant base current; a short-circuit detection circuit connected between the emitter and the collector of said transistor so as to generate a short-circuit detection signal representing that a short circuit has occurred in said pair of branched output transmission lines when the emitter-collector voltage of said transistor exceeds a predetermined value; and a line-disconnecting control circuit connected to said short-circuit detection circuit so as to cause said transistor to be switched off via said constant current circuit when said line-disconnecting control circuit is operated by said short-circuit detection signal, thereby disconnecting said pair of branched output transmission lines. - View Dependent Claims (4, 5, 6, 7, 8, 9, 18, 19, 20, 21, 22, 23, 24)
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2. A transmission line-monitoring apparatus for use in a fire alarm system which includes a fire control panel, a pair of transmission lines extending from said fire control panel and doubling as power supply lines and signal lines, and at least one unit inserted in series in said transmission lines, said unit having a transmission line-monitoring apparatus and a plurality of terminal devices connected in parallel to each other on an output side of said monitoring apparatus, said monitoring apparatus comprising:
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a transistor inserted in at least one of said transmission lines, the emitter and the collector of said transistor being connected in series between said at least one of said transmission lines and one of a pair of output transmission lines; a constant current circuit connected to the base of said transistor so as to supply a constant base current; a short-circuit detection circuit connected between the emitter and the collector of said transistor so as to generate a short-circuit detection signal representing that a short circuit has occurred in said pair of output transmission lines of said monitoring apparatus when the emitter-collector voltage of said transistor exceeds a predetermined value; and a line-disconnecting control circuit connected to said short-circuit detection circuit so as to cause said transistor to be switched off via said constant current circuit when said line-disconnecting control circuit is operated by said short-circuit detection signal, thereby disconnecting said pair of output transmission lines. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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3. A transmission line-monitoring apparatus for use in a fire alarm system which includes a fire control panel, a pair of main transmission lines extending from said fire control panel and doubling as power supply lines and signal lines, and at least one transmitter connected to said transmission lines, at least one pair of branched transmission lines branched off from said main transmission lines, the transmission line-monitoring apparatus connected between said pair of branched transmission lines, a pair of branched transmission lines on the output side of said monitoring apparatus, and a plurality of terminal devices connected in parallel to each other between said pair of branched output transmission lines, said monitoring apparatus comprising:
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a transistor inserted in at least one of said pair of branched transmission lines, the emitter and the collector of said transistor being connected in series between said at least one of said pair of branched transmission lines and a corresponding one of said pair of branched output transmission lines; a constant current circuit connected to the base of said transistor so as to supply a constant base current; a short-circuit detection circuit connected between the emitter and the collector of said transistor so as to generate a short-circuit detection signal representing that a short circuit has occurred in said pair of branched output transmission lines when the emitter-collector voltage of said transistor exceeds a predetermined value; and a line-disconnecting control circuit connected to said short-circuit detection circuit so as to cause said transistor to be switched off via said constant current circuit when said line-disconnecting control circuit is operated by said short-circuit detection signal, thereby disconnecting said pair of output transmission lines.
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Specification