Communications: electrical – Continuously variable indicating – With meter reading
Patent
1993-10-04
1995-10-24
Horabik, Michael
Communications: electrical
Continuously variable indicating
With meter reading
340825160, 370 15, 370 161, 370 8512, H04L 1116
Patent
active
054613701
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a fire alarm system in which fire receivers, transmitters (monitoring transmitters to which fire detectors are connected, control transmitters to which devices to be controlled such as fire doors are connected, monitoring/control transmitters), and a plurality of terminal devices such as analog type fire detectors and addressable fire detectors are connected by means of loop-signal lines.
BACKGROUND ART
A fire alarm system using loop-signal lines has been well known. In this type of fire alarm system, fire receivers are connected with a plurality of terminal devices through loop-type signal lines. Thus, even if an abnormality such as a disconnection or a short-circuit occurs halfway along the signal line, this system is capable of controlling devices such as fire doors at the time of fire monitoring or during a fire because each terminal device is connected to a fire receiver through a signal line beyond a position where the abnormality occurs.
In such a conventional fire alarm system, signals can be transmitted between the fire receiver and the terminal devices by making polling signals flow to the loop-signal line unidirectionally at a normal operating time. When any terminal device does not respond, the conventional system determines that terminal devices located after the non-responding terminal device cannot be polled due to a disconnection or a short-circuit, and calls the non-responding terminal device by supplying a polling signal to the loop-signal line in the opposite direction. Consequently, an abnormality generated in the loop-signal line and the generating position are detected.
However, this conventional system takes a long time to detect an abnormality, because, when any terminal device does not respond to a unidirectional polling, the device must be polled in the opposite direction to detect an abnormality in the loop-signal line and the position where the abnormality occurs.
An object of the present invention is to provide a fire alarm system which is capable of detecting an abnormality immediately when an abnormality such as a disconnection occurs in the loop-signal line.
DISCLOSURE OF INVENTION
According to the present invention, there is provided a fire alarm system having a fire receiver to which a plurality of terminal devices are connected through loop-signal lines, the fire alarm system comprising; a first loop-signal line for connecting the fire receiver and a plurality of the terminal devices in the form of a loop and transmitting signals to the loop in a specified direction; and a second loop-signal line for connecting the fire receiver and a plurality of the terminal devices in the form of a loop and transmitting signals in an opposite direction relative to the first loop-signal line. Each of the fire receiver and the terminal devices include; a signal transmitting means for transmitting signals to the first and second loop-signal lines at the same time; a first signal receiving means for receiving signals input from the first loop-signal line; a second signal receiving means for receiving signals input from the second loop-signal line; and a reception determining means for determining whether a difference in signal receiving time between the receiving of signals by the first signal receiving means and the receiving of signals by the second signal receiving means is within a specified interval of time.
In the fire alarm system configured as described above, the fire receiver or terminal device transmits the same signals from its own signal transmitting means to the first and second loop-signal lines in opposite directions at the same time, and the other fire receiver or terminal devices receive a signal transmitted through the first and second loop-signal lines by means of the first and second signal receiving means in order to detect a difference in signal receiving time, thereby detecting an abnormality of transmission, for example, whether there is a disconnection or a short-circuit in the first loop-signal line or the s
REFERENCES:
patent: 4446551 (1984-05-01), Seo
patent: 4542496 (1985-09-01), Takeyama et al.
patent: 4704714 (1987-11-01), Tomizawa et al.
patent: 4973953 (1990-11-01), Shimokawa et al.
Igarashi Akira
Kobayashi Takashi
Tsumuji Akio
Horabik Michael
Nohmi Bosai Ltd.
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