Fire alarm system
First Claim
1. In a fire alarm system comprising a receiver in combination with fire detecting terminal means connected thereto through a common signal transmission line comprising two wires,said fire detecting terminal means including:
- a sensor for sensing a fire-indicative parameter such as a smoke density to be measured and producing an analog signal representative thereof;
a level-signal output section for transmitting a level signal to the receiver, said level-signal output section including level-shifting means connected between the wires of the transmission line so as to cause the level-shifting of the level signal when the sensed parameter has a level higher than a predetermined threshold level;
an analog-digital converter converting the analog signal from the sensor into a corresponding digital signal;
a binary information transmission section for transmitting the digital signal in the form of a superimposed signal upon the level signal,the level signal and the digital signal being transmitted in a time-division multiplexing manner over the transmission line; and
said receiver including;
first means responsive to the level-shifting of the level signal for determining fire presence;
second means responsive to the digital signal transmitted from the analog-digital converter for determining fire presence based thereon independently of the first means;
the improvement comprising;
said fire detecting terminal means including;
comparator means connected to the level-shifting means, said comparator means has the threshold level with which the value of the analog signal from the sensor is compared so that it actuates the level-shifting means to make the shifting of the level signal when the analog signal has a level higher than the threshold level, and said threshold level being selected independently of a criterion utilized in determining fire presence by the second means receiving the superimposed signal including the information of the sensed parameter.
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Accused Products
Abstract
An improved fire alarm system utilizes receiver and fire detecting terminals connected thereto through a signal transmission line comprising two wires. The fire detecting terminal operates on two mode, one being a contact-closure mode of transmitting to the receiver a level signal whether or not a significantly higher fire-indicative quantity is detected, and the other being intelligent mode of transmitting a digital signal indicative of the sensed quantity in the form of a superimposed signal upon the level signal in answer to the instruction from the receiver for precise and convenient analysis thereof in determining fire presence on the side of the receiver. The fire detecting terminal includes a comparator having its own threshold with which the value of the sensed analog quantity is compared for providing the level-shifted signal when the sensed analog quantity has a level higher than the threshold, notifying fire presence independently of the intelligent mode. The threshold level can be selected independently of a criterion utilized in determining first presence based upon the digital signal on the receiver, so that the above two modes can have the same sensitivity against possible fires. Accordingly, the contact-closure mode can well stand for a back-up fire detection without reduction in sensitivity.
99 Citations
11 Claims
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1. In a fire alarm system comprising a receiver in combination with fire detecting terminal means connected thereto through a common signal transmission line comprising two wires,
said fire detecting terminal means including: -
a sensor for sensing a fire-indicative parameter such as a smoke density to be measured and producing an analog signal representative thereof; a level-signal output section for transmitting a level signal to the receiver, said level-signal output section including level-shifting means connected between the wires of the transmission line so as to cause the level-shifting of the level signal when the sensed parameter has a level higher than a predetermined threshold level; an analog-digital converter converting the analog signal from the sensor into a corresponding digital signal; a binary information transmission section for transmitting the digital signal in the form of a superimposed signal upon the level signal, the level signal and the digital signal being transmitted in a time-division multiplexing manner over the transmission line; and said receiver including; first means responsive to the level-shifting of the level signal for determining fire presence; second means responsive to the digital signal transmitted from the analog-digital converter for determining fire presence based thereon independently of the first means; the improvement comprising; said fire detecting terminal means including;
comparator means connected to the level-shifting means, said comparator means has the threshold level with which the value of the analog signal from the sensor is compared so that it actuates the level-shifting means to make the shifting of the level signal when the analog signal has a level higher than the threshold level, and said threshold level being selected independently of a criterion utilized in determining fire presence by the second means receiving the superimposed signal including the information of the sensed parameter. - View Dependent Claims (2, 3)
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4. In a fire alarm system comprising a receiver in combination with fire detecting terminal means connected thereto through a common signal transmission line comprising two wires,
said fire detecting terminal means including: -
a sensor for sensing a fire-indicative parameter such as a smoke density to be measured and producing an analog signal representative thereof; a level-signal output section for transmitting a level signal to the receiver, said level-signal output section including level-shifting means connected between the wires of the transmission line so as to cause the shifting of the level signal when the sensed parameter has a level higher than a predetermined threshold level; an analog-digital converter converting the analog signal from the sensor into a corresponding digital signal; an binary information transmission section for transmitting the digital signal in the form of a superimposed signal upon the level signal, the level signal and the digital signal being transmitted in a time-division multiplexing manner over the transmission line; and said receiver including; first means responsive to the shifting of the level signal for determining fire presence; second means responsive to the digital signal transmitted from the analog-digital converter for determining fire presence based thereon independently of the first means; the improvement comprising; said fire detecting terminal means including;
comparator means connected to the level-shifting means, said comparator means has the threshold level with which the value of the analog signal from the sensor is compared so that it actuates the level-shifting means to make the shifting of the level signal when the analog signal has a level higher than the threshold level, and said threshold level being selected independently of a criterion utilized in determining fire presence by the second means receiving the superimposed signal including the information of the sensed parameter; andsaid level-signal output section including supervising means for checking the operation of the digital signal transmission and for actuating the level-shifting means only when the supervising means sees that the digital signal transmission is is out of operation. - View Dependent Claims (5, 6, 7)
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8. In a fire alarm system comprising a receiver in combination with fire detecting terminal means connected thereto through a common signal transmission line comprising two wires,
said fire detecting terminal means including: -
a sensor for sensing a fire-indicative parameter such as a smoke density to be measured and producing an analog signal representative thereof; a level-signal output section for transmitting a level signal to the receiver, said level-signal output section including switching means connected between the wires of the transmission line so as to be closed when the sensed parameter has a level higher than a predetermined reference level; an analog-digital converter converting the analog signal into a corresponding digital signal; a binary information transmission section for transmitting the digital signal in the form of a superimposed signal upon the level signal, the level signal and the digital signal being transmitted in a time-division multiplexing manner over the common signal transmission line; and said receiver including; first means responsive to the contact-closure signal from the switching means for determining fire presence; second means responsive to the digital signal transmitted from the analog-digital converter for determining fire presence based thereon independently of the first means; the improvement comprising; said fire detecting terminal means including;
comparator means connected to the level-shifting means, said comparator means has the threshold level with which the value of the analog signal from the sensor is compared so that it actuates the level-shifting means to make the shifting of the level signal when the analog signal has a level higher than the threshold level, and said threshold level being selected independently of a criterion utilized in determining fire presence by the second means receiving the superimposed signal including the information of the sensed parameter; andsaid level-signal output section including supervising means for checking the operation of the digital signal transmission and for actuating the switching means only when the supervising means sees that the digital signal transmission is out of operation. - View Dependent Claims (9, 10, 11)
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Specification