IL104298A

IL104298A - Method and apparatus for detecting a fire condition

Info

Publication number: IL104298A
Application number: IL104298A
Authority: IL
Original assignee: Spectronix Ltd
Priority date: 1992-09-08
Filing date: 1993-01-01
Publication date: 1998-02-08
Also published as: IL103094A0; IL104298A0

Description

METHOD AND APPARATUS ICR DETECTING A FIRE CJGNDITICN METHD AND APPARATUS FOR DETECTING A FIRE CONDITION The present application is for a patent-of-addition to Patent Specification No.1 03094 filed September 8 , 1 992 , and relates to improvements in or modifications to the method and apparatus .for. detecting a fire condition described therein.

Patent Specification 1 03094 describes a method of detecting a fire condition in a monitored region including the following operations: (a) concurrently monitoring the region by first and second sensors sensitive to the radiation of first and second frequency bands to produce first and second measurements of the radiation variations emitted from the monitored region; (b) concurrently monitoring the region by a third sensor sensitive to the radiation of a third frequency band to produce a third measurement of the radiation variations emitted from the monitored region; (c) determining the correlation between the first and third measurements to produce a first correlation value; (d) determining the correlation between the second and third measurements to produce a second correlation value; and (e) utilizing the first and second correlation values in determining the presence or absence of a fire condition in the monitored region.

In the preferred embodiment described in that patent application, operation (e) includes: comparing the ratio of the first and second correlation values to produce a correlation ratio; comparing the correlation ratio with a predetermined threshold; and utilizing the results of the latter comparison in determining the presence or absence of a fire condition in the monitored area.

According to further features described in that application, operation (ej- -further includes: comparing the first correlation value with a predetermined threshold; comparing the second correlation value with a predetermined threshold; and utilizing also the results of the latter two comparisons, together with the result of comparing the correlation ratio with a predetermined threshold, in determining the presence or absence of a fire condition in the monitored area.

It has been found that the false alarm rate of the method can be decreased, without significantly decreasing the sensitivity, when the auto-correlation of at least one of the first, second and third measurements with respect to itself is determined without normalization to produce an auto- correlation value, and the auto-correlation value is also utilized in determining the presence or absence of a fire condition in accordance with operation (e).

According to the preferred embodiment described herein, the auto-correlation of each of the first, second and third measurements with respect to itself is determined without normalization to produce first, second and third auto-correlation values, which values are utilized in determining the presence or absence of a fire condition in operation (e) .

According to the further features in the preferred embodiment described herein, operation (e) includes comparing the ratio of the first and second auto-correlation values to produce a first auto-correlation ratio; comparing the ratio of the second and third auto-correlation values to produce a second auto-correlation ratio; comparing each of the auto-correlation ratios with a predetermined threshold; and utilizing the results of the latter comparison in determining the presence or absence of a fire condition in t-he monitored area.

Preferably, the ratio of the second and third auto-correlation values are compared to both a high threshold and a low threshold.

The invention of the present application also provides apparatus for detecting a fire condition in accordance with the above method.

With reference to the accompanying drawings, Fig. 1 is a block diagram illustrating one form of apparatus for detecting a fire condition in accordance with the embodiment of the invention in the present application; and Fig. 2 is a block diagram illustrating the auto-correlation circuit for effecting auto-correlation of the output of one of the sensors, it being appreciated that a similar circuit is used for each of the other two sensors .

The apparatus illustrated in Fig. 1 of the drawings is very similar to that illustrated in Fig. 1 of Patent Specification 103094. To facilitate understanding, the same reference numerals have been used for corresponding parts, and the new parts are identified by reference numerals starting with "1,00".

Thus, as shown in Fig. 1 , the output of sensor IR^ , after passing through its bandpass filter 2 and amplifier 12, is auto-correlated without normalization in auto-correlation circuit 100. In a similar manner, the outputs of the two the sensors IR2 and IR^ are auto-correlated in circuits 102 and 104, respectively, to produce second and third auto-correlation values.

The ratio of the first auto-correlation value from circuit 100, and of the second auto-correlation value from circuit 102, is determined in a ratio circuit 106, and is compared to a predetermined threshold value 108. Similarly, the ratio of the second and third auto-correlation values, from circuits 102 and 104, respectively, is determined by ratio circuit 110, and its output is compared to a predetermined high threshold value in circuit 112, and also to a predetermined low threshold value in circuit 114.

The outputs of threshold circuits 108 and 114 are fed to AND-gate 36, with the outputs of the other signals as described in Patent Specification 103094. The output of that gate is fed to the CPU for use in determining the presence or absence of a fire condition in the monitored area in the same manner as described in Patent Specification 103094.

Fig. 2 illustrates the auto-correlation circuit 100 for sensor IR^ . The auto-correlation value is determined by moving the signal outputted from sensor IR^ over itself, without normalization, and summing the products of all the points of the two signals. It will be appreciated that auto-correlation circuits 102 and 104 for the two other sensors IR2' IR3 are constructed and operate in the same manner.

Claims

WHAT IS CLAIMED IS:

1. The method of detecting a fire condition in a monitored region according to any one of Claims 1-7 of Patent Specification 103094, wherein the auto-correlation of at least one of said first, second and third measurements with respect to itself is*- determined without normalization to produce an auto-correlation value, and said auto-correlation value is also utilized in determining the presence or absence of a fire condition in accordance with operation ( e) .

2. The method according to preceding Claim 1 , wherein the auto-correlation of each of said first, second and third measurements with respect to itself is determined without normalization to produce first, second and third auto-correlation values, which values are utilized in determining the presence or absence of a fire condition in operation (e) .

3. The method according to preceding Claim 2, wherein said operation (e) further includes: comparing the ratio of said first and second autocorrelation values to produce a first auto-correlation ratio; comparing the ratio of said second and third autocorrelation values to produce a second auto-correlation ratio; comparing each of said auto-correlation ratios with a predetermined threshold; and utilizing the results of the latter comparison for determining the presence or absence of a fire condition in the monitored area.

4. The method according to preceding Claim 3, wherein said ratio of the second and third auto-correlation values are compared to both a high threshold and a low threshold .

5. The apparatus according to any one of Claims 8-15 of Patent Specification 103094, further including auto-correlating means for auto-correlating at least one of said first, second and third measurements with respect to itself without normalization to produce an auto-correlation value, and said auto-correlation value also being utilized in determining the presence or absence of a fire condition in accordance with operation (e).

6. The apparatus according to preceding Claim 5, wherein said auto-correlating means auto-correlates each of said first, second and third measurements with respect to itself without normalization to produce first, second and third auto-correlation values, which values are utilized in determining the presence or absence of a fire condition in operation (e) .

7. The apparatus according to preceding Claim 6, wherein said operation (e) further includes: means for comparing the ratio of said first and second auto-correlation values to produce a first auto-correlation ratio; means for comparing the ratio of said second and third auto-correlation values to produce a second auto-correlation ratio; means for comparing each of said auto-correlation ratios with a predetermined threshold; and means for utilizing the results of. the latter comparison in determining the presence or absence of a fire condition in the monitored area.

8. The apparatus according to preceding Claim 7, wherein said means for comparing the ratio of the second and third auto-correlation values with a predetermined threshold compares said ratio with both a high threshold and a low threshold . vocate, atent ttorney Beit Amot Mishpat 8 Shaul Hamelech Blvd. 64733 Tel Aviv