IL105351A

IL105351A - Method and apparatus for detecting a fire condition

Info

Publication number: IL105351A
Application number: IL105351A
Authority: IL
Original assignee: Spectronix Ltd
Priority date: 1992-09-08
Filing date: 1993-04-09
Publication date: 1998-02-08
Also published as: EP0926647A3; EP0926647A2; IL105351A0; EP0926647B1

Description

METHOD AND APPARATUS FOR DETECTING A FIRE CONDITION ' METHOD AND APPARATUS FOR DETECTING A FIRE CONDITION The present application is for a patent-of-addition to Patent Application No.103094 filed September 8, 1992, and also to Patent-of-Addition Application 104298 filed January 1, 1993, and relates to improvements in or modifications to the method and apparatus for detecting a fire condition described therein.

Patent Application 103094 describes a method of detecting a fire condition in a monitored region including: (a) concurrently monitoring the region by a first sensor sensitive to radiation within a first bandwidth which includes the C02 emission band, by a second sensor sensitive to radiation within a second bandwidth which includes wavelengths mainly lower than the CO2 emission band, and by a third sensor sensitive to the radiation within a third bandwidth which includes wavelengths mainly higher than the CO2 emission band, and producing first, second and third measurements of radiation variations emitted from the monitored region; and (b) utilizing the measurements in determining the presence or absence of the fire condition in the monitored region.

According to further features in the preferred embodiment described in that patent application, the measurements are utilized in determining the presence or absence of a fire condition in the monitored region by determining the correlation between each pf at-least two of said three measurements, with one of said three measurements, to produce at least two correlation values; comparing the ratio of the two 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 region.

In the preferred embodiment of the invention described in that patent application, a first correlation is determined between the first and third measurements to produce a first correlation value, and a second correlation is determined between the second and third measurements to produce a second corrrelation value, which two correlation values are compared to producer he -correlation ratio :which is compared with the predetermined threshold and utilized in determining the presence or absence of a fire condition in the monitored area.

According to the improvement in the present application, the method is as set forth according to Claim 2 of Patent Application 103094, wherein the correlation is determined between each of the measurements, with respect to itself, without normalization to produce first, second and third auto-correlation values, "respectively;^ and the first auto-correlation value is compared with the third autocorrelation value to produce a correlation ratio which is compared to a predetermined threshold and utilized in determining the presence or absence of a fire condition in the monitored"region . - - - - -■·-— · According to further features in the described preferred embodiments, the second auto-correlation value is compared with the third auto-correlation value to produce a second correlation ratio, which is compared to a predetermined threshold and utilized in determining the presence or absence of a fire condition in the monitored region; also, the first auto-correlation value is compared to a predetermined threshold and is also utilized, in determining the presence or absence of a fire condition in the monitored region.

According to still further features in preferred embodiments of the invention described in the present application, a correlation is determined between the first measurement and one of the other two measurements to produce a cross-correlation value; and the cross-correlation value is normalized, compared with a predetermined threshold, and utilized in determining the presence or absence of a fire condition in the monitored region.

In one embodiment described herein, the cross-correlation value is determined between the first and second measurements; in such an embodiment, the cross-correlation value is normalized by multiplying . it by itself and dividing the product by the product of the first and second autocorrelation values.

According to a second embodiment described herein, the cross-correlation value is determined between the first and third measurements, in which case the: .cross-correlation value is normalized by multiplying it by itself and dividing the product by the product of the first and third autocorrelation values.

Particularly good results have been obtained when the first sensor senses radiation within the 4.3-4.6 um emission band, the second sensor senses radiation within the 3.8-4.2 emission band; and the third sensor senses radiation within the 4.8-5.1 μπι emission band.

However, it has also been found that a welding operation occurring in the monitored area using a welding electrode having an organic coating thereover which is evaporated, may produce a false "fire" alarm. It has also been found that such "false alarms" can be reduced by using, for the second sensor, one which is-sensitive to -"-radiation within the 0.2-1.5 ym emission band, particularly within the 0.4-1.1 μπι emission band.

Figs. 1 and 2 are block diagrams illustrating two forms of apparatus constructed in accordance with the embodiments of the invention described in the present application. The illustrated apparatus in both figures is very similar to that described in Patent Applications 103094 and 104298, and to facilitate understanding, the same reference numerals have been used for corresponding parts.

The system illustrated in Fig. 1 thus includes three sensors IR^ , II^ and for concurrently monitoring the radiation emitted from the monitored region. The outputs of the sensors are fed via the three bandpass filters 2, 4, 6 and their respective amplifiers 12, 14 and 16, so as to produce three measurements of the radiation variations emitted from the monitored region within the three bands of the filters.

Each of the three measurements is auto-correlated with respect to itself without normalization to produce three auto-correlation values (block 1 00 ) , C22 (block 1 02 ) and C33 (block 1 04 ) . Auto-correlation value is compared with auto-correlation value C22 in a ratio circuit 1 06 to produce a correlation ratio ( ^ / ) which is compared with a predetermined threshold 1 08 . Autocorrelation value C22 is compared with auto-correlation value ratio circuit 1 1 0 , . to.- produce a correlation ratio which is compared with another predetermined threshold-Π 2 .-—In-addition the-auto-correlation value is compared with a threshold 1 1 4 . These three comparisons are fed to an AND-circuit 36 and utilized in determining the presence or absence of a fire condition in the monitored area, such that the AND-circuit 36 produces an output, indicating a fire condition, when there is coincidence between all its inputs.

AND-circuit 36 includes a fourth input which represents the cross-correlation value between the measurement of the first sensor IR and the second sensor IR2 after normalization. Thus, the circuit illustrated in Fig. 1 produces a cross-correlation value representing the cross-correlation between the measurements of sensors IR^ and IR2 · This cross-correlation value is normalized in circuit -1 1 8 by multiplying this value by itself, and dividing the product by the product of the auto-correlation value received from circuit 100 and the auto-correlation value received from circuit 102. The output of circuit 118 is compared with another threshold 120 and applied as the fourth input into the AND-circuit 36.

Thus, the AND-circuit 36 will produce an output, indicating a fire condition, only when there is coincidence between all four of its inputs. If any of its inputs is negative, no fire condition will be indicated.

The arrangement illustrated in Fig. 1 has been found to have a relatively high sensitivity to detecting fires, _ and a relatively _.low_false alarm rate, particularly.. when the first sensor IR^ is sensitive to radiation within the -4.3-4.-6—vim-bandy- the—second-sensor I-R^—is sensitive—to ~~ radiation within the 3.8-4.2 band, and the third sensor IR^ is sensitive to radiation of about 4.8-5.1, preferably 5.0 yxm .

However, it has been found that the system as described above may be falsely actuated to indicate a fire condition when a welding operation is being performed in -the monitored area, which welding operation involves the evaporation of a coating of an organic material on the welding electrode. Such organic materials, when evaporated, produce an emission within the CC^ bandwidth- However, it. has also been found that if the illustrated system is changed so that the second sensor is selected so as to be sensitive to radiation within the 0.2-1.5 band (which is below the C02 emission band) , particularly of a wavelength from 0.4-1.1 μιη,' the rate of false alarms caused by such a welding operation occurring in the monitored area is substantially reduced.

Fig. 2 illustrates a system which is substantially the same as described above with respect to Fig. 1, and which operates in substantially the same manner, except that the fourth input to the AND—gate 36 is produced by the cross-correlation of the output of the first sensor IR^ with the third sensor I -j/ rather than with the second sensor IR2. Thus, as shown in Fig. 2, box 116 indicating the cross-correlation value Cj ^ ^s replaced by box 216 indicating the cross-correlation value an<^ this, value .. is normalized in circuit 218 and compared to a predetermined threshold 220 before being applied as the- fourth input to the AND-gate 36. Circuit 218 thus normalizes the value by multiplying it by itself, and dividing the product by the product of the auto-correlation values C^. and C22* In all other respects, including the change in sensor IR2 in order to reduce its sensitivity to false alarms produced by a welding process occurring in the monitored area, the system illustrated in Fig. 2 is constructed and operates in substantially the same manner as described above with respect to the system of Fig. 1.

Claims

WHAT IS CLAIMED IS:

1. The method according to Claim 2 of Patent Application 103094, wherein the correlation is determined between each of said measurements, with respect to itself, without normalization to produce first, second and third auto-correlation values, respectively; and said first auto-correlation value is compared with said third autocorrelation value to produce a correlation ratio which is compared to a. predetermined threshold and utilized in determining the presence-. or absence of a fire condition in the monitored region. _ ... __

2. The method according to preceding Claim 1, wherein said second auto-correlation value is compared with said third auto-correlation value to produce a second correlation ratio, which is compared to a predetermined threshold and utilized in determining the presence or absence of a fire condition in the monitored region.

3. -The method according to preceding Claim 2, wherein said first auto-correlation value is compared to a predetermined threshold and is also utilized in determining the presence or absence of a fire condition in the monitored region.

4. The method according to any one of preceding Claims 1-3, wherein a correlation is determined between said first measurement and one of said other two measurements to produce a cross-correlation value, and said cross-correlation value is normalized, compared with a — predetermined threshold, and utilized in determining the presence or absence of a fire condition in the monitored region .

5. . The method according to Claim 4 , wherein said cross-correlation value is determined between said first and second measurements.

6. . The method according to Claim 5 , wherein said cross-correlation value is determined by multiplying the cross-correlation value by itself, and dividing the product by the product of said first and second auto-correlation values .

7. The method according to Claim 4, wherein said cross-correlation value is determined between. said first and third measurements .

8. The method according to Claim 7, wherein said cross-correlation value is normalized by multiplying it by itself, and dividing the product by the product of said first and third auto-correlation values.

9. The method according to any of the preceding Claims 1-8, wherein said first sensor senses radiation within the 4.3-4.6 μπι emission band, said second sensor senses radiation within the 3.8-4.2 emission band; and said third sensor senses radiation within the 4.8-5.1 μιη emission band . .

10. The method according to Claim 9, wherein said second sensor senses radiation within the 0.2-1.5 μιπ emission band. Advocate, Patent Attorney Beit Amot Mishpat 8 Shaul Hamelech Avenue 64733 Tel Aviv