JP2004303266A - Smoke sensing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect smoke density based on the count of scattered light even if the flow rate of intake air changes, without needing to measure the flow rate of intake air. <P>SOLUTION: A light receiving part outputs light receiving signals (a) obtained by receiving the light scattered by smoke particles, through a light receiving element every time the smoke particles pass the imaging position of laser beams in a smoke detecting region. A smoke density detecting part detects smoke density based on the integrated value per unit time of the light receiving signals (a) from the light receiving part. The smoke density can be accurately detected since the integrated value per unit time does not change even if the flow rate of suction air changes. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a smoke detection device that determines a fire by optically detecting smoke particles floating in air sucked from a monitoring area using laser light.

2. Description of the Related Art Conventionally, in order to detect a fire occurring in a clean space typified by a clean room of a computer room or a semiconductor manufacturing facility at an extremely early stage, an ultra-high sensitivity smoke detector has been used. This ultra-high sensitivity smoke detector sucks air from piping installed in a clean space, passes smoke particles contained in the sucked air through a smoke detection area irradiated with a laser diode, and detects smoke particles detected by a light receiving element. Of the received light pulse signals caused by the scattered light, the number of received light pulse signals exceeding a predetermined threshold per unit time is counted, and 0.05 to 0.20% / m is calculated based on the count number per unit time. Detects weak smoke density in the range.
JP-A-7-151680

  However, in such an ultra-high sensitivity smoke detection device that detects smoke density by pulse counting of a received light pulse signal, the number of scattered light per unit time changes due to a change in the flow rate of air to be sucked. As a result, there is a problem that accurate detection of smoke density is not possible.

  In order to solve this problem, in the conventional apparatus, the flow rate of the sucked air is measured by a flow meter, a correction coefficient is obtained from the set flow rate and the detected flow rate, and the count number per unit time is corrected. That is, when the actual detected flow rate Q increases with respect to the set flow rate Qr, the count number per unit time increases and the smoke density becomes higher. Therefore, the correction coefficient K = Qr / Q is obtained. The count value per unit time is multiplied and corrected to a count value converted into the set flow rate Qr so that a correct smoke density can be detected.

  However, in order to correct the number of counts per unit time due to a change in the flow rate of the suction air, a flow meter is required, which considerably increases the cost of the apparatus. Further, there is also a problem that when a trouble occurs in the flow meter, the smoke density cannot be accurately detected.

The present invention has been made in view of such a conventional problem, and does not require the measurement of the flow rate of the intake air. It is an object of the present invention to provide an ultra-high sensitivity smoke detection device capable of detecting air.

  To achieve this object, the present invention is configured as follows. First, the present invention is a smoke sensing device that optically detects smoke particles floating in air sucked from a monitoring area to judge a fire, and sucks laser light from an emission surface of a laser diode by an imaging lens. A light projecting unit that forms an image in a smoke detection area through which air passes, and a laser that is orthogonal to the light projecting optical axis of the laser light and diffuses past the image forming position with respect to the image forming position of the laser light by the image forming lens. A light-receiving element arranged in a direction parallel to the direction of the electric field of light, and the light-receiving element receives light scattered by the smoke particles each time the smoke particles pass through the imaging position of the laser light in the smoke detection area. And a smoke density detecting section for detecting a smoke density based on an integrated value per unit time of the received light pulse signal from the light receiving section.

  As described above, when detecting the smoke density from the integrated value of the received light pulse signal per unit time, if the actual flow rate is increased with respect to the reference set flow rate, the speed of the smoke particles passing through the smoke detection space increases, The number of received light pulse signals of scattered light per unit time also increases. However, since the time required for the smoke particles to pass through the smoke detection region is reduced, the time during which scattered light can be received is also reduced, and the integrated value determined by the waveform area of the received light pulse signal decreases. As a result, even if the number of light receiving pulse signals increases, the integrated value of the light receiving pulse decreases accordingly, and the integrated value of the light receiving pulse per unit time does not change due to the cancellation of both.

  Conversely, if the actual flow rate is reduced with respect to the reference set flow rate, the speed of the smoke particles passing through the smoke detection space is reduced, and the number of scattered light reception pulse signals per unit time is also reduced. However, since the time required for the smoke particles to pass through the smoke detection region becomes longer, the time during which scattered light can be received becomes longer, and the integral value determined by the waveform area of the received light pulse signal increases. As a result, even if the number of received light pulse signals decreases, the integrated value of the received light pulse signal increases accordingly, and the integrated value of the received light pulse per unit time does not change due to the cancellation of the two.

As a smoke density detection unit that detects smoke density based on the integrated value of the received light pulse per unit time, for example, a predetermined threshold is set for the received light pulse signal from the light receiving unit, and a received light pulse signal component exceeding this threshold is output. A slice processing unit, an integration unit that integrates the light receiving pulse signal sliced by the slice processing unit for each unit time, a hold unit that extracts and holds the integration value for each unit time by the integration unit, and a hold unit. And a smoke density conversion unit for converting the integrated value held in the above into smoke density.

  According to the present invention, for a received pulse signal of scattered light obtained by passing smoke particles, a total value of pulse width per unit time or an integrated value per unit time is obtained, and smoke density is detected based on these values. Therefore, even if the flow rate of the suction air changes, the total pulse width value or the integral value per unit time does not change, and the scattered light due to the passage of the smoke particles is received without being affected by the change in the flow rate of the suction air. Accordingly, a minute smoke density can be detected accurately.

Further, since there is no influence of the flow rate fluctuation, there is no need to provide a flow meter for detecting the flow rate of the intake air unlike the conventional apparatus, so that the structure can be made simple, compact, and inexpensive.

  FIG. 1 shows the overall configuration of the smoke detector of the present invention. In FIG. 1, a smoke detector 1 is installed to detect smoke caused by a fire in a computer room or a clean room where semiconductor manufacturing facilities are installed at an extremely early stage, and is installed in a monitoring area of the smoke detector 1. The detection pipe 2 is connected. The detection pipe 2 is, for example, a T-shaped pipe and has a plurality of suction holes 3.

  The detection pipe 2 is connected to the inlet of the smoke detector 4 provided in the smoke detector, and the outlet side is opened to a chamber provided with the suction device 7. In the monitoring state, the suction device 7 sucks air at a predetermined flow rate set in advance by driving the motor, so that the air sucked from the suction hole of the detection pipe 2 installed in the warning area causes the smoke detection unit 4 to flow. And is discharged from the suction device 7.

  Although the suction flow rate of the suction and suction by the suction device 7 is determined in terms of design, the actual flow rate fluctuates with respect to the set flow rate due to fluctuations in the rotation of the motor and the like. The passing speed of smoke particles contained in the air passing through the air fluctuates. The smoke detector 4 is provided with a laser diode (LD) 5 that performs single polarization oscillation having an electric field component in a predetermined deflection direction and a photodiode (PD) 6 as a light receiving element. As the photodiode 6, for example, a PIN photodiode is used. used.

The detection of airborne particles (aerosol) including smoke particles present in the sucked air passing through the smoke detector 4 is performed by detecting the scattered light due to the irradiation of the laser light from the laser diode 5 with the photodiode 6, and detecting the scattered light. Is output to the signal processing unit 8 to perform signal processing for smoke density detection. In the present invention, as signal processing for detecting smoke density based on the received light pulse signal in the signal processing unit 8, the number of received light pulse signals per unit time is counted and the smoke density is calculated as in the related art. Instead of converting
(1) The sum of the pulse widths of the light receiving pulse signals obtained per unit time, and (2) the smoke density is detected based on one of the integrated values of the light receiving pulse signals obtained per unit time.

  FIG. 2 is an explanatory view of a scattered light type smoke particle detection structure used in the present invention provided in the smoke detector 4 of FIG. In FIG. 2, the laser beam emitted from the laser diode 5 performs so-called single polarization oscillation in which the direction of the electric field of the laser beam is determined to be a predetermined direction, and includes a laser diode chip 5a inside. The laser light emitted from the laser diode 5 spreads as a diffusion wave toward the light projection optical axis 11.

  An image forming lens 9 is arranged following the laser diode 5, condenses the laser light from the laser diode 5, and forms a light source image of the laser diode 5 at an image forming position 10 where an airflow 13 of the smoke-detected air passes. That is, a light source image (far field pattern) on the emission surface of the laser diode chip 5a is formed to form a minute spot area of about 1 μm.

  At an imaging position 10 of the light source image of the laser diode 5 by the imaging lens 9, the photodiode 6 is disposed with a light receiving optical axis 12 set in a direction orthogonal to, for example, θ = 90 ° on the light projecting optical axis 11. are doing. The arrangement direction of the photodiode 6 is, for example, the direction of the electric field E indicated by an arrow in an elliptical pattern (near field pattern) 14 indicating the light intensity distribution in the optical axis cross-sectional direction of the laser light diffused past the imaging position 10. It is arranged in the direction parallel to.

  By arranging the photodiode 6 as a light receiving element in a direction parallel to the direction of the electric field E, the scattered light due to the smoke particles passing through the minute spot at the image forming position 10 is the largest according to the experiment of the present inventor. Light can be received with high efficiency.

  FIG. 3 is a block diagram of the signal processing unit 8 of FIG. A control unit 15 is provided in the signal processing unit. The laser diode 5 is connected to the control unit 15 via the light emitting circuit unit 16, and the output of the photodiode 6 is input connected via the light receiving circuit unit 17. . Further, a suction device 7 having a motor is connected. The control unit 15 is provided with a smoke density detection unit 18. FIG. 4 is a circuit block diagram of the smoke density detection unit 18 provided in the control unit 15 of FIG. The embodiment of the circuit block of the smoke density detection unit 18 in FIG. 4 detects the smoke density based on the total value of the pulse widths of the scattered light reception pulse signals obtained per unit time T. For this purpose, the smoke density detection section 18 includes an amplification circuit 20, a comparison circuit 21, an integration circuit 22, a hold circuit 24, a smoke density conversion circuit 25, and a timer circuit 26. The amplifying circuit 20 receives as input a received light pulse signal that has received laser light scattered by smoke particles passing through the imaging position 10 received by the light receiving element 6 of FIG. 2, and this received light pulse signal is a weak signal. After that, the signal is amplified by a predetermined amplification factor, and then output to the comparison circuit as a light receiving pulse signal a.

  FIG. 5A shows a received light signal a output from the amplifier circuit 20. Each time a smoke particle passes through the image forming position 10 of the laser beam, which is a smoke detection area, a received light pulse signal a1, a2 due to its scattered light. , A3, a4,... Are obtained. The light receiving pulse signals a1 to a4 have signal heights that are directly proportional to the size of the smoke particles, and pulse widths that are directly proportional to the time that the smoke particles pass through the smoke detection spot area where the laser light is imaged.

  The speed at which the smoke particles pass through the smoke detection area is directly proportional to the suction flow rate by the suction device 7. Therefore, when the suction flow rate exceeds the set flow rate, the passing speed of the smoke particles in the smoke detection region also increases, and as a result, the pulse width of the received light pulse signal decreases. Conversely, when the intake air flow decreases, the speed of the smoke particles passing through the smoke detection region also decreases, and in this case, the pulse width of the received light pulse signal increases.

Subsequent to the amplifier circuit 20 of FIG. 4, a comparison circuit 21 is provided. As shown in FIG. 5A, the threshold value TH is set to a predetermined value exceeding the noise level in the comparison circuit 21 in order to detect the pulse widths of a1 to a4 that change in an analog manner, and the light receiving pulse a1 exceeding the threshold value TH is set. The rectangular wave shaping signal b of FIG. 5B having a width of .about.a4 is output. The rectangular wave shaping signal b is a signal converted into a pulse width when the light receiving signals a1 to a4 are compared with the threshold value TH. An integrating circuit 22 is provided subsequent to the comparing circuit 21 in FIG. 4, and integrates the rectangular wave forming signal b corresponding to the pulse width of the light receiving pulse signals a1 to a4 in FIG. An integrated addition signal c as shown is output. The integration signal c is used to obtain an integrated addition value of the four rectangular wave shaping signals b1 to b4 over the unit time T. , Tw3, Tw4, the total pulse width T4, ie, Tw = Tw1 + Tw2 + Tw3 + Tw4
Will have a level proportional to.

  Since the reset signal d is output from the timer circuit 26 every unit time T as shown in FIG. 4D, the hold circuit 24 provided subsequent to the integration circuit 22 outputs the integration signal at the rising edge of the reset signal d. 22 and takes in and holds the integrated signal c. The reset signal d from the timer circuit 26 is also given to the integrating circuit 22 at the same time, and the reset of the integrating circuit 22 is started every unit time T.

  The smoke density conversion circuit 25 converts the total pulse width value of the received light pulse signal of the unit time T held in the hold circuit 24 into smoke density. The conversion table for converting the total value of the pulse width into the smoke density includes parameters such as the particle diameter of the smoke particles, the passing speed of the smoke detector, the level of the received pulse signal for the smoke particles, and the threshold value TH for waveform shaping. By deciding, it can be prepared as a theoretical value.

  Next, the operation of the embodiment using the circuit block of FIG. 4 will be described. As shown in FIG. 5A, the amplifying circuit 20 has a peak level proportional to the particle diameter of the smoke particles every time the smoke particles pass through the smoke detection region which is a beam spot of the image forming region where the laser beam is focused. The light receiving pulse signal is input, and the light receiving pulse signals a1, a2, a3, a4,... As shown in FIG. The light receiving pulse signal a from the amplifier circuit 20 is input to the comparison circuit 21 and is compared with a preset threshold value TH.

  For example, the light receiving pulse signal a1 is at the L level as shown in the rectangular wave shaping signal b1 in FIG. 4 (B) while being lower than the threshold value TH, rises to the H level when the threshold value TH is exceeded, and passes through the peak level. When the voltage falls below the threshold value TH again, the waveform is shaped into a rectangular wave signal that falls to the L level. As a result, the light receiving pulse signal a1 is converted into a rectangular wave shaping signal b1 having a pulse width Tw1 obtained by cutting the pulse waveform at the threshold value TH.

  Similarly, the light receiving pulse signals a2, a3, and a4 are also converted into rectangular wave shaping signals b2, b3, and b4 having pulse widths Tw2, Tw3, and Tw4 viewed from the threshold value TH. In the case of FIG. 5, four light receiving pulse signals a1 to a4 are obtained during the unit time T. Therefore, the integration circuit 22 that has been reset-started by the reset signal d from the timer circuit 26 charges the capacitor over the H-level period of the square wave shaping signals b1 to b4, like the integration signal c in FIG. Is performed.

  Therefore, at the rising timing at which the reset signal d is obtained after the unit time T has elapsed, the integration addition signal c has a value proportional to the total pulse width Tw of the pulse widths Tw1 to Tw4 of the four rectangular wave shaping signals b1 to b4. This is held by the hold circuit 24 and output to the smoke density conversion circuit 25 over the next unit time T, whereby the smoke density conversion output corresponding to the final integrated addition value is performed.

  Here, assuming that the suction flow rate of the air by the suction device 7 is increased from the state shown in FIG. 5, the speed of the smoke particles passing through the smoke detection area is increased, and the number of the light receiving pulse signals a obtained during the unit time T is reduced. To increase. For example, assuming that the smoke density is the same, if the flow velocity is doubled, the number of received light pulse signals obtained in the unit time T is doubled from eight in FIG. 5A to eight.

  Therefore, the rectangular wave shaping signal b obtained by the comparison process using the threshold value TH also becomes half of the pulse widths Tw1 to Tw4 before the flow velocity doubles, and further four square wave shaping signals are added during the unit time T. . As a result, in the integration addition signal c of FIG. 5C, since there are eight rectangular wave shaping signals in the cycle T, the flow rate increases even if one integration time determined by the pulse width is short. The number of integration increases from the previous four times to eight times, and the level of the integration addition signal c finally obtained in the unit time T hardly changes. Conversely, if the flow rate of the intake air in FIG. 5 is reduced to, for example, a half flow rate, the number of smoke particles passing through the smoke detection area is also reduced to half, and the light reception in FIG. The pulse signal decreases from four in the figure to two when the flow rate of the intake air is halved. However, as the flow velocity decreases, the pulse width of the received light pulse signal is doubled, and as a result, the integration result by the integration signal c hardly changes.

  In the embodiment of FIG. 4 described above, the smoke density is detected based on the total value of the pulse width of the received light pulse signal obtained at T per unit time, so that the amount of intake air fluctuates. However, as long as the smoke density does not fluctuate, a constant pulse width total value is always obtained, and high-precision smoke density detection can be realized without fluctuation of the air intake flow rate.

  FIG. 6 shows a part of the circuit block shown in FIG. 4 that is realized by MPU program control. 6, the amplifier circuit 20 is the same as that of the embodiment of FIG. 4, but an AD converter 27 is provided to convert the light receiving signal a of FIG. 5A into digital data using a predetermined sampling clock. , MPU 28. The MPU 28 includes a comparison unit 210, an integration unit 220, a hold unit 240, a smoke density conversion unit 250, and a timer unit 260.

  These processing units of the MPU 28 are basically realized by hardware of the comparison circuit 21 to the timer circuit 26 shown in FIG. 4 by program control of the MPU 28, and there is no fundamental difference. FIG. 7 shows another embodiment of the smoke density detecting section 18 provided in the control section of FIG. 3. In this embodiment, an integrated value of the received light pulse signal is obtained for each unit time T, and the integrated value is calculated. The smoke density is detected based on the smoke density. For this reason, the embodiment of FIG. 7 is different from the embodiment of FIG. 4 in that a slice processing circuit 30 is provided following the amplification circuit 20, and the other configurations are similarly the integration circuit 22 and the hold circuit 24. , The smoke density conversion circuit 25 and the timer circuit 26.

  FIG. 8 is a timing chart of the embodiment of FIG. 7, and the received light pulse signal amplified by the amplifier circuit 20 is as shown in FIG. 8A, which shows the result of amplification of the received light pulse signal in FIG. 5 (A). The slice processing circuit 30 extracts a signal component exceeding a slice level set for cutting a noise component, and a predetermined slice level SL for cutting a noise component with respect to the received light pulse signal a of FIG. 8B, and outputs the slice signal b of FIG. 8B from which the signal components lower than the slice level SL have been removed to the integration circuit 22.

  The integration circuit 22 integrates the slice signal b for each unit time T. Here, since the slice signals b1 to b4 are obtained corresponding to the light receiving signals a1 to a4, the integration circuit 22 integrates the respective slice signals b1 to b4 and outputs an integrated signal c of FIG. 8C. . As a result, the value of the integration signal c from the integration circuit 22 at the elapse of the unit time T is a value proportional to the total value of the area waveform components of the four slice signals b1 to b4 obtained during the unit time T. This is converted into a smoke density by the smoke density conversion circuit 25.

  Even in the embodiment of FIG. 7 in which the smoke density is detected by calculating the cumulative integration of the received light pulse signal per unit time T, the unit time of the received light pulse signal is increased when the suction flow rate of air from the outside by the suction device 7 is increased. As the number at T increases and the suction flow decreases, the number decreases; conversely, as the suction flow increases, the signal width decreases, and as the suction flow decreases, the signal width increases.

  Therefore, the value of the integrated signal c obtained by integrating the slice signal b at the time when the unit time T has elapsed is substantially constant even if the suction flow rate changes unless the smoke density changes. For this reason, the smoke density can be accurately measured without being affected by the fluctuation of the flow rate of the intake air by the suction device.

  FIG. 9 is a block diagram in which a part of the embodiment of FIG. 7 is realized by program control by the MPU, and corresponds to FIG. 6 showing the first embodiment. That is, an AD converter 27 is provided following the amplifier circuit 20, and converts the light receiving pulse signal of FIG. 8A into digital data by a predetermined sampling clock. In the MPU 28, a slice processing unit 300, an integration unit 220, a hold unit 240, a smoke density conversion unit 250, and a timer unit 260 are provided as functional blocks corresponding to the hardware of the slice processing circuit 30 to the timer circuit 26 in FIG. I have.

Even in the embodiment in which the smoke density is obtained from the integrated value of the received light pulse signal per unit time T, more accurate detection of the smoke density can be realized without being affected by the fluctuation of the flow rate of the intake air. In the above-described embodiment, as shown in FIG. 2, the laser light from the laser diode 5 is narrowed down to the image forming position 10 by the image forming lens 9 to form a light source image of a minute beam spot, and the beam spot at this image forming position is formed. The laser beam from the laser diode 5 is converted into parallel light by using a collimating lens instead of the imaging lens 9 while passing the airflow of smoke particles inhaled from the outside. The present invention can be applied to a smoke sensing device provided with a parallel optical system in which a photodiode 6 as a light receiving element is disposed at a predetermined configuration angle θ.

Explanatory drawing of the whole structure of the smoke sensing device according to the present invention. Explanatory drawing of a scattered light type smoke particle detection structure according to the present invention having a sensitivity test function 1 is a block diagram of the signal processing device of FIG. FIG. 3 is a circuit block diagram of the smoke density detection unit in FIG. 3 for detecting smoke density based on the total pulse width per unit time. FIG. 3 is a timing chart showing the operation of the smoke density detection unit in FIG. FIG. 3 is a functional block diagram of the smoke density detection unit in FIG. 3 using an MPU that detects smoke density based on the total pulse width per unit time. FIG. 3 is a circuit block diagram of the smoke density detection unit in FIG. 3 for detecting smoke density based on the integrated value of the received light pulse per unit time. FIG. 7 is a timing chart showing the operation of the smoke density detection unit. FIG. 3 is a functional block diagram of the smoke density detection unit in FIG. 3 using an MPU that detects smoke density based on an integrated value of a received light pulse per unit time.

Explanation of reference numerals

1: Smoke detector 2: Detection pipe 3: Suction hole 4: Smoke detector 5: Laser diode 5a: Laser diode chip 6: Photodiode (light receiving element)
7: suction device 8: signal processing unit 9: imaging lens 10: imaging position (smoke detection area)
11: Light-emitting optical axes 12, 19: Light-receiving optical axis 15: Control unit 16: Light-emitting circuit unit 17: Light-receiving circuit unit 18: Smoke density detection unit 20: Amplifier circuit 21: Comparison circuit 22: Integration circuit 24: Hold circuit 25: Smoke density conversion circuit 26: Timer circuit 27: A / D converter 28: MPU
30: Slice processing circuit

Claims (2)

In a smoke detection device that optically detects smoke particles floating in the air inhaled from the monitoring area to judge a fire,
A light emitting unit that forms an image of a laser beam from an emission surface of a laser diode on a smoke detection area through which intake air passes through an imaging lens;
With respect to the imaging position of the laser light by the imaging lens, the laser light is arranged in a direction perpendicular to the projection optical axis of the laser light and in a direction parallel to the electric field direction of the laser light diffused past the imaging position. A light receiving element,
Each time a smoke particle passes through the imaging position of the laser light in the smoke detection area, a light receiving unit that outputs a light receiving pulse signal obtained by receiving light scattered by the smoke particle by the light receiving element,
A smoke density detection unit that detects smoke density based on an integral value per unit time of a light reception pulse signal from the light reception unit,
A smoke detection device comprising:
In the smoke detection device according to claim 1, the smoke density detection unit includes:
A slice processing unit that sets a predetermined threshold value for the light receiving pulse signal from the light receiving unit and outputs a light receiving pulse signal component exceeding the threshold value,
An integration unit that integrates the received light pulse signal sliced by the slice processing unit for each unit time;
A holding unit that extracts and holds the integral value per unit time by the integrating unit,
A smoke density conversion unit that converts the integrated value held in the holding unit into smoke density,
A smoke sensing device comprising:

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