JP2761240B2 - Infrared light receiving type fire detector - Google Patents

Description

[Detailed Description of the Invention] [Industrial application field] The present invention detects the power of a specific infrared wavelength emitted from the flame of a fire generated in a monitoring area, and determines the occurrence of the fire and its direction. The present invention relates to a fire detection device capable of receiving infrared light.

[Related Art] Conventionally, a large number of fire detecting devices of an infrared ray receiving type have been proposed. This type of device detects the occurrence of a fire by detecting infrared rays specific to a flame. FIG. 7 shows the spectral characteristics of sunlight, illumination light, and flame. As shown in the figure, a peak formed by resonance emission of CO ₂ exists at a wavelength of about 4.3 μm in the spectral characteristics of the flame when a fire occurs. On the other hand, in the case of sunlight or illumination light, radiant energy near a wavelength of 4.3 μm is small. Therefore, if the occurrence of a fire is determined by infrared rays near this wavelength, the sensitivity for detecting a flame can be set high, which is convenient. As a specific method of flame detection, a method of extracting only the flicker frequency peculiar to the flame and detecting it, and a method of detecting the flame by determining the amount of infrared energy near the wavelength 4.3 μm specific to the flame are proposed. (No. 56-28544, No. 55-25862, No.
61-8398, JP-A-62-255832, JP-A-62-157580).

[Problems to be solved by the invention] However, in the conventional infrared ray detection type fire detection device,
If strong sunlight directly enters the infrared detecting element or flickers after being reflected by a metal or the like, malfunction may occur. In addition, a malfunction may occur in response to the shaking of a leaf of a tree entering through a window. In addition, non-fire flames,
For example, a stove or a gas stove flame may be determined to be a fire. If such a conventional detection device is used to detect a fire or the light of the fire, and a fire extinguishing agent is automatically emitted in that direction, a fire detection error or a fire detection direction error may occur. If there was a detection, there was a risk that fire extinguisher would cause damage. Further, if the detection sensitivity of infrared rays is set low to prevent erroneous detection, there is a possibility that the fire extinguishing agent may be delayed and the fire cannot be extinguished.

The present invention has been made in view of such a point,
The aim is to detect fires based on both the criteria of increasing the power of the flame due to the fire and the area of the flame, and to detect the occurrence of the fire with an algorithm that minimizes malfunctions. In a simple and inexpensive configuration.

[Means for Solving the Problems] In the present invention, in order to solve the above problems, as shown in FIG. 1, an infrared detecting element 2 and a field of view of the infrared detecting element 2 are circularly scanned. A circular scanning optical system 1;
A preamplifier 3 for amplifying an output signal of the infrared detecting element 2, a signal processor 4 for converting an output of the preamplifier 3 into a signal for flame detection, and an output of the signal processor 4 A judgment unit 5 for judging the occurrence of a fire on the basis of the signal, and an output unit 6 for outputting a fire occurrence signal based on a signal from the judgment unit 5, wherein the judgment unit 5 determines that a signal for flame detection exceeds a predetermined level. First judgment means for judging "flame detection" when the "flame detection" is judged, and detecting that the level of a signal for flame detection has increased to a predetermined ratio or more after the judgment of "flame detection". A second determination means for determining whether the scanning range in which the signal for flame detection has a high level after the determination of the "flame detection" is expanded to a predetermined ratio or more. And at least a third determining means for determining Is determined by the determination section "flame detection", "flame increased", it is characterized in that the means for at least outputting fire occurrence signal triplicate for "flame expansion".

Here, the first determining means includes means for storing a maximum value of a signal waveform when a signal for flame detection first exceeds a predetermined level, and the second determining means includes a signal for flame detection. It is preferable that a means for judging “increase in flame” when detecting that the value has increased by a predetermined ratio or more with respect to the stored maximum value.

The infrared detecting element 2 is a pyroelectric element, and the first judging means is means for storing a time interval between a maximum value and a minimum value of a signal waveform when a signal for flame detection first exceeds a predetermined level. When the third determining means detects that the time interval between the maximum value and the minimum value of the signal for flame detection has expanded to a predetermined ratio or more with respect to the stored time interval, It is preferable to use means for judging “enlargement”.

[Operation] In the present invention, since the circular scanning optical system 1 is used to scan the visual field of the infrared detecting element 2 as described above,
Although it is a simple and inexpensive configuration, it is possible to detect the flame caused by the fire in a wide detection area, and because the width of the flame when looking at the flame from the center of the circular scan is expanded,
An increase in the area of the flame can be determined. When the signal for flame detection exceeds a predetermined level, "flame detection"
And a second judging means for judging "flame increase" by detecting that the level of a signal for flame detection has increased beyond a predetermined ratio after the "flame detection" has been judged. A third judging means for judging "flame expansion" by detecting that the scanning range in which the signal for flame detection has a high level after the "flame detection" is judged has been expanded to a predetermined ratio or more; At least means for “flame detection”, “flame increase”,
At least three signals of "flame expansion" are output, so by using these three signals,
It is possible to reliably determine whether or not a fire has occurred, and it is possible to reliably prevent the automatic fire extinguishing system from malfunctioning due to non-fire flame or reflection of sunlight.

Embodiment FIG. 2 shows a state of circular scanning in a fire detection device according to an embodiment of the present invention. The detector is located on the ceiling and monitors fires on the floor. In the figure,
F indicates the field of view, Q indicates the scanning direction, and F ₀ indicates the entire effective field of view. Reference numeral 11 denotes a rotation center of the viewing plane F, which coincides with the viewing center c of the infrared detecting element 2. As is apparent from the figure, the flame H of the fire viewed from above becomes an image extending in the radial direction from the center of the visual field c except when it occurs at the center of the visual field c. In consideration of the above points, a rectangular slit-shaped field of view is provided, and a fire is effectively and efficiently detected by using a circular scanning method that rotates the field of view around the end point, and the direction of the fire is detected. Can be determined.
In FIG. 2, Dv indicates the instantaneous visual field width. Dv is set by an optical system so as to have an optimal size in consideration of the width of the flame to be detected. Generally, it is set to be slightly smaller than the minimum width of the flame to be detected.

FIG. 3 shows an example of a circular scanning optical system. As shown in FIG. 1A, the distance Rb from the front surface of the light receiving surface of the infrared detecting element 2 is shown.
, The rotating shaft 11 at the center of the rotating plate 10 is arranged on the center of the visual field c on the light receiving surface of the infrared detecting element 2, and the rotating plate 10 is rotated by a driving mechanism such as a motor. As shown in FIG. 3 (b), the rotary plate 10 is provided with a rectangular slit A having a length La and a width Da, and only infrared rays radiated from the object surface B that pass through the slit A are infrared rays. It is configured to be incident on the detection element 2. The instantaneous visual field on the object surface is similar to the shape of the slit A. When the distance from the rotating plate 10 to the object surface B is Ra, the instantaneous visual field length Lv on the object surface and the visual field width Dv are expressed by the following equations. Become like

Further, assuming that a viewing angle at which the instantaneous visual field looks at the object plane B in the radial direction in the circular scanning is θ, θ is as follows.

The instantaneous field of view is circularly scanned with the center of the field of view of the light receiving surface of the infrared detecting element 2 as an axis. Therefore, the total field of view of the object plane B by circular scanning is 2θ.

In FIG. 3, if a convex cylindrical lens is provided at the slit A, a desired optical gain can be obtained. In the structure shown in FIG. 3, upon detecting a fire, the instantaneous visual field width Dv on the object surface is a main factor for determining the flame width resolution. In order to increase the flame width resolution, the smaller the instant visual field width Dv is, the better. Therefore, although it is necessary to reduce the opening width Da of the slit A, the amount of received infrared light is reduced in proportion to this, and a sufficient S / N ratio may not be obtained. In view of this, a cylindrical lens is arranged at the slit A to provide a light condensing function in the scanning direction so as to obtain a predetermined instantaneous visual field width Dv and a necessary optical gain. In FIG. 3, when a cylindrical lens is arranged at the slit A, and assuming that the diameter of the light receiving surface of the infrared detecting element 2 is d, the visual field length Lv and visual field width Dv of the instant visual field on the object surface are as follows. become.

As can be seen from the above equation, the instantaneous visual field width Dv is determined by an appropriate Rb or d regardless of the aperture Da of the cylindrical lens.
To obtain a predetermined instantaneous visual field width Dv. Further, the optical gain can be increased by increasing the opening width Da of the cylindrical lens.

In the example of the configuration of the circular scanning optical system shown in FIG. 4, as another means for obtaining the optical gain, the rotating plate 10 on which the concave cylindrical mirror M is fixed is set with the center of the visual field c of the light receiving surface of the infrared detecting element 2 as an axis. It is configured to rotate.
The distance from the mirror surface of the cylindrical mirror M to the light receiving surface of the infrared detecting element 2 is Rb, the distance from the mirror surface of the cylindrical mirror M to the object surface B is Ra, the mirror length of the cylindrical mirror M is Lm, the mirror width is Dm, Infrared detector 2
Let d be the light receiving surface diameter of d, the instantaneous visual field length Lv on the object surface, visual field width Dv, and the following equation are obtained in the same manner as when a cylindrical lens is used.

Therefore, a predetermined instantaneous visual field width Dv can be obtained by selecting an appropriate Rb or d, and an optical gain can be increased by increasing the mirror width Dm of the cylindrical mirror M. In the radial direction in the circular scanning, the viewing angle θ at which the instantaneous visual field looks at the object plane B
Is as follows: Further, the total viewing angle at which the detection device looks at the object plane B is 2θ.

FIG. 5 shows the optical relationship between the cylindrical mirror M, the light receiving surface of the infrared detecting element 2, and the instantaneous visual field F formed on the object surface B. Here, if the focal length of the cylindrical mirror M is f and the radius of curvature of the cylindrical mirror M is r, then f = 2r. In addition, the infrared detecting element 2
Has an optically conjugate relationship with the instantaneous field of view on the object surface, the following equation holds.

1 / f = 1 / Ra + 1 / Rb Next, FIG. 6 shows a driving mechanism of the circular scanning optical system. The drive mechanism shown in FIG. 1 includes a rotary plate 10 on which a concave cylindrical mirror M is mounted so that a generatrix direction is parallel to a radial direction, and a motor 12 for driving the rotary plate 10 to rotate. I have. The infrared detecting element 2
The light receiving surface is arranged so as to face the rotating plate 10, and the center of the visual field c is arranged on the rotating shaft 11 of the rotating plate 10. The infrared ray emitted by the detected human body is reflected by the cylindrical mirror M and received by the infrared detecting element 2. The circular mirror M rotates together with the rotating plate 10 to create a circular visual field. Unless the reflectivity of the surface of the rotating plate 10 is set to be considerably lower than the reflectivity of the mirror M, infrared rays from outside the instantaneous field of view may also enter the infrared detecting element 2, and S as a flame detection signal Care must be taken as the / N ratio will be poor. For example,
If the surface of the rotating plate 10 other than the mirror M is black and the difference in reflectance with the surface of the mirror M is large, a light receiving signal with a good S / N ratio can be obtained. Reference numeral 13 denotes a rotation cycle detection unit which is configured using, for example, a photosensor or a magnetic sensor, and generates a synchronization signal every time the rotating disk 10 makes one rotation. As shown in FIG. 6, the rotation cycle detector 13 is attached near the outer periphery of the rotating plate 10. The attachment position may be near the rotating shaft 11, but there is an advantage that a sharp rising synchronization signal can be obtained because the peripheral speed is higher near the outer periphery of the rotating plate 10.

Here, a circuit configuration of a fire detection device using the optical system will be described with reference to FIG. The output of the infrared detecting element 2 is amplified by the preamplifier 3 and then input to the bandpass filter 41. As the infrared detecting element 2, an inexpensive pyroelectric element that does not require cooling is used. Since this pyroelectric element contains many low frequency components as background noise, in the bandpass filter 41,
It cuts unstable low-frequency components and unnecessary high-frequency components to improve the S / N ratio. The output of the bandpass filter 41 is input to the A / D converter 42, A / D converted by the A / D converter 42, and output to the microcomputer 51 constituting the determination unit 5. Microcomputer 51
The motor drive unit 12 operates according to the control signal from the controller and is controlled to rotate at a predetermined constant speed. In the rotation cycle detection unit 13, a synchronization signal is output to the microcomputer 51 every one rotation in synchronization with the scanning of the circular scanning optical system 1.
The microcomputer 51 operates the A / D converter 42 based on the synchronizing signal from the rotation cycle detecting unit 13 and sequentially takes in the waveform from the A / D converter 42 every one rotation. The microcomputer 51 sends to the output unit 6 signals indicating non-fire (normal state), fire expansion, fire increase, flame detection, fire direction, fire range, and the like according to an algorithm described later. The output unit 6 displays these signals, controls an automatic fire extinguishing system according to these signals, and performs evacuation guidance broadcasting.

By the way, the infrared rays radiated from the flame at the time of the fire
As shown in FIG. 7, a characteristic feature is that a peak due to resonance emission of CO ₂ exists near a wavelength of 4.3 μm. Therefore, the infrared detecting element 2 is used by adding a band-pass filter for passing infrared light having a wavelength of about 4.3 μm as shown in FIG. When a cylindrical lens is used in the circular scanning optical system 1, germanium, silicon, sapphire, polyethylene, or the like may be used as a lens material. The amount is attenuated.
In addition, it is expensive and is not suitable for practical use. On the other hand, when a cylindrical mirror is used, for example, even with a polished aluminum mirror, the reflectance around a wavelength of 4.3 μm is 9%.
Since good characteristics exceeding 0% can be easily obtained, an optical gain can be easily obtained and it can be provided at a low cost.

In the circular scanning optical system, the infrared detecting element 2
It is necessary to make the center of the visual field c of the light receiving surface coincide with the rotation axis 11 of the rotating plate 10, and when scanning is performed using a driving unit such as a motor, there may be a structural problem. In this case, an effective circular scanning optical system having a simple structure can be provided by using an annular ultrasonic motor having a hollow center of rotation. An effective circular scanning optical system can also be provided by making the outer periphery of the rotary plate 10 into a gear shape and applying a driving force from the outer peripheral side of the rotary plate 10.

Next, an algorithm for fire occurrence determination will be described. The first feature of the present algorithm is to judge the occurrence of a fire based on both criteria of increasing the power of the flame due to the fire and increasing the area of the flame. Here, the increase in the area of the flame is determined by the fact that the width of the flame when the flame is viewed from the center of the circular scanning is increased. As a second stage before issuing a fire occurrence signal, when a signal exceeding a predetermined level is detected, a warning signal indicating "flame detection" or the like is output. A third feature is that when a fire flame is detected, a direction from the center of the field of view of the rotational scanning is output as a fire occurrence direction signal.

Hereinafter, the present algorithm will be described in detail. Fire flames are generally characterized by a small area at first. That is, as shown in FIG. 2, when the flame H occurs in the effective visual field, the width of the flame H viewed from the rotation center is small. Although the infrared radiation power from the flame H is small, the area of the flame H increases and the radiation power increases as the fire progresses. The principle of the present algorithm is to detect the progress of the fire and distinguish between flames caused by fire and non-fire flames.

First, as shown in FIG. 2, when the instantaneous visual field F crosses the flame H in the effective visual field, a waveform as shown in FIG. In the figure, the origin of the time axis is the time at which the period signal is obtained from the rotation period detection unit 13. The maximum value of this waveform is V _H , the minimum value is V _L , the time when the maximum value is obtained is t _H , and the time when the minimum value is obtained is t _L. Since these detection times t _H and t _L are based on the synchronization signal from the rotation period detection unit 13, when the rotating plate 10 is controlled to a constant speed, the times t _H and t _L are the rotation periods. It can be converted into a direction or a scanning angle from the rotation center with reference to the mounting position of the detection unit 13.

FIG. 11 shows how the flame gradually increases and the detected waveform at that time. FIG. 11 (a) shows a case where the flame is small. In this case, the microcomputer 51
12. As shown in the flowchart of FIG. 12, the detection waveform stored in the input buffer from the A / D converter 42 is loaded into the memory for one scan by using the synchronization signal as a trigger in the program step # 1, and detected in the program step # 2. maximum value V _H and the minimum value V _L of the waveform, and its detection time t _H, seek t _L. Then, in program step # 3, the threshold value of flame detection
Compare with V _S. When the maximum value V _H of the detected waveform is less than or equal to the threshold V _S of flame detection is determined in program step # 4 and V _H ≦ V _S, the process proceeds to program step # 5, the normal state indicating a non-fire Output a signal. Then return to # 1,
Similar processing is repeated for the detection waveform obtained in the next scan.

FIG. 11 (b) shows a case where the fire progressed and the flame became large. In this case, in program step # 3, the maximum value V _H of the detected waveform is greater than the threshold V _S of the first flame detection, the maximum value of the obtained detected waveform in this scanning
V _H and detection time t _H, by using the _{t L, V HS = V H} , seeking T _S = t _L -t _H, and stores them as reference values for the following fire determination. In the scanning at this time, program step # 4
Since it is determined in the determination and V _H> V _S, the process proceeds to program step # 6, obtaining the flame detection time T = t _L -t _H. The flame detection time T indicates the width of the flame as viewed from the center of the visual field. After the determination in program steps # 7 and # 8, a flame detection signal is output in program step # 9, and a scanning time _TF indicating the direction of fire occurrence is calculated in program step # 10, and the process returns to # 1. .

FIG. 11 (c) shows that the fire spread and the flame detection time T = t _L −
This shows a case where t _H becomes longer. At this time, since the flame power is not so large, the maximum value V _{H of the} detected waveform is obtained.
Smaller than M times the reference value V _HS is a program for judging step # 7 is determined to V _H <M · V _HS, the process proceeds to program step # 8, and K times of flame detection time T is the reference value T _S Be compared. If it is determined in the program step # 8 that T ≧ K · T _S , the process proceeds to #program step # 11, and the fire expansion signal is output.

FIG. 11 (d) shows a case where the fire progresses further, the radiation power of the flame increases, and the width of the flame increases. At this time, it is determined in the program step # 7 that V _H ≧ M · V _HS, and the program shifts to the program step # 12.
Since it is determined that .gtoreq.K.multidot.T _S and the program proceeds to program step # 14, both the fire increase signal and the fire increase signal are output.

In program step # 8, a fire spread (T ≧ K ·
Before the determination as T _S ), program step # 7
If it is determined that the fire has increased ( _VH ≧ M · V _HS ), the program proceeds from program step # 12 to program step # 13, and only the fire increase signal is output.

Here, K is a fire expansion judging coefficient, which is a coefficient for determining how wide the width of the flame is to be judged as a fire. M is a fire increase determination coefficient, which is a coefficient that determines the extent to which the fire is determined to be a fire when the radiation power of the flame is converted to the output signal of the infrared detection element 2. Since the values of these coefficients M and K vary depending on the environment in which the fire detector is installed, the size of the monitoring range, the height at which the fire detector is installed, etc., by setting the optimal values according to the installation state, It becomes possible to detect fire effectively.

Finally, a method of calculating the scanning time _TF indicating the fire occurrence direction in the program step # 10 will be described. As shown in Fig. 11, the center direction of the fire flame
By using the synchronization signal from the rotation period detection unit 13 as a reference, the scan angle is obtained as a scan angle viewed from the scan center. When the rotating plate 10 is rotating at a constant speed, the scanning angle corresponds to the scanning time. As a result of repeating the experiment, it was found that the scanning time _TF from the point of occurrence of the synchronization signal to the center of the flame due to the fire can be approximated by the following equation.

T _F = T _H + a · T−b · T _S −c The third and fourth terms in the above equation indicate that the instantaneous visual field crosses the flame when the radial distance from the scanning center is different even if the flame has the same size. Since the speed is different, the detection waveform is dull when the flame is close, and is a correction term for correcting an error of the detection time T due to the sharpness of the detection waveform when the flame is far. The values of the constants a, b, and c in the above equation are determined by selecting appropriate values according to the height above the floor where the fire detection device is installed, the length of the field of view in the radial direction, etc. The scanning time T _F can be obtained with high accuracy. For example, height 15
m, radius 7m, a = 0.5, b = 0.315, c = 0.0
At 25, good results were obtained.

In the above formula, the fire occurrence direction is represented by the scanning time _TF . However, when the rotation cycle of the visual field is set to, for example, 10 seconds, and the center direction of the flame is represented by the angle θ from the rotation cycle detection unit 13, θ = 360 ( T _H + a · T−b · T _S −c) / 10 [deg]. If a plurality of fire detection devices capable of detecting such a fire occurrence direction are used, a fire occurrence position can be determined based on a plurality of fire occurrence direction signals.

[Effects of the Invention] As described above, the present invention relates to an infrared light receiving type fire detecting device that detects infrared rays emitted from a fire flame and determines the occurrence of a fire, as a circular scanning optical system for scanning the field of view of the infrared detecting element. The use of a scanning optical system has the effect of being able to detect a fire in a wide detection area while having a simple and inexpensive configuration, and the width of the flame when the flame is viewed from the center of the circular scan is expanded. This has the effect that the increase in the area of the flame can be determined. When the signal for flame detection exceeds a predetermined level, a signal of "flame detection" is output, and after this "flame detection" is determined, the level of the signal for flame detection increases to a predetermined ratio or more. Detecting that the flame has increased, and outputs a signal of "flame increase". Also, it is determined that the scanning range in which the signal for flame detection becomes a high level after the determination of "flame detection" is expanded to a predetermined ratio or more. By detecting and outputting the signal of "flame expansion", by utilizing these three signals, it is possible to reliably determine the presence or absence of a fire, and to reflect non-fire flame and sunlight. Malfunctions of the automatic fire extinguishing system due to such factors can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention, FIG. 2 is a plan view showing a scanning state of a visual field in the present invention, and FIG. 3 (a) is a schematic configuration diagram of an optical system used in the present invention. FIG. 4B is a bottom view of a main part of the above, FIG. 4A is a schematic configuration diagram of another optical system used in the present invention, FIG. 4B is a bottom view of a main part of the same, and FIG. FIG. 6 is a front view of a rotary drive mechanism of the optical system, and FIG. 7 is a spectral radiant energy characteristic of a flame to be detected and illumination light and sunlight not to be detected according to the present invention. FIG. 8, FIG. 8 is a diagram showing a spectral transmittance characteristic of a band-pass filter provided in the infrared detecting element used in the present invention, FIG. 9 is a block diagram of one embodiment of the present invention, and FIG. Waveform diagram showing waveforms, eleventh
FIG. 12 is an operation explanatory diagram showing an algorithm for detecting a fire occurrence in the above, and FIG. 12 is a flowchart showing processing contents of the microcomputer used in the above. 1 is a circular scanning optical system, 2 is an infrared detecting element, 3 is a preamplifier, 4 is a signal processor, 5 is a determiner, and 6 is an output.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Takashi Horii 1048 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Works Co., Ltd. (72) Inventor Kunio Sasahara 3-14-1, Nakahara, Mitaka City, Tokyo Metropolitan Government Fire and Disaster Management Agency Fire Research Institute Third Research Department (56) References JP-A-63-56799 (JP, A) JP-A-56- 7196 (JP, A) JP-A-2-69896 (JP, A) JP-A-60-134185 (JP, U) JP-A-60-164291 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G08B 17/12 G08B 17/00 G01J 1/02

Claims (3)

(57) [Claims] An infrared detecting element, a circular scanning optical system for circularly scanning the field of view of the infrared detecting element, a preamplifier for amplifying an output signal of the infrared detecting element, and an output of the preamplifier. A signal processing unit that converts the signal into a signal for flame detection, a determining unit that determines a fire occurrence based on an output of the signal processing unit, and an output unit that outputs a fire occurrence signal based on a signal from the determining unit. A determination unit configured to determine “flame detection” when a signal for flame detection exceeds a predetermined level; and a signal for flame detection after the “flame detection” is determined. A second determination means for detecting that the level of the flame has increased to a predetermined ratio or more, and determining "flame increase"; and a scan in which a signal for flame detection becomes a high level after the "flame detection" is determined. Detects that the range has expanded beyond the specified ratio At least three signals of “flame detection”, “flame increase”, and “flame enlargement” determined by the determination unit. An infrared receiving type fire detecting device. The first determining means includes means for storing a maximum value of a signal waveform when a signal for flame detection first exceeds a predetermined level, and the second determining means includes means for detecting a flame. 2. An infrared light receiving type fire detecting device according to claim 1, wherein said means is for judging "increase in flame" when it is detected that said signal has increased to a predetermined ratio or more with respect to said stored maximum value. . 3. The infrared detecting element is a pyroelectric element, and the first judging means determines a time interval between a maximum value and a minimum value of a signal waveform when a signal for flame detection first exceeds a predetermined level. A third determining means for detecting that the time interval between the maximum value and the minimum value of the signal for flame detection has expanded to a predetermined ratio or more with respect to the stored time interval. 3. An infrared light receiving type fire detecting device according to claim 1, wherein the device is a means for judging "expansion of flame".