JPH1061950A - Flame detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flame detector which can realize stable detection of a flame. SOLUTION: Ultraviolet rays 14 in a long wavelength range is extracted from a flame emitted from a burner 20 through a filter 12 and received by a photo detector 11. A signal with a specified frequency band is taken out by a bandpass filter 16 from among output signals from the photo detector 11 to compare the intensity of the signal component with this specified frequency band with a specified level of a reference signal from a reference signal generator 18 by a comparator 17. Based on the results of the comparison, an output is produced to indicate the presence of the flame from an external output part 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame detector for detecting the presence or absence of a flame in a combustion device such as a boiler.

[0002]

2. Description of the Related Art Conventionally, as a means for detecting a flame, an ultraviolet ray or an infrared ray emitted by the flame is received by a light receiving element, and if the detection signal is equal to or higher than a predetermined reference value, "flame present" is output. It is known to output "no flame" if the value is equal to or less than a predetermined reference value.

[0003] Among them, an ultraviolet ray type for receiving ultraviolet rays emitted by a flame is disclosed, for example, in Japanese Patent Laid-Open Publication No. 52-1078.
There is one disclosed in Japanese Patent Publication No. 7 (1995). That is, FIG. 6 shows a schematic configuration of such an ultraviolet flame detecting device.
One end of a detection tube 1 for detecting ultraviolet light is connected to a high-voltage power supply 3 via a current limiting resistor 2, and the other end is grounded via a signal detecting resistor 4. In this case, the detection tube 1
In the ultraviolet wavelength band, a short wavelength range (for example, a wavelength of 260 nm)
A pulse operation type detector having the following sensitivity is used. For example, uv-tron (manufactured by Hamamatsu Photonics) is used as a trade name. Here, the reason why the sensitivity is provided only in the short wavelength region is to receive only the ultraviolet rays emitted by the flame without being affected by the ultraviolet rays emitted by the sunlight and the electric lamp.

In such a configuration, when the ultraviolet rays 5 emitted from the flame enter the detection tube 1, discharge is started in the detection tube 1, and a specified amount of current flows through the signal detection resistor 4.
By measuring the voltage generated at the signal detecting end 41 of the signal detecting resistor 4 by the current flowing through the signal detecting resistor 4, it is possible to detect that the ultraviolet rays 5 emitted from the flame have entered the detecting tube 1. Become. In this case, in the detection tube 1, once the discharge is started by the ultraviolet rays 5, the ultraviolet rays 5
Since the specified amount of current continues to flow even when the incident light stops, in the actual flame detection, the high voltage power supply 3 is periodically turned on and off to perform a pulse operation, and the number of pulses per unit time corresponds to the flame. Ultraviolet intensity is detected. Furthermore, in the above-mentioned ultraviolet flame detection device, in addition to the basic structure, a bactericidal lamp and a component for preventing a malfunction due to ultraviolet rays in a short wavelength range radiated by an ozone generating lamp are added to improve practicality. ing.

On the other hand, as an infrared type which receives infrared rays emitted by a flame, for example, as disclosed in Japanese Patent Publication No. 56-45043, the infrared rays emitted by the flame when detecting the infrared rays emitted by the flame are disclosed. In order to distinguish between infrared rays emitted from the boiler and the inner wall of the boiler, an infrared flicker method for detecting a signal only in a frequency band unique to the infrared rays emitted by the flame has been proposed. These ultraviolet type or infrared type are selected and used according to the conditions of the target flame fuel, environment, cost and the like.

[0006]

However, according to the above-mentioned ultraviolet type which receives ultraviolet rays, it is well known that the emission spectrum in the ultraviolet range of a flame has a longer wavelength range (in comparison with the radiation intensity in a short wavelength range). 260 nm to 420 nm)
Has a higher radiation intensity, and particularly, a line spectrum (wavelengths of 306 nm and 309 nm) caused by OH groups in the fuel component shows a higher radiation intensity. From this, there has been a problem in that conventional detection of only ultraviolet rays in a short wavelength range has low detection sensitivity and cannot perform stable flame detection.

Therefore, a method of detecting ultraviolet rays in a long wavelength range is conceivable. However, since ultraviolet rays in a long wavelength range are included in a large amount of ultraviolet rays radiated by sunlight and electric lamps, these ultraviolet rays are also detected at the same time. Therefore, stable flame detection could not be performed where sunlight and electric light coexist. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a flame detection device that can realize stable flame detection.

[0008]

According to a first aspect of the present invention, there is provided a filter means for extracting ultraviolet rays having a longer wavelength range from a flame, a light receiving means for receiving the ultraviolet rays from the filter means, and an output from the light receiving means. Band-pass filter means for extracting a signal of a predetermined frequency band from the signals, and detection for detecting the presence or absence of the flame based on a comparison between a strength of a signal component of a predetermined frequency band extracted from the band-pass filter means and a predetermined reference value. Means.

According to a second aspect of the present invention, in the second aspect, the filter means is 270 nm to 38 nm in an ultraviolet band.
A band that transmits a long wavelength range of 0 nm is used, and a band-pass filter unit that passes a signal in a frequency band of 100 to 800 Hz is used.

As a result, according to the present invention, it is possible to realize stable flame detection without being affected by sunlight or electric light, and it is also possible to detect internal flame of the flame. In other words, for example, the ability to discriminate a flame can be enhanced for a measurement object composed of a plurality of burners.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a flame detecting device to which the present invention is applied. In the figure, reference numeral 11 denotes an ultraviolet light receiving element, which has sensitivity in a long wavelength region (260 nm to 420 nm) of ultraviolet light.
For example, an optoelectronic still camera multiplier tube or a photodiode is used. Specifically, the wavelength 306n of the ultraviolet light
m, those having good detection sensitivity in the vicinity of 309 nm are desirable.
The light receiving element 11 has at least DC to 1 kHz.
z frequency band is required, and desirably, DC to 10
Those having a frequency band of kHz or more are used. The light receiving element 11 has a light receiving surface 111, and converts the ultraviolet light received on the light receiving surface 111 into an electric signal by photoelectric conversion.

Ultraviolet light 14 is incident on a light receiving surface 111 of the light receiving element 11 via a filter 12 and a collimator 13. In this case, the filter 12
The sensitivity wavelength band of the light receiving element 11 is in the visible region (420 nm or more)
It has a function of transmitting a predetermined ultraviolet region and absorbing or reflecting other wavelength regions. As the transmission wavelength band of the filter 12, for example, a filter that transmits a long wavelength range of 270 nm to 380 nm in an ultraviolet band is used. In particular, in the vicinity of a line spectrum (wavelengths 306 nm and 309 nm) emitted by OH groups. Good transmission characteristics are desirable. Specifically, it is a color glass filter called an ultraviolet transmission visible absorption filter having a transmission wavelength band of 270 nm to 380 nm (HOYA
Company, product name UV-340) is used.

As the filter 12, another interference filter may be used. If the sensitivity wavelength band of the light receiving element 11 is only in the ultraviolet region, it can be omitted. The collimator 13 is for improving the directivity, and its element may be constituted by a lens system.

The electric signal output from the light receiving element 11 is
The signal is sent to the band pass filter 16 via the controller 15. Here, the controller 15 drives the light receiving element 11 and controls the electric signal from the light receiving element 11 to be transmitted to the band-pass filter 16. The band-pass filter 16 allows only a predetermined fractional number of signals to pass therethrough.
00-800 Hz, if desired, frequency band 400-
One that passes only a signal of 800 Hz is used.

The signal passed through the band pass filter 16 is sent to a comparator 17. The comparator 17 determines whether a reference signal of a predetermined level is given from the reference signal generator 18 and the signal level sent from the band-pass filter 16 is equal to or higher than the reference signal level. To the external output unit 19
Output to The external output unit 19 outputs “flame present” if the signal level sent from the band-pass filter 16 is equal to or higher than the reference signal level from the comparison result of the comparator 17, and outputs “flame present” if the signal level is equal to or lower than the reference signal level. , "No flame" is output.

Now, in such a configuration, the case where the flame from the burner is detected will now be described. As shown in FIG.
And the outer flame 202. Among them, the inner flame 201 has many OH groups, and therefore, the ultraviolet rays emitted by the inner flame 201 include a line spectrum (wavelength 306n) emitted by the OH groups.
m, 309 nm) and the ultraviolet intensity is high.

In this state, when the light emitted from the inner flame 201 of the flame from the burner 20 is incident on the filter 12, the ultraviolet light 14 emitted from the OH group is transmitted and passes through the collimator 13 to the light receiving element 11. And is output as an electrical signal.

When the electric signal from the light receiving element 11 is sent to the band pass filter 16 via the controller 15, only the signal in the frequency band including the specific frequency component of the ultraviolet light 14 emitted from the OH group is extracted. The reference signal is sent to a comparator 17 where it is compared with a reference signal of a predetermined level from a reference signal generator 18.

From the result of comparison by the comparator 17, if the signal level from the band-pass filter 16 is higher than the reference signal level, "flame present" is output. No flame "is the external output unit 19
Flame 2 of the flame output from the burner 20
From 01, the presence or absence of a flame can be detected.

FIG. 2 shows an experimental example for confirming the characteristic difference between the inner flame 201 and the outer flame 202 constituting the flame from the burner 20. In this case, the arrangement of the light receiving element 11 is changed to the inner flame. The ultraviolet rays 14 are respectively moved to the positions corresponding to the outer flame 201 and the outer flame 202, and the ultraviolet rays 14 respectively emitted are measured, and the frequency is analyzed by the frequency analyzer 21.
In FIG. 2, the same parts as those in FIG.

In this case, the light receiving element 11 uses a photomultiplier tube (Hamamatsu Photonics Co., Ltd., product name PMT-H5784-04).
The voltage applied to the light receiving element 11 is set to 460V. The filter 12 is an ultraviolet transmission visible absorption filter,
The one having a transmission wavelength band of 270 nm to 380 nm (HOYA, product name UV-340) is used.
5 mm and a length of 27 mm are used. The frequency analyzer 21 is FFT-ANALYZER (Ono Sokki Co., Ltd., product name CF-360)
Is used. The burner 20 is LPG-fired, the flame temperature is 1500 ° C., and the center line of the flame and the light receiving element 1
The distance from the first light receiving surface 111 is set to 18 cm.

First, as shown in FIG. 2, the light receiving element 11 is arranged corresponding to the inner flame 201 of the burner 20, and from this state, the light receiving element 11 is driven by the controller 15 so that the light is received by the light receiving element 11. An electric signal corresponding to the ultraviolet light emitted by the inner flame 201 is sent to the frequency analyzer 21 to perform a frequency analysis of the ultraviolet light at this time.
1. Translate the collimator 13 and the filter 12 in parallel,
The light receiving element 11 is made to correspond to the external flame 202 of the burner 20,
This time, an electric signal corresponding to the ultraviolet light emitted by the outer flame 202 received by the light receiving element 11 is sent to the frequency analyzer 21,
Similarly, the frequency analysis of the ultraviolet light at this time was performed.

As a result, the frequency analysis result of the ultraviolet rays emitted from the inner flame 201 is as shown in FIG.
FIG. 4 shows the results of the frequency analysis of the ultraviolet light emitted by the device.
In the Hz band, a signal was observed only in the inner flame 201, and it was confirmed that the outer flame 202 did not exist. At this time DC
The intensity of the components was 12 dB for the internal flame 201, whereas the external flame 202 was 0 dB. It was also found that the external flame 202 was about one digit lower in ultraviolet intensity than the internal flame 201.

Further, in order to examine the possibility that the frequency component of the outer flame 202 is buried in noise and cannot be observed, the voltage applied to the light receiving element 11 is increased to 600 V, and the sensitivity of the outer flame 202 is increased with the sensitivity of the measurement system raised. Ultraviolet light was re-measured.

As a result, as shown in FIG. 5, under this condition, the DC component of the outer flame 202 is about 14 dB,
Although the result is similar to the case of the internal flame 201 shown in FIG. 3 described above, when the results of FIG. 3 and FIG. 5 are compared in detail, in the frequency band of 400 to 800 Hz, only the signal of the internal flame 201 is observed. As a result, it was found that the external flame 202 was not observed or that the level was very low even if observed.

Therefore, as is apparent from the results of the experiment, the electric signal output from the light receiving element 11
Frequency band 100 to 80 by band pass filter 16
By extracting only a signal of 0 Hz and, if desired, a frequency band of 400 to 800 Hz, and comparing this signal level with a predetermined reference level, it is possible to detect only the ultraviolet rays emitted by the inner flame 201 of the flames of the burner 20. it can. In this case, since the intensity of the DC component of the ultraviolet rays emitted by the inner flame 201 is sufficiently large, the ultraviolet rays can be reliably detected without being affected by the ultraviolet rays of sunlight or electric light. Flame detection can be realized. Further, by detecting the internal flame 201 having a sufficiently large intensity of the DC component of the ultraviolet rays emitted from the flame of the burner 20, for example, an individual measurement target can be distinguished from a measurement target constituted by a plurality of burners. Since the flame detection can be performed while the flame is being detected, the ability of discriminating the flame for each burner can be enhanced.

[0027]

As described above, according to the present invention, it is possible to realize stable flame detection without being affected by sunlight or electric light, and to detect internal flame among flames. Thus, for example, the ability to discriminate a flame can be enhanced even for a measurement object constituted by a plurality of burners.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a flame detection device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating frequency analysis of ultraviolet light emitted by a flame according to one embodiment.

FIG. 3 is a diagram showing a result of frequency analysis of ultraviolet light emitted by the internal flame according to the embodiment;

FIG. 4 is a diagram showing a frequency analysis result of ultraviolet light emitted by the outer flame of one embodiment.

FIG. 5 is a diagram showing a frequency analysis result of ultraviolet light emitted by the outer flame of the embodiment.

FIG. 6 is a diagram showing a schematic configuration of an example of a conventional flame detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Light receiving element, 111 ... Light receiving surface, 12 ... Filter, 13 ... Collimator, 14 ... Ultraviolet light, 15 ... Controller, 16 ... Bandpass filter, 17 ... Comparator, 18 ... Reference signal generator, 19 ... External output part, Reference numeral 20: burner, 201: internal flame, 202: external flame, 21: frequency analyzer.

Claims (2)

[Claims] 1. A filter means for extracting ultraviolet rays having a longer wavelength range from a flame, a light receiving means for receiving ultraviolet rays from the filter means, and a band-pass filter for extracting a signal of a predetermined frequency band from an output signal from the light receiving means. Means for detecting presence or absence of the flame based on a comparison between the intensity of a signal component in a predetermined frequency band extracted from the band-pass filter and a predetermined reference value. . 2. The filter means has a wavelength of 270 nm in the ultraviolet band.
Those that transmit a long wavelength region of m to 380 nm are used,
The bandpass filter means has a frequency band of 100 to 800.
2. The flame detection device according to claim 1, wherein a device that passes a signal of Hz is used.