JPS60133217A - Flame detector - Google Patents

Abstract

PURPOSE:To ensure the detection of flame even though the shapes of the flame are changed due to the change in burning conditions and the like and to perform self-checking without using a mechanical shutter, by guiding light beams from the different parts of the flame, converting the light beams into electric signals by photoelectric conversion parts, and judging the presence of the flame based on said electric signals. CONSTITUTION:Light detecting parts 3a, and 3b and 3c are constituted by the tip parts of optical fibers. The light detecting part 3a is obliquely provided in the upward direction. The light detecting part 3b is provided at a slant angle smaller than the light detecting part 3a. The light detecting part 3c is provided approximately horizontally. The detected light beams from the light detecting parts 3a, 3b and 3c are transmitted to photoelectric conversion parts 5a, 5b and 5c and converted into the corresponding electric signals, which are sent to an operating part 8. In the operating part 8, the signal having the maximum value among the input signals is held. The maxium value is compared with the threshold level concerning to the presence or absence of the flame. When the value is larger than the threshold level, a flame ON signal is outputted. When the value is less then the threshold level, a flame OFF signal is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flame detection device for determining whether a burner of a combustion device such as a boiler is ignited or extinguished.

The flame detection device includes an optical flame detection device that detects the light V emitted by the flame, an ion current flame detection device that electrically detects ions generated in the flame, and a combustion sound that is generated during combustion. There are combustion sound type flame detection devices, etc., which are selected and used as appropriate depending on the target combustion device. For example, in commercial boilers, conventionally, an optical flame detection device is used for the main burner, and an optical flame detection device or an ion current flame detection device is used for the ignition burner. However, the ionic current type flame detection device requires the electrode rod to be installed in the flame or very close to the flame in order to detect the ionic current, so it is not suitable for continuous use due to the heat resistance of the material. . Therefore, in order to continuously detect the presence or absence of flame, only optical flame detection devices are currently used. It is classified into DC light detection method, which focuses on the amount of light emitted by the flame (DC component light amount), and AC light detection method, which focuses on the fluctuating amount of light (light amount of AC component). specific wavelength range (e.g. ultraviolet range,
(visible region, near-infrared region, infrared region, etc.), and are classified into, for example, ultraviolet DC light detection method, infrared infrared region C light detection method, etc. In the AC light detection method, the fluctuation component (
AC component) specific frequency band (e.g. 10~lOO
Hz band, etc.), it is subdivided into, for example, a 10-100Hz band AC photodetection method. Among these, the DC light detection method is effective in cases where the number of burners is very small and the wall temperature of the combustion chamber is low, or when the fuel can be expected to emit light unique to a specific wavelength range. The AC optical detection method is considered to be more effective in cases where there are many burners, such as in boilers, and where the flames of each burner are closely related to each other, causing the flame shape to fluctuate in a complex manner both temporally and spatially. It is said. In addition, regarding the AC light detection method, which frequency/band AC is used for each wavelength range emitted by the flame?
It is unclear whether light detection is the most effective method. As mentioned above, there are various types of optical flame detection devices, but even in the optical flame detection system, flame detection is determined depending on whether the detection signal (size or level) is larger or smaller than a certain threshold level. fire/extinguishing judgment.

By the way, the flame in the boiler furnace is a type of fuel. load.

Combustion conditions such as air-fuel ratio, and other burner points in the furnace.

The flame shape force varies greatly depending on the extinguishing conditions. For this reason, conventional optical flame detection devices have a drawback in that it is difficult to reliably detect the presence or absence of flame. In addition, in conventional optical flame detection devices, a mechanical shutter is installed in front of the light receiving surface of the photoelectric conversion section. With the self-check mechanism installed, does it output a flame OFF signal when the shutter is closed? It used to be possible to improve the reliability of flame detection by checking the operation of the flame detection device itself, but since the self-check mechanism uses a mechanical shutter, the flame detection device itself is large and expensive. (However, it had the disadvantage of causing malfunctions.)

The purpose of the present invention is to eliminate these conventional drawbacks, to be able to reliably detect flames even if the flame shape changes due to changes in combustion conditions, etc., and to be able to detect flames reliably without using a mechanical shutter. To provide a flame detection device capable of performing seven self-checks.

To achieve this objective, the present invention guides light from different parts of the flame, converts each of these lights into electrical signals by a photoelectric converter, and determines the presence or absence of a flame based on the converted electrical signals. It is a characteristic that I tried to do.

The present invention will be explained below based on the embodiment shown in FIG.
Ru.

FIG. 1 is a block diagram of a flame detection device according to an embodiment of the present invention. In the figure, 1 is the flame inside the furnace, and 2 is the wind box on the outer wall of the furnace. 3a.

3b and 3C are photodetecting sections that detect the light of the flame 1, respectively; these are photodetecting sections 3a, 3b, and 3c%! Both are composed of the tip portions of optical fibers, the photodetector 3a is installed with an upward slope, and the photodetector 3b is installed at an angle above the photodetector 3.
It is installed at an inclination smaller than a, and the photodetector s30 is installed almost horizontally. A broken line a indicates a detection field of view of the photodetector 3a, a broken line indicates a detection field of view of the photodetector 3b, and a broken line C indicates a detection field of view of the photodetector 3C. 4 is a detection unit 3a;
3b and 3c, which constitutes a light transmission section and a light detection section 3a.

3b and 3C transmit the detected light. The optical transmission section 4 is provided with an appropriate air cooling mechanism. 5a.

Reference numerals 5b and 5c are photoelectric conversion units that receive detection lights from the photodetectors 3a, 3b, and 3c transmitted by the optical transmission unit 4, respectively, and convert them into electrical signals corresponding to each detection light. Photoelectric conversion units 5a and 5b.

5C uses optical sensors that all have the same detection wavelength range. 6a, 6b, 6c are photoelectric conversion units 5a, 5b,
A preamplifier 9 selectively amplifies the output signal of the amplifier 5c, and a switching unit 7 switches the output signals of the amplifiers 6a, 6b, and 6c. Reference numeral 8 denotes an arithmetic processing section which sequentially inputs the signals switched by the switching section 7 and judges whether there is a flame or not, including a self-contained signal. 9 connects the switching unit 7 to the amplifying units 6a and 6.
b.

It outputs a command signal for switching the signal of 6C in a predetermined switching sequence (M order, timing), inputs the plant control signal g, and sends the required control signal to the arithmetic processing unit 8. This is a switching control unit that outputs.

Next, the operation of this embodiment will be explained in Figs.
This will be explained with reference to characteristic diagrams of output signals in each visual field shown in FIGS. Optical inspection section 3a
, 3b, 3c)! Light is detected from the fields of view a, b, and C, respectively, and this detected light is transmitted to the photoelectric conversion unit 5a via the optical transmission unit 4.
, 5b. 5c.

The photoelectric conversion units 5a, 5b, and 5c each receive these detection lights and output electric signals corresponding to the detection lights. Here, photoelectric conversion ffB5a, 5 when flame l exists
b, 5c17) The output signals are shown in FIGS. 2(I)-@) and 3(I)-GII). Figure 2 (Il~(111
1) Is there a near-infrared sensor in the photoelectric conversion units 5a, 5b, and 5c?
An example of the output signal in the field of view C, b, a when using
FIGS. 3(I) to 3) are examples of output signals in the field of view Ce bea when the photoelectric conversion units 5a, 5b, and 5cK infrared sensor sensors are used.

In addition, the horizontal axis of each figure shows the AC light fluctuation frequency7)
From these figures, it can be seen that in the presence of flame, there is a particularly large difference between the output signal in the visual field a and the output signal in the visual field A.

The output signals of such photoelectric conversion units 5m, 5b, and 5c are output to amplification units 6a, 6b, and 6c, respectively.
, 6b, and 6c selectively amplify only the components of these signals having a constant fluctuation frequency (for example, 100 Hz) or higher. Each amplified signal is sequentially switched by the switching section 7 and sent to the arithmetic processing section 8. In the arithmetic processing unit 8, the amplification unit 6a,
6b.

The signal having the maximum value among the input signals from 6c is held, and this maximum value is compared with the threshold level for flame presence/absence, and if it is above the threshold level, the flame ON signal! , and if it is less than the threshold level, the flame OFF signal power is output. The signal shown in Figure 1! shows such a flame ON/OFF determination signal. In this way, since the flame is captured in the fields of view a, b, and c in the three directions of the flame IF, even if the flame shape changes over time by becoming longer or shorter, the switching unit 7 can control the amplification units 6a and 6b. Flame can be detected while switching the three output signals from 6C (during 1 cycle), and a flame ON signal can be reliably output.

Next, the self-check operation of this embodiment will be explained with reference to FIG. 4. In an optical transmission section composed of an optical fiber, there is a risk of accidents such as disconnection due to the heat resistance of the optical fiber. When such an accident occurs, it may be determined that there is no flame even if the flame l is present. Therefore.

To determine that there is no flame, it is necessary to confirm that there is no abnormality such as a disconnection in the optical transmission section 4, and then perform the determination 7 that the flame is OFF when the signal level is less than the threshold level. now,
Assume that in the presence of flame I, a break has occurred in the optical fiber extending from the detection section 3b that transmits an important signal for determining the presence of a flame. In this case, the outputs of the photoelectric conversion units 5c, 5b, and 5a using near-infrared sensors are shown in FIGS. 4(I) to (III), with the AC light fluctuation frequency plotted on the horizontal axis.
Shown below. As is clear from the figure, the output of the photoelectric conversion section 5b is extremely small compared to the output level shown in FIG. 2 (II), and only a small amount of output is produced in the low frequency range. Therefore, as described above, for example, only the components above 1001 (z) are transmitted to the amplifiers 6a and 6b.

When selectively amplified with 6C, each field of view a, b, and c are xooH
Since there is no fluctuating frequency component higher than z, the arithmetic processing unit 8 outputs a flame OFF signal even though the flame l exists.□However, in this embodiment, the arithmetic processing unit 8 Add an abnormality determination function to prevent incorrect determinations. That is, the arithmetic processing unit 8 includes means for comparing whether the level of the low frequency component (e.g., DC to 5 Hz) of the input signal of each visual field is below a certain threshold level, and 1Hz)
A means for determining the level relationship between input signals is provided. See the table below.

The relationship between the signal levels in normal and abnormal cases!
(When a near-infrared sensor is used in the photoelectric conversion section.)

Then, by each of these means, it is determined that the level of the low frequency component of the input signal in each field of view is below the threshold level, and that the magnitude relationship of the signal levels between each transmission path is in a relationship other than the normal state shown in the table above. When this occurs, the optical transmission path abnormality signal f is output from the arithmetic processing unit 8 to issue an abnormality alarm. This can prevent an erroneous determination, that is, a determination that there is no flame even though there is a flame.

As mentioned earlier, the shape of the flame varies greatly depending on combustion conditions such as load and air-fuel ratio. For this reason, the magnitude relationship of the low frequency signal levels between the above-mentioned transmission lines also changes. Therefore, in this embodiment, the load.

A plant control signal g related to the combustion state such as the air-fuel ratio is input to the switching control section 9, and according to this input, the arithmetic processing section 8
The threshold level and the normal magnitude relationship of the signal level between each transmission path are changed. This allows for a wide range of responses to changes in flame shape.

In this way, in this example, three optical fibers are used,
Since each of these tips is used as a photodetector and the field of view of each photodetector is different, the flame can be reliably detected even if the shape of the flame changes. Furthermore, since an optical fiber is used, the optical transmission section can be configured to be small. Furthermore, since the arithmetic processing section is provided with a means for comparing the signal levels of each of these photodetecting sections and a means for comparing the magnitude relationship of the signal levels, self-check can be performed without providing a mechanical shutter mechanism. This can contribute to simplifying the device and reducing its cost. Furthermore, since the threshold level in the means for comparing the signal levels and the magnitude relationship in the means for comparing the magnitude relationship of the signal levels are changed based on the plant control signal, the Check what you can do.

In addition, in the description of the above embodiment, an example was explained in which three optical fibers V are used as the photodetector, but the number is not limited to three, and may be two or four or more, and
It is not necessarily limited to optical fibers; other suitable photodetectors can be used. Furthermore, each photoelectric conversion section does not necessarily need to be composed of optical sensors having the same detection wavelength range, but can also be composed of optical sensors having different detection wavelength ranges. In addition, the plant control signal input to the switching control unit is not only used to improve the self-check function (but can also be used as follows: The photoelectric conversion section is composed of optical sensors with various different detection wavelength ranges, the amplification section V is composed of amplifiers that selectively amplify various frequency bands, and the switching section 7 is switched and controlled according to the plant control signal. By inputting only a predetermined signal to the arithmetic processing unit, the detection field of view 9 can be made to follow at least one of the detection wavelength range of interest and the frequency band of AC light in response to changes or changes in combustion conditions. In addition, it is possible to perform more accurate flame detection by diversifying the criteria for determining the presence or absence of flame.Furthermore, the threshold level for determining the presence or absence of flame in the arithmetic processing section can be changed in accordance with the plant control signal. It can also be made to follow changes or changes in combustion conditions.

As described above, in the present invention, a plurality of light guide parts with different fields of view are provided for the flame, and the light from these light guide parts is converted into electric signals corresponding to the light guide parts. Since 5 is set to determine the presence or absence of flame, flame can be reliably detected even if the flame shape changes, and
Self-check can be performed without using a mechanical shutter 2.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a flame detection device according to an embodiment of the present invention, FIGS. 2(I), (n), (m), and FIGS. 3(I), (
II), Tsukuda) and FIGS. 4(I), (II), ■) are characteristic diagrams of output signals in each field of view. l...Flame, 2...Wind box, 3a. 3b, 3c...Photodetection section, 4...Optical transmission section, 5a. 5b, 5c...Photoelectric conversion section, 6g, 6b, 6c
...Amplifying section, 7...Switching section, 8...
... Arithmetic processing unit, 9... Switching control unit, a, b
, c... Field of view.

Claims (1)

[Claims] 1. A plurality of light guide parts that guide light from different parts of the flame;
Features include a photoelectric conversion section that converts the light guided by the light guide section of and into electrical signals, and a calculation processing object that determines whether there is a flame based on each signal of the photoelectric conversion section of and. flame detection device.