JP2006329474A - Flame detecting device in combustor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flame detecting device capable of surely detecting flame even the combustion flame of small light quantity such as blue combustion flame, when the flame is detected by using a photodiode. <P>SOLUTION: This flame detecting device comprises a backward voltage variable means 13 for switching backward voltage applied to the photodiode 9 from a small value to a large value by signal output from a current output adjusting portion 122 of a controller 12. The photo-electric current is increased by switching the backward voltage to the large value. In addition thereto, a load resistance value of a load resistance 151 is determined to be smaller than a limit resistance value of the photodiode itself to allow large photo-electric current to flow. Further a current limiting means 15 is mounted for limiting the maximum current to be less than an allowable maximum current value to prevent flowing of electric current over the allowable maximum electric current to the photodiode to complement them. The flame is detected by comparing the photo-electric current after current-voltage conversion, amplification and A/D conversion, with a determination value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flame detection device in a combustor used for detecting the state of a combustion flame of a combustor.

  Conventionally known as a flame detection device is that the light of a combustion flame is converted into an electric signal by a light receiving element (photosensor) such as a photodiode, and ignition and extinguishing are detected based on this electric signal output. (See, for example, Patent Document 1). In this device, the amount of incident light from the combustion flame is converted into a current signal by a photodiode, the current signal output from the photodiode is converted into a voltage signal by a current-voltage conversion circuit, and the converted voltage signal is converted into a digital signal by AD conversion. When the output value by this digital signal is larger than a preset ignition determination value, the output is turned ON, while when the output value is smaller than the fire extinguishing determination value, the output is turned OFF. And while it is set as ignition detection by the change from OFF to ON, it is set as fire extinguishing detection by the change from ON to OFF.

JP 2004-232971 A

  However, when a photodiode such as the conventional flame detector is used as an optical sensor, there is a possibility that the combustion flame cannot be reliably detected.

  In other words, development is progressing to achieve cleaner combustion and efficient combustion such as low NOx combustion, etc. However, if such development is advanced, the combustion flame tends to be more blue fire combustion, and the combustion flame As a result of the decrease in the amount of light emitted, the output from the light receiving element is further weakened, and it may be difficult to obtain accurate or reliable ignition detection or extinguishing detection. In particular, low NOx combustion is realized when burned using synthetic liquid fuel (GTL; Gas To Liquid: petroleum synthesized using natural gas as a raw material), which has been developed for practical use in recent years. Although shown, the combustion tends to be a blue fire combustion than the conventional one. This blue fire combustion flame has low luminance and the light emission amount of the flame becomes weak, and as a result, the output from the optical sensor becomes extremely weak. As a result, there is a possibility that ignition detection or the like cannot be performed accurately.

Here, when a phototransistor PT which is a kind of optical sensor is taken as an example as shown in FIG. 5, the relationship between the optical input I _B and the photocurrent I _C in this phototransistor PT (see FIG. 5A) is the current. It is determined by the amplification factor h _FE (h _FE = I _C / I _B ). If the optical input I _B is reduced, the photocurrent I _C (I _C = h _FE × I _B ) is also reduced and a detection limit occurs. . For example, as shown in FIG. 5B, the relationship between the collector-emitter voltage V _CE and the photocurrent I _C when the combustion flame is red and blue is shown. although I _B serves as a light current I _C is also large becomes large, the magnitude of the load resistance R _L of the light current I _C is also small, and the case when the optical input I _B is small as in the case of blue fire Does not affect much.

On the other hand, when the photodiode PD of the reverse voltage connection type is taken as an example as shown in FIG. 6, since the photodiode PD (see FIG. 6A) is a current element, the photocurrent I _C is the received light. although electromotive current proportional to the amount of results, the light current I _C itself is the size and the resistance value of the load resistor R _L, varies depending on the magnitude of the reverse voltage V _R. For example, as shown in FIG. 6B, the relationship between the output voltage V and the photocurrent I _C when the combustion flame is red and blue is shown, the light input becomes large in the case of red fire. In both the case of red fire and the case of blue fire where the light input becomes small, the photocurrent I _C becomes easier to flow and increases as the load resistance _RL becomes smaller than large. However, if the photocurrent I _C is too flows excessively, the photodiode PD itself will be destroyed, it becomes impossible to perform its function. Therefore, in order to prevent this breakdown from occurring, the resistance value of the load resistance _RL is fixed to a predetermined value or more. However, if the resistance value of the load resistance _RL is fixed to a predetermined value or more, the value of the photocurrent is also limited to the corresponding value. Therefore, when the photodiode is used for flame detection, the flame illuminance Even if it receives weak light (the above-mentioned NOx reduction flame or the above-mentioned GTL combustion flame), there arises a problem that it becomes difficult to detect the combustion flame.

  The present invention has been made in view of such circumstances, and an object of the present invention is to produce a combustion flame with a small amount of light such as a blue fire combustion flame when detecting a flame using an optical sensor such as a photodiode. Even so, an object of the present invention is to provide a flame detection device that can reliably detect the flame.

  In order to achieve the above object, a flame detection process for detecting a state of the combustion flame by a photodiode that outputs a photocurrent upon receiving incident light from a combustion flame of a combustor and an output value based on the photocurrent Various inventions having the following specific items were completed for a flame detection apparatus in a combustor equipped with means.

  In the first invention, reverse voltage variable means for making variable the reverse voltage applied to the photodiode, and current limiting means for limiting the maximum current flowing through the photodiode to a maximum allowable current value of the photodiode itself, And a current output adjusting means for increasing the photocurrent value with respect to the light input at the photodiode by changing and controlling the reverse voltage to a larger value side by a signal output to the reverse voltage varying means. Item 1).

  In the case of the present invention, when a signal is output from the current output adjusting means and the reverse voltage is changed to a larger value side by the reverse voltage variable means, the photocurrent value for the light input of the light received from the combustion flame by the photodiode is greatly changed. Will be. For this reason, even when a light with a small amount of light is received from a combustion flame such as a blue fire, it becomes possible to generate a photocurrent of a predetermined value or more, and in the flame detection processing means based on the output value based on the photocurrent. It becomes possible to reliably detect the state of the combustion flame such as the above-mentioned blue fire. On the other hand, even when a large light input is received from the combustion flame due to combustion abnormality or the like, the photocurrent generated in the photodiode by the current limiting means is limited to the allowable maximum current value or less of the photodiode itself, The photodiode can be protected by reliably avoiding damage to the photodiode caused by changing the reverse voltage to the large value side. That is, it is possible to achieve both flame detection of a combustion flame such as blue fire and protection of the photodiode.

  In the second invention, the load resistance value for the photodiode is set smaller than the limit resistance value of the photodiode itself, and the maximum current flowing through the photodiode is less than the maximum allowable current value of the photodiode itself. Current limiting means for limiting the current to the current level (Claim 2).

  In the case of the present invention, since the resistance value of the load resistor is set smaller than the limiting resistance value of the photodiode itself, the photocurrent easily flows and the photocurrent with respect to the light input of the light received from the combustion flame by the photodiode. The value will increase more. For this reason, even when a light with a small amount of light is received from a combustion flame such as a blue fire, it becomes possible to generate a photocurrent of a predetermined value or more, and in the flame detection processing means based on the output value based on the photocurrent. It becomes possible to reliably detect the state of the combustion flame such as the above-mentioned blue fire. On the other hand, even when a large light input is received from the combustion flame due to combustion abnormality or the like, the photocurrent generated in the photodiode by the current limiting means is limited to the allowable maximum current value or less of the photodiode itself, The photodiode can be protected by reliably avoiding the damage of the photodiode caused by setting the resistance value of the load resistor to be small. Therefore, according to the present invention, it is possible to achieve both flame detection of a combustion flame such as blue fire and protection of the photodiode.

  In the third invention, reverse voltage variable means for varying the reverse voltage applied to the photodiode, and a load resistance in which a load resistance value for the photodiode is set smaller than a limit resistance value of the photodiode itself, The current limiting means for limiting the maximum current flowing through the photodiode to be equal to or less than the maximum allowable current value of the photodiode itself, and the reverse voltage is controlled to be changed to a larger value side by a signal output to the reverse voltage variable means. Current output adjusting means for increasing the photocurrent value with respect to the light input in the photodiode is provided.

  In the case of this invention, it becomes possible to exhibit the action of the action of the first invention and the action of the second invention, and the flame detection in the state of a combustion flame with a small input light quantity such as blue fire Thus, it becomes possible to more reliably realize the protection of the photodiode while avoiding the damage of the photodiode.

  As described above, according to the flame detection device in the combustor of any one of claims 1 to 3, reliable flame detection in the state of a combustion flame with a small amount of input light such as blue fire, and a photodiode It is possible to realize both the protection of the photodiode by avoiding the damage. In particular, according to the first aspect of the present invention, the increase in the photocurrent due to the change of the reverse voltage to the large value side by the current output adjusting means using the reverse voltage variable means and the large value side change of the reverse voltage are complemented. By limiting the maximum current flowing through the photodiode to the allowable maximum current value or less by the limiting means, the above-described compatibility can be realized. According to the second aspect of the present invention, the maximum current flowing through the photodiode by the current limiting means is compensated for by increasing the photocurrent by setting the resistance value of the load resistance to be smaller than the limiting resistance value and the small setting of the load resistance value. By limiting to the allowable maximum current value or less, the above-described compatibility can be realized. According to the third aspect, it is possible to obtain an effect having both the effect of the first aspect and the effect of the second aspect, and it is possible to achieve the above-described compatibility more reliably.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 shows that of a water heater as an example of a combustor to which a flame detection apparatus according to an embodiment of the present invention is applied. The water heater includes a combustor 1, a heat exchanger 2 that heats and heats the combustion heat from the combustor 1, and a water supply channel that is connected to a water pipe or the like and supplies tap water or the like to the heat exchanger 2. 3 and a hot water supply passage 4 for supplying hot water heated by the heat exchanger 2 and supplying hot water to a downstream hot water supply curan or the like through a hot water supply passage (not shown) are installed in the case 5. .

  The combustor 1 includes a combustion burner 6 for burning fuel supplied from a fuel supply system (not shown), a blower fan 7 for supplying combustion air to the combustion burner 6, and an igniter 8 as an igniter. I have. The combustion burner 6 is composed of, for example, a gun type burner, and is configured to atomize and burn liquid fuel. In the vicinity of the combustion burner 6, a photodiode 9 is disposed as a light receiving element (photosensor) that emits light based on the combustion flame formed in the combustion burner 6 and outputs a current signal proportional to the amount of light. ing.

  The water supply path 3 is provided with a solenoid valve 10 for adjusting the flow rate and a flow rate sensor 11 for detecting the water supply flow rate, and a controller 12 is disposed at an appropriate position in the case 5. The controller 12 includes a CPU, a memory, a storage device, and the like, and detects the state of the combustion flame of the combustion burner 6 in addition to hot water supply control based on the combustion control of the combustor 1 based on a preinstalled program. The processing part (the flame detection process part and photocurrent output adjustment part mentioned later) on the control of the flame detection apparatus to perform is performed.

  The hot water supply control unit uses, for example, detection information from the flow sensor 11 that a hot water supply curan (not shown) is opened by a user and water from the water supply path 3 enters and the flow rate is equal to or higher than a predetermined minimum operation flow rate. After confirmation, the fuel supply system is operated (for example, the fuel supply valve is opened), and the igniter 8 ignites the combustion burner 6. And hot water supply is continued, adjusting the combustion amount of the combustion burner 6 so that the hot water supply temperature becomes a predetermined hot water supply temperature based on the temperature detected from the hot water temperature sensor (not shown). At that time, the air supply amount is changed according to the combustion amount or the like by the operation control of the blower fan 7. If the detection information from the flow sensor 11 falls below the minimum operating flow rate as the hot water supply curan is closed, the fuel supply of the combustion supply system is stopped, the combustion burner 6 is extinguished, and the blower fan 7 is operated for a certain time after the extinction. To scavenge the combustion exhaust gas. The above processing is executed based on the output of the ignition detection or extinguishing detection output from the flame detection processing unit, and when ignition detection is not output despite starting combustion, it is determined that combustion failure has occurred and combustion is not performed. A safety process such as a forced stop process is executed.

  FIG. 2 shows an example of a circuit for realizing various means constituting the flame detection device and the controller 12. In FIG. 2, reference numeral 13 is a reverse voltage variable means, 151 is a load resistance, 15 is a current limiting means, and 16 is a photocurrent analog. The controller 12 includes a hot water supply control unit (not shown), a flame detection processing unit 121, and a photocurrent output adjustment unit 122.

The reverse voltage varying means 13 switches between a low value V _L1 (see FIG. 3) and a large value V _L2 as the reverse voltage V _L applied to the photodiode 9 from the reverse voltage power source. by, the magnitude changes the optical current value with respect to an optical input of the photodiode 9, i.e. is intended to output adjustment, switching between the reverse voltage V _L1 and V _L2 is the voltage signal from the photocurrent output adjustment unit 122 of the controller 12 This is performed by outputting (applied voltage switching signal). Specifically, an applied voltage switching signal is output from the controller 12 according to the required combustion amount calculated from the hot water supply flow rate or the set temperature information, and this is changed to an input voltage by the reverse voltage variable means 13. Thus, the base voltage to the transistor 133 is switched, and the reverse voltage V _L applied to the cathode side of the photodiode 9 is switched between V _L1 and V _L2 to be variable.

The resistance value R _{L1 of the} load resistor 151 is set to be smaller than the limit resistance value (= V _L / Imax) in the specification as the device of the photodiode 9.

R _L1 <V _L / Imax
Here, _VL is a reverse voltage, and Imax is a maximum output current.

Since the current limiting means 15 has set the resistance value R _L1 of the load resistor 151 to be smaller than the limiting resistance value as described above, an excessive photocurrent is generated to compensate for this and prevent the photodiode 9 from being damaged. In order to prevent the flow, a function as a current limiter is realized. That is, since the load resistor 151 is set to a resistance value smaller than the limit resistance value, a large photocurrent flows when there is a large light input to the photodiode 9, so that damage to the photodiode 9 is avoided. The maximum current flowing through the photodiode 9 is limited to be equal to or less than the allowable maximum current value.

  The flame detection processing unit 121 performs each determination process of ignition detection and fire extinguishing detection according to the output value based on the photocurrent signal from the photodiode 9. Specifically, if the output value fluctuates from a small value side to a large value side with a predetermined ignition judgment value set in advance, it is determined that the ignition is detected, while the output value after the ignition detection is the same as above. If it changes from a large value side to a small value side with a fire extinguishing judgment value set in advance as a boundary, it is judged that fire extinguishing is detected. The output value used for the flame detection is converted from the photocurrent signal into a voltage signal by a current-voltage conversion circuit (for example, using a resistor 151), or A / D conversion is performed through a predetermined photocurrent analog reading circuit 16. Then, the flame detection processing unit 121 takes in the information. In addition, it is possible to determine and detect that vibration combustion, other abnormal combustion, or the like has occurred by taking in an analog signal to the flame detection processing unit 121 and monitoring a continuous change.

In the above case, even if the light input is a small blue fire as shown in FIG. 3, by changing the reverse voltage value from the small value V _L1 to the large value V _L2 , the small value V _{L1 is changed.} In this case, when the photocurrent value I _C1 is switched to the large value V _L2 , it can be changed to a larger photocurrent value I _C2 . By performing the flame detection in the flame detection processing unit 121 based on the photocurrent value I _C2 , the flame detection can be surely performed even for a flame having a blue fire combustion tendency.

In addition, the photodiode 9 is also protected by the current limiting by the current limiting means 15 (see I _{CUT in} FIG. 3). That is, the load resistance 14 is set to be equal to or less than the limit resistance value so that the photocurrent with respect to the light input is increased, and the reverse voltage is switched to the larger value side so as to increase the photocurrent. Even if the flame detection is ensured, it is possible to prevent the allowable maximum current of the photodiode 9 from flowing when the light input becomes unexpectedly large, and the photodiode 9 is surely damaged. Can be avoided and protected.

Second Embodiment
FIG. 4 shows a circuit example for realizing various means constituting the flame detection apparatus as the second embodiment, in which the reference numeral 15b denotes a current limiting means, 16b denotes an amplifier circuit, and 17 denotes a load resistance. The second embodiment is the same as the first embodiment except that the reverse voltage variable means is omitted, and the same components are denoted by the same reference numerals and detailed description thereof is omitted. To do.

As described in the first embodiment, the load resistor 17 has a resistance value R _L set smaller than the limit resistance value (= V _L / Imax) in the specification of the photodiode 9.

R _L <V _L / Imax
As a result, the photocurrent generated in the photodiode 9 is further increased, so that a photocurrent of a predetermined value or more flows even for weak light such as blue fire.

The current limiting means 15b includes, for example, an operational amplifier 155 and a transistor 156 to which an output from the operational amplifier 155 is added as a base current, and flows to the photodiode 9 depending on the resistance value _RL of the load resistor 17 and the constant of the operational amplifier 155. The current is limited so that the photocurrent falls within the allowable maximum current of the photodiode 9 as a device. As a result, when the resistance value _RL of the load resistor 17 is set to be smaller than the limit resistance value as described above, an excessive photocurrent is prevented from flowing in order to compensate for this and prevent the photodiode 9 from being damaged. Therefore, the function as a current limiter is realized.

  And in this embodiment, even if it is a combustion flame, such as a blue fire, by the said load resistance 17, a photocurrent more than predetermined value is received in response to the light input, and the flame detection process part 121 ensures flame detection. On the other hand, even when a large light input such as red fire is received due to an abnormality in the combustion state or the like, the current limiting means 15b causes the photodiode 9 to emit light having an allowable maximum current value or less. Since the current is limited, the device such as the photodiode 9 can be reliably protected from being damaged.

<Other embodiments>
The present invention is not limited to the above-described embodiments, but includes other various embodiments. That is, in each said embodiment, although the combustor 1 of the hot water heater was shown as a combustor with which a flame detection apparatus is mounted, this invention is not limited to this but is used as a flame detection apparatus in various combustors other than the hot water heater. Can be applied.

  In addition, an amplifier circuit is not essential, but when mounted, the amplification factor can be changed so that, for example, at the time of shipment from the factory, the use conditions of the water heater at the shipping destination (for example, the type of fuel used), etc. Accordingly, it is possible to change and set the amplification factor suitable for flame detection determination such as ignition detection, thereby further ensuring the flame detection.

  Further, in the first embodiment, in addition to the installation of the reverse voltage variable means 13, the resistance value of the load resistor 151 is set smaller than the limit resistance value in the specification as the device of the photodiode 9, and the photodiode 9 The generated photocurrent is further increased. However, the present invention is not limited to this, and the resistance value of the load resistor may be larger than the limiting resistance value. In this case, the reverse voltage varying means 13 and the current limiting means 15 The increase in photocurrent generated in the photodiode 9 by installation and the avoidance of excessive current flow may be achieved.

It is a mimetic diagram showing an example of a combustor to which an embodiment of the present invention is applied. It is a figure which shows the circuit example of the flame detection apparatus of 1st Embodiment. It is a relationship figure of the voltage (reverse voltage) and photocurrent in a 1st embodiment. It is a figure which shows the circuit example of the flame detection apparatus of 2nd Embodiment. FIGS. 5A and 5B are diagrams for explaining the problem using a phototransistor as an example, FIG. 5A is a circuit example using the phototransistor, and FIG. 5B is a relationship diagram between voltage and photocurrent. FIGS. 6A and 6B are diagrams for explaining the problem by taking a photodiode as an example, FIG. 6A is a circuit example using the photodiode, and FIG. 6B is a relationship diagram between voltage and photocurrent.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Combustor 9 Photodiode 13 Reverse voltage variable means 17, 151 Load resistance 15, 15b Current limiting means 121 Flame detection processing part (flame detection processing means)
122 Current output adjustment unit (current output adjustment means)

Claims (3)

In a combustor provided with a photodiode that receives incident light from a combustion flame of a combustor and outputs a photocurrent, and a flame detection processing means that detects the state of the combustion flame according to an output value based on the photocurrent A flame detection device,
Reverse voltage variable means for varying the reverse voltage applied to the photodiode;
Current limiting means for limiting the maximum current flowing through the photodiode to be equal to or less than the allowable maximum current value of the photodiode itself;
Current output adjusting means for increasing the photocurrent value with respect to the light input to the photodiode by changing and controlling the reverse voltage to a larger value side by a signal output to the reverse voltage variable means. Flame detection device for a combustor. In a combustor provided with a photodiode that receives incident light from a combustion flame of a combustor and outputs a photocurrent, and a flame detection processing means that detects the state of the combustion flame according to an output value based on the photocurrent A flame detection device,
A load resistance for which the load resistance value for the photodiode is set smaller than the limiting resistance value of the photodiode itself;
A flame detection device in a combustor, comprising: current limiting means for limiting a maximum current flowing through the photodiode to a value equal to or less than an allowable maximum current value of the photodiode itself. In a combustor provided with a photodiode that receives incident light from a combustion flame of a combustor and outputs a photocurrent, and a flame detection processing means that detects the state of the combustion flame according to an output value based on the photocurrent A flame detection device,
Reverse voltage variable means for varying the reverse voltage applied to the photodiode;
A load resistance for which the load resistance value for the photodiode is set smaller than the limiting resistance value of the photodiode itself;
Current limiting means for limiting the maximum current flowing through the photodiode to be equal to or less than the allowable maximum current value of the photodiode itself;
Current output adjusting means for increasing the photocurrent value with respect to the light input at the photodiode by changing and controlling the reverse voltage to a larger value side by a signal output to the reverse voltage variable means. Flame detection device for a combustor.

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