JPH0423168B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a device for detecting the state of combustion of gas, oil, etc., using the flame of the combustion device.

BACKGROUND ART Conventionally, since combustion type heaters such as fan heaters burn indoors, it is necessary to reliably detect flame ignition, misfire, decrease in indoor oxygen concentration, or incomplete combustion. Frame rod sensors are widely used as this type of detection sensor. This sensor detects the combustion state by detecting the ion current of the flame, and there is one such as that disclosed in Japanese Utility Model Application Publication No. 145422/1983, for example. This operation will be explained using FIG. 5.

Fuel gas is ejected from a nozzle 1, mixed with air through a mixing pipe 2, and then delivered to the inner surface 4 of a combustion plate 3 formed of wire mesh.
It forms a flame 5 and burns. 6 is a flame rod inserted into the flame 5, and a DC power source 7 is applied between it and the combustion plate 3, and a resistor 8
The configuration is such that it is detected by

With the above configuration, the flame current If is detected by the voltage drop across the resistor 8, and when this output becomes below or above a certain threshold value, abnormal combustion is determined, fuel supply is stopped, and the fire is extinguished. Alternatively, the amount of fuel supplied or the amount of combustion air supplied is controlled by increasing or decreasing so that the flame current If is maintained within a constant width.

Problems to be Solved by the Invention However, flames generally fluctuate, and the flame current also fluctuates greatly accordingly. For this reason, in order to control combustion, it was generally used to install an integral circuit in the flame current detection circuit and convert it into a stable DC voltage for detection, but this integral element increases the detection time constant, making it difficult to actually Even if abnormal combustion occurs, it takes time to detect it, which poses the problem of causing accidents such as the generation of carbon monoxide and misfires.

Means for Solving the Problems In order to solve the above problems, the combustion detection device of the present invention detects a flame rod inserted into a flame, a power supply circuit that applies voltage to this flame rod, and a current flowing through this flame rod. A flame current detection circuit is provided, and the flame current detection circuit includes an abnormality detection circuit that detects the flame current through a first integration circuit with a short time constant and outputs an output to stop combustion when this value reaches a predetermined value. and a control signal detection circuit that detects the flame current through a second integral circuit with a long time constant and outputs a control output that varies the amount of fuel supply or combustion air so that this value remains constant. The structure is as follows.

Effect With the above configuration, the flame current is detected through an integral circuit with a long time constant so that a highly accurate and stable flame current output can be obtained for controlling the combustion state.
For urgent detection such as sudden changes in air-fuel ratio or misfire, flame current is detected through an integrating circuit with a short time constant, and combustion is stopped instantaneously.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 shows a principle diagram illustrating the configuration of the present invention.

In FIG. 1, a gas burner 9 is introduced into the burner 9 from a gas inlet 10 through a control valve 11. Combustion air is also supplied to the burner 9 by a fan motor 12 to form a flame 13. A flame rod 14 is inserted into the flame 13, and a DC voltage is applied between it and the burner 9 by a power supply circuit 15. This may be a configuration in which multiple flame rods are inserted into the flame. Further, the applied voltage may be an alternating current voltage. 16 within the broken line in the figure is the combustion detection device of the present invention,
Flame current detection circuit 1 that detects flame current If flowing from flame rod 14 to burner 3 through flame 13
It has 7. The flame current detection circuit 17 includes an abnormality detection circuit 19 containing a first integration circuit 18 and a control signal detection circuit 21 containing a second integration circuit 20. The abnormality detection circuit 19 detects that the flame current If has reached an abnormal combustion level, outputs a signal to the control valve drive circuit 22, and closes the control valve 11.

FIG. 2 shows this relationship graphically. In the figure, the horizontal axis λ indicates the air-fuel ratio, and the larger λ is, the greater the amount of air is. The vertical axis If indicates the flame current. Now, assuming that the normal combustion range of the burner 9 is part A in the figure, if the combustion air supply fan 12 breaks down or the intake port is clogged, λ will shift to a smaller value. Along with this, a flame electric current
If also decreases, the abnormality detection circuit 19 detects that the current If is decreasing.
If ₁ or less, a signal is output to close the control valve 11. Furthermore, if a misfire occurs for some reason, the flame 13 disappears, so the flame current If also becomes zero. At this time as well, since it is less than the threshold value If ₁ , the control valve 11 is closed to stop the fuel supply. In addition to this, the abnormality detection circuit 19 may also be configured to provide a separate threshold If ₂ to detect a decrease in the amount of fuel supplied, and close the control valve 11 even when the current If exceeds this threshold. Also,
In addition to abnormality detection, it may also be used to detect ignition of the burner 9.

The control signal detection circuit 21 outputs a signal to the fan motor drive circuit 23 to control the rotation speed of the fan motor 12 so that the flame current If becomes a predetermined set value If ₀ . Now, if the flame current If becomes larger than the set value If ₀ , the rotational speed of the fan motor 12 is lowered to lower the value of the air-fuel ratio λ and bring the flame current If closer to If ₀ .
When If becomes small, the rotation speed of the fan motor 12 is increased to increase If, and the control is performed so that If becomes close to ₀ . Although this specification describes a configuration in which the rotation speed of the fan motor 12 is controlled by a signal from the control signal detection circuit, a similar function can be obtained with a configuration in which fuel is controlled. Furthermore, in Fig. 2, as the air-fuel ratio λ increases, the flame current If also increases, but depending on how the air-fuel ratio is set, it is also possible to have a characteristic in which the flame current If decreases as the air-fuel ratio λ increases, In this case, the same operation can be achieved by reversing the control direction in FIG.

FIG. 3 shows a specific circuit diagram. DC voltage 15, resistor 24, flame rod 14, burner 9, resistor 2
5 are connected in series. Frame rod 14
When there is a flame in the burner 9, a minute current of several microamperes flows due to the ionic current, and this is the flame current If. Resistor 24 is a current limiting resistor. In the circuit shown in FIG. 3, the flame current If is detected as the voltage drop _e0 generated across the resistor 25 due to the flame current If. e ₀ is input to the first integrating circuit 18 of the abnormality detection circuit 19. The first integrating circuit 18 is connected to the resistor 2.
6 and a capacitor 27, and the integral time constant is determined by these constants. First integrating circuit 18
The output e ₁ of is input to the voltage comparison circuit 28. The voltage comparison circuit 28 compares the potential e ₁ proportional to the flame current If with the potential e _f1 corresponding to the abnormality detection level If ₁ explained in FIG. 2, and when e ₁ ≦e _f1 , the output e _a becomes low. This is output to the control valve drive circuit 22. The control valve drive circuit 22 operates the control valve 11 when the potential e _a becomes low.
Outputs a signal to close the fuel and stops the fuel.

If the burner 9 misfires and there is no flame in the flame rod 14, the flame current If=0, and therefore both e ₀ and e ₁ become zero. Therefore, in the comparison circuit 28, e ₁ ≦e _f1
is established, the output e _a becomes low and the control valve 11 is closed. This prevents unburned gas from flowing out from the burner 9.

The output e ₁ of the first integrating circuit 18 is simultaneously input to the second integrating circuit 20 of the control signal detection circuit 21 . Similarly to the first integrating circuit 18, the integration time constant of the second integrating circuit 20 is determined by a resistor 29 and a capacitor 30. The output e ₂ of the second integrating circuit 20 is input to an operational amplifier 31 . The operational amplifier 31 amplifies the difference potential between the potentials e _f0 and e ₂ corresponding to the flame current If ₀ at the standard air-fuel ratio in FIG. 2, and outputs it to the fan motor drive circuit 23. Resistors 32 and 33 determine the amplification factor. The fan motor drive circuit 23 increases or decreases its rotation speed in accordance with this signal voltage to control the amount of combustion air.

In FIG. 3, the second integrating circuit 20 receives the output e ₁ of the first integrating circuit 18 as an input, but it may be configured to directly input the output e ₀ .

Here, the integration time constant of the second integration circuit 20 is the first
The integration time constant of the integration circuit 18 is designed to be sufficiently larger than the integration time constant of the integration circuit 18.

Figure 4 shows this relationship. In FIG. 4, the horizontal axis indicates elapsed time, and the waveforms of potentials e ₀ , e ₁ , and e ₂ are shown.

The flame current If is extremely unstable due to flame fluctuations and other causes, and the detected potential e ₀ also changes greatly in proportion to this. In Figure 4, timing T ₁ to T ₂
When transitioning to , the air-fuel ratio λ becomes smaller and the flame current If decreases, but this is difficult to detect because the fluctuation range of the potential e ₀ is large. Therefore, the fluctuation width of the output _e1 of the first differentiating circuit 18 having a small integration time constant (1/10 to several seconds) is greatly reduced, and the change in the flame current If becomes clear. Therefore, abnormal combustion is detected using this output. However, in the control signal detection circuit 21, if there is a fluctuation like the potential _e1 , it is amplified by the amplifier 31,
Stable rotation speed control of the fan motor 12 becomes difficult. Therefore, a sufficiently large integration time constant (several seconds to tens of seconds) is passed through the second integration circuit 20, and its output e ₂
is almost a direct current voltage. Therefore, feedback can be provided to stabilize the rotation speed control of the fan motor 12. However, since the integration time constant is large, the change is slow, and even when the timing changes from _T1 to _T2 , the output _e2 does not change easily.
For this reason, if an abnormality is detected using the potential _e2 , for example, even if the burner 9 misfires, it will take a long time to detect it, and during this time unburned gas will flow out, which is very dangerous. In this way, abnormality detection that requires high detection speed is performed using a small integral time constant, and fan motor control that requires stability of the detected current is performed using a long time constant.

Although this embodiment has been described using a detection circuit using a gas burner, the same function can be achieved even when using an oil burner. In this case, the control valve 12 may be a fuel pump for refueling.

Effects of the Invention As explained above, the combustion detection device of the present invention has the following effects.

1 or more combustion is detected with a small integral time constant, so the response is fast, and the detection signal for combustion control is detected with a large integral time constant, so a stable detection signal can be obtained. In this way, the optimal signal for each detection can be obtained, and a highly accurate combustion system can be realized that utilizes only the advantages of contradictory characteristics such as fast response, stable and high accuracy.

2. Similarly, by using only one flame rod to detect the flame state, the same performance as using two flame rods can be obtained, so the configuration is simple and highly reliable.

3. Each detection circuit can independently design the detection level and setting value to any desired value.
It is also possible to set multiple detection levels, making it widely applicable to combustors of various combustion methods.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of a combustion detection device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between the air-fuel ratio λ and flame current If, and Fig. 3 is a specific circuit diagram of Fig. 1. FIG. 4 is a time chart showing voltage waveforms at various parts in FIG. 3, and FIG. 5 is a configuration diagram of a conventional combustion detection device. 9...Burner (flame rod sensor electrode),
13... Combustion flame, 14... Flame rod (electrode of flame rod sensor), 15... Power supply circuit,
16... Combustion detection device, 17... Flame current detection circuit, 18... First integrating circuit, 19... Abnormality detection circuit, 20... Second integrating circuit, 21... Control signal detection circuit, If ₁ ...predetermined value.

Claims (1)

[Claims] 1. A flame rod sensor that is inserted into a combustion fire and detects the combustion state of the fire using flame ion current;
The flame rod sensor has a power supply circuit that applies a voltage between the electrodes, and a flame current detection circuit that detects the current flowing through the flame rod sensor, and the flame current detection circuit has a first integration circuit with a short time constant. An abnormality detection circuit detects the flame current through a circuit and outputs an output to stop combustion when this value reaches a predetermined value, and a second integration circuit with a long time constant detects the flame current. A combustion detection device comprising a control signal detection circuit that outputs a control output that varies the fuel supply amount or combustion air supply amount so that it is constant.