JPH0235207B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion detection device using a flame rod sensor configured to detect the presence or absence of a flame or the state of combustion by inserting it into a flame and detecting the flame current.

Conventionally, this type of combustion detection device using the flame rod method has been widely used because the sensor section has the advantages of being inexpensive, robust, and quick in response.
FIG. 1 shows an example of this, and is an example of use in a Bunsen type gas burner. In this configuration, gas flows in from the inlet 1, passes through the safety valve 2, and is ejected from the nozzle 3. Here, it mixes with the primary air 4 to form a flame 7 in the flame hole 6 of the burner 5. Reference numeral 8 indicates a flame rod inserted into the flame 7, and the flame ion current (hereinafter referred to as flame current) iF flowing between the flame hole 6 of the burner 5 and the flame rod 8 is detected by the flame detection circuit 9, and the flame 7, that is, the flame is detected. Outputs an output that closes the safety valve 2 when the current iF disappears. 10 is a flame detection circuit 9
shows an AC power supply that drives the flame current iF.
The flame current iF is a method that applies an alternating current voltage and utilizes the rectifying effect of the flame for the purpose of determining whether there is a contact accident between the flame rod 8 and the burner 5.

In this case, the magnitude of the flame current iF is determined by the applied voltage, the distance between the flame hole 6 of the burner 5 and the flame rod 8, the shape of the flame, the ion state, and the flame rod 8 and the burner 5.
It varies greatly depending on the area etc. For this reason, the installation accuracy of the flame rod 8 is strictly required, and since it changes slightly depending on the shape of the burner flame hole 6,
Their design and construction were highly sophisticated and complex. Bunsen burners include line burners and other types of burners, and burners other than Bunsen burners and kerosene burners come in a wide variety of shapes. It is very difficult to detect the absolute value of a constant flame current iF through these devices, and for this reason, it is currently often used as a flame detector to detect the presence or absence of a flame current iF, that is, the presence or absence of a flame. However, due to the recent trend toward pollution-free combustion, there is a growing demand for combustion control that monitors not only the presence or absence of flame but also the combustion state of the flame to maintain optimal combustion at all times, or a combustion safety function that automatically stops combustion in the event of abnormal combustion. For this purpose, it is necessary to detect the absolute value of the flame current iF. However, as mentioned above, it is difficult to detect the flame current iF stably due to variations between devices or products, so we design the detection circuit according to the device and make high-precision adjustments to the mounting position of the flame rod 8 and the detection level. Not only did this increase the cost, but it also raised concerns about reliability.

Furthermore, since the impedance of the flame is very high and the flame current iF is very small, it is difficult to obtain a sufficiently high S/N ratio of the detection circuit to a predetermined value. There was an increase in current iF. However, considering the risk of a short circuit between flame rod 8 and burner 5, it is not possible to apply a very high voltage, and the flame current
The challenge was to increase iF.

Furthermore, a major problem with the prior art is the occurrence of malfunctions. In Figure 2, 11 is the burner 5
This is a heated member such as a heat exchanger that is heated by a heat exchanger. Reference numeral 12 indicates a structure such as a case, which is generally a metal part and is electrically connected to the burner 5. Therefore, the flame current normally flows from the flame rod 8 to the burner 5 as shown in the figure.
When the flame was extended by a lift, etc., a flame current like iF' in the figure also flowed, which caused malfunction. Conventionally, methods such as insulating the burner 5 with an insulator have been considered to solve this problem, but the structure is complicated.

The present invention solves the above-mentioned conventional problems, and is capable of detecting a large and stable flame current even when a low voltage is applied, regardless of the shape of the burner or the mounting position of the flame rod. The purpose is to provide a detection device.

Furthermore, it is an object of the present invention to provide a combustion detection device that is highly durable, has a simple structure, and is highly safe, without using a burner as a pole, and thus eliminating a complicated insulation structure.

To achieve the above object, the present invention uses two flame rods, one of which is wound into a coil to increase the surface area and flame detection current, and the other is wound into a coil. The structure is such that the flame current between the two rods is detected by inserting the rods, and a stable output can be obtained by simply managing the gap between the two rods, regardless of the shape of the burner or the distance between the burner and the rods.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 3 shows an example of the flame detector for a Bunsen gas burner. The frame rod 13 has an outer rod 14 and an inner rod 15 which are wound into a coil, and are electrically insulated from each other by an insulating insulator 16. Further, the insulating insulator 16 is attached to a structure 17 such as a case while maintaining insulation from the frame rod 13. The detection circuit 9 is connected to the outer rod 1.
4 and the inner rod 15 to detect the flame current therebetween. The operation of safety valve 2 is the same as that of the conventional first valve.
Since it is the same as the figure, the explanation here will be omitted.

Figure 4 shows that the relationship between applied voltage V _F and flame current i F is 2.
It shows the characteristics exhibited by the area ratio of the book's frame rods. In the figure, the horizontal axis V _F indicates the voltage applied to the frame rod, and +V _F indicates the case where the voltage is applied to the inner rod 15 and the outer rod 15, and -V _F indicates the case where the voltage is applied to the inner rod 15 and the outer rod.
The vertical axis iF indicates the flame current, and iF in the direction shown in FIG. 3 is indicated by +iF, and the opposite direction is indicated by -iF. In other words, FIG. 4 shows the flame rectification characteristics. Here, A, B, and C are obtained by changing the area ratios of the respective frame rods 14 and 15, and the area ratios are A>B>C.
In other words, curve C consists of two frame rods 14 and 15.
When the area ratios of the two rods are almost equal, curve A shows the case where the ratio of the two rod areas is large, and since the +iF characteristic is hardly affected by the area ratio, it can be said that the larger the area ratio, the greater the rectifying effect.

In the case of the frame rod structure of this embodiment, the inner rod 15 is straight, whereas the outer rod 14 is wound in a coil shape, so that the area ratio becomes very large.

Here, when an AC voltage is applied between each flame rod 14 and 15, V _F
An imbalance occurs in the flame current iF between + and -.
Since the detection circuit 9 smoothes this and detects it as a DC voltage, characteristic C results in almost zero output DC voltage, but characteristic A allows a large DC output to be obtained.

This eliminates the drawbacks of the conventional configuration shown in FIG. In other words, in the conventional configuration, the burner 5 is generally considered to have a sufficiently larger area than the flame rod 8, and the characteristic A shown in Fig. 4 is expected, but the area varies depending on the shape of the burner 5, resulting in different characteristics. was unstable. Furthermore, the distance from the burner changes depending on the mounting position of the rod, resulting in large variations in the value of the flame current, but the above-described embodiment can eliminate this drawback.

Further, it is only necessary to manage the coil winding diameter and rod diameter of the outer rod 14 and the rod diameter of the inner rod 15, and high precision is not required in the mounting direction or mounting position, and the assembly is easy and there is an effect that it is difficult to break down.

Next, another embodiment of the present invention will be described based on FIG. In this embodiment, the primary air 4 is forcibly supplied by a fan 19 rotated by a fan motor 18. 20 is a combustion state monitoring circuit which detects the flame current iF and outputs a combustion state signal according to its magnitude. Reference numeral 21 indicates an air blowing control circuit that drives a damper motor 22 that controls the amount of primary air 4 supplied to the burner 5. In this configuration, burner 5
The amount of primary air can be automatically controlled so that the fuel is always in the optimum combustion state.

An example of the control circuit with the above configuration will be explained below based on FIG. 6.

flame rod sensors 14, 15 and resistor 23,
24 series circuits are connected to an AC power supply 10, and the divided potentials of resistors 23 and 24 are smoothed by a capacitor 25 and input to the gate of an N-channel junction field effect transistor (hereinafter referred to as FET) 26.
The drain of the FET 26 is connected to the + potential of the DC power supply 28 through a resistor 27, and the source is connected to the - potential of the DC power supply 28. At the same time, the connection point between the drain of the FET 26 and the resistor 27 is connected to the negative input terminal of the operational amplifier 30 via the resistor 27, and the potential _ea is input to the positive input terminal of the operational amplifier 30.
Further, the output is negatively fed back to the negative input terminal by the resistor 31, and the operational amplifier 30 constitutes an inverting amplifier circuit.

Now, when the flame is burning normally, the flame current
iF is large, so the gate potential of FET26 e _b
becomes higher. As a result, the FET 26 becomes conductive and the drain potential _ec decreases. As a result, operational amplifier 3
The output potential e _d of 0 is the difference between the potentials e _c and e _a through resistors 31 and 2.
It is inverted and amplified with an amplification factor of 9 and output.

In this embodiment, a window comparator system for switching the rotational direction of the DC damper motor 22 is adopted for the blower control circuit 21, but it is of course possible to use a system in which the blower motor 18 is an AC motor and performs phase control, or another method.

Comparators 32 and 33 in the circuit constitute a window comparator, each of which is a generally known comparator with an open collector output. The outputs _ed of the combustion state monitoring circuit 20 are connected to the positive and negative input terminals of comparators 32 and 33, respectively. Also, voltage dividing resistors 34, 3
The potentials e _f and e _g divided by voltages 5 and 36 are also connected to the input terminals, respectively, as shown in the figure. Further, the outputs of both comparators are connected to the + potential of the power supply 28 through resistors 37 and 38, respectively, and are also connected to the damper motor 22.

Now, the potential e _d during normal combustion is designed to have the relationship e _f > e _d > e _g . At this time, comparator 3
2 becomes a low output, and current flows into the comparator 32 through the resistor 37. Similarly, the comparator 31 also has a low output, and current flows to the comparator 33 through the resistor 38.
Therefore, there is no potential difference between both ends of the damper motor 22, and the damper motor 22 does not rotate.

Next, when there is insufficient air and incomplete combustion occurs, the flame current iF becomes smaller. Therefore, the potential _eb decreases, so that _ec increases and _ed decreases. As a result, e _f > e _g > e _d , the comparator 32 has a low output, and the comparator 33 has a high output (open). Therefore, current flows through the resistor 38, damper motor 22, and comparator 32, causing the damper motor 22 to rotate and open the damper. As a result, normal combustion returns to e _f > e _d > e _g again.
The relationship becomes such that the damper motor 32 stops at that point.

In this embodiment, the combustion is controlled by the damper motor 22, but there are other methods to stop the combustion when abnormal combustion occurs using the output of the combustion state monitoring circuit 20, _or to notify by a buzzer or other means. Various methods can be considered, such as a method of automatically operating a ventilation fan. Although not shown, it goes without saying that a circuit for closing the safety valve 2 as shown in FIG. 3 is also used when the flame current iF disappears due to burner misfire or the like.

As described above, according to the present invention, the following effects are obtained.

(1) Two flame rods insulated from each other are used, one of which is formed into a coil shape, and the other flame rod is installed inside it, so the area ratio of the two flame rods can be increased, and therefore the flame Since the rectification effect is large and the output voltage obtained by smoothing the rectification can be increased, the S/N ratio of the detection circuit is large and reliable operation can be performed.

(2) Also, since the burner does not double as a pole, the rectification effect does not change even if the shape or area of the burner changes, making it possible to obtain stable output and requiring a complicated structure to insulate the burner. There is no.

(3) Furthermore, only the dimension control of the distance between the rods eliminates the influence of the mounting position and direction of the frame rods, making it easy to process parts and assemble them, resulting in a highly reliable safety device.

(4) Furthermore, as a unique effect of the present invention, since the two flame rods are both insulated from the burner and the case, for example, when the flame lifts and comes into contact with the case, etc., which has the same potential as the burner, the current bypasses. Malfunctions are eliminated and safety is extremely high.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams and operation explanatory diagrams of a conventional combustion detection device, Figure 3 is a block diagram of a combustion detection device that is an embodiment of the present invention, and Figure 4 shows the rectification effect of the device. FIG. 5 is a configuration diagram of a combustion detection device according to another embodiment of the present invention, and FIG. 6 is a control circuit diagram of the same device. 7... Combustion flame, 9... Flame detection circuit (combustion monitoring circuit), 10... AC power source, 13... Pair of flame rods, 14... First flame rod having a coiled portion at the tip, 15... Straight line a second frame rod shaped like 16...insulator (insulator);
17...Structure, IF...Flame current.

Claims (1)

[Claims] 1. An alternating current voltage is applied between a pair of flame rods inserted into the combustion flame of a burner, an insulator that holds the flame rods at a constant distance from each other and fixes them while electrically insulating them from the structure, and the flame rods. The flame rod includes a combustion monitoring circuit that monitors the combustion state of the flame using a flame current flowing due to the rectification of the flame, and the pair of flame rods includes a first flame rod having a coiled portion at the tip thereof, and a first flame rod having a coiled portion at the tip thereof, and a combustion monitoring circuit that monitors the combustion state of the flame by the flame current flowing due to the flame rectification action. A combustion detection device comprising a straight second flame rod disposed through the flame rod.