JPH026408B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a flame detection device used in a combustion control device such as a water heater equipped with a gas burner, etc., and includes a pressure switch as means for detecting the presence or absence of a flame. This invention relates to a device having a voltage comparison circuit as means for inputting the signal of the pressure switch and determining the presence or absence of a flame.

A combustor that uses a pressure switch as a means for detecting the presence or absence of a flame is a combustor, such as a pulse combustor, in which the pressure within the combustion chamber becomes considerably high due to combustion.

A pulse combustor is a combustor that generates flame intermittently, that is, in pulses over time, unlike a general combustor that continuously generates a combustion flame. There are various types of pulse combustors, but for example, a valve that controls the supply of gaseous fuel and air to the combustion chamber, and the combustion chamber and exhaust pipe serve as a heat exchanger.

The above combustor operates by supplying fuel and air to the combustion chamber through a valve, and then igniting it with an igniter to cause explosive combustion.The valve closes due to the pressure, while the combustion gas passes through the exhaust pipe. It is then discharged. This discharge creates a negative pressure in the combustion chamber, which opens the valve and sucks in fuel and air, while the vibration of the air column caused by the combustion chamber and the exhaust pipe causes residual combustion flame or hot gas in the exhaust pipe. returns to the combustion chamber, and using this as an ignition source, the inhaled fuel explodes and burns. This pressure rise causes the previous combustion lung gas to be exhausted. This is 1
This cycle is repeated continuously. In other words, combustion occurs intermittently, that is, in a pulsed manner.

The internal circuit of the combustion control device must have a fail-safe function to prevent a dangerous situation from occurring even if a short-circuit failure occurs at any point or time.

[Prior Art] A voltage comparison circuit is used in a circuit for determining the presence or absence of a flame in a combustion control device.

In the combination of the pressure switch and the voltage comparator circuit, the pressure switch that is turned ON when there is a flame is generally used, and is connected to the inverting input terminal of the voltage comparison circuit. ) to output Hi level.

[Problem to be solved by the invention] In the above combination, the pressure switch
When the pressure switch is OFF, for example, if the resistance connected in parallel with the pressure switch is short-circuited, the pressure switch will
This is equivalent to turning it on, and the voltage comparator will output a Hi level, causing a malfunction.

In order to solve this problem, it is conceivable to add a flame rod type rectifier type flame detection circuit. That is, an equivalent flame circuit consisting of a resistor and a diode is provided in series with a pressure switch, and an alternating current is applied to this series circuit via a capacitor or resistor, and when the pressure switch is turned on, the alternating current is half-wave rectified. Japanese Patent Publication No. 37289/1983 has proposed a system in which the voltage obtained in a capacitor or resistor is inputted to a voltage comparator circuit via a smoothing circuit (Japanese Patent Publication No. 37289/1989).

However, in the above device, the current that can flow through the flame equivalent circuit is very small (generally about 500 μA), so the value of the current that flows through the pressure switch is also very small. This causes a problem in that the pressure switch is susceptible to poor contact.

In order to prevent poor contact, it is necessary to increase the current value, but since the current is a rectified pulsating current and a capacitor is inserted between it and the AC power supply, it is necessary to reduce the resistance value of the flame equivalent circuit. However, the current value does not increase much. Furthermore, if the value of the resistance of the flame equivalent circuit is made small, if a leakage occurs in the wiring that short-circuits the pressure switch, the voltage obtained at the capacitor will reach a negative voltage even if the resistance value of the leakage is large. It had the disadvantage of being dangerous.

[Problems to be Solved by the Invention] An object of the present invention is to simultaneously prevent poor contact of a pressure switch and false flame detection due to leakage.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a flame detection device disclosed in Japanese Patent Publication No. 63-37289, which is a prior art, in which a second diode is connected at least in parallel to the diode in the flame equivalent circuit. It is equipped with a resistance.

[Example] The present invention will be described below with reference to an example shown in the drawings.

In Fig. 1, 1 is a DC power supply, and 2 is a combustion control integrated circuit.For example, HA manufactured by Hitachi, Ltd.
−16605W. This integrated circuit 2 includes a temperature detection circuit, a timer, a control circuit, an output circuit (not shown) for a blower, a fuel valve, an igniter, etc., and a voltage comparison circuit 3 for an input circuit that determines the presence or absence of flame. ing.

The voltage comparator circuit 3 operates as if there is a flame when the output terminal 4 is at Hi level. In the voltage comparator circuit 3, the voltage at the inverting input terminal 5 and the non-inverting input terminal 6 is 0V.
In this case, one having a negative offset voltage f as shown in FIG. 2 is used. Non-inverting input terminal 6 is connected to ground.

A pressure switch 10 is activated by detecting the pressure in the combustion chamber, and is turned on when the pressure is high, that is, when there is a flame. Reference numeral 11 denotes an equivalent circuit of a flame, which is composed of a diode 12 and resistors 13 and 14. The values of the resistors 13 and 14 are, for example, the same, and each is, for example, 22KΩ.

15 is an AC power supply, and 16 is a step-up transformer which outputs a voltage of 100 to 200V, which is higher than that of a commercial AC power supply, to the secondary side. 17 is a capacitor as an impedance network, and 18 is a load resistor. Resistance 19,2
0 and capacitors 21 and 22 constitute a smoothing circuit. 23 and 24 are resistors that apply a bias voltage.

Here, a pressure switch 10, a flame equivalent circuit 11
If electrodes in contact with the flame are provided at points B and G, respectively, transformer 16 and capacitor 1
7. The structure of the smoothing circuit and resistors 23 and 24 is the same as that of the flame rod type flame detection device.

The operation of this configuration will be explained with reference to FIG. A, B, 5, 6, 4 in Figure 2 are A, B, 5, 6, 4 in Figure 1,
It shows the voltage waveforms at points 5, 6, and 4.
10 shows the operation of the pressure switch 10.

The AC power supply 15 is boosted by a step-up transformer 16, and the AC power is connected to a capacitor 17 and a flame equivalent circuit 1.
1 to the pressure switch 10.
Since there is no flame until the ignition operation starts, the pressure switch 10 is turned off. Therefore, in this state, the AC waveform appears as it is at both ends of the capacitor 17. Here, the alternating current component is removed by passing through a smoothing circuit including resistors 19 and 20 and capacitors 21 and 22, and as a result, no direct current component is obtained at both ends of the capacitor 17. On the other hand, the resistor 23,
Since the divided voltage potential 24 is set higher than 0V, the voltage comparator circuit 3 outputs the Lo level in this state.

A known igniter is driven by the integrated circuit 2 in accordance with the Lo level output, and when the igniter is ignited, the pressure inside the combustion chamber rises, causing the pressure switch 1 to be activated.
0 turns on at _t1 . As a result, when point B is on the positive side of the alternating current (during the positive half cycle of the alternating current), a current flows from the parallel circuit of the resistor 13 via the resistor 14 and the diode 12 toward the pressure switch 10. When point G is on the positive side of AC (negative half cycle of AC), current flows from pressure switch 10 to resistor 14. pressure switch 10
The resistors 13 and 14 are set so that the value of the current flowing through the resistors 13 and 14 is larger during a positive half cycle than during a negative half cycle. Therefore, capacitor 1
7 is charged so that the side facing resistor 19 is negative. Therefore, the voltage at point B is as shown in Figure 2 B.
From t ₁ , it deviates to the negative side (downward) by the DC voltage corresponding to the substantial difference in the current flowing in each direction in the positive and negative half cycles. This DC negative voltage is smoothed by the smoothing circuit, and the input voltage at the inverting input terminal 5 is
This becomes a negative voltage lower than the offset voltage f. On the other hand, the voltage at the non-inverting input terminal 6 is constant at 0V.
Therefore, at time _t2 , the output terminal 4 of the voltage comparator circuit 3 is
It becomes Hi level and outputs a flame signal. As a result, the control circuit confirms that ignition and combustion continues, and continues the supply of fuel.

The above is a case of normal operation.

Now, let us consider a case where the capacitor 21, the resistor 24, or the voltage comparator circuit 3 (particularly on the inverting input terminal side) is short-circuited while the pressure switch 10 is in the OFF state.
In this case, the voltage at the inverting input terminal 5 only drops to 0V and does not drop to (-)fV, so
The voltage comparator circuit 3 does not invert and does not output a flame presence signal. Therefore, even if this short-circuit failure occurs during ignition or combustion, or even if ignition does not occur or the flame goes out midway, the voltage comparison circuit 3 will generate a no-flame signal based on the output of the pressure switch 10.
Outputs Lo level. Therefore, the control circuit stops the ignition operation or the combustion operation after a certain period of time determined by the timer, so it is safe.

Note that the distance between C, pressure switch 10, and G is the specified insulation distance specified by safety standards (for example, AGA
According to the standard, it is designed to have a diameter of 0.8 mm) and there shall be no short circuit. It is also assumed that there is no short-circuit failure of the pressure switch 10, which is a UL standard product.

In addition, if a disconnection fault occurs, the flame equivalent circuit 1
It is safe because the rectifying effect due to 1 is not obtained. In addition, for disconnection between the non-inverting input terminal 6 and the ground, for example, provide another voltage comparison circuit,
Use a double circuit to deal with it.

Now, as shown in the aforementioned Special Publication No. 63-37289,
Considering the case where the flame equivalent circuit 11 does not include the resistor 14 in the present invention, the pressure switch 10
The magnitude of the current flowing through the resistors 13, 18, 1
It is determined by the values of 9, 20, 23, and 24. Therefore, even if the resistor 13 is made smaller, the value of the current flowing through the pressure switch 10 will not become that large. However, if the resistor 13 is made smaller, if there is a leak at point C, the potential at point B will be reduced even if the leak resistance is large. The voltage becomes negative and the voltage comparator circuit 3 outputs Hi level. In order to prevent this, the resistor 13 must be made large. That is, if the value of the resistor 13 is increased in this way, contact failure is likely to occur, while if the value of the resistor 13 is decreased, it becomes susceptible to leakage, and it is impossible to achieve both.

However, in the present invention, the resistor 14 is connected in parallel.
, the value of the current flowing through the pressure switch 10 can be increased. Therefore, it is not necessary to increase the value of the resistor 13. In addition, since a negative voltage is generated at point B based on the difference in current value between the positive half cycle and the negative counter cycle, in other words, when there is a leak, current flows even during the negative half cycle. , if there is any leakage, a negative voltage value large enough to invert the voltage comparator circuit 3 cannot be obtained at point B. Therefore, the flame presence signal is not output when a leakage failure occurs.

For example, the applied AC voltage is 120V, the resistance is 13,1
If 4 is 22KΩ each, 5 is applied to pressure switch 10.
mA can be obtained (at this level, poor contact can generally be prevented), and erroneous flame detection can be prevented for leaks with a leak resistance of 200KΩ. Note that it is generally considered that the values of the resistors 13 and 14 are the same.

It is also conceivable to provide the resistor 14 in parallel only to the diode 12. However, it is considered that setting the resistors 13 and 14 is easier in the configuration of the embodiment shown in FIG.

In addition, when a flame rod type flame detection device and a pulse combustor are combined, the frequency of the applied alternating current is made sufficiently larger than the frequency of pulse combustion so that a sufficient positive half cycle of alternating current can be applied to the flame. For example, when the frequency of pulse combustion is 50 to 80 Hz, it is necessary to apply an alternating current of, for example, about 200 Hz or more.

In the embodiment of FIG. 1, the capacitor 17
The capacitance of is inversely proportional to the magnitude of the frequency of the alternating current applied by transformer 16. Therefore, if we try to pass a large current through the contacts of the pressure switch 10 without causing contact failure, and if we make the frequency the same as the frequency of the commercial AC power supply (50Hz, 60Hz), the capacitance of the capacitor 17 will become large and expensive. becomes. The embodiment shown in FIG. 3 was made to improve this point.

In Figure 3, 26 is an AC power supply, for example
It is a low voltage of 24V. Note that the other configurations are the same as in FIG. 1.

According to this configuration, the highest voltage at point B is [(voltage of AC power supply 26 x value of resistor 13)/(value of resistor 13)
value + value of resistor 27)]. This voltage is smoothed by a smoothing circuit and becomes a negative voltage.

As described above, since the resistor 27 is used in the embodiment shown in FIG. 3, the cost can be reduced. Note that if the resistor 27 is used, the flame detection sensitivity will be lower than that of the capacitor method, and in particular, in a general flame rod type flame detection circuit that does not use a pressure switch, the flame has a high impedance, so conventionally the resistor method cannot be used. However, in the pressure switch, the resistance 13 of the flame equivalent circuit 11 is artificially set, so the impedance can be kept low and the switch can be used satisfactorily. It is capable of passing a large current that does not cause

Another embodiment shown in FIG. 4 will be described. The pressure switch 10B used is one that turns off when there is a flame. The flame equivalent circuit 11 is a pressure switch 10B.
are provided in parallel to each other, and their connection points are at the connection terminals 10a, 10b of the pressure switch 10B. The other configurations are similar to the embodiment shown in FIG.

The operation of this configuration is the same as that in FIG. 3, except for the operation of the pressure switch 10B. According to this configuration, when the pressure switch 10B detects a flame and turns off, the flame equivalent circuit 11 is energized and a flame current flows, so the voltage comparison circuit 3 detects the flame. Between B and G or pressure switch 1
If 0B is short-circuited, no flame equivalent current will be obtained, so it is safe. Incidentally, since the flame equivalent circuit 11 is connected in parallel to the pressure switch 10B, a malfunction will occur if a disconnection occurs between the connection point and the pressure switch 10B. However, the connection terminals 10a and 10b of the pressure switch 10B are thick members, and in particular, the connection between the terminal 10b and the resistor of the equivalent circuit is secured by screwing to the housing, so it is safe. Disconnections in other parts are the same as in the embodiment shown in FIG.

[Effects of the Invention] As explained above, according to the present invention, the combination of a pressure switch and a voltage comparison circuit is safe against short-circuit failures of resistors, etc., and also prevents flame detection due to poor contact and leakage of the pressure switch. It is possible to obtain a flame detection device that can consistently prevent flames.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a flame detection device according to an embodiment of the present invention. FIG. 2 is a diagram showing voltage waveforms at various parts of FIG. 1, FIG. 3 is a circuit diagram of main parts of a flame detection device according to another embodiment of the present invention, and FIG. 4 is a diagram showing still another embodiment of the present invention. FIG. 3 is a circuit diagram of main parts of the flame detection device of FIG. 1...DC power supply, 2...Combustion control integrated circuit,
3... Voltage comparison circuit, 10, 10B... Pressure switch, 11... Flame equivalent circuit, 12... Diode, 13, 14... Resistor, 15... AC power supply, 1
6...Step-up transformer, 17...Capacitor, 26
...AC power supply, 27...resistance.

Claims (1)

[Claims] 1. Consisting of a pressure switch that senses the increase in pressure due to combustion in the combustion chamber and turns on to issue a signal indicating that there is a flame, and a voltage comparison circuit that inputs the signal of the pressure switch to an inverting input terminal, In the flame detection device, the comparator circuit outputs a high level signal based on the flame presence signal from the pressure switch, and the voltage comparator circuit has a negative offset voltage, and its non-inverting input terminal is connected to ground. A flame equivalent circuit is provided, the flame equivalent circuit being connected to a diode and a first resistor in series, and a second resistor provided in parallel to at least the diode, and connecting the flame equivalent circuit, a contact point of the pressure switch, and an AC power source. an impedance network is provided in series, the output of the impedance network is connected to the inverting input terminal via a smoothing circuit and a bias circuit, and the value of the first resistor and the value of the second resistor are A flame detection device characterized in that the value of the current flowing through the contact via the diode is set to be larger than the value of the current flowing through the contact in a direction opposite to the direction without passing through the diode. 2. The flame detection device according to claim 1, wherein the second resistor is provided in parallel to a series circuit of the first resistor and the diode. 3 Turns OFF due to increased pressure due to combustion in the combustion chamber.
and a voltage comparison circuit that inputs the signal of the pressure switch to an inverting input terminal, and the voltage comparison circuit changes to Hi level based on the flame presence signal of the pressure switch. In a flame detection device that outputs a signal, the voltage comparison circuit has a negative offset voltage, its non-inverting input terminal is connected only to ground, and a diode and a first resistor are connected in series. and providing a flame equivalent circuit comprising at least a second resistor provided in parallel with the diode, and providing a circuit in which the flame equivalent circuit and the contact of the pressure switch are connected in parallel in series with the AC power source and the impedance network; The output of the impedance network is connected to the inverting input terminal via a smoothing circuit and a bias circuit, and the values of the first resistor and the second resistor are connected to the contact via the diode as well. A flame detection device characterized in that a current value flowing through the contact point is set to be larger than a current value flowing through the contact point in a direction opposite to the aforementioned direction without passing through the diode. 4. The flame detection device according to claim 1 or 3, wherein the impedance network is a resistance. 5. The flame detection device according to claim 1 or 3, wherein the impedance network is a capacitor.