JPH0730912B2 - Combustion device combustion state detection circuit - Google Patents

Description

The present invention relates to a combustion state detection circuit for detecting a combustion state such as ignition, misfire or incomplete combustion of a combustion flame in a combustion device such as a small gas water heater or a gas stove.

[Prior Art] In a combustion device such as a water heater, the occurrence of incomplete combustion causes gas poisoning, etc., so it is necessary to prevent this. Currently, small water heaters prevent incomplete combustion. The system (hereinafter referred to as non-combustion prevention) is legally required to be installed.

FIG. 4 shows an example of a non-combustion prevention system for a small water heater. In FIG. 4, 1 is a pilot thermocouple, 2 is a non-combustible thermocouple, 10 is a control circuit, 11 is a gas valve, 12 is a pilot burner, 13 is a main burner, 14 is an igniter, 15 is a power battery, and 16 is a push switch. Reference numerals 17, 17 are abnormality indicator lights.

In this small water heater, at the time of ignition, the gas valve 11 is opened by the control signal of the control circuit 10, the gas is supplied to the pilot burner 12, the igniter 14 is discharged to ignite the gas, and then the pilot burner 12 Main burner on fire
I have set fire to 13. The pilot thermocouple 1 is used to detect ignition and misfire of the pilot burner flame.
The incombustible thermocouple 2 is used to detect whether the flame of the main burner 13 is incompletely burned.

That is, in the incomplete combustion state, the combustion flame of the main burner 13 causes a lift-up phenomenon, so that the non-combustible thermocouple 2
Is heated more strongly than when it is completely burned, generating a larger thermoelectromotive force. The noncombustion prevention system detects incomplete combustion based on the thermoelectromotive force of the noncombustion protection thermocouple 2, and takes countermeasures such as closing the gas valve 11 at the time of incomplete combustion.

FIG. 5 shows a conventional combustion state detection circuit for detecting a combustion state such as incomplete combustion, ignition or misfire. In this circuit, the pilot thermocouple 1 and the noncombustible thermocouple 2 are connected at their negative terminals so that they are connected in series with opposite polarities, and the positive terminal of the pilot thermocouple 1 is grounded. The detection output is taken out from the positive terminal side of the non-combustible thermocouple 2 and the ignition / misfire detection circuit 21 and the non-combustion prevention circuit
Entered as 22 and.

In this combustion state detection circuit, when the incomplete combustion occurs, the thermoelectric power of the non-combustible protection thermocouple 2 is generated in the direction of canceling out the thermoelectromotive force of the pilot thermocouple 1, so this change is prevented.
22 to detect incomplete combustion.

[Problems to be Solved by the Invention]

In the conventional combustion state detection circuit, ignition and misfire are detected by using the difference in thermoelectromotive force between the pilot thermocouple 1 and the noncombustible thermocouple 2. The circuit with this configuration can perform ignition / misfire detection without problems during cold start, where both thermocouples 1 and 2 are started and detected when they are not heated.

However, since there is a difference in thermal time constant between pilot thermocouple 1 and noncombustible thermocouple 2 at the time of hot start in which combustion is detected by starting from the state after thermocouples 1 and 2 are once heated, both The temperature changes of the thermocouples 1 and 2, that is, the thermoelectromotive force changes are not always in the same relation with respect to time, so that the detection output fluctuates with time and ignition detection becomes unstable.

Also, if the type of gas used is different, such as natural gas or city gas, the magnitude of the thermoelectromotive force extracted from the series circuit of both thermocouples 1 and 2 will differ due to the difference in the thermal power of these gases. The control circuit must be readjusted for each gas type, which has a large effect on the control system.

Therefore, in the past, pilot thermocouple 1 and non-combustible thermocouple 2
In order to prevent variations in the thermoelectromotive force characteristics of the above, these had to be strictly selected and used so that the thermoelectric power characteristics were within the allowable range.

Therefore, it is an object of the present invention to provide a combustion state detection circuit for a combustion device that can detect ignition, etc., stably even with respect to hot start or a difference in gas species while detecting incomplete combustion. .

[Means for Solving the Problems]

In the combustion state detection circuit for a combustion device according to the present invention, an ignition detection thermocouple and an incomplete combustion detection thermocouple are connected in series with opposite polarities, and a terminal on the ignition detection thermocouple side of this series connection circuit is used as a reference. The thermoelectromotive force between the connection points of the ignition detection thermocouple and the incomplete combustion detection thermocouple and the reference potential is introduced to the ignition detection circuit as an output from the sensor and connected to the series connection circuit. The thermoelectromotive force between the terminal on the thermocouple side for incomplete combustion and the reference potential is guided to the incomplete combustion detection circuit as an output from the sensor.

[Action]

If the thermocouple sensor is configured as described above, only the thermoelectromotive force of the ignition detection thermocouple is input to the ignition detection circuit as the sensor output, so that the operation of the ignition detection circuit does not occur even if hot start is performed. It will not be unstable.

Further, as in the conventional case, the difference in thermoelectromotive force between both thermocouples is input to the incomplete combustion detection circuit to detect incomplete combustion.

〔Example〕

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

FIG. 1 shows a combustion state detection circuit of a combustion device as an embodiment of the present invention. In this embodiment, a small water heater equipped with a non-combustion prevention system as shown in FIG. 2 is used as a combustion device.

In FIG. 1, the pilot thermocouple 1 has its positive electrode terminal grounded to the ground serving as a reference potential, and its negative electrode terminal connected to the negative electrode terminal of the noncombustible thermocouple 2. Non-combustible thermocouple 2
The positive electrode terminal of is connected to the non-combustion protection circuit 6.

In the non-combustion protection circuit 6, the positive terminal of the non-combustion protection thermocouple 2 is connected to the inverting input terminal of the operational amplifier 4 via the resistor R5. Here, the non-inverting input terminal of the operational amplifier 4 is grounded via the resistor R6. The operational amplifier 4 constitutes an inverting amplifier circuit together with the resistors R5 and R6, the feedback resistor R7 and the capacitor C4, and a positive voltage power source is used as a single power source for operating the operational amplifier. The positive terminal of the non-combustible thermocouple 2 is grounded through a noise removing capacitor C3 and a reverse bias preventing diode D2, respectively.

On the other hand, the negative terminal of the pilot thermocouple 1 is connected to the ignition / misfire detection circuit 5. In this ignition / misfire detection circuit 5,
The negative terminal of the pilot thermocouple 1 is input to the inverting input terminal of the operational amplifier 3 via the resistor R2, and is also grounded via the resistor R1. The non-inverting input terminal of the operational amplifier 3 is a resistor
Grounded via R3. This operational amplifier 3 also has resistors R2, R3,
An inverting amplifier circuit with a feedback resistor R4 and capacitor C2, it is used amplifier operation power source even a positive voltage supply V _B in single power supply. The negative terminal of the thermocouple 1 is grounded by a diode D1 for preventing reverse bias and a capacitor C1 for noise removal.

The operation of this embodiment circuit will be described below.

In the circuit of this embodiment, the operational amplifier 3 of the ignition / misfire detection circuit 5 detects and amplifies the thermoelectromotive force of the pilot thermocouple 1 with respect to the ground, and ignites /
Detects misfire. In this case, the thermoelectromotive force of pilot thermocouple 1 is about 150 mV at the maximum. On the other hand, the operational amplifier is normally guaranteed to operate with a single power supply and with a maximum negative input voltage of –0.5V to –0.3V.
Therefore, the operational amplifier 3 can sufficiently operate with a single power supply even for a negative voltage input of about −150 mV extracted from the pilot thermocouple 1, and the negative voltage input is inverted and amplified to a positive voltage output and output. Used to detect ignition and misfire.

On the other hand, regarding the non-combustion prevention circuit 6, the difference between the two thermoelectromotive forces is input from the series connection circuit of the pilot thermocouple 1 and the noncombustion protection thermocouple 2, and the incomplete combustion state is detected while ensuring safety. Since the circuit is the same as a conventionally known circuit, detailed description will be omitted.

As described above, in the embodiment circuit, since the operational amplifier is powered by a single power source, the circuit configuration can be simplified.

Various modifications are possible in carrying out the present invention. For example, in the above-mentioned embodiment, one end of the thermocouple is grounded, but it is not limited to this, and it may be connected to some reference potential. Further, in the above-described embodiment, the positive terminal of the pilot thermocouple 1 is grounded. However, the negative terminal is grounded, and the positive terminals of the thermocouples 1 and 2 may be connected to each other to form a series connection circuit. Yes, in this case, a non-inverting amplifier is used as the amplifier. FIG. 2 shows such a modification. In the figure, the negative terminal of the thermocouple 1 is grounded, the positive terminal thereof is input to the non-inverting input terminal of the operational amplifier 3 via the resistor R101, and the inverting input terminal is grounded via the resistor R102 and the resistor R103. Is connected to the output terminal via a parallel circuit of a capacitor and a capacitor. Here, the resistor R101 is Becomes The nonflammable thermocouple 2 side has the same configuration.

According to this configuration, when the output voltage of the thermocouple 1 is V _T ,
The output voltage V _O of the operational amplifier 3 is Becomes

FIG. 3 is a diagram showing still another modification of the present invention. In this modification, the operational amplifier on the thermocouple 1 side has a variable gain configuration, and the offset can be adjusted.

In FIG. 3, the non-inverting input terminal of the operational amplifier 3 on the thermocouple 1 side is grounded via the resistor R110, and the resistor R111 is connected.
To the movable contact terminal of the variable resistor VR1 via. The variable resistor VR is connected between the power supply V _B and the ground. Further, resistors R107 and R108 are provided between the output terminal and the inverting input terminal of the operational amplifier 3.
A series circuit is connected, and the connection point between the resistors R107 and R108 is grounded via the resistor R109 and the transistor Q1. The gain change signal GS is input to the base of the transistor Q1. Here, each resistance is R111 = R2 R107 + R108 = R110 R107 << R108 ″ R110.

With such a configuration, the offset of the operational amplifier 3 can be adjusted by the variable resistor VR1, and the gain of the operational amplifier 3 can be changed by the gain change signal GS. That is, the gain change signal
When GS = “L”, the output voltage V _O is When the gain change signal GS = "H", Becomes

The offset adjustment method may be performed by connecting a variable resistor to the output terminal of the operational amplifier 3 in addition to the above method.

[Advantages of the Invention] According to the present invention, it is possible to detect ignition or the like in a stable manner even with respect to hot start or a difference in gas species while detecting incomplete combustion. As a result, the tolerance in selecting the thermoelectromotive force characteristics of the pilot thermocouple and the noncombustible thermocouple can be doubled as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a diagram showing a combustion state detection circuit of a combustion device as an embodiment of the present invention, FIG. 2 is a diagram showing another embodiment of the present invention, and FIG. 3 is a further embodiment of the present invention. Fig. 4 is a diagram showing an example of a non-combustion prevention system in a small water heater, and Fig. 5 is a diagram showing a conventional combustion state detection circuit using the non-combustion prevention system. In the figure, 1 ... Pilot thermocouple 2 ... Non-combustion protection thermocouple 3,4 ... Operational amplifier 5 ... Ignition / misfire detection circuit 6 ... Non-combustion protection circuit R1 to R7, R101 to R111 ... Resistors C1 to C4 …… Capacitor D1, D2 …… Diode VR1 …… Variable resistance

Claims (1)

[Claims] 1. An ignition detection thermocouple and an incomplete combustion detection thermocouple are connected in series with opposite polarities, and a terminal on the ignition detection thermocouple side of this series connection circuit is connected to a reference potential to detect the ignition. Electromotive force between the connection point of the thermocouple for incomplete combustion and the thermocouple for incomplete combustion detection and the reference potential is introduced as an output from the sensor to the ignition detection circuit, and the thermocouple side for incomplete combustion in the series connection circuit is connected. Combustion state detection circuit of a combustion device configured so that a thermoelectromotive force between the terminal of and the reference potential is guided to the incomplete combustion detection circuit as an output from the sensor.