JPH0118329B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion control safety device, and more specifically, it is a safety device installed in combustion equipment using oil, gas, etc., which detects the combustion state and electrically processes the detected output. The present invention relates to a combustion control safety device that automatically controls the opening and closing of a fuel supply path.

In safety devices for oil and gas combustion equipment, sensors based on perovskite oxides are provided for detecting incomplete combustion and misfires. This sensor is an oxygen sensor that applies the change in resistance value depending on the oxygen concentration, and unlike the conventional oxygen sensor based on zirconia oxide (ZrO ₂ ), it generates an electromotive force based on the difference in oxygen partial pressure. Since this method does not utilize any of the above, the structure can be simplified, and the detection accuracy is also good and reliability is high.

However, in the previously proposed oxygen sensors based on perovskite oxides, the first
As shown by the broken line C1 in FIG. b, only a characteristic in which the internal impedance of the sensor changes rapidly near the equivalence point (near the air-fuel ratio 1) with respect to changes in oxygen concentration is used.

However, according to our research, the perovskite oxide film exhibits an output caused by a sudden change in impedance when the air-fuel ratio is around 1, as shown by the solid line C2 in Figure 1b, and it also shows the same output even when the air-fuel ratio is around 1.25. It has been found that the output results from a reversible rapid impedance change. For example, this is a metal oxide P-type semiconductor film having a perovskite structure in which a perovskite oxide film is fixed and a mixture film of perovskite oxide powder and inert glass powder is sintered (hereinafter referred to as For simplicity, these metal oxide P-type semiconductors are abbreviated as "MOSP sensors"). This is here
The basic resistance characteristics of the MOSP sensor with respect to the air-fuel ratio are as shown in Figure 1a, and in this figure, the electrical resistance value changes rapidly and reversibly by about 3 orders of magnitude at zone a and point b.

On the other hand, as is clear from the graph of the air-fuel ratio of combustion exhaust gas versus gas concentration (%) in Figure 2, when the air-fuel ratio is less than 1, CO and CO ₂ become the main constituents, and when the air-fuel ratio is about 1.4 or more, CO2 becomes the main component. When it becomes NOx
accounts for most of the constituent components. Figures 1b and 2
As is clear from comparing the figures, the curve C2 and the NOx concentration curve correspond to each other in the portion where the air-fuel ratio is 1.4 or higher. It is well known that this nitrogen oxide (NOx) is harmful to the human body, and a safety device that can control even such a combustion state with excess air is desired.

Therefore, the main object of the present invention is to detect the incomplete combustion state and the NOx generation state with one element using the above-mentioned so-called MOSP sensor,
By providing a combustion control safety device that automatically controls the opening and closing of the fuel supply path by electrically processing this detection output, and by using a combination of a MOSP sensor and a high-temperature thermistor, combustion control at the initial stage of combustion can be performed. It's about doing it efficiently.

Therefore, to summarize the present invention, there is provided a combustion control safety device in which a change in the resistance value of an oxygen sensor placed in a flame is detected by an electric circuit, and a fuel supply path is controlled based on the detected output. The oxygen sensor is a metal oxide P-type semiconductor having a perovskite structure, and the electric circuit detects any significant change in resistance value of the metal oxide P-type semiconductor in response to an excess or deficiency of oxygen in a flame atmosphere. It is characterized by being made in the manner that it is done.

Another invention includes the configuration of the first invention as a main part, and further includes a high-temperature thermistor provided on an alumina substrate as a support for the metal oxide P-type semiconductor, and an electrical signal derived from the thermistor. The present invention is characterized in that the fuel supply path is controlled in accordance with a combination with an electrical signal based on the metal oxide P-type semiconductor.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 3 constitutes an embodiment of the first invention.
A schematic diagram of a MOSP sensor (mainly composed of NiLaO ₃ ) placed in a gas combustion flame is shown, and FIG. 4 shows an electrical circuit diagram for processing the sensor output.
In FIG. 3, a sensor portion 3 of a MOSP sensor 2 formed on an alumina substrate (or ceramic substrate) 1 is placed in an outer flame 4 of a combustion flame. Reference numerals 5 and 5 are lead wires led out from the sensor section 3 and connected to the circuit shown in FIG. 4. 6 is the burner head. This burner uses gas and has an external flame of 4
The temperature is high and is kept in the range of 350-1000℃.

Equipped with a sensor section 3 whose main component is NiLaO ₃
The characteristics of the MOSP sensor 2 are represented by a curve C2' as shown in FIG. The complete combustion region is an air-fuel ratio in the range of approximately 1.0 to 1.25, and the sensor output is a normalized value of approximately 0.1V to 0.2V. Incomplete combustion occurs when the air-fuel ratio is approximately 1.0 or less, and the sensor output is a normalized value of approximately 0.9 to 1.0V. Region where there is a transition from complete combustion to incomplete combustion (air-fuel ratio of 1.25 to
1.5) shows a sudden increase in resistance value in response to a decrease in oxygen partial pressure in the flame atmosphere and the presence of cyclic gases, and this is used to detect incomplete combustion. On the other hand, the region where NOx generation is observed is the region where the air-fuel ratio is approximately 1.4 or higher, and the sensor output quickly changes from the normalized value of 0.1 V to 0.9 V (at the air-fuel ratio of 1.25 to 1.5, the resistance changes rapidly). zone). In other words, the output value increases significantly until a combustion state in which NOx is present is reached, so this sudden change zone can be used to reduce the harmful effects of excessive supply air.
This is used to detect NOx generation. Furthermore, it is possible to create a device that can control the air-fuel ratio to be in the range of 1.0 to 1.25, that is, in the complete combustion range.

Since this sensor 2 can apply either alternating current or direct current, it is equivalently represented by a variable resistor 10 in the electric circuit 9 of FIG. In this circuit 9, terminal 1
A power supply V for the electronic circuit is connected between 1 and 11,
A commercial power source for a load is connected between the terminals 12, 12. A series connection between a relay contact 13 and a fuel supply/cutoff solenoid valve 14 is connected to this commercial power supply, and in this example, a relay coil 1 of an electronic circuit 9 is connected.
When the current flowing through 5 is cut off, the contact 13
is turned OFF, the solenoid valve 14 is closed, and the fuel (gas) is turned OFF.
is configured to stop the supply of

An operational amplifier is used for the comparator 20 of the electronic circuit 9. A voltage divided by a resistor 21 and a resistor 22 is applied to a non-inverting input of the comparator 20 as a comparison voltage. As shown in Fig. 5, this comparison voltage is a voltage corresponding to approximately 0.8V in the normalized sensor output, and is a voltage corresponding to approximately 0.8V in the normalized sensor output.
This is the judgment level for NOx generation. Resistance 23, 24
is for providing positive feedback to the comparator 20, and functions to provide a stable output against fluctuations in the vicinity of the critical value of the comparison input. Note that it is preferable that either one of the resistor 21 and the resistor 22 that provides the divided voltage be a variable resistor. Since the preset level can be varied in consideration of the characteristics of various sensors, it increases versatility and is advantageous in terms of adjustment.

A voltage divided by a resistor 25 and a variable resistor 10 is applied to the inverting input of the comparator 20 . The comparator 20 sets a low level (hereinafter referred to as "L") when the sensor (variable resistor 10) detects incomplete combustion or NOx generation state, that is, exceeds a determination level.
If it is below the determination level, it continues to output a high level (hereinafter abbreviated as "H"). The output part of the comparator 20 is connected to the base of an NPN transistor 27 via a resistor 26, and the collector of the transistor 27 is connected to the coil 15 of the relay. That is, when the comparator 20 outputs "H", the resistor 2
The connection point between 6 and the resistor 28 is positively biased, the transistor 27 becomes conductive, and current flows through the coil 15.
The switch contact 13 is held in the ON state. The solenoid valve 14 is opened and the supply of fuel gas is continued. On the other hand, when the output of the comparator 20 is reversed to "L", the transistor 27 is turned off, the relay contact 13 is turned off, and the solenoid valve 14 is abruptly closed.

Since the output level of the comparator 20 becomes "H" after ignition, the transistor 27 becomes conductive via the resistors 24, 26, and 28, and the relay 1
5 is turned on, the fuel supply solenoid valve 14 operates to maintain the combustion state. If a cause arises that increases the sensor output during combustion operation (in the case of incomplete combustion or NOx generation), the output of the comparator 20 becomes "L" because the sensor output reaches the level of incomplete combustion and NOx generation. Transistor 27 enters the cutoff state, turning off relay 15.
Therefore, the combustion supply solenoid valve 14 is stopped, and combustion is stopped. In this way, the combustion control device operates safely.

Next, a modification example using a wide range of output characteristics of the MOSP sensor 2 is shown in FIG. In this variant, the sensor output is not simply used for comparison to a specific level, but rather is processed as an analog signal (which may later be digitized) and used to adjust the combustion air volume or the fuel supply. It is used as a control signal. As shown in Figure 6,
A signal from the MOSP sensor 2 is input to a control circuit 30. Due to a change in firepower for some reason, the 5th
In the case where even the complete combustion state shown in the figure deviates from the optimal state (point P1 or P2 on curve C2')
For example, a control signal is given to the combustion blower 31 or the fuel supply device 32 so that the combustion state always reaches the optimum complete combustion state (from P1 or P2 along the curve C2' in the direction of the arrow). The supply amount is changed by analog or digital control of the valves provided for the supply. In addition, 33, 34
indicate the air supply route and the fuel supply route, respectively.
In addition, if the combustion state suddenly changes and exceeds the judgment level shown in Figure 5, incomplete combustion or
Of course, the control circuit 30 acts to stop combustion immediately upon determining that NOx is generated. The main components of the MOSP sensor are
In addition to NiLaO ₃ , CrLaO ₃ , La ₂ Cu ₂ O ₄ , GeTiO ₃ ,
PrTiO ₃ , NdTiO ₃ and the like are promising.

Next, a second invention that has a certain relationship with the first invention described above will be described with reference to an example. In this embodiment, two sensors are integrated into the same base. That is, a high-temperature thermistor film is further sintered and fixed on the alumina substrate serving as the support for the MOSP sensor 2 in the embodiment of the first invention. The characteristics of MOSP sensor 2 are as shown in curve C2 in Figure 1, and the high-temperature thermistor film is similar to a combustion flame that exhibits an extremely large negative resistance change at a temperature of 200 to 1000°C, as shown in the semilogarithmic graph in Figure 7. It does not change over time even if it is exposed inside or under atmospheric pressure, and it is not sensitive to gases at high temperatures.

The composite sensor films sintered and fixed to the tips of the alumina substrates 1 are placed in the outer flame 4 in the same manner as shown in FIG. FIG. 8 is an electrical circuit diagram when this composite sensor is used. In this circuit diagram, variable resistor 10 is equivalent to MOSP sensor 2
, and the high temperature thermistor film is shown equivalently having a resistance 35. In addition, the same reference numbers as in Fig. 4 indicate the same or equivalent parts,
Depending on whether the relay coil 15 is ON or OFF, a load solenoid valve 14 similar to that shown in FIG. 4 is controlled.

A voltage divided by resistors 41 and 42 is input to a non-inverting input of a comparator 40, which is an operational amplifier, and is used as a reference voltage. And the inverting input has a resistor 45
and the divided voltage of the equivalent resistance 35 of the thermistor are given. The resistors 44 and 43 are for providing positive feedback to the comparator 40.
The output of is connected to the anode of the diode 50 via the resistor 46, and the cathode side is connected to the transistor 27.
connected to the base of The output of the comparator 20 is connected to this same base via a resistor 26.

The comparator 60 consisting of an operational amplifier is
The output of the comparator 20 is forced to "H" until the sensor part 3 of the MOSP sensor 2 reaches the operating temperature.
A resistor 61 is connected to the inverting input of the comparator 60 as a reference voltage.
62 divided voltages are applied, while the non-inverting input is connected to the inverting input of the comparator 40. Resistors 63 and 64 are for providing positive feedback,
A resistor 66 connected to the output of the comparator 60
The connection point between the resistor 68 and the resistor 68 is connected to the base of an NPN transistor 69. The collector of the transistor 69 is connected to the inverting input of the comparator 20 via a resistor 67.

The high temperature thermistor 35 is for checking ignition. The burner is ignited and the thermistor 35
When the resistance value of decreases, the comparator 40 becomes "H"
outputs and turns on transistor 27, relay 15
energizes the load solenoid valve to operate the fuel supply valve in the direction of opening. Thermistor 35 is
Operating temperature of sensor part 3 of MOSP sensor (350~
Since it detects and judges the presence or absence of flame at temperatures below 1000°C, it has the advantage of being able to confirm ignition at a much higher speed than conventional sensors.

Until the MOSP sensor 2 reaches the operating temperature, the comparator 60, transistor 69, and resistor 67 lower the inverting input level to the non-inverting input level of the comparator 20, so the output of the comparator 20 is maintained at "H". Further, when the sensor section 3 of the MOSP sensor reaches the operating temperature, the output level of the comparator 60 becomes "L", and thereafter follows the output of the sensor 10. This prevents the safety device from operating due to incomplete combustion or the like in the early stages of combustion. After reaching operating temperature, the manner in which sensor 10 monitors combustion conditions and controls safety devices is similar to the operation of circuit 9 in FIG.

By the way, in the above-mentioned embodiments and modifications, all the sensors were arranged directly in the flame. However, in a more preferred embodiment, this oxygen sensor is fixedly provided to the flame radiation section and housed in a cylindrical case provided with a ventilation path in the direction in which the flame rises. In this way, it is possible to prevent the output of the oxygen sensor from fluctuating due to flame fluctuations. FIG. 9 shows a sensor housed in a case, and FIG. 10 shows a schematic diagram of the cased sensor in use. As shown in FIG. 9 (a is a front view, b is a plan view, and c is a right side view), the sensor case 70 has a cylindrical shape with a closing portion 71 at one end.
An annular U-groove 72 is formed at a short distance from. The case 70 is fixedly attached to the mounting body 74, and the alumina substrate portion of the sensor 2' is also fixedly attached to the mounting body 74. The mounting body 74 is fixed to a predetermined portion of the burner body (not shown) by screwing or the like through a mounting hole 74'.
The annular U-groove 72 is provided with circular holes 73, 73 at the top and bottom, and when the case is installed in a flame, a ventilation path is formed in the direction rising from the flame. Sensor 2'
The sensor section 3' is fixed so as to be located exactly in this ventilation path. Lead wires 5 and 7 from sensor 2'
6,75 have been derived. Lead wire 5 is
It is from a MOSP sensor, and the lead wire 75 is from a high temperature thermistor. Lead wire 76
is a common lead between these two (so-called common lead). This sensor 2' is assumed to be a composite sensor of the above-mentioned modification, but of course MOSP
A sensor alone may be used.

As can be clearly seen with reference to FIG. 10, the flame 4 rises up as if licking the annular U-groove 72, and maintains a steady state within the air passage. Therefore, if the sensor 2' is housed in such a case 70, fluctuations in the sensor output due to flame fluctuations can be significantly reduced.

As described in detail above, according to the present invention, the oxygen sensor placed in the flame is a metal oxide P-type semiconductor having a perovskite structure, and the electrical signal derived from this oxygen sensor detects the lack of oxygen in the flame atmosphere. Since this signal corresponds to a significant change in resistance value due to excess oxygen, a single element is used to detect incomplete combustion and NOx generation, and this detection output is used to automatically open and close the fuel supply path. It can be controlled and has a great effect on environmental safety measures based on combustion. Furthermore, when used in combination with a thermistor film, it exhibits a great effect on combustion control, especially in the early stages of combustion.

[Brief explanation of drawings]

Figure 1a is a characteristic diagram of the oxygen sensor, Figure 1b is a modified output characteristic diagram of the oxygen sensor, Figure 2 is a characteristic diagram of combustion exhaust gas, Figure 3 is a schematic diagram of the usage state of one embodiment, and Figure 4 The figure is an electric circuit diagram according to one implementation, FIG. 5 is a modified output characteristic diagram of the oxygen sensor used in one implementation, FIG. 6 is a block diagram of a modified example, FIG. 7 is a characteristic diagram of a high temperature thermistor, and FIG. FIG. 8 is an electric circuit diagram when a composite sensor is used, FIG. 9 is a diagram showing a storage case for the sensor, and FIG. 10 is a schematic diagram of the cased sensor in use. 2...MOSP sensor, 3...sensor section, 4...
...Outer flame, 9...Electronic circuit, 10...Variable resistance, 1
4... Solenoid valve, 20, 40, 60... Comparator, 35... High temperature thermistor equivalent variable resistance, 7
0... Cylindrical case, 73... Circular hole forming a ventilation path.

Claims (1)

[Scope of Claims] 1. A combustion control safety device that detects a change in the resistance value of an oxygen sensor placed in a flame using an electric circuit, and controls a fuel supply route based on the detected output, comprising: As a sensor, a metal oxide P-type semiconductor film having a perovskite structure is used, in which a mixture film of perovskite oxide powder and inert glass powder is sintered on a perovskite-type oxide film, and with respect to the output of the sensor, The above electric circuit is configured by providing a judgment level setting means for setting a judgment level corresponding to an oxygen deficiency state and an oxygen excess state, and a comparison means for comparing the output of the sensor with the set judgment level. Characteristic combustion control safety device. 2. The oxygen sensor is fixedly provided to the flame radiation part, and is housed in a cylindrical case provided with a ventilation passage in the direction in which the flame rises, and the sensor part of the oxygen sensor is positioned in the ventilation passage. The combustion control safety device according to claim 1, wherein the combustion control safety device is arranged to prevent flame fluctuation.