JPH0210346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a combustion detection device for a combustor, and is particularly intended to improve oxygen deficiency detection characteristics.

Conventional configurations and their problems In general, indoor combustors such as oil fan heaters use indoor air as combustion air, so if combustion continues for a long time in a closed room, it will become oxygen deficient and cause abnormal combustion such as red flame combustion. This can lead to the generation of carbon monoxide, which can endanger human life. For this reason, it has recently become common practice in this type of combustor to provide, in addition to the misfire detection circuit, an oxygen deficiency detection circuit having an oxygen deficiency detection level set higher than the misfire detection level.

FIG. 3 shows a conventional combustion detection device equipped with this oxygen deficiency detection circuit, in which 31 is a misfire detection comparator, 32
is an oxygen deficiency detection comparator, and both of these are level 3
One input is the charging potential of a capacitor 35 that charges the flame current between the flame rod 34 and the flame rod 34. The other non-inverting input of each of the comparators 31 and 32 receives a reference level (potential) determined by resistors 36, 37, and 38. The misfire detection level of the misfire detection comparator 31 is determined by the resistance 36,
The oxygen deficiency detection level is determined by the series resistance of the resistances 37 and 38.

In such a circuit configuration, when an oxygen deficiency state occurs, the charging potential of the capacitor 35 becomes lower than the oxygen deficiency detection level, and the output of the oxygen deficiency detection comparator 32 is inverted from the normal output. The combustion control circuit 38 then receives this output and, for example, stops combustion.

However, in the conventional circuit, since the oxygen deficiency detection level is fixed at a constant value as shown in FIG. 2, there have been problems such as malfunctions when the indoor temperature drops. In other words, when the indoor temperature changes, the charging potential (frame level) obtained by the capacitor 35 changes to a second level due to a change in the air-fuel ratio due to a change in air density.
Changes as shown in the figure. However, the oxygen deficiency detection level is fixed at a constant value as described above. Therefore, when the indoor temperature is low, there is no margin between the flame level and the oxygen deficiency detection level, and a slight change in combustion conditions may cause a malfunction in which the engine operates even though there is no oxygen deficiency condition. On the other hand, as the room temperature rises, the difference between the flame level and the oxygen deficiency detection level becomes larger, so that even if an oxygen deficiency condition occurs, it cannot be detected.

Purpose of the Invention The present invention has been made in view of the above points.
The purpose is to change the oxygen deficiency detection level in response to changes in indoor temperature and set the difference from the flame level to always be constant, so that the oxygen deficiency detection circuit operates properly. be.

Structure of the Invention In order to achieve the above object, the present invention forms an in-phase amplification circuit using an indoor temperature detection thermistor provided for combustion control, and sends its output to the level setting side of the oxygen deficiency detection circuit. It is configured to connect and correct the set level of the oxygen deficiency detection circuit according to changes in the indoor temperature, and is activated when the indoor temperature drops extremely and the output of the amplification circuit drops to the lower limit set level. The effect can be further improved by providing a comparator whose output is connected to the inverting input side of the amplification circuit, and by providing a limiter circuit to reduce the degree of amplification from decreasing in the output of the amplification circuit. It is becoming possible to increase it.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1. Reference numeral 1 indicates an AC power source for passing a flame current, 2 a limiting resistor, 3 a burner, 4 a flame rod, and 5
is a capacitor, which is charged by the flame current flowing between the flame rod 4 and the burner 3. 6 is a resistor for discharging the charging potential of the capacitor 5, which determines the misfire delay. 7 and 8 are diodes, comparators 13 and 14
This is for input protection. 9 to 12 are resistances, 10,
The potential V _A determined by the series resistances 11 and 12 is the misfire detection level, and the potential V _B determined by the series resistances 10 and 11 and 12 is the oxygen deficiency detection level. 1
3 is a comparator for oxygen deficiency detection, 14 is a misfire detection comparator, 15 is a combustion control circuit composed of a microcomputer, etc., 16 is a DC power supply for the control circuit, 17 is a thermistor for indoor temperature detection, 18 and 19 are resistors. , 20 are comparators forming a room temperature detection circuit for combustion control. 21 to 23 are resistors, and 24 is an operational amplifier, forming an in-phase amplification circuit that inputs the room temperature detection thermistor 17, and whose output is connected to the reference potential of the oxygen deficiency detection comparator 13 via a diode 25. Setting side
Connected to _VB . The degree of amplification of the amplification circuit 24 is determined by the ratio of the resistors 22 and 23. 26 and 27 are resistors, which set the lower limit level on the low temperature side. 28 is a comparator for the lower limiter, the output of which is connected to the inverting input side of the amplification circuit 24 via a diode 29 to increase the degree of amplification.

To explain the operation of the above configuration, first, the amplification degree 24 changes depending on the room temperature condition.
The output state is determined by the degree of amplification determined by and 23.
In the present invention, as shown in the broken line in Fig. 2, the room temperature is 17
℃ or higher, the output of the amplifier 24 is set to be higher than the oxygen deficiency detection level V _B , so the output of the amplifier 24 does not contribute to the oxygen deficiency detection level V _B due to the diode 25. . In other words, the upper limit value of the oxygen deficiency detection level is the potential determined by the resistors 10, 11, and 12. Also, if the room temperature is below 0℃, resistor 2
Since the lower limit limiter circuit 28 set in 6 and 27 has an output of 0, the inverting input of the amplifier 24 is lowered to the _LOW level via the diode 29, and its amplification degree is increased. The output is designed to hardly change even if the room temperature detection thermistor 17 changes. That is, a lower limiter action is provided so that the oxygen deficiency detection level hardly changes at room temperature below 0°C. In other words, the oxygen deficiency detection level V _B is changed depending on the room temperature in the range of room temperature from 0°C to 17°C.

In such a circuit, first, when the room temperature is high, the resistance value of the thermistor 17 for detecting the room temperature is small, so the non-inverting input potential of the amplifier 24 becomes high, and its output is also amplified by a factor determined by the resistors 22 and 23. Therefore, the voltage becomes high, and its contribution to lowering the oxygen deficiency detection level V _B is small. However, when the room temperature is high, the combustion condition is good, so the flame level hardly decreases and there are no problems such as malfunctions. Next, when the room temperature decreases, the resistance value of the room temperature detection thermistor 17 increases, and the non-inverting input potential of the amplifier 24 decreases.
The output potential also decreases. When the output potential of the amplifier 24 decreases, the oxygen deficiency detection level V _B also decreases to approximately the same potential as shown in FIG. When the room temperature decreases, the combustion air also decreases, resulting in an excess air phenomenon, and the combustion state also becomes a lifting state, causing the flame level to decrease, but as explained above, the oxygen deficiency detection level also decreases. Therefore, a constant difference is maintained between the frame level and the frame level, similar to when the room temperature is high. Therefore, even if the flame level changes somewhat due to changes in combustion conditions, there is no problem of malfunction. By giving temperature characteristics to the oxygen deficiency temperature level in this way, the combustion range at low temperatures can be widened, and the oxygen deficiency characteristics at high temperatures can be improved. In addition, in this embodiment, the oxygen deficiency detection level is kept almost constant at extremely low temperatures, so the difference from the flame level can be maintained almost constant even at extremely low temperatures, and there is an advantage that oxygen deficiency can be detected reliably. .

Effects of the Invention As is clear from the above description of the embodiments, the present invention utilizes a thermistor for detecting room temperature for combustion control also as a temperature correction circuit for oxygen deficiency detection level, thereby configuring an oxygen deficiency detection level temperature correction circuit. It is possible to improve the combustion range in the high temperature range and the oxygen deficiency characteristics in the high temperature range, and it is possible to provide a highly reliable combustion detection device that does not malfunction and is inexpensive.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a combustion detection device showing an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between oxygen deficiency detection level and flame level, and Fig. 3 is a circuit diagram of a conventional combustion detection device. It is. 3...burner, 4...flame rod, 10~
12...Resistor, 13,14...Comparator, 15...
Combustion control circuit, 17... room temperature detection thermistor,
24... operational amplifier, 28... comparator.

Claims (1)

[Claims] 1. Combustion comprising a first set level for detecting the presence or absence of a combustion flame and a second set level set at a level higher than the first set level for detecting abnormal combustion such as during oxygen deficiency. A combustion detection device comprising a detection circuit and an output of an in-phase amplification circuit having an input thermistor for indoor temperature detection connected to a level setting side of the combustion detection circuit. 2. The combustion detection device according to claim 1, wherein the amplification circuit is configured to increase the amplification degree when the output of the amplification circuit decreases to a lower limit setting level to reduce the decrease in output. 3. The combustion detection device according to claim 1, wherein the room temperature detection thermistor also serves as a thermistor used for combustion control.