JPS6199024A - Combustion detector - Google Patents

Abstract

PURPOSE:To attempt to improve the combustion range in a low-temperature zone and the oxygen deficiency characteristic in a high-temperature zone by constituting an oxygen deficiency detection level temperature correction circuit by concurrently using a room temperature detecting thermistor as one for the temperature correction of the oxygen deficiency detection level. CONSTITUTION:In a case where the room temperature is high, the resistance value of a room temperature detection thermistor 17 is small. Hence, a non-inversional input potential of an amplifier 24 becomes high, and the output thereof becomes a high voltage, and the degree of contributing to lowering an oxygen deficiency detection level VB is small. When the room temperature is lowered, the resistance value of the room temperature detection thermistor 17 becomes large, the non-inversional input voltage of the amplifier 24 is lowered, and the output potential is also lowered. When the output potential of the amplifier 24 is lowered, the oxygen deficiency detection level VB is lowered to the substantially same potential. When the room temperature is lowered, combustion air is also lowered, and hence an air surplus phenomenon occurs. This causes the flame level to lower. However, since the oxygen detection level is also lowered, a constant difference is maintained in a substantially the same manner as the case where the room temperature is high, between the oxygen detection level and the flame level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a combustion detection device for a combustor.In general, indoor combustors such as petroleum 7 unheaters use indoor air as combustion air, so they cannot be used for long periods in a closed room. Continuing to burn for a long time results in a lack of oxygen, which causes abnormal combustion such as red-flame combustion, and generates 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, where 31 is a misfire detection comparator, 32 is an oxygen deficiency detection comparator, and these are connected to a burner 33 and a flame rod 3.
One input is the charging potential of the capacitor 35 that charges the flame current between the two. And each of the above comparators JL
The other non-inverting input of 32 receives a reference level (potential) determined by resistors 36, J7, and 38. The misfire detection level of the misfire detection comparator 31 is determined by the resistances 3t3 and 37.
The oxygen deficiency detection level is determined by the series resistance of the resistance 36 and the resistance 37.3B.

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. That is, when the indoor temperature changes, the charging potential (frame level) obtained by the capacitor 35 changes as shown in FIG. 2 due to a change in the air-fuel ratio due to a change in air density. However, the oxygen deficiency detection level is fixed at a constant value as described above. Therefore, when the room 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 combustion engine operates even though there is no oxygen deficiency condition. or,
On the other hand, when the room temperature rises, the difference between the flame level and the oxygen deficiency detection level becomes so large that even if an oxygen deficiency condition occurs, it cannot be detected.

Purpose of the Invention The present invention was made in view of the above-mentioned points, and it changes the oxygen deficiency detection level in response to changes in indoor temperature, and sets the difference from the flame level to always be constant. The purpose is to ensure that the defect detection circuit operates properly.

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 connects its output to the level setting side of the oxygen deficiency detection circuit. However, the configuration is such that the set level of the oxygen deficiency detection circuit is corrected in accordance with changes in indoor temperature. Furthermore, a comparator is provided which operates when the indoor temperature drops extremely and the output of the amplification circuit drops to the lower limit set level, and the output thereof is connected to the inverting input side of the amplification circuit to increase the number of amplifiers. The effect can be further enhanced by providing a limiter circuit to reduce the drop in the output of the amplifier circuit.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1.
2 is a limiting resistor, 3 is a burner, 4 is 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. 7.8 is a diode, comparator 13,
This is for capturing 14 inputs. 9 to 12 are resistances, 10.1
The potential vA determined by the series resistances 1 and 12 is the misfire detection level, and the potential vB determined by the series resistances 10 and 11.12 is the oxygen deficiency detection level. 13 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, and 18.19 is a resistor. , 20 are comparators forming a room temperature detection circuit for combustion control.

21 to 23 are resistors, 24 is an operational amplifier, forming an in-phase amplifier circuit that receives the room temperature detection thermistor 17 as an input;
The output thereof is connected via a diode 25 to the reference potential setting side (VB) of the oxygen deficiency detection comparator 13. The amplifier of the amplifier circuit 24 is determined by the ratio of the resistors 22 and 23. 26 and 27 are resistances that set the lower limit level on the low temperature side. Reference numeral 28 designates a comparator for the lower limit limiter, the output of which is connected to the inverting input side of the amplification circuit 24 via a diode 29 to increase the amplification.

In the above configuration, the operation will be explained. First, the output state of the amplifier 24 is determined by the amplifier 24 defined by the resistors 22 and 23 depending on the room temperature condition.

In the present invention, the room temperature is 17°C as shown by the broken line in Figure 2.
In the above case, the output of the amplifier 24 is at the oxygen deficiency detection level v
Since it is set to be higher than B, the diode 26
The output of the amplifier 24 does not contribute to the oxygen deficiency detection level vB. In other words, the upper limit of the oxygen deficiency detection level is the potential determined by the resistors 10 and 11.12. In addition, when the room temperature is below O''C, the lower limiter circuit 28 set by the resistors 26 and 27 outputs 0, so the inverting input of the amplifier 24 is lowered to Low level via the diode 29. The amplification degree is increased, and the output of the amplifier 24 is thermistor 1 for detecting room temperature.
Even if 7 changes, it hardly changes. That is, a lower limit mittah effect is provided so that the oxygen deficiency detection level hardly changes at room temperature below 0°C. -29 room temperature 0
The oxygen deficiency detection level (VB) is changed depending on the room temperature in the range of 17°C to 17°C.

In such a circuit, first, when the room temperature is high, the resistance value of the room temperature detection thermistor 17 is small, so the non-inverting input potential of the amplifier 24 is not high, and its output is also connected to the resistors 22 and 23.
Since it is amplified by a magnification determined by , the voltage becomes high, and its contribution to lowering the oxygen deficiency detection level VB is small. However, when the room temperature is high, the combustion condition is good, so the 7-rem 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, the non-inverting input potential of the amplifier 24 decreases, and the output potential similarly decreases. When the output potential of the amplifier 24 decreases, the oxygen deficiency detection level VB 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. In order to
A constant difference is maintained between the frame level and the frame level, which is almost the same as 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 detection 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 description of the embodiments, the present invention consists of an oxygen deficiency detection level temperature correction circuit in which a room temperature detection thermistor for combustion control is also used for temperature correction of the oxygen deficiency detection level. It is possible to improve the combustion range in a lower temperature range and the oxygen deficiency characteristics in a higher temperature range, and it is possible to provide a highly reliable combustion detection device that does not malfunction at a low cost.

[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. be. a...Burner, 4...Frame level, 10-12...Resistance, 13.14...
・Comparator, 15... Combustion control circuit, 17...
...Thermistor for room temperature detection, 24... Arithmetic amplifier, 28... Comparator.

Claims (3)

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