JPH0138211B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a combustion state detection device for detecting incomplete combustion of gas, oil, etc. combustion equipment, and in particular to a device for detecting an oxygen concentration battery using zirconia (ZrO ₂ ). It was used as.

Configuration of conventional examples and their problems In recent years, zirconia sensors have begun to be applied to detect the combustion state of combustion equipment because the electromotive force changes suddenly from 0V to 0.8V when the air-fuel ratio λ≦1. In this case, temperature changes in the internal resistance of the zirconia element are often used to detect burner ignition. FIG. 1 shows an example of this detection circuit. 1 is a zirconia element and is equivalent to an electromotive force ei and an internal resistance Ri. 2 is connected to the DC power source 3 through a series resistor Rs having zirconia elements connected in series. a and g indicate detection output terminals. Now, before combustion, the internal resistance Ri is several 100M
Ω, which is sufficiently larger than the series resistor 2, and the output potential is approximately equal to that of the series power supply 3. When the burner burns, the internal resistance Ri decreases due to the temperature, and becomes a value that is sufficiently smaller than the series resistance 2.
The partial pressure potential of Ri becomes almost zero, and it can be detected that the burner has burned. If there is currently a shortage of combustion air in the burner, the air-fuel ratio λ≦1 and an electromotive force ei is generated. Therefore, the output terminal voltage eo becomes ep·Ri/Rs+Ri+ei, and since Ri≪Rs, eo≒ei, and incomplete combustion can be detected by the value of eo. Here, ep indicates the voltage of the power supply 3.

However, the internal resistance Ri is greatly influenced by the ambient temperature of the element. For example, if the temperature of the element is low, Ri increases, and the divided potential becomes high. There was a problem in that the value was the same as ei, making it impossible to distinguish between incomplete combustion.

Purpose of the Invention The present invention solves the above-mentioned conventional problems, and detects the sensor temperature based on changes in the internal resistance of the sensor, and further detects changes in the electromotive force of the sensor without being affected by the internal resistance. It is.

Structure of the Invention In order to achieve this object, the present invention provides a power supply circuit that applies voltage through a series resistor connected to a zirconia sensor, a switch circuit that connects and disconnects the power supply circuit, and an oscillation unit that turns the switch circuit on and off. A detection circuit is provided to detect the potential at both ends of the zirconia sensor, and the combustion state of the burner is determined by this. With this configuration, changes in internal resistance when a voltage is applied to the sensor and changes in electromotive force when no voltage is applied are detected in a time-division manner, making it possible to always detect both signals.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows a circuit system diagram of an embodiment of the present invention. In the figure, a switch circuit 4 is connected in series with the zirconia sensor 1 and the series resistor 2, and the power supply circuit 3 is switched on and off using the output of the oscillation section 5. Reference numeral 6 indicates a detection circuit section that detects the output potential a of the zirconia sensor 1 and converts it into a detection signal es, and the detection circuit section 6 obtains a synchronization signal eo from the oscillation section 5.

With the above configuration, the application of the power supply voltage to the zirconia sensor 1 is periodically repeated according to the signal from the oscillation unit 5, and the potential a of the sensor 1 is measured by measuring the electromotive force ei and measuring the change in the internal resistance Ri. It will be done.

FIG. 3 shows a specific circuit example. In this circuit, the burner is ignited by the temperature change of the zirconia sensor 1.
It is configured to detect fire extinguishing and detect incomplete combustion due to lack of air or excess air based on changes in electromotive force. In FIG. 3, parts that operate in the same way as in FIGS. 1 and 2 are marked with the same symbols.

A switch circuit 4 consisting of a transistor 7 and resistors 8 and 9 is connected to the zirconia sensor 1 and the series resistor 2, and the switch circuit 4 includes a comparator 10, a resistor 11,
12, 13, 14, and a capacitor 15. The output a of the sensor 1 is sent to the detection circuit section 6
is input. The detection circuit section 6 includes a comparator 16 that detects ignition/extinguishment of the burner, and comparators 17 and 18 that detect the combustion state.

The comparator 16 inputs the potential a of the sensor 1 to its negative input terminal, and the divided potential b of the resistors 19 and 20 to its positive input terminal. b potential is transistor 2
1 to synchronize with the oscillation section 5. The transistor 21 is configured to be conductive when the output eo of the oscillation section 5 is a high output. In other words, when the output eo of the oscillator 5 is a low output, the switch circuit 8 becomes conductive.
Potential a when power is supplied to sensor 1 through series resistor 2 (resistor 2 and internal resistance Ri of sensor 1)
The divided potential b of the resistors 19 and 20 is compared with the divided potential b of the resistors 19 and 20. Further, when the switch circuit 4 is cut off, it operates to make the potential b zero. Therefore, as shown in FIG. 4, when the temperature of the sensor 1 increases and the internal resistance Ri decreases so that the divided potential a≦b, the output _es1 of the comparator 16 becomes high. Next, the oscillator 5
Therefore, when no voltage is applied to the sensor 1, the potential a becomes the electromotive force ei, but at this time the transistor 21 becomes conductive and the potential b≈0V. From the above, the potential a>b and the output _es1 becomes a low output. When the burner burns and the sensor 1 is at a sufficiently high temperature, the output es ₁ of the comparator 16 generates a pulse signal that is synchronized with the oscillator 5, and this is converted into the ignition output es ₁ by the detection transformer 22. ′ is obtained.

When the temperature of the sensor 1 is low, the potential a is high and a>b with the switch circuit 4 conducting, and the output _es1 becomes a low output. Therefore, es ₁ does not become a pulse signal and continues to maintain a low output, detecting that the burner is not burning.

Comparators 17 and 18 constitute a window comparator, and both comparators 17 and 18 go high when potential a is in the relationship c≧a≧d with respect to the divided potentials c and d of resistors 23, 24, and 25. otherwise, one of the comparators will have a low output.
When either comparator goes low, diode 2
6 and 27, the potential es ₂ becomes low. Resistor 23,
A transistor 28 is connected in series with 24 and 25 and synchronized with the oscillation section 5, and operates so that when the output eo of the oscillation section 5 is low, the transistor 28 is cut off and the potentials c and d become zero. do. That is, the output eo of the oscillator 5 becomes high, the switch circuit 4 is in an off state, and the output _es2 becomes high when the electromotive force ei of the sensor 1 is between the potentials c and d as shown in FIG. Further, when the output eo of the oscillator 5 becomes a low output, es ₂ also becomes a low output, and a pulse signal synchronized with the oscillator 5 is detected as a normal combustion signal es ₂ ' through the transformer 29. Combustion becomes abnormal, the electromotive force ei increases or decreases, and the potential a becomes a>c or a<
d, the pulse signal stops and abnormal combustion is detected. As described above, if there are pulse signals at the outputs es ₁ ′ and es ₂ ′ of the transformers 22 and 29, it can be determined that the burner is burning normally. The burner is extinguished due to the loss of the es ₁ ′ pulse signal.
Abnormal combustion in the burner can be detected due to the disappearance of the es ₂ ′ pulse signal.

Here, the configuration was configured to detect es ₁ and es ₂ as pulse signals by transformer coupling, but instead of using them as pulse signals, es ₁ high is detected when the switch circuit is on, and
It may be possible to only detect that _es2 is high when the switch circuit is off.

FIG. 4 shows the characteristics of the internal resistance of the sensor 1, with the horizontal axis showing the temperature T and the vertical axis showing the internal resistance Ri on a log scale. Here, the design is such that when the temperature of the sensor 1 rises and the internal resistance becomes Ri(b), the divided potential a with respect to the resistor 2 becomes equal to the potential b.

FIG. 5 shows the characteristics of the electromotive force of the sensor 1, with the horizontal axis showing the air-fuel ratio λ and the vertical axis showing the electromotive force ei. The sensor 1 suddenly generates an electromotive force when λ=1 (theoretical air amount is supplied), but the burner usually burns at λ=1.2 to 1.3. Combustion is normal when the potential is between ei (c) and ei (d); when it is higher than ei (c), there is incomplete combustion due to lack of air; when it is lower than ei (d), there is danger of lift combustion due to excess air. state.

FIG. 6 shows another embodiment, and shows an example in which control is performed by a microcomputer (hereinafter referred to as CPU) 30. In this example, the oscillation section 5 as shown in FIG. 3 is constructed inside the CPU 30, and only the drive signal for the switch circuit 4 is outputted from the output terminal 31. In addition, the detection circuit unit 6 sequentially switches and determines the sensor potential a and the reference potential f to be compared with the comparator 34 using the synchronization signals 32 and 33 from the oscillation unit of the CPU 30, and the output h is inputted to the CPU 30 from the input 35. The CPU 30 performs various processing according to the program and outputs an output signal es from the output 36.

In addition, in the present invention, when the switch circuit 4 is turned on, the potential a of the sensor 1 is equal to the series resistance 2 and the internal resistance of the sensor 1.
The electromotive force ei is added to the divided potential of Ri, and although the configuration is not such that only changes in internal resistance are detected, the electromotive force ei is small, about 0.8V at maximum, and can be ignored.
If it cannot be ignored, the electromotive force ei obtained when the switch circuit 4 is turned off may be stored and subtracted from it. Furthermore, by using comparators 16, 17, and 18 whose input terminals have sufficiently large impedance, the internal resistance Ri when the switch circuit is off can be ignored. Furthermore, it is easy to detect internal resistance and electromotive force as analog values and perform some kind of control.

Effects of the Invention As explained above, according to the present invention, a zirconia oxygen concentration battery sensor is used to detect flame ignition and extinguishing based on changes in internal resistance due to the temperature of one sensor, and detect air deficiency and extinguishment based on electromotive force characteristics. It can also be used to detect incomplete combustion due to excess air, etc.
In particular, since internal resistance and electromotive force are sequentially detected in a time-sharing manner, changes in internal resistance and electromotive force can be detected independently and accurately. Furthermore, since both characteristics are constantly checked, even if an abnormality occurs in either of them, the response can be quickly detected, which greatly improves safety when applied to safety devices. Furthermore, it is easy to apply a microcomputer, etc., and in this case, the number of parts is small and more complex detection and control can be easily performed.

As mentioned above, it has many effects.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a conventional detection circuit using a zirconia sensor, Fig. 2 is a system diagram showing an embodiment of the present invention, Fig. 3 is a specific circuit diagram of the main part, and Fig. 4 is a circuit diagram showing an example of a conventional detection circuit using a zirconia sensor. FIG. 5 is a characteristic diagram showing the relationship between the temperature and internal resistance of the zirconia sensor, FIG. 5 is a characteristic diagram showing the relationship between the air-fuel ratio and electromotive force of the zirconia sensor, and FIG. 6 is a circuit diagram showing another embodiment. 1... Combustion state detection sensor (zirconia sensor), 2... Series resistance, 3... Power supply circuit, 4...
switch circuit, 5... oscillation section, 6... detection circuit section.

Claims (1)

[Claims] 1. An oxygen concentration battery type combustion state detection sensor using zirconia that detects the combustion state of the combustion flame of a burner and generates an electromotive force, a series resistor connected in series to the combustion state detection sensor, and the combustion state A power supply circuit that applies a voltage to the detection sensor via the series resistor, a switch circuit that turns on and off the application of this voltage, an oscillator that drives the switch circuit, and two different ON and OFF states of the switch circuit. A combustion state detection device comprising a detection circuit section that detects the potentials at both ends of the combustion state detection sensor in two states to determine the combustion state of the burner.