JPH0437330B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a combustion detection device that detects the combustion state of a gas, oil, etc. combustion device using a flame.

BACKGROUND ART Conventionally, since combustion type heaters such as fan heaters burn indoors, it is necessary to reliably detect flame ignition, misfire, decrease in indoor oxygen concentration, or incomplete combustion. Frame rod sensors are widely used as this type of detection sensor. This sensor detects the combustion state by measuring the ionic current of the flame, and for example, there is a sensor as disclosed in Japanese Utility Model Application Publication No. 145422/1983. This operation will be explained using FIGS. 3 and 4.

FIG. 3 shows a configuration diagram of a gas burner. Combustion gas is ejected from a nozzle 1, mixed with air through a mixing tube 2, and burned by forming a flame 5 on the inner surface 4 of a combustion plate 3 formed of a wire mesh. Reference numeral 6 denotes a flame rod inserted into the flame 5, which is configured to apply a DC power source 7 between it and the combustion plate 3, and to detect the ionic current If of the flame as a voltage drop across a resistor 8.

The oxygen concentration in the air, the ion current If, and the characteristics of carbon monoxide (CO) generated from the burner are
As shown in the figure. Here, the controller (not shown) determines that there is no ignition or misfire when the current If is a relative value of 0.5 or less, and when the current If is 7 or more, it determines that there is abnormal combustion due to insufficient oxygen concentration, etc. Forcibly stop supply.

Problems to be Solved by the Invention However, with the conventional configuration as described above, it is possible to detect incomplete combustion, ignition, and misfire of the burner, but since the flame current value is generally very small, on the order of several microamperes, it is difficult to detect flame rod 6. When carbon adheres and becomes electrically conductive with the combustion plate 3, or when the humidity inside the burner increases and the air resistance value decreases, the flame current If decreases to the relative value 7 in Figure 4 even if the oxygen concentration is high. The above phenomenon occurred and there was a problem in that it was difficult to distinguish it from abnormal combustion.

As a means to solve this problem, a method has been put into practical use that applies alternating current instead of the direct current power source 7 and detects the flame by utilizing the rectifying characteristics of the flame. Figure 5 shows this characteristic. In FIG. 5, A shows the applied voltage waveform, and B shows the waveform of the current I flowing through the flame.

It is known that the flame has a rectifying characteristic in which a large amount of current I flows when applied to the rod 6 and the combustion plate 3, and a small amount of current flows when applied in the opposite direction. The controller smoothes this alternating current and detects the combustion state based on the direct current If'.
With this configuration, if carbon adheres to the rod 6 and it shoots, current will flow in both the positive and negative directions, resulting in loss of rectification characteristics and a smoothed DC current.
Since If' decreases to almost zero, the insulation deterioration of the rod 6 can be detected.

However, in this method, the current If′ is the current If′ when DC is applied.
(1/5 to 1/10)
There is a problem in that the detection circuit requires an expensive circuit with a good S/N ratio.

Means for Solving the Problems In order to solve the above problems, the combustion detection device of the present invention has a configuration in which an AC voltage of a constant period is applied by a power supply circuit between the electrodes of a pair of flame rod sensors inserted into a flame. A flame current detection resistor is connected in series with the flame rod sensor, and the current flowing through this resistor is measured by a current measurement circuit. There is a positive current detection circuit that detects the combustion state of the flame by the positive current that flows when a voltage is applied in the direction, and a negative current detection circuit that detects insulation deterioration of the flame rod sensor by the negative current that flows when the voltage is applied in the negative direction. This configuration includes a current detection circuit.

Effects With the above configuration, the present invention uses a positive current detection circuit to check combustion conditions such as ignition, misfire, and incomplete combustion, and uses a negative current detection circuit to check for flame rod sensor shoot and insulation deterioration. , can be detected separately, and both have the effect of directly detecting the DC current value.

Embodiments Hereinafter, embodiments of the present invention will be described based on FIGS. 1 and 2. FIG. 1 is a circuit diagram showing one embodiment of the combustion detection device of the present invention, in which a series circuit of a flame rod sensor 10 and a current detection resistor 11 is connected to an AC power source 9. Frame rod sensor 1
Here, one electrode is connected to the frame rod 12,
Although the other electrode is constituted by the conductive burner 13, it may also be constituted by two flame rods.

The constant voltage diodes 14 and 15 are for making the AC power supply 9 a constant voltage. The potential at the connection point between the flamerod sensor 10 and the current detection resistor 11 is input to the operational amplifier 16.
The current If flowing to 0 is detected. Operational amplifier 1
Reference numeral 6 is driven by a DC power supply 17 to form a voltage follower circuit, which is converted into an output voltage lg proportional to the flame current If and inputted to the current measurement circuit 17.

The current measurement circuit 18 is composed of a positive current detection circuit 19 and a negative current detection circuit 20, and outputs X and Y respectively. A burner controller (not shown) is configured to read the values of each output X and Y in synchronization with the AC power source 9.

Here, the positive current detection circuit 19 constitutes an inverting amplifier circuit with respect to the reference potential lc using an operational amplifier 21 and resistors 22, 23, and outputs the potential X as an analog voltage depending on the combustion state of the burner. The detection circuit 20 compares the potential lg and the threshold value ld using a voltage comparator 24, and outputs an output Y as a high or low digital signal.

The current measurement circuit 18 is not limited to this configuration; for example, the output lg of the operational amplifier 16 can be converted into an analog/
The current detection circuit 18 may be converted into a digital value by a digital conversion circuit, and the current detection circuit 18 may be configured within a program of a microcomputer or the like.

Next, the operation will be explained. FIG. 2 shows the characteristics of each part of the circuit in FIG. 1, and FIG. 5A shows the voltage waveform l _AC of the AC power supply 9, and
5, it is clipped to Z+ and Z-.

FIG. 2D shows the state of the flame ion current If flowing through the flame rod sensor 10. The flame current If will be explained assuming that the direction shown by the arrow in FIG. 1 is the positive direction, and the opposite direction is the negative direction. The current If switches between positive and negative in synchronization with the alternating current voltage l _AC .

Similarly to FIG. 4, the current value of the forward current If+ changes depending on the combustion state of the burner. Negative current If
- is normally a very small value due to the flame rectification characteristics explained in FIG. 5, but when the insulation deteriorates due to adhesion of carbon or the like to the flame rod sensor 10, the current If- increases.

FIG. 2E shows the characteristics of the output voltage lg of the operational amplifier 16. Since the negative potential of the power supply 17 of the operational amplifier 16 and the burner 13, which is one electrode of the flamerod sensor 10, are connected, the AC voltage is
l The output voltage eg corresponding to the current If which changes positive and negative in synchronization with _AC is converted from the negative potential of the DC power supply 17 to a positive voltage value and output.

The potential eg corresponding to the current If+ changes as lg+′ or lg+″ depending on the combustion state of the flame.
Depending on this value, a controller (not shown) performs various combustion controls such as igniting the burner, detecting misfire, or varying the combustion supply amount and air amount.

Further, the potential lg- corresponding to the current If- rises to lg-' because the current If- increases due to insulation deterioration of the frame rod sensor 10, and the negative current detection circuit 2
0, if this potential lg- exceeds the threshold value ld, it is determined that insulation has deteriorated. Here, when the comparator 24 is normal, the output Y is low level, and when the insulation is degraded, the output lg-
When becomes equal to or greater than the threshold value ld, the output Y becomes high level.

It is also possible to correct the detected value of the current If+ according to the value of the current If-, and in this case, reliable combustion state detection is possible even under high humidity conditions or when the insulation of the flame rod sensor has deteriorated to a certain extent. It becomes possible.

Effects of the Invention As explained above, the combustion detection device of the present invention has the following effects.

(1) The combustion state is checked using the direct current absolute value of the flame current If+ when the positive half cycle Z+ of the AC power source l _AC is applied, so compared to the conventional configuration in which the AC current is smoothed, the combustion state is There is no current loss, it is possible to detect large current values, a simple current measurement circuit is required, and it is less susceptible to disturbances such as noise.

(2) Insulation deterioration of the flame rod sensor can be detected by measuring the DC absolute value of the flame current If- when the negative half cycle Z- of the AC power source l _AC is applied, and by using the rectifying effect of the flame. Therefore, even if the flame rod sensor does not shoot completely and there is a large resistance of several megohms due to carbon adhesion, it can be reliably detected, and a highly reliable shot check can be realized.

(3) AC power can be realized by simply applying commercial power through an isolation transformer, and does not require an AC generating circuit such as a transmitting circuit.

(4) Similarly, since the configuration is such that each detection is performed periodically every half cycle of AC, the combustion detection device is constantly monitored no matter what state of combustion is in progress, thus providing a highly safe combustion detection device. I can do it.

In this way, useful effects can be obtained by combining the advantages of the DC application method and the AC application smoothing detection method of the prior art.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the combustion detection device of the present invention, FIG. 2 is a characteristic diagram explaining its operation, FIG. 3 is a configuration diagram explaining a conventional example, and FIG. 4 is a characteristic diagram thereof. FIG. 5 is a characteristic diagram illustrating another conventional example. 9... AC power supply circuit, 10... Flame rod sensor, 11... Flame current detection resistor, 12... Flame rod (electrode of flame rod sensor), 1
3...Burner (flame rod sensor electrode),
18...Current measurement circuit, 19...Positive current detection circuit, 20...Negative current detection circuit, If...Flame ion current.

Claims (1)

[Claims] 1. A flame rod sensor that is inserted into the combustion flame and detects the combustion state of the flame using flame ion current;
The frame rod sensor includes an AC power supply that applies an AC voltage between electrodes, a flame current detection resistor connected in series with the flame rod sensor, and a current measurement circuit that measures the current flowing through the detection resistor. , the current measurement circuit includes a positive current detection circuit that detects the combustion state of the flame by a positive current flowing when a voltage is applied in a positive direction to the flame rod sensor in synchronization with an AC voltage, and a positive current detection circuit that applies a voltage in a negative direction. This combustion detection device consists of a negative current detection circuit that detects the insulation deterioration of the flame rod sensor based on the negative current that flows when the combustion occurs.