JPS61243216A - Combustion sensing device - Google Patents

Abstract

PURPOSE:To enable a positive sensing of a deterioration of insulation of flame rod sensor by a method wherein AC voltage is applied across the electrodes of the flame rod sensor, an electric current in a resistor connected in series with the flame rod sensor is measured by an electric current measuring circuit, and in the electric current measuring circuit, an electric current value is measured when a voltage is applied to the flame rod sensor in a positive direction and a loading direction in synchronism with AC voltage. CONSTITUTION:An electric current If+ of a flame ion current If flowing in a flame rod sensor 10 in a positive direction shows a variation in response to a state of combustion in a burner. The electric current If- in a negative direction normally shows a quite low value due to a characteristic of smoothing characteristic of the flame. However, when its insulating characteristic is deteriorated due to an adhesion of carbon, etc. to the flame rod 12, the valve of If- will be increased. An output lg from a calculation amplifier 16 is made such that the electric current If is converted to a voltage value from a minus potential of DC power supply 17 in cynchronism with a switching AC voltage lAC. The potential lg is varied in response to a state of combustion and a controller may perform various controls. The value lg- corresponding to the electric current If- is increased due to a deterioration in insulation of the flame rod sensor 10 and then a negative current sensing circuit 20 may determine the deterioration of insulation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a device for detecting the state of combustion of gas, oil, etc., using the flame of the combustion device.

BACKGROUND OF THE INVENTION 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 detecting the ionic current of the flame.
There is something like a public notice. This operation will be explained using FIGS. 3 and 4.

Fuel 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 made of wire mesh. A flame rod 6 is inserted into the flame 5, and a DC power source 7 is applied between it and the combustion plate 3, and the ionic current If of the flame is detected by a resistor 8. Oxygen concentration in the air and ionic current If1 The characteristics of CO generated from the burner are shown in FIG. Here, the controller (not shown) determines that there is no ignition or misfire when If is a relative value of 0.5 or less, and when 11 is 7 or more, it determines that abnormal combustion is due to lack of oxygen, etc., and forces combustion. Stop at approx.

Problems to be Solved by the Invention However, with the conventional configuration as described above, incomplete combustion of the burner and ignition misfire can be detected, but carbon adheres to the flame rod 6 and electrical resistance of several MΩ with respect to the combustion plate 3 occurs. If conduction occurs due to a large resistance, or if the internal humidity increases and the resistance value decreases, the problem is that even if the oxygen concentration is high, If will be 7 or more, making it difficult to distinguish it from abnormal combustion. there were.

As a means to solve this problem, there has been a method of applying alternating current instead of the direct current power source 7 and detecting the flame by utilizing the rectifying characteristics of the flame. This characteristic is shown in FIG. 5, where A shows the applied voltage characteristic and B shows the current characteristic. It is known that the current flowing to the flame has a rectifying characteristic in that a large amount of current (2) flows when it is applied to the rod 6 (2) and e is applied to the combustion plate 3, and less current flows when it is applied in the opposite direction.

The controller smoothes this alternating current and converts it into a direct current I.
The combustion state is detected by f'. If carbon adheres to the rod 6 and short-circuits it, the rectifying properties will be lost 1
1 is used to determine whether the rod 6 is short-circuited by decreasing the value.

However, in this method, 11' has a value significantly smaller than If when direct current is applied (1 to -L), and there is a problem that the detection circuit is expensive.

Means for Solving the Problems In order to solve the above problems, the combustion detection device of the present invention includes:
The configuration is such that a constant cycle AC voltage is applied by a power supply circuit between the electrodes of a pair of flame rod sensors inserted into the flame, and a flame current detection resistor connected in series with the flame rod sensor is provided to detect the current flowing through this resistor. The current measurement circuit includes a positive current detection circuit that measures the current value when a positive voltage is applied to the frame rod sensor in synchronization with the AC voltage, and a negative current detection circuit that measures the current value when a positive voltage is applied to the frame rod sensor in synchronization with the AC voltage. This configuration includes a negative current detection circuit that measures the current value when applied.

According to the above-described structure, the present invention uses a positive current detection circuit to check combustion conditions such as ignition, misfire, and incomplete combustion, and checks short-circuit conditions of the flame rod sensor using a negative current detection circuit separately, and also checks both combustion conditions such as ignition, misfire, and incomplete combustion. Both have the effect of directly detecting the DC current value.

EXAMPLES Examples of the present invention will be described below based on FIG. 1 and FIG. FIG. 1 is a circuit diagram showing an 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. Although the frame rod sensor 10 is constructed here with a frame rod 12 as one electrode and a conductive burner 13 as the other electrode, it may be constructed with two frame rods.

Constant voltage diode 14.15d is for making the AC power supply 9 a constant voltage. The potential at the connection point between the frame rod sensor 1o and the detection resistor 11 is input to an operational amplifier 16, and a current If flowing through the frame rod sensor 10 is detected. The operational amplifier 16 is driven by a DC power supply 17 and constitutes a voltage 770 circuit, which is converted into an output voltage proportional to the flame current If and inputted to the current measurement circuit 18.

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

Here, an operational amplifier 21 and resistors 22 and 23 constitute an inverting amplifier circuit for the positive current detection circuit 19Fi reference potential ec, and the potential X is configured to output an analog potential depending on the combustion state of the burner. The current detection circuit 20 has a potential ad
The voltage comparator 24 compares the signal with the voltage, converts it into a high-low digital signal, and outputs it to the Y terminal. The current measurement circuit is not limited to this configuration, for example, the operational amplifier 16
The output eg may be converted into a digital value by an A10 conversion circuit, and the current measurement circuit 18 may be configured by 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 shown in FIG. 1, and shows the voltage waveform of the CIr1 AC power supply 9, which is regulated to Z+ and Z- by voltage regulating diodes 14 and 15.

D is the flame ion current (
(hereinafter referred to as current). Since the direction shown in FIG. 1 is written as a positive direction and the opposite direction as a negative direction, the polarity is switched between positive and negative in synchronization with the alternating current voltage eAC. As with FIG. 4, the current value of the forward current If+ changes depending on the combustion state of the burner. The current If- in the negative direction is normally a very small value due to the flame rectification characteristics explained in Fig. 5, but if the insulation deteriorates due to adhesion of carbon etc. to the frame rod 12, If- increases. come.

FIG. 2 shows the output eg of the operational amplifier 16, and the current If
is the DC power supply 17 in synchronization with the switching AC voltage aAC.
The negative potential of is converted to a voltage value. current I
The electric potential egJ” corresponding to f+ is changed to eg+ according to the combustion state.
and eg-t'', and the controller performs various controls according to this value. Also, eg- corresponding to the current ET rises to eg/ due to insulation deterioration of the frame rod sensor 4j10, and the negative current detection circuit 20 If this @g- becomes equal to or higher than ed, it is determined that the insulation has deteriorated.It is also possible to correct the bell for the detection of the current If+ according to the value of the cut current If-,
At this time, reliable combustion detection is possible even under high humidity conditions.

As described in detail, the combustion detection device of the present invention has the following effects.

(1) The combustion state is checked by detecting the direct current absolute value of the flame current If+ when the AC power supply eAC is applied, so compared to the conventional configuration that smoothes the alternating current, there is no negative current loss and it is possible to detect with a large current. This simplifies the design of the current measurement circuit and makes it less susceptible to noise. Furthermore, AC power can be obtained by simply applying commercial power through an isolation transformer, without requiring an oscillation circuit or the like, and with a simple configuration.

(2) Since insulation deterioration of the flame rod sensor 10 is detected by the flame current in the opposite direction and the absolute value of the direct current, the flame rod sensor 10 detects it by using the rectifying effect of the flame. Even if a short circuit is caused by a large resistance of several MΩ due to carbon adhesion, etc., it can be reliably detected and a highly reliable short check can be performed.

As described above, useful effects can be obtained by combining the advantages of the DC application and AC application smoothing detection methods of the prior art.

[Brief Description of the Drawings] Fig. 1 is a circuit diagram showing one embodiment of the combustion detection device of the present invention;
Fig. 2 is a characteristic diagram showing its operation, and Fig. 3 is a conventional structure I.
ff, FIG. 4 is a characteristic diagram thereof, and FIG. 5 is a characteristic diagram illustrating another conventional example. 9... AC power supply circuit, 10... Flame rod sensor, 11... Flame current detection resistor, 1
2...Frame rod (electrode of frame rod sensor), 13...Burner (electrode of frame rod sensor), 18...Current measurement circuit, 19.
...Positive current detection circuit, 20...Negative current detection circuit, If...Flame ion current. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure (Fig. 3)

Claims (1)

[Claims] a flame rod sensor that is inserted into a combustion flame and detects the combustion state of the flame using flame ion current; an AC power supply that applies an alternating current voltage between electrodes of the flame rod sensor; and a flame current that is connected in series with the flame rod sensor. It has a detection resistor and a current measurement circuit that measures the current flowing through the detection resistor, and the current measurement circuit is a positive current detection circuit that flows when a voltage is applied in a positive direction to the frame rod sensor in synchronization with an AC voltage. and a negative current detection circuit that flows when a voltage is applied in the negative direction.