JPS60164117A - Flame detecting device - Google Patents

Abstract

PURPOSE:To obtain the flame detecting device operated under less miss-operation condition by a method wherein a larger electric voltage than the comparing electric voltage is generated when a flame exists between a flame rod and a burner, then a nearly same electric voltage as the comparing electric voltage is generated when the flame does not exist between above location. CONSTITUTION:When a flame 9 exists between a flame rod F and a burner 8, an equivalent circuit shown by a mark 11 is formed between the flame rod F and the burner 8 by an electric rectifying action. Therefore, an electric current is flowed to a resistor R7 through the flame 9 and the burner 8 from the frame rod F, consequently, an electric voltage V1 correspond to the electric current flowed to the flame 9 is generated at the both ends of the resistor R7. When the flame does not exist between the flame rod F and the burner 8, the electric current is not flowed between the F and the 8. Thereby, a low cost and less miss-operation rectification type detector can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a flame detection device for detecting flame in gas or oil burning equipment.

(b) Conventional technology Generally, flame detection devices such as gas and oil burning equipment are used.

Using the DC method, which uses the flame's electrical resistance to apply a DC voltage to the flame rod and detects the current flowing through the flame, and the flame's current rectification effect.

There was a rectification method in which flames were detected by applying alternating current voltage to the flame rod and detecting the direct current component of the current flowing at this time.

(c) Problems with the conventional method However, although the former method is inexpensive in terms of cost, the problem is that the frame rod comes into contact with the burner.

If the flame rod and burner come into indirect contact with carbon, etc. and electrical continuity occurs, the flame detector will falsely detect the presence of a flame even though there is no flame, and even if the flame goes out for some reason. , the oil spill continued and became dangerous.

Furthermore, during combustion, if the insulation of external equipment such as a temperature detection switch that is connected to the same circuit as the flame detection device deteriorates for some reason, and a misfire occurs for some reason, the oil will continue to leak out and be dangerous. It became a situation.

In addition, when electrically controlling gas or oil-burning equipment and relying on a flame detection device to detect extinguishing, extinguish the fire with a fire extinguisher switch, etc. when the flame rod comes in contact with the burner, or when the insulation of external equipment is degraded. In this case, the flame detection device assumes that there is a flame and cannot proceed to the primary step, such as post-purge or ignition operation.

Next, let's talk about the problems with the latter rectification method, such as the frame rod coming into contact with the burner.

When the insulation of external equipment deteriorates, the current flowing through the flame detection device changes from rectified current to alternating current, making it possible to distinguish between flame current and abnormal current, thus preventing the dangerous situation mentioned above. It is possible to avoid it. However, in order to obtain alternating current, a transformer dedicated to the flame detection device is required, which has the disadvantage of complicating the circuitry and increasing costs.

B) Object of the Invention The present invention provides a rectification type flame detector that does not use a dedicated transformer for the flame detector, is powered by a DC power supply, is inexpensive, and does not malfunction.

(E) Structure of the Invention According to the present invention, a device for detecting a flame formed by a burner includes a flame rod provided to correspond to the flame caused by the burner, and a pulse voltage for applying a pulse voltage to the flame rod. a generating circuit, a constant voltage circuit that sets a voltage lower than the pulse voltage, a resistor connected between the constant voltage circuit and the burner, a voltage generated across the resistor, and the constant voltage circuit. and a voltage comparison circuit that receives the output voltage of the differential amplifier circuit as an input signal, and detects the presence or absence of a flame based on the output voltage of the voltage comparison circuit. A flame detection device is obtained.

(F) EXAMPLE The flame detection device of the present invention will be explained below based on the electric circuit diagram shown in FIG.

In the figure, 1 is an astable multi-by-break, 2 is the first constant voltage circuit, 3 is the second constant voltage circuit, 4 is the flame detection section, 5 is the differential amplifier circuit, 6 is the smoothing delay circuit, and 7 is the voltage comparison It is a circuit.

Next, to explain each circuit in detail, the IC of astable multivibrator 1 is the first operational amplifier.

Input voltage Vco is applied to the positive input terminal via resistor R1, and positive feedback is applied from the output terminal via resistor "2+R3."

The negative input terminal is grounded via a capacitor C1 and connected to the output terminal via a resistor R4 in order to provide stable and accurate square wave oscillation.

The first constant voltage circuit 2 includes a first Zener diode ZD,
and a resistor R6, and serves to keep the output voltage level of the astable multivibrator 1 constant.

In the second constant voltage circuit 3, a resistor R6 and a second Zener diode zD2 are connected in series with each other and connected to a DC bias voltage cc. Further, the anode side of the second Zener diode zD2 is grounded, and its voltage is applied to the negative input terminal of the second operational amplifier IC2.

The flame detection unit 4 includes a resistor R2 in the first constant voltage circuit 2,
Frame rod bar F connected to.

It has a resistor R7 connected between the burner 8, which forms the flame, and the cathode side of the second Zener diode ZD2.

The differential amplifier circuit 5 has a positive input terminal connected to one end of the resistor R7, and a negative input terminal connected to the resistor R via a resistor R8.
7 and a second operational amplifier IC2 connected to the other end of the operational amplifier IC2. The amplification factor of this second operational amplifier C2 is determined by two resistors R8+R9.

The smoothing delay circuit 6 includes a resistor R0° connected between the output side of the second operational amplifier C2 and the negative input side of the sixth operational amplifier IC3, which will be described later.

It includes a capacitor c2 and a resistor R11 whose one end is grounded.

The voltage comparison circuit 7 is connected to a sixth operational amplifier IC3.

Resistor R1 that applies positive feedback to the positive hexagonal terminal of the operational amplifier
2+ R14 and the resistor RI connected to the positive hexagonal terminal
3 and a DC bias voltage V. C is resistor R1□,
Based on the voltage divided by R, 8, R, 4.

This circuit compares the output of the smoothing delay circuit 6.

Next, the operation of the above circuit will be explained. The pulse voltage generated by the astable multivibrator 1 is generated by the first constant voltage circuit 2.

After the output voltage level is made constant, as shown as the voltage at the 0 point in FIG. 2, it is applied to the frame rod F. In this case, the pulse ON-OFF duty ratio is not particularly important, but 1:1 is more advantageous for signal processing.

Here, if a flame 9 exists between the flame rod F and the burner 8, due to the electrical rectification effect of the flame, there will be a gap between the flame rod F and the burner 8 as indicated by symbol 11 in FIG. The equivalent circuit shown is formed. That is, an equivalent circuit is formed in which the anode of a diode is connected to the frame rod F side, one end of a resistor is connected in series to the cathode side, and the other end of this resistor is connected to the burner 8. Therefore 9. Current flows from flame rod F through flame 9 and burner 8 to resistor R7;

A voltage V depending on the current flowing through the flame 9 is applied to both ends of the resistor R7.
occurs. The voltage v1 is the second operational amplifier IC20.
A voltage V applied to the input terminal and expressed by the following formula at the zero point on the output side of the differential amplifier circuit. occurs. However, vZD2 is the voltage of the second constant voltage circuit zD2.

R.

Vo --XV, +Vzn2 --- Song (1) 8 The waveform at this 0 point is shown in FIG. That is, when the pulse voltage at point ■ in FIG. 1 is off, it is V. = ZD, nil, when ON is V, the voltage is multiplied by the amplification factor of the differential amplifier A"'R' / R8 ZDz
The voltage becomes the sum of V.

After that, the pulse voltage V. is applied to the smoothing delay circuit 6 and after smoothing the waveform, is applied to the negative input terminal of the voltage comparison circuit 7. The voltage at point 0 at this time is a in Figure 6.
become that way.

The voltage comparator circuit 7 has a DC bias voltage ■ which is a flame level reference voltage. The pulse voltage V is based on the voltage obtained by dividing C by the resistors R1□+R13+R14. Compared to the negative input, the output voltage is a digital output of 1 and 0, which makes it possible to detect the presence or absence of a flame and further monitor the state of the flame.

In addition, the constant voltage VZD2 in the second constant voltage circuit 3 must be set to +Vzo, > Vzo2 in order to swing the pulse within the constant voltage VZD in the first constant voltage circuit 2, (7) range. The case of vZD 2 "" 2 VZDl is most advantageous.

Moreover, the resistor R8+R9 is the amplification factor A=of the differential amplifier circuit 6.
This is because it is a resistance for determining R9/B.

The value should be determined according to the flame current.

Next, if there is no flame 9 between the flame rod F and the burner 8, no current will flow between F-8.

Therefore, the voltage V between the terminals of the resistor R7 is 013Q, and equation (1) is expressed as vo==vzp2.The voltage waveform at point 2 becomes a DC waveform as shown in FIG. Further, the waveform at the 0 point of the smoothing delay circuit 6 becomes a straight line as shown in FIG.

Further, a current exceeding a certain reference value may flow between F-8 due to direct contact between the frame rod F and the burner 8 or indirect contact with carbon, or due to a decrease in insulation resistance of external equipment. At this time, an equivalent circuit shown by the symbol 12 in FIG. 1 is formed, and the current flows alternately from F→8 and 8→F. Therefore, the second constant voltage circuit 3
Centering around the voltage VZD, when the pulse at the @ point is ON, current flows through the resistor R7 toward the Zener diode ZD2, and vice versa when it is OFF.
A current flows from R2 to resistor R7. Therefore, the voltage v1 between the terminals of the resistor R7 is the voltage of the second constant voltage circuit 3
Centering on D2, equal voltages are generated above and below, as shown in FIG. Therefore, when the voltage is smoothed by the smoothing delay circuit 6, it becomes a voltage that is approximately equal to the voltage in the case where there is no flame, as shown by the straight line b in FIG.

Note that the astable multivibrator used in the two circuits may be substituted by dividing the frequency of the oscillation pulse for operating the microcomputer in equipment that uses a microcomputer or the like to configure the control circuit.

Furthermore, as shown in FIG. 7, the same objective can be achieved by inserting a smoothing capacitor C3 in parallel with the resistor R7 instead of the smoothing delay circuit 6.

(G) Effects of the Invention According to the present invention, the flame is connected to the frame rod,
If there is a voltage between the burner and the grounded burner, a voltage greater than a certain comparison voltage VZD will be generated, and if there is no flame or if there is electrical continuity between the flame rod and the burner. Since a voltage almost equal to the comparison voltage VZD is generated, the voltage generated is high only when there is a flame, and by detecting that voltage, the system can avoid malfunctions like in the past. , it is possible to obtain a flame detection device with a high safety factor.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram of the flame detection device of the present invention. Figures 2 to 6 are diagrams of voltage waveforms at each point in the figure, in which the horizontal axis represents time and the vertical axis represents voltage, respectively.
The figure shows the voltage at the 0 point, Figure 3 shows the voltage at the 0 point, and Figure 4 shows the voltage at the 0 point when there is no flame. Figure 5 shows the voltage at point 0 when the flame rod and burner are electrically connected, Figure 6 shows the voltage at point 0, where line a is when there is a flame and line a is when there is no flame. FIG. 7 is a circuit diagram showing only the main parts of a modified example. In the figure, 1 is an astable multi-pipe leak circuit (pulse generation circuit), and 2 is a first constant voltage circuit. 3 is a second constant voltage circuit, 4 is a flame detection section, 5 is a differential amplifier, 6 is a smoothing delay circuit, 7 is a voltage comparison circuit, 8 is a burner,
F is a frame rod.

Claims (1)

[Claims] 1. In a device for detecting a flame formed in a burner,
A flame rod provided to correspond to the flame generated by the burner, a pulse generation circuit that applies a pulse voltage to the flame rod, and a constant voltage circuit that sets a voltage lower than the pulse voltage. a resistor connected between the constant voltage circuit and the burner;
The voltage comparison circuit includes a differential amplifier circuit whose input signals are the voltage generated across the resistor and the voltage of the constant voltage circuit, and a voltage comparison circuit whose input is the output voltage of the differential amplifier circuit. A flame detection device characterized by detecting the presence or absence of a flame based on the output voltage of the flame detector. Remaining days below