JPH0745932B2 - Flame current detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety device for detecting a combustion state of a flame of a combustion device for gas oil or the like.

2. Description of the Related Art Conventionally, safety devices have been widely used in combustion equipment to detect flame ignition, misfire and incomplete combustion, and prevent unsafe operation.
A flame rod is a commonly used sensor for detecting this kind of combustion state. This sensor inserts an electrode rod into the flame and detects a flame ion current flowing between the burner and the electrode rod.

This operation will be described with reference to FIGS. 7 and 8. 7th
The figure shows an example of a gas burner, and fuel gas is ejected from the nozzle 1.
Combustion plate 33 made of gold steel mixed with air by mixing tube 2
A flame 5 is formed on the inner surface 4 of the and burns. Reference numeral 6 is a flame rod inserted in the flame 5, to which an AC power source 7 is applied between the flame rod 5 and the combustion plate 3, and the ion current _{If of the} flame is detected by the resistor 8 and smoothed by the capacitor 9 to obtain a detection signal. By the way, it is generally known that the flame 5 has a current rectifying action. This characteristic is shown in FIG. (A) shows the waveform of the applied AC voltage, and (B) shows the waveform of the flame current flowing at this time. A large amount of flame current flows when a voltage is applied to the combustion plate 3 to the flame rod 6 (X region), and a small amount of current flows when applied in the opposite direction. (Y region) This current _If is smoothed by the capacitor 9 and the direct current component _If is detected by a detection circuit (not shown) to determine the combustion state. Here, consider a case where there is a short circuit such as insulation failure or soot between the frame rod 6 and the combustion plate 3. At this time, no matter which direction the voltage is applied, a current flows and the rectification characteristic disappears. Therefore, the smoothed current I
_{Since f'is} reduced, it is possible to distinguish the current due to the flame and the insulation failure. However, as a drawback of this detection means, the current value _If detected as shown in FIG. 8 (B) is a value (1/5 to 1/10) that is significantly smaller than the actual current _If , and the detection efficiency is low. There is a problem of being bad.

As another detection means, there is one that applies a DC voltage to the combustion plate 3 to the frame rod 6. In this case, the flame current _If becomes a direct detection current, and the detection efficiency is higher than that in the case of AC application. However, in this case, it is not possible to distinguish between the flame and the insulation failure of the frame rod, and when the insulation is deteriorated, it is determined that the flame is burning even if there is no flame.

As a detection means having both of these advantages, it is conceivable to apply JP-A-60-164117 as shown in FIG. This is the frame rod connected to the contact a of the switch 10, detects a flame current I _f while applying a DC voltage of the combustion plate to determine the combustion state, periodically connected to the contact b frame DC voltage is applied to the combustion plate on the rod to check the insulation failure of the frame rod.When the reverse voltage is applied, almost no current flows under normal conditions due to the rectification characteristics of the flame, but when insulation is defective, current flows. Therefore, short check is possible.

Problems to be Solved by the Invention The configuration of FIG. 9 is capable of checking the insulation failure of the frame rod and has a good detection efficiency of the flame current _If . However, it is conceivable that the relationship between the flame current _If and the detection output V _O changes due to a failure of the operational amplifier 11, variations in the voltage dividing resistors 12 and 13, a failure, etc., making accurate detection impossible. The same applies to the means for applying the AC voltage shown in FIG. In order to solve this, the output V _O is measured before the burner is ignited, and if there is no flame and this value is output above a certain value, it is judged that there is something abnormal on the circuit. , A sequence in which the ignition operation is not performed can be considered. However, in the case of performing the initial check, it may flow flame current I _f equal currents due to moisture when the frame rods near the condensation at low temperature, will not shift to the next operation detects this during the initial check. Condensation may evaporate and dry when the burner burns, so that it does not matter even if it shifts to the ignition operation. In the conventional configuration in which an AC voltage is applied, when dew condensation occurs, a current flows, but since there is no rectification characteristic, the output current _{If '} is zero, so it is determined to be normal, and the next sequence can be performed. As described above, in the configuration of FIG. 9, it is not possible to determine the failure of the circuit component because the initial check cannot be performed, and in the worst case, it is determined that there is a flame even if there is no flame, and furthermore, the insulation failure cannot be determined. There is.

Means for Solving the Problems In order to solve the above problems, the flame current detection device of the present invention detects the combustion state of the flame by the flame ion current measured by a pair of electrodes inserted in the combustion flame of the burner. The frame rod sensor, a DC power supply circuit that applies a voltage between the electrodes of the frame rod sensor, a switching circuit that switches the polarity of the DC voltage that is applied to this frame rod sensor by this power supply circuit, and a current that flows in the frame rod sensor. A detection circuit for measuring, and a positive current detector for detecting and storing a current flowing when a voltage is applied to the frame rod sensor in the positive direction in synchronization with the switching circuit,
Negative current detection unit that detects and stores the current when voltage is applied in the negative direction, and combustion that determines an abnormality when the detected values of the positive current detection unit and the negative current detection unit are not at predetermined values during burner combustion. The abnormality determination unit, the reset unit that outputs a signal for stopping the fuel supply means of the burner due to the abnormal output of the combustion abnormality determination unit, and the difference between the detection outputs of the positive current detection unit and the negative current detection unit before the burner burns And an initial abnormality determination unit that determines that the detection circuit is abnormal when the output of the arithmetic unit is not within a predetermined initial abnormality determination value and outputs an abnormal output to the reset unit. It was done.

Effect The present invention has the above-described configuration, and determines the combustion state by applying a positive voltage during combustion of the burner, determines the insulation deterioration of the flame rod by applying a negative voltage, and further determines the difference in current when positive and negative voltages are applied before combustion. Is used to determine the detection circuit abnormality.

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an example of applying the present invention to an oil combustor.
Is a DC power supply circuit and has power supplies e _a and e _b inside, but this may be provided by dividing one power supply. 15 is a switching circuit, switched by the switch potential _{e ~} potential e ₊ and _{e b} of _{e a.} The switching circuit 15 periodically switches contacts by a controller such as a microcomputer (not shown), but may be an electronic switch. The common terminal of the switching circuit 15 is connected to the frame rod 16 that constitutes one electrode of the frame rod sensor. The frame rod 16 is inserted into the combustion flame of the burner 17, and the burner 17 also serves as the other electrode of the frame rod sensor. Apart from the burner 17, an electrode inserted into the flame may be provided facing the frame rod 16. Burner here
17 supplies the fuel of the fuel tank 18 by the fuel pump 19,
It is vaporized in the vaporization mixer 20, mixed with the combustion air from the fan motor 21, and burned. The pump 19 is controlled by the signal of the pump drive unit 22 to control the required fuel flow rate. Pump drive
The combustion amount and the air amount of the fan motor 21 and the fan motor 21 are controlled by signals from a controller such as a microcomputer.

Burner that doubles as one electrode of the frame rod sensor
The resistor 17 is connected to the midpoint potential e _o of the power supplies e _a and e _b of the power supply circuit 14 through the resistor 23. The potential difference generated by the current flowing through the resistor 23 is connected to both inputs of the operational amplifier 25 of the detection circuit 24. The operational amplifier 25 constitutes a non-inverting amplifier circuit with the resistors 26 and 27, and amplifies the potential across the resistor 23 to obtain the output potential e _c . And output potential e _c is divided by resistors 28 and 29 min potential e _d, it is measured as a current value flowing between the flame rod 16 and burner 17 this potential e _d into digital values by the A / D converter 30 It

The output of the A / D conversion unit 30 is a positive current detection unit 31 that detects a current _{If +} flowing when the switching circuit 15 is connected to the contact a.
Is input to the negative current detector 32 that detects the current _If − when it is connected to the contact b. The combustion abnormality determination unit 33 determines the current combustion state of the burner 17 based on the outputs of the positive current detection unit 31 and the negative current detection unit 32. 2 and 3 show the determination state of the combustion abnormality determination unit. Figure 2 shows the relationship between the output voltage e _d between the flame current I _f.

Now, when there is no flame in the burner 17 and neither flame currents I _{f +} and I _f− flow, there is no voltage drop across the resistor 23. Therefore, due to the characteristics of the operational amplifier 25, the output potential e _c becomes e _c = e _o , and the detection potential e _d is the potential e obtained by dividing it by the resistors 28 and 29.
It becomes _do . Other than this, it is constant regardless of the state of the switching circuit 15. Next, when a flame is formed in the burner 17, if the switching circuit 15 is connected to the contact a, the flame current _{If +} flows and a voltage drop occurs in the resistor 23. Since the operational amplifier 25 is a non-inverting amplifier circuit, its output potential _ed is proportional to the flame current _{If +} (solid line in FIG. 2). When Thus potential e _d becomes constant threshold value e _d1 above, the burner 17
Judge that is ignited. During the combustion, when the electric potential becomes equal to or lower than e _{d1, the} burner 17 misfires and the fuel supply is stopped. If the burner 17 becomes abnormally burned, the flame current I
_{When f +} increases and the output potential _ed becomes _{equal to} or higher than e _a2 , this is detected and the fuel supply is stopped. The relationship between the flame current _If and the air-fuel ratio m is shown in FIG. The behavior of the flame current _If depends on the value of the air-fuel ratio m. The state just described is a burner that burns normally when the air-fuel ratio is set to point V in FIG. 3, and is normal when it is between the flame currents I _f2 and I _f1 corresponding to the threshold values e _d1 and e _d2. Judge as combustion. Further, when the set air-fuel ratio is set to the W point near m = 1 by the design of the burner, the normal combustion occurs when the flame current is I _f2 or more and the abnormal combustion occurs when I _f2 or less. Although not limited, the following description will proceed with an example of setting V.

Next, the case where the switching circuit 15 is connected to the contact b will be described. When the burner 17 burns normally, the current _If- hardly flows due to the rectifying action described in FIG. Therefore, the output e _d is a value close to almost e _dO.
When the insulation between the frame rod 16 and the burner 17 deteriorates, a current _If- flows. Thus the voltage drop of the reverse direction is generated in the resistor 23, the output e _d is the voltage output downward from the potential e _dO in proportion to the current I _f-. (FIG. 2 dashed) wherein the output e _d is determined to insulation degradation time more than the threshold value e _d3. These operations are executed by the combustion abnormality determination unit 33, and when some abnormality occurs, a signal is output to the reset unit 34 to stop the operation of the pump drive unit 22 and stop the combustion. The switching circuit 15 periodically switches the contacts a and b. This operation is shown in FIG. In the figure, timings O, Q, and S show the states when connected to the contact a of the switching circuit 15, and P and R show the states when connected to the contact b. The combustion abnormality determination unit 33 has timing O,
When the state of P continues, it is determined that the combustion is normal, the state of Q is incomplete combustion, the state of R is insulation deterioration, and the state of S is misfire.

Here if the value of the voltage dividing resistors 28 and 29 is changed is shifted ordinate value e _d is no change to cause potential e _dO of Figure 2. On the other hand because the threshold e _d1 to e _d3 is a fixed value in the combustion abnormality determining unit 33. When the contact a is connected, even if there is no flame in the burner 17, it is determined that the ignition has occurred, and when the contact b is connected, the point is also determined as normal. That is, regardless of the state of the burner 17, the states of O and P in FIG. 4 are always maintained, and it is dangerous because the abnormality determination is completely impossible. This check the output e _d before ignition of the burner 17 in order to solve, there is a method of determining that the circuit in abnormal of what such occurred when there is an output of e _d> e _d1 when this . However, if there is condensation on the burner 17 and the rod 16 as described above, the potential _ed
This situation cannot be used because the situation of> _ed1 is reached, which causes the reset unit 34 to operate.

Therefore, the present invention uses the switching circuit 15 before the ignition of the burner 17.
The output at contact point a and the output at contact point b of the
The difference between the outputs is calculated according to. (The output ratio may be calculated) The initial abnormality determination unit 36 determines an abnormality based on the calculation result. The output state of the burner 17 before combustion is explained in FIG. 5 as in FIG. In the figure, T is the contact point a,
U is when connected to the contact b. Figure 5 (A) are all states at the output of the normal T, U either current I _{f +,} the output e _d for I _f- does not flow becomes e _dO. Therefore, since the difference is zero, the output of the calculation unit becomes zero, and the initial abnormality determination unit 36 compares this value with a predetermined initial abnormality determination value, determines that the operation is normal, and operates to burn the burner 17. Move to. In this embodiment, the initial abnormality determination unit is set to zero or a value close to zero as the initial abnormality determination value, and if the output of the calculation unit is equal to or less than this value, it is normal, and if it is more than this value, it is abnormal. Is configured to output. Further, in FIG. 5B, the case where dew condensation is formed on the frame rod 16, but at this time, both I _{f +} and I _f− flow due to the resistance of the dew condensation water. From this, the same output in the T and U states +
.DELTA.e _d, but -Derutai _d occurs the difference (+ .DELTA.e _d and -Δ
Since e _d has the opposite polarity, the sum calculation may be performed), which is zero as in FIG. If it becomes the normal determination if .DELTA.e _d was deteriorated insulation of the frame rod 16 instead of condensation, in this case determines the state of FIG. 4 R after start of combustion. In the case of dew condensation, the state of R in FIG.

Next, when the voltage division ratios of the resistors 28 and 29 are deviated, the output when both I _{f +} and I _f− are zero becomes _{edO ′} as shown in FIG. 5 (C).
It has a different value from _dO . The difference between this for the design value e _dO .DELTA.e
Since _d is composed + .DELTA.e _d, the -Derutai _d are positive direction, .DELTA.e
The difference (sum) of _d does not become zero. Similarly the difference in .DELTA.e _d may have condensed in Figure 5 (D) abnormality determining an initial abnormality determination unit 36 because it does not become zero. When the resistors 28 and 29 are scattered in the opposite directions, e _{dO ′} is generated below e _dO , but it is possible to similarly determine the abnormality. In this way, the deviation of the design value e _dO can be determined before combustion, and this is not affected by dew condensation.

FIG. 6 is a flow chart showing a main part of a program when the above operation is realized by a microcomputer. In FIG. 6, the same numbers as in FIG. 1 are marked on the flow corresponding to the functional units of FIG.

In the present embodiment, the petroleum vaporization type combustor has been described as an example, but the same effect can be obtained with gas fuel. In this case, a solenoid valve or the like may be used instead of the pump 19. In addition, the calculation unit 35
The calculation method may be other than the method shown in FIGS. 5 and 6, and may be determined by the difference between positive and negative currents. If necessary, the voltage ratio of the potentials e _a and e _b of the power supply circuit 14 may be different, but in this case, the calculation unit 35 needs to perform a correction calculation for this voltage ratio.

Effects of the Invention As described above, the flame current detecting device of the present invention has the following effects.

(1) Since the configuration is such that a DC voltage is applied to the flame rod sensor to detect the absolute value of the flame current, the detection efficiency is better than that of the conventional AC application configuration, and a low flame current can be detected.
It is possible with a good S / N ratio.

(2) By periodically applying a DC voltage in the opposite direction by the switching circuit during combustion, it is possible to accurately detect deterioration of the insulation of the frame rod sensor and shorts due to soot and rod bending as well as the AC application method.

(3) Since the circuit abnormality is determined by applying a positive / negative voltage before combustion of the burner and the current difference, it is possible to accurately determine only the circuit abnormality without erroneous detection when dew condensation occurs on the frame rod sensor.

(4) As described above, all the abnormalities such as burner combustion state abnormality, flame rod sensor abnormality, and detection circuit portion abnormality can be determined. Therefore, the flame current detection device is very safe and has good performance. Can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a flame current detection device showing an embodiment of the present invention, FIG. 2 is a characteristic diagram for explaining input / output states of the device, and FIG. 3 is a burner air-fuel ratio m and flame current I. characteristic diagram of _f ,
FIG. 4 is an operation explanatory diagram of the combustion abnormality determination unit, FIG. 5 is an operation explanatory diagram of the initial abnormality determination unit, FIG. 6 is a flowchart, FIG. 7 is a circuit diagram of a conventional example, and FIG. 8 is FIG. FIG. 9 is a circuit diagram of another conventional example. 14 …… DC power supply circuit, 15 …… Switching circuit, 16 ……
Frame rod (one electrode of frame rod sensor), 17 ... Burner (the other electrode of frame rod sensor), 22 ... Fuel pump (fuel supply means), 24 ... Detection circuit, 31 ... Positive current detection unit , 32 ... Negative current detector, 33 ...
... Combustion abnormality determination unit, 34 ... Reset unit, 35 ... Calculation unit,
36: Initial abnormality determination unit, _If: Flame ion current, _edO , e
_d1 , e _d2 , e _d3 …… _{Predetermined} value.

Claims (1)

[Claims] 1. A flame rod sensor having a pair of electrodes inserted into the combustion flame of a burner for detecting the combustion state of the flame by flame ion current; and a DC power supply circuit for applying a voltage between the electrodes of the flame rod sensor. A switching circuit that switches the polarity of the voltage applied to the frame rod sensor by the power supply circuit, a detection circuit that measures the current flowing in the frame rod sensor, and a positive direction to the frame rod sensor in synchronization with the switching circuit. A positive current detection unit that detects and stores a current that flows when a voltage is applied, a negative current detection unit that detects and stores a current when a voltage is applied in the negative direction, and a positive current detection unit and a negative current detection unit during burning of the burner. If an abnormality is determined when the detection value of each of the current detectors is not a predetermined value, the abnormality of the combustion abnormality determiner and the abnormality of the combustion abnormality determiner are detected. A reset unit that outputs a signal to stop the fuel supply means of the burner by force, the positive current detection unit detected before burning the burner, and a calculation unit that calculates the difference between the detection outputs of the negative current detection unit, A flame current detection device comprising: an initial abnormality determination unit that determines that the detection circuit is abnormal and outputs an abnormal output to the reset unit when the output of the arithmetic unit is not within a predetermined initial abnormality determination value.