JP5832948B2 - Flame detection device - Google Patents

Description

  The present invention relates to a flame detection device that detects the presence or absence of a flame.

  2. Description of the Related Art Conventionally, an electron tube used for detecting the presence or absence of a flame based on ultraviolet rays emitted from a flame in a combustion furnace or the like is known. The electron tube includes a sealing device filled and sealed with a predetermined gas, an electrode support pin penetrating the sealed container, and two electrodes supported in parallel in the sealing device by the electrode support pin. Is. In such an electron tube, when a predetermined voltage is applied between the electrodes via the electrode support pins, when one of the electrodes arranged opposite to the flame is irradiated with ultraviolet rays, electrons are emitted from the electrode by the photoelectric effect. The electrons are excited one after another to form an avalanche with the other electrode. Therefore, the presence or absence of a flame can be detected by measuring a change in impedance between electrodes, a change in voltage between electrodes, a current flowing between electrodes, and the like. Therefore, various methods for detecting the presence or absence of a flame have been conventionally proposed.

  For example, a method has been proposed in which the current flowing between the electrodes is integrated, and when the integrated value is equal to or greater than a predetermined threshold value, there is a flame, and when the integrated value is less than the threshold value, it is determined that there is no flame. (For example, refer to Patent Document 1).

JP 2011-141290 A

  However, in the above-described method, since the current flowing between the electrodes is integrated, it takes an integration time even when the flame is extinguished, so it takes time to detect the extinction, and as a result, the presence or absence of the flame is detected. It was difficult to do quickly.

  Therefore, an object of the present invention is to provide a flame detection device that can detect the presence or absence of a flame more quickly and reliably.

In order to solve the above-described problems, a flame detection apparatus according to the present invention includes an envelope and a pair of electrodes disposed opposite to each other inside the envelope, and when the electrodes are irradiated with ultraviolet rays, the electrodes and electron tube electron emission occurs between the applying unit for applying a voltage which periodically changes between the electrodes, a detection unit for detecting a voltage waveform to show a time change of voltage between the electrodes, the voltage detecting section detects An analysis unit that analyzes whether or not a discharge waveform is established in the waveform and a determination unit that determines the presence or absence of flame based on the analysis result by the analysis unit, the analysis unit detects the maximum voltage in the voltage waveform The voltage value at the time when the voltage drops below the predetermined voltage value within the predetermined time from the time when the discharge is performed is set as the discharge sustain voltage, and the discharge waveform is established in the voltage waveform when the discharge sustain voltage is subsequently maintained for the predetermined time. the voltage waveform output to the determination unit It is characterized in further comprising a determination unit that determines presence or absence of flame Zui.

  According to the present invention, the voltage waveform indicating the time change of the voltage between the electrodes provided in the electron tube is detected, and the presence / absence of flame is determined based on this voltage waveform. Can be done more quickly.

FIG. 1 is a block diagram showing a configuration of a flame detection apparatus according to an embodiment of the present invention. FIG. 2 is a diagram for explaining a discharge waveform. FIG. 3 is a flowchart for explaining the operation of the flame detection apparatus according to the embodiment of the present invention. FIG. 4 is a flowchart for explaining the waveform analysis processing. FIG. 5 is a diagram illustrating a voltage waveform when the current is small. FIG. 6 is a diagram illustrating a voltage waveform when the current is large. FIG. 7 is a block diagram showing a modification of the flame detection device according to the embodiment of the present invention. FIG. 8 is a diagram for explaining a discharge waveform and a current signal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Configuration of flame detection device>
As shown in FIG. 1, the flame detection apparatus according to the present embodiment includes a flame sensor 1, an external power supply 2, and a computing device 3 to which the flame sensor 1 and the external power supply 2 are connected.

  The flame sensor 1 includes a cylindrical envelope whose both ends are closed, an electrode pin that passes through the envelope, and two electrodes that are supported in parallel by the electrode pins inside the envelope. It is composed of an equipped electron tube. Such an electron tube is disposed so that the electrode faces a device such as a burner that generates a flame. As a result, when ultraviolet light is irradiated to the electrode in a state where a predetermined voltage is applied between the electrodes, electrons are emitted from the electrode due to the photoelectric effect, and the electrons are excited one after another between the other electrode. Form an avalanche. As a result, the voltage, current, and impedance between the electrodes change.

  The external power source 2 is a known AC commercial power source having a voltage value of 100 [V] or 200 [V], for example.

  The arithmetic device 3 includes a power supply circuit 11 connected to the external power supply 2, an applied voltage generation circuit 12 and a trigger circuit 13 connected to the power supply circuit 11, and an output terminal 12 a of the applied voltage generation circuit 12. A voltage dividing resistor 14 connected together with the electrode pins, a voltage detecting circuit 15 connected to the voltage dividing circuit 14, and a sampling circuit 16 connected to the voltage detecting circuit 15 and the trigger circuit 13 are provided.

  The power supply circuit 11 supplies AC power input from the external power supply 2 to the applied voltage generation circuit 12 and the trigger circuit 13 and obtains power for driving the arithmetic device 3.

  The applied voltage generation circuit 12 boosts the alternating voltage applied by the power supply circuit 11 to a predetermined value and applies it to the flame sensor 1. In the present embodiment, a voltage of 400 [V] is applied to the flame sensor 1.

  The trigger circuit 13 detects a predetermined value point of the AC voltage applied by the power supply circuit 11 and inputs the detection result to the sampling circuit 16. In the present embodiment, the trigger circuit 13 detects the minimum value point at which the voltage value is minimum. Thus, by detecting a predetermined value point for the AC voltage, it is possible to detect one cycle of the AC voltage. The trigger circuit 13 may detect a zero value point at which the voltage value becomes zero.

  The voltage dividing resistor 14 generates a reference voltage from the inter-terminal voltage of the flame sensor 1 and inputs the reference voltage to the voltage detection circuit 15. Here, since the inter-terminal voltage of the flame sensor 1 is a high voltage of 400 [V] as described above, if the voltage is input to the voltage detection circuit 15 as it is, a large load is applied to the voltage detection circuit 15. Further, as will be described later, this embodiment plots not the actual value of the inter-terminal voltage of the flame sensor 1 but the time change of the inter-terminal voltage of the flame sensor 1, that is, the value of the inter-terminal voltage per unit time. The presence or absence of a flame is determined based on the shape of the voltage waveform obtained by doing so. Therefore, the voltage dividing resistor 14 expresses a change in the voltage between the terminals of the flame sensor 1 and generates a reference voltage having a low voltage value, which is input to the voltage detection circuit 15.

  The voltage detection circuit 15 detects the voltage value of the reference voltage input from the voltage dividing resistor 14 and inputs it to the sampling circuit 16.

The sampling circuit 16 determines the presence or absence of a flame based on the voltage value of the reference voltage input from the voltage detection circuit 15 and the trigger time point input from the trigger circuit 13.
Here, when no flame is generated, the voltage waveform between the electrodes of the flame sensor 1 has a gentle sinusoidal shape (hereinafter referred to as a “normal waveform”) as shown by a symbol a in FIG. Have. On the other hand, when a flame is generated and the flame sensor 1 is irradiated with ultraviolet rays, the voltage value falls near the positive extreme value as shown by symbol b in FIG. It has a characteristic shape (hereinafter, referred to as “discharge waveform”) that returns to a sinusoidal shape after being maintained for a time. This is because when an electrode is irradiated with ultraviolet rays and electrons are emitted from the electrode due to the photoelectric effect, the electrons are excited one after another, and an avalanche is formed between the other electrodes, and current is generated by this avalanche. This is because the electron emission accompanied by light emission occurs due to the rapid increase, and the voltage between the electrodes rapidly decreases.
Therefore, the sampling circuit 16 determines the presence or absence of a flame based on the shape of such a voltage waveform. Such a sampling circuit 16 includes an A / D converter 161 that generates a voltage value and a voltage waveform by A / D converting an input reference voltage, a voltage value generated by the A / D converter 161, and A storage unit 162 that stores the voltage waveform, an analysis unit 163 that analyzes the voltage waveform stored in the storage unit 162, and a determination unit 164 that determines the presence or absence of flame based on the analysis result of the analysis unit 163. .

<Operation of flame detector>
Next, the operation of the flame detection apparatus according to the present embodiment will be described with reference to FIG.

  First, the arithmetic device 3 is in a state where a predetermined alternating voltage is applied to the flame sensor 1 by the applied voltage generation circuit 12. In such a state, the trigger circuit 13 has the AC voltage input from the external power supply 2 to the power supply circuit 11, that is, the value of the voltage applied to the flame sensor 1 by the applied voltage generation circuit 12 has passed the minimum value point. Whether or not is detected.

  When the applied voltage passes through the minimum value point (step S11: YES), the A / D converter 161 of the sampling circuit 16 converts the reference voltage for one period input from the voltage detection circuit 15 into A / D at a predetermined time interval. The voltage value is detected by conversion (step S12). When the detected voltage value is plotted, a voltage waveform indicating a time change of the voltage value as shown in FIG. 2 is generated. As an example, in this embodiment, the voltage value is detected every 0.1 [msec], and if the frequency of the external power supply 2 is 50 [Hz], one cycle is 16.7 [msec]. The number of detected voltage values is 167. The detected voltage value for one cycle is stored in the storage unit 162.

  When the voltage value for one period is acquired, the analysis unit 163 performs a waveform analysis process for analyzing whether or not a voltage waveform including the detected voltage value is established as a discharge waveform (step S13). Details of this waveform analysis processing will be described later. Further, the processing result of the waveform analysis process is stored in the storage unit 162.

  When the waveform analysis process is performed, the determination unit 164 confirms whether or not a voltage waveform of four cycles or more is established as a discharge waveform among the voltage waveforms for the latest ten cycles (step S14).

  When the voltage waveform of four or more cycles among the voltage waveforms for the latest 10 cycles is established as the discharge waveform, the determination unit 164 determines that there is a flame (step S15).

  On the other hand, when the voltage waveform established as the discharge waveform is less than four cycles, the determination unit 164 determines that there is no flame (step S16).

<Waveform analysis processing>
Next, the waveform analysis processing by the analysis unit 163 will be described with reference to FIG. Here, the analysis unit 163 performs the following waveform analysis processing on the voltage waveform in which the voltage values for one period are plotted.

  First, the analysis unit 163 detects the maximum voltage value (hereinafter referred to as “maximum voltage”) in the voltage waveform (step S21).

  When the maximum voltage is detected, if the voltage value drops by 50 [V] or more within 0.3 [msec] from the time of this maximum voltage, the maximum voltage is set as the discharge start voltage, and this discharge start voltage exists. It is confirmed whether or not to perform (step S22). As described above, in the case of the discharge waveform, the voltage value falls near the positive extreme value. Therefore, in the present embodiment, it is determined whether or not the discharge waveform is established by detecting whether or not the voltage drops more than a predetermined voltage value within a predetermined time from the time when the maximum voltage is detected. Yes.

  If there is no discharge start voltage (step S22: NO), it is determined that the voltage waveform is not established as a discharge waveform (step S30), and the analysis result is output (step S29).

  On the other hand, when the discharge start voltage exists (step S22: YES), the discharge delay time is set from the time when the minimum value point is passed to the time when the maximum voltage is reached (step S23). Further, a period in which the voltage deviation after the discharge start voltage is within 20 [V] is set as the discharge time (step S24).

  When the discharge time is set, it is confirmed whether or not the discharge time is 3 [msec] or more (step S25). As described above, in the case of the discharge waveform, the predetermined voltage value is maintained for a predetermined time after the voltage value falls near the positive extreme value. Therefore, in the present embodiment, whether or not the discharge waveform is established is determined based on whether or not the voltage value continues for a predetermined time or more.

  If the discharge time is less than 3 [msec] (step S25: NO), it is determined that the voltage waveform is not established as a discharge waveform (step S30), and the analysis result is output (step S29).

  On the other hand, when the discharge time is 3 [msec] or more, the average voltage during the discharge time is calculated, and this value is set as the discharge sustain voltage. And it is confirmed whether this discharge maintenance voltage is 120 [V] or more (step S27).

  If the discharge sustaining voltage is less than 120 [V] (step S27: NO), it is determined that the voltage waveform is not established as a discharge waveform (step S30), and the analysis result is output (step S29).

  On the other hand, when the discharge sustain voltage is 120 [V] or higher (step S27: YES), it is determined that the voltage waveform is established as a discharge waveform (step S30), and the analysis result is output (step S29).

  As shown in FIG. 2, the voltage waveform b when the electrons are emitted by being irradiated with ultraviolet rays, that is, the discharge waveform, is discharged when the voltage value increases linearly from the minimum value point to reach the maximum voltage. It has a characteristic shape of decreasing to a linear function after falling to the sustain voltage and maintaining the discharge sustain voltage for a predetermined time. On the other hand, the voltage waveform a when electrons are not emitted has a sinusoidal shape. Therefore, in the present embodiment, the discharge start voltage, the discharge sustain voltage, the discharge time, and the discharge delay time are set based on the difference in the shape of the voltage waveform depending on whether or not electrons are emitted. These values exist in the voltage waveform b established as the discharge waveform, but do not exist in the voltage waveform a not established as the discharge waveform. Therefore, it is confirmed whether or not the voltage waveform is established as a discharge waveform by checking the presence or absence of the discharge start voltage, the discharge sustain voltage, the discharge time, and the discharge delay time.

  As described above, according to the present embodiment, the A / D conversion unit 161 generates a voltage waveform indicating the time change of the voltage value between the electrodes of the flame sensor 1, and the analysis unit 163 analyzes the voltage waveform. Then, the determination unit 164 determines the presence / absence of flame based on the analysis result of the analysis unit 163, so that the integration time or the like is unnecessary as in the conventional case, so that the presence / absence of the flame can be detected more quickly and reliably. it can.

In addition, when light intensity is insufficient, an applied voltage is insufficient, or an electron tube is out of gas, the current flowing between the electrodes of the flame sensor 1 is reduced. Then, as indicated by reference numeral c in FIG. 5, a portion where a constant discharge sustain voltage is detected in the discharge waveform becomes a sine wave shape for a plurality of cycles.
Further, when the arithmetic device 3 breaks down or the applied voltage becomes excessive, the current flowing between the electrodes of the flame sensor 1 increases. Then, as shown by the symbol d in FIG. 6, the portion where a constant discharge sustain voltage is detected in the discharge waveform becomes convex.
Thus, the voltage waveform changes depending on the amount of current flowing between the electrodes of the flame sensor 1, and this amount of current changes depending on the state of the flame sensor 1 and the arithmetic device 3. Therefore, it is possible to detect the state of the flame sensor 1 and the arithmetic device 3 based on the voltage waveform. Thereby, for example, the analysis unit 163 sets a threshold value for detecting the characteristic portion of the discharge waveform shown in FIGS. 5 and 6 such that the discharge start voltage exists but the discharge sustain voltage does not exist. The state of the flame sensor 1 and the arithmetic unit 3 can be detected as well as the presence or absence of a flame.

  In the present embodiment, the case where the presence / absence of a flame is detected based on the voltage waveform has been described. However, the presence / absence of a flame may also be detected using a current signal. This case will be described below with reference to FIGS.

  7 is connected to a load resistor 17 provided between the arithmetic device 3 shown in FIG. 1 and the ground of the flame sensor 1 and a connection end of the load resistor 17, and the flame sensor 1 is provided with a current detection circuit 18 connected in series to 1.

Here, the current detection circuit 18 is composed of, for example, a load resistor or a photocoupler, detects the current value input from the flame sensor 1, and inputs the current value to the sampling circuit 16 as a current signal. In this case, the sampling circuit 16 detects the flame based on the voltage value of the reference voltage input from the voltage detection circuit 15, the trigger time point input from the trigger circuit 13, and the current signal input from the current detection circuit 18. Determine presence or absence.
Here, as shown in FIG. 8, when the flame sensor 1 is irradiated with ultraviolet rays to emit electrons, the current signal shows a substantially step-like response simultaneously with the start and end of the emission of electrons from the flame sensor 1. Therefore, in the determination of the presence or absence of the discharge start voltage in the voltage waveform analysis process described above (step S22), the analysis unit 162 has substantially the same timing (for example, ± 2 [msec] when the current signal rises and the voltage waveform falls. ] Within a predetermined time α), it is determined that the voltage waveform is established as a discharge waveform. Thereby, the presence or absence of a flame can be detected more reliably.

  Further, in the present embodiment, the numerical values for determining the discharge start voltage, the discharge time, and the discharge sustain voltage are not limited to the above-described values, and it goes without saying that they can be set as appropriate.

  In this embodiment, the case of using a sine wave voltage waveform has been described as an example. However, the voltage waveform is not limited to a sine wave, and various waveforms such as a triangular wave can be appropriately used as long as the falling of the voltage can be detected. It can be used freely.

  The present invention can be applied to various devices in which the voltage between terminals of an electron tube changes depending on the presence or absence of discharge, such as a flame detection device using an electron tube.

  DESCRIPTION OF SYMBOLS 1 ... Flame sensor, 2 ... External power supply, 3 ... Arithmetic unit, 11 ... Power supply circuit, 12 ... Applied voltage generation circuit, 13 ... Trigger circuit, 14 ... Voltage dividing resistor, 15 ... Voltage detection circuit, 16 ... Sampling circuit, 17 DESCRIPTION OF SYMBOLS ... Load resistance, 18 ... Current detection circuit, 161 ... A / D conversion part, 162 ... Memory | storage part, 163 ... Analysis part, 164 ... Determination part.

Claims (1)

An envelope, a pair of electrodes disposed opposite to each other inside the envelope, and an electron tube that emits electrons between the electrodes when irradiated with ultraviolet rays;
An application unit for applying a periodically changing voltage between the electrodes;
A detection unit for detecting a voltage waveform indicating a time change of the voltage between the electrodes;
An analysis unit for analyzing whether a discharge waveform is established in the voltage waveform detected by the detection unit;
A determination unit that determines the presence or absence of flame based on the analysis result by the analysis unit ,
The analysis unit sets a voltage value at a time when the voltage drops below a predetermined voltage value within a predetermined time from the time when the maximum voltage is detected in the voltage waveform as a discharge maintaining voltage, and the discharge maintaining voltage is maintained for a predetermined time thereafter. In this case, the flame detection apparatus outputs an analysis result indicating that a discharge waveform is established in the voltage waveform to the determination unit .

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