A gas water heater and a flame detection method and device thereof

Abstract

The application discloses a gas water heater and a flame detection method and device thereof. The flame detection method comprises the following steps: receiving a detection value of a flame detection parameter at a current time; obtaining a flame state at a previous time, and determining a threshold value required for judging a flame detection result at the current time according to the flame state at the previous time; and determining the flame detection result at the current time according to a relationship between the detection value of the flame detection parameter at the current time and the threshold value. When determining the flame state at the current time, the application determines a comparison threshold value required for judging the flame state at the current time according to the flame state at the previous time, thereby improving the accuracy of flame detection.

Description

Technical Field

[0001] This invention belongs to the field of gas water heater technology, specifically, it relates to a gas water heater and its flame detection method and device. Background Technology

[0002] Flame detection during the use of gas water heaters is not only closely related to safety, but also tightly linked to the control logic of the gas water heater. A simple and reliable flame detection circuit is an essential component of a smart gas water heater.

[0003] Utility model patent CN 201742316 U discloses a flame sensing circuit for a gas water heater, including a flame sensing module, a comparator module, and an oscillation boost module. A flame sensing pin is electrically connected to the flame sensing module and transmits signals to it. The flame sensing module transmits signals to the comparator module, which in turn transmits signals to the main control circuit. The flame sensing circuit is integrated on a separate sensing circuit board and electrically connected to the main control circuit on the main control board of the gas water heater via an interface. The comparator module and the oscillation boost module obtain DC power from the main control circuit on the main control board through the interface. The oscillation boost module boosts the DC power and oscillates it to form AC power to supply the flame sensing module. The aforementioned document describes a scheme using a comparator to detect flames, which is costly.

[0004] Patent application CN 107991713 A discloses a flame sensing system for gas-fired instantaneous water heaters and wall-hung boilers, including a flame sensing needle, a flame sensing oscillation circuit, a power supply circuit, and a microprocessor. The system further includes a flame sensing circuit and an AD acquisition circuit. The power supply circuit provides power to the system. The output of the flame sensing oscillation circuit supplies AC voltage to the energy input of the flame sensing circuit. The flame sensing circuit converts flame information into a flame signal through the flame sensing needle. The signal input of the AD acquisition circuit is connected to the signal output of the flame sensing circuit, and the output of the AD acquisition circuit is connected to the signal input of the microprocessor, which performs signal recognition. The aforementioned document describes a flame AD value detection circuit for judging combustion status; however, it lacks a clear boundary between the presence and absence of flame, has a small flame detection tolerance, and is prone to misjudgment when switching combustion states.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a flame detection method for a gas water heater. When determining the flame state at the current moment, the reference threshold required for judging the flame state at the current moment is determined by the flame state at the previous moment, thereby improving the accuracy of flame detection.

[0007] Another objective of this invention is to provide a flame detection device for a gas water heater, which, when determining the flame state at the current moment, determines a reference threshold required for judging the flame state at the current moment based on the flame state at the previous moment by a determination module, thereby improving the accuracy of flame detection.

[0008] Another object of the present invention is to provide a gas water heater that employs the flame detection method described above or includes the flame detection device described above.

[0009] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0010] A flame detection method for a gas water heater includes the following steps:

[0011] Receive the detection value of the flame detection parameters at the current moment;

[0012] Obtain the flame state at the previous moment, and determine the threshold required to judge the flame detection result at the current moment based on the flame state at the previous moment;

[0013] The flame detection result at the current moment is determined based on the relationship between the detected value of the flame detection parameters at the current moment and the threshold.

[0014] Furthermore, the step of obtaining the flame state at the previous moment and determining the threshold required to judge the flame detection result at the current moment based on the flame state at the previous moment includes:

[0015] The flame state at the previous moment is obtained. If the flame state at the previous moment is no flame, then the first threshold K1 is determined as the threshold required to judge the flame detection result. If the flame state at the previous moment is flame, then the second threshold K2 is determined as the threshold required to judge the flame detection result.

[0016] Wherein, the second threshold K2 is greater than the first threshold K1.

[0017] Furthermore, determining the flame detection result at the current moment based on the relationship between the detected value of the flame detection parameters at the current moment and the threshold includes:

[0018] If the flame state at the previous moment was no flame, then when the detected value of the flame detection parameter at the current moment is less than the first threshold K1, a signal indicating that there is a flame is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the first threshold K1, a signal indicating that there is no flame is output.

[0019] If the flame state at the previous moment was "with flame", then when the detected value of the flame detection parameter at the current moment is less than the second threshold K2, a signal indicating "with flame" is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the second threshold K2, a signal indicating "without flame" is output.

[0020] Furthermore, the flame detection parameters include the flame's AD value.

[0021] Furthermore, obtaining the flame state at the previous moment includes:

[0022] If the MCU port voltage in the flame detection circuit was low at the previous moment, then the flame state at the previous moment was no flame.

[0023] If the MCU port voltage in the flame detection circuit was high at the previous moment, then the flame state at the previous moment was "flame present".

[0024] In the flame detection circuit, one end of the AC high-voltage source AC is connected to the reference ground, and the other end is connected to one end of the capacitor C1 through resistor R2. The other end of the capacitor C1 is connected to resistor R5, and the other end of R5 is connected to the flame detection probe. Resistor R6 connects the reference ground and the casing ground. One end of resistor R3 is connected to the junction A of capacitor C1 and resistor R5. The other end of resistor R3 is connected to the cathode of diode D2. The anode of diode D2 is connected to the reference ground. Diode D1 and resistor R1 are connected in parallel, and their two ends are respectively connected to the power supply VCC and the junction of resistor R3 and diode D2. One end of resistor R4 is connected to the junction of resistor R3 and diode D2. The other end of resistor R4 is connected to one end of capacitor C2. The other end of capacitor C2 is connected to the reference ground. The junction of resistor R4 and capacitor C2 is connected to the microcontroller MCU.

[0025] A flame detection device for a gas water heater, comprising:

[0026] The first detection module is used to detect the current value of the flame detection parameters;

[0027] The second detection module is used to detect the flame state at the previous moment;

[0028] The determining module is used to determine the threshold required to judge the flame detection result at the current moment based on the flame state detected by the second detection module at the previous moment;

[0029] The logic judgment module is used to determine the flame detection result at the current moment based on the relationship between the detection value of the flame detection parameter at the current moment and the threshold.

[0030] Furthermore, the logic judgment module includes:

[0031] The first judgment unit is used to determine the flame detection result at the current moment when the flame state at the previous moment is no flame.

[0032] If the flame state at the previous moment was no flame, then when the detected value of the flame detection parameter at the current moment is less than the first threshold K1, a signal indicating that there is a flame is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the first threshold K1, a signal indicating that there is no flame is output.

[0033] Furthermore, the logic judgment module includes:

[0034] The second judgment unit is used to determine the flame detection result at the current moment when the flame state at the previous moment was "there is a flame".

[0035] If the flame state at the previous moment was "with flame", then when the detected value of the flame detection parameter at the current moment is less than the second threshold K2, a signal indicating "with flame" is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the second threshold K2, a signal indicating "without flame" is output.

[0036] Furthermore, it also includes a flame detection circuit;

[0037] In the flame detection circuit, one end of the AC high-voltage source AC is connected to the reference ground, and the other end is connected to one end of the capacitor C1 through resistor R2. The other end of the capacitor C1 is connected to resistor R5, and the other end of R5 is connected to the flame detection probe. Resistor R6 connects the reference ground and the casing ground. One end of resistor R3 is connected to the junction A of capacitor C1 and resistor R5. The other end of resistor R3 is connected to the cathode of diode D2. The anode of diode D2 is connected to the reference ground. Diode D1 and resistor R1 are connected in parallel, and their two ends are respectively connected to the power supply VCC and the junction of resistor R3 and diode D2. One end of resistor R4 is connected to the junction of resistor R3 and diode D2. The other end of resistor R4 is connected to one end of capacitor C2. The other end of capacitor C2 is connected to the reference ground. The junction of resistor R4 and capacitor C2 is connected to the microcontroller MCU.

[0038] A gas water heater employs the flame detection method described above or includes the flame detection device described above.

[0039] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0040] 1. When determining the flame state at the current moment, the present invention uses the flame state at the previous moment to determine the reference threshold required to judge the flame state at the current moment, thereby improving the accuracy of flame detection.

[0041] 2. This invention increases the flame detection tolerance. When the flame sensing needle in the flame detection circuit oxidizes over time, causing some of the sensing to become faulty, or when there is a deviation in the flame detection range, the flame state can be detected well because of the existence of the flame tolerance range.

[0042] 3. The present invention provides a hysteresis interval between the first threshold and the second threshold. By using the hysteresis interval judgment method, the problem of flame detection failure caused by relying on only a fixed value to determine the presence or absence of flame in the prior art can be effectively avoided.

[0043] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0044] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0045] Figure 1 This is a schematic flowchart of the flame detection method for the gas water heater of the present invention;

[0046] Figure 2 This is a schematic flowchart of the flame detection method in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the flame detection device for the gas water heater of the present invention;

[0048] Figure 4 This is a schematic diagram of the flame detection circuit of the present invention.

[0049] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0051] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0052] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0053] like Figures 1 to 4 As shown, the present invention provides a gas water heater and a flame detection method and apparatus thereof.

[0054] The flame detection method includes the following steps: receiving the detection value of the flame detection parameter at the current moment; obtaining the flame state at the previous moment, and determining the threshold required to judge the flame detection result at the current moment based on the flame state at the previous moment; and determining the flame detection result at the current moment based on the relationship between the detection value of the flame detection parameter at the current moment and the threshold.

[0055] In the above scheme, when determining the flame state at the current moment, the detection value of the flame detection parameter at the current moment is first obtained, and then the flame state at the previous moment is obtained. The reference threshold required to judge the flame state at the current moment is determined by the flame state at the previous moment. Then, the detection value of the flame detection parameter at the current moment is compared with the reference threshold. Logical judgment is performed based on the comparison result to obtain the final flame detection result at the current moment. In this way, the flame state at the current moment can be accurately determined by different reference thresholds, thereby improving the accuracy of flame detection.

[0056] The above is the core idea of ​​this invention. In order to enable those skilled in the art to better understand the technical solution of this invention, the invention will be further described in detail below with reference to the accompanying drawings.

[0057] In some embodiments of the present invention, such as Figure 1 The flame detection methods for the gas water heaters shown include:

[0058] S1 receives the detection value of the flame detection parameters at the current moment.

[0059] The detected values ​​of the flame detection parameters can be digital signals. These are obtained by the flame detection circuit from the ion current of the burner flame, which is then amplified, filtered, and transmitted to the analog circuit. The analog circuit then converts the signals into digital signals.

[0060] Therefore, the flame detection parameters of the present invention include the AD value of the flame.

[0061] S2, obtain the flame state at the previous moment, and determine the threshold required to judge the flame detection result at the current moment based on the flame state at the previous moment.

[0062] In actual use, the detection interval can be once every 0.5s or 1s. After the previous detection is completed, the current detection will obtain the flame state of the previous moment, which is the flame state obtained from the flame detection result of the previous moment. It should be noted that when the power is turned on for the first time, the previous moment is the standby state of the gas water heater, and its flame state is the default no flame state.

[0063] After obtaining the flame state at the previous moment, the threshold required to judge the flame state at the current moment is determined based on the flame state at the previous moment. That is, whether the flame was present or not at the previous moment determines the threshold for judgment at the current moment, and the threshold corresponding to whether the flame was present or not is different.

[0064] S3, determine the flame detection result at the current moment based on the relationship between the detected value of the flame detection parameters at the current moment and the threshold.

[0065] Once the threshold is obtained, it can be compared with the current flame detection parameter value to determine the flame state at the current moment, and output the signal corresponding to the flame state so that the gas water heater controller can perform the next control step based on the signal.

[0066] In the above scheme, obtaining the flame state at the previous moment and determining the threshold required to judge the flame detection result at the current moment based on the flame state at the previous moment includes: obtaining the flame state at the previous moment; if the flame state at the previous moment is no flame, then determining a first threshold K1 as the threshold required to judge the flame detection result; if the flame state at the previous moment is flame present, then determining a second threshold K2 as the threshold required to judge the flame detection result. Wherein, the second threshold K2 > the first threshold K1.

[0067] In detail, the presence or absence of flame at the previous moment corresponds to different thresholds. The second threshold K2 corresponding to the presence of flame at the previous moment should be greater than the first threshold K1 corresponding to the absence of flame at the previous moment.

[0068] The above solution increases the flame detection tolerance. When the flame sensing needle in the flame detection circuit oxidizes over time, causing partial sensing failure, or when there is a deviation in the flame detection range, the existence of the flame tolerance range allows for accurate detection of the flame state. In other words, this invention creates a hysteresis interval between the first and second thresholds. Using this hysteresis interval judgment method effectively avoids the problem of flame detection failure caused by relying on only a fixed value to determine the presence or absence of a flame in existing technologies.

[0069] In some embodiments of the present invention, determining the flame detection result at the current moment based on the relationship between the detected value of the flame detection parameters at the current moment and the threshold includes:

[0070] If the flame state at the previous moment was no flame, then when the detected value of the flame detection parameter at the current moment is less than the first threshold K1, a signal indicating that there is a flame is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the first threshold K1, a signal indicating that there is no flame is output.

[0071] If the flame state at the previous moment was "with flame", then when the detected value of the flame detection parameter at the current moment is less than the second threshold K2, a signal indicating "with flame" is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the second threshold K2, a signal indicating "without flame" is output.

[0072] In practical applications, when the burner of a gas water heater transitions from standby to successful ignition, it is necessary to determine whether ignition was successful.

[0073] At this time, after the igniter discharges and the gas valve opens, the detection values ​​of the flame detection parameters at the current moment are obtained. Since the previous moment was in standby mode, the flame state at the previous moment was a no-flame state. The threshold used to determine the current flame state is determined to be the first threshold K1. Figure 2 As shown.

[0074] When the detected value of the flame detection parameter at the current moment is less than the first threshold K1, a signal indicating a flame is output, indicating successful ignition. The flame size can be adjusted by regulating the proportion of the gas valve. When the detected value of the flame detection parameter at the current moment is greater than or equal to the first threshold K1, a signal indicating no flame is output, indicating ignition failure. The igniter is then controlled to discharge again, or the gas valve is controlled to close, etc.

[0075] In other practical scenarios, when backflow of air from the flue causes the burner to extinguish, if the signal of flame extinguishing is not detected in time and the gas valve cannot be closed promptly, gas leakage may occur, leading to an accident. Therefore, it is necessary to determine whether the flameout was successful when the burner of a gas water heater transitions from combustion to extinguishment.

[0076] At this point, the detection values ​​of the flame detection parameters at the current moment are obtained. Since the previous moment was a combustion state, the flame state at the previous moment is considered to be a flame state. The threshold used to determine the current flame state is determined to be the second threshold K2. Figure 2 As shown.

[0077] When the detected value of the flame detection parameter at the current moment is less than the second threshold K2, a signal indicating that there is a flame is output, indicating that the flame is burning normally, and the flame size can be adjusted by adjusting the proportion of the gas valve. When the detected value of the flame detection parameter at the current moment is greater than or equal to the second threshold K2, a signal indicating that there is no flame is output, indicating that the flame is extinguished, and the igniter should be controlled to discharge again or the gas valve should be controlled to close, etc.

[0078] In some embodiments of the present invention, obtaining the flame state at the previous moment includes: if the MCU port voltage in the flame detection circuit at the previous moment is low, then the flame state at the previous moment is no flame; if the MCU port voltage in the flame detection circuit at the previous moment is high, then the flame state at the previous moment is flame present.

[0079] like Figure 4 As shown, in the flame detection circuit, one end of the AC high-voltage source AC is connected to the reference ground, and the other end is connected to one end of the capacitor C1 through resistor R2. The other end of the capacitor C1 is connected to resistor R5, and the other end of R5 is connected to the flame detection probe. Resistor R6 connects the reference ground and the casing ground. One end of resistor R3 is connected to the junction A of capacitor C1 and resistor R5. The other end of resistor R3 is connected to the cathode of diode D2. The anode of diode D2 is connected to the reference ground. Diode D1 and resistor R1 are connected in parallel, and their two ends are respectively connected to the power supply VCC and the junction of resistor R3 and diode D2. One end of resistor R4 is connected to the junction of resistor R3 and diode D2. The other end of resistor R4 is connected to one end of capacitor C2. The other end of capacitor C2 is connected to the reference ground. The junction of resistor R4 and capacitor C2 is connected to the microcontroller MCU.

[0080] In the above scheme, the AC high-voltage power supply AC applies high voltage to the sensing needle through resistors R2, C1, R5, and R6. When the sensing needle detects a flame, due to the ionization effect, a unidirectional current is formed in the circuit containing the sensing needle, flowing from A through R5. Assuming that the power supply is in the positive half-cycle at this time, there will be a potential difference UA between point A and the reference ground, causing the power supply VCC to form a current in R1, which reduces the voltage at the junction of R1 and R4.

[0081] When the AC current of the high-voltage AC power supply flows from C1 to R2, i.e. during the negative cycle, the voltage at the junction of R1 and R4 is clamped to a low voltage due to the presence of diode D2.

[0082] When there is no flame, the main current path in the positive half-cycle is R2 C1 R3 R4 C2, and the junction of capacitors C2 and R4 should be at a high level.

[0083] The flame detection circuit used in this invention is simple and reliable, and the flame detection tolerance is increased. When the flame sensing needle oxidizes over time, causing some poor sensing, or when there is a deviation in the flame sensing detection range, the flame value can be detected well because of the existing flame tolerance range.

[0084] like Figure 3 As shown, the flame detection device for a gas water heater provided by the present invention includes:

[0085] The first detection module is used to detect the current value of the flame detection parameters;

[0086] The second detection module is used to detect the flame state at the previous moment;

[0087] The determining module is used to determine the threshold required to judge the flame detection result at the current moment based on the flame state detected by the second detection module at the previous moment;

[0088] The logic judgment module is used to determine the flame detection result at the current moment based on the relationship between the detection value of the flame detection parameter at the current moment and the threshold.

[0089] Specifically, the logic judgment module includes:

[0090] The first judgment unit is used to determine the flame detection result at the current moment when the flame state at the previous moment is no flame.

[0091] If the flame state at the previous moment was no flame, then when the detected value of the flame detection parameter at the current moment is less than the first threshold K1, a signal indicating that there is a flame is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the first threshold K1, a signal indicating that there is no flame is output.

[0092] The second judgment unit is used to determine the flame detection result at the current moment when the flame state at the previous moment was "there is a flame".

[0093] If the flame state at the previous moment was "with flame", then when the detected value of the flame detection parameter at the current moment is less than the second threshold K2, a signal indicating "with flame" is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the second threshold K2, a signal indicating "without flame" is output.

[0094] The flame detection device also includes a flame detection circuit.

[0095] like Figure 4As shown, in the flame detection circuit, one end of the AC high-voltage source AC is connected to the reference ground, and the other end is connected to one end of the capacitor C1 through resistor R2. The other end of the capacitor C1 is connected to resistor R5, and the other end of R5 is connected to the flame detection probe. Resistor R6 connects the reference ground and the casing ground. One end of resistor R3 is connected to the junction A of capacitor C1 and resistor R5. The other end of resistor R3 is connected to the cathode of diode D2. The anode of diode D2 is connected to the reference ground. Diode D1 and resistor R1 are connected in parallel, and their two ends are respectively connected to the power supply VCC and the junction of resistor R3 and diode D2. One end of resistor R4 is connected to the junction of resistor R3 and diode D2. The other end of resistor R4 is connected to one end of capacitor C2. The other end of capacitor C2 is connected to the reference ground. The junction of resistor R4 and capacitor C2 is connected to the microcontroller MCU.

[0096] The flame detection device provided in this embodiment of the invention can employ the flame detection method described in the above method embodiment, which will not be repeated here.

[0097] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0098] The gas water heater provided by the present invention employs the flame detection method described above, or includes the flame detection device described above.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A flame detection method for a gas water heater, characterized in that: Includes the following steps: Receive the detection value of the flame detection parameters at the current moment, wherein the flame detection parameters include the AD value of the flame; Obtain the flame state at the previous moment, and determine the threshold required to judge the flame detection result at the current moment based on the flame state at the previous moment, including: The flame state at the previous moment is obtained. If the flame state at the previous moment is no flame, then a first threshold K1 is determined as the threshold required to judge the flame detection result. If the flame state at the previous moment is flame, then a second threshold K2 is determined as the threshold required to judge the flame detection result. Wherein, the second threshold K2 > the first threshold K1. The flame detection result at the current moment is determined based on the relationship between the detected value of the flame detection parameters at the current moment and the threshold, including: If the flame state at the previous moment was no flame, then when the detected value of the flame detection parameter at the current moment is less than the first threshold K1, a signal indicating that there is a flame is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the first threshold K1, a signal indicating that there is no flame is output. If the flame state at the previous moment was "with flame", then when the detected value of the flame detection parameter at the current moment is less than the second threshold K2, a signal indicating "with flame" is output; when the detected value of the flame detection parameter at the current moment is greater than or equal to the second threshold K2, a signal indicating "without flame" is output.

2. The flame detection method for a gas water heater according to claim 1, characterized in that: The process of obtaining the flame state at the previous moment includes: If the MCU port voltage in the flame detection circuit was low at the previous moment, then the flame state at the previous moment was no flame. If the MCU port voltage in the flame detection circuit was high at the previous moment, then the flame state at the previous moment was "flame present". In the flame detection circuit, one end of the AC high-voltage source AC is connected to the reference ground, and the other end is connected to one end of the capacitor C1 through resistor R2. The other end of the capacitor C1 is connected to resistor R5, and the other end of R5 is connected to the flame detection probe. Resistor R6 connects the reference ground and the casing ground. One end of resistor R3 is connected to the junction A of capacitor C1 and resistor R5. The other end of resistor R3 is connected to the cathode of diode D2. The anode of diode D2 is connected to the reference ground. Diode D1 and resistor R1 are connected in parallel, and their two ends are respectively connected to the power supply VCC and the junction of resistor R3 and diode D2. One end of resistor R4 is connected to the junction of resistor R3 and diode D2. The other end of resistor R4 is connected to one end of capacitor C2. The other end of capacitor C2 is connected to the reference ground. The junction of resistor R4 and capacitor C2 is connected to the microcontroller MCU.

3. A flame detection device for a gas water heater, characterized in that: For implementing the flame detection method as described in claim 1 or 2, including The first detection module is used to detect the current value of the flame detection parameters; The second detection module is used to detect the flame state at the previous moment; The determining module is used to determine the threshold required to judge the flame detection result at the current moment based on the flame state detected by the second detection module at the previous moment; The logic judgment module is used to determine the flame detection result at the current moment based on the relationship between the detected value of the flame detection parameters at the current moment and the threshold, including: The first judgment unit is used to determine the flame detection result at the current moment when the flame state at the previous moment is no flame; if the flame state at the previous moment is no flame, then when the detection value of the flame detection parameter at the current moment is less than the first threshold K1, a signal with flame is output; when the detection value of the flame detection parameter at the current moment is greater than or equal to the first threshold K1, a signal without flame is output. The second judgment unit is used to determine the flame detection result at the current moment when the flame state at the previous moment was "flame present". If the flame state at the previous moment was "flame present", then when the detection value of the flame detection parameter at the current moment is less than the second threshold K2, a signal indicating "flame present" is output; when the detection value of the flame detection parameter at the current moment is greater than or equal to the second threshold K2, a signal indicating "no flame present" is output.

4. The flame detection device for a gas water heater according to claim 3, characterized in that: It also includes a flame detection circuit; In the flame detection circuit, one end of the AC high-voltage source AC is connected to the reference ground, and the other end is connected to one end of the capacitor C1 through resistor R2. The other end of the capacitor C1 is connected to resistor R5, and the other end of R5 is connected to the flame detection probe. Resistor R6 connects the reference ground and the casing ground. One end of resistor R3 is connected to the junction A of capacitor C1 and resistor R5. The other end of resistor R3 is connected to the cathode of diode D2. The anode of diode D2 is connected to the reference ground. Diode D1 and resistor R1 are connected in parallel, and their two ends are connected to the power supply VCC and the junction of resistor R3 and diode D2, respectively. One end of resistor R4 is connected to the junction of resistor R3 and diode D2. The other end of resistor R4 is connected to one end of capacitor C2. The other end of capacitor C2 is connected to the reference ground. The junction of resistor R4 and capacitor C2 is connected to the microcontroller MCU.

5. A gas-fired water heater, characterized in that, The flame detection method as described in claim 1 or 2 or the flame detection device as described in claim 3 or 4 is employed.

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