Liquid level detection circuit, liquid level detection device and liquid level detection method

Abstract

The invention discloses a liquid level detection circuit, a liquid level detection device and a liquid level detection method. The detection circuit is composed of a PWM signal generating circuit, a condensate water connecting branch and a detection branch. When the PWM wave is at a high level, the detection branch has no output; and when the PWM wave is at a low level, the detection branch is conducted to charge the second capacitor. When the condensate water cup is not full of water, the two detection electrodes are open-circuited, the electrodes are in a high resistance state, only the detection branch is connected, and condensate water detects output voltage; when the condensate water cup is full of water, the two electrodes in the condensate water cup make contact with condensate water, a resistor with the resistance value determined by condensate water components is formed between the two electrodes, when the condensate water connecting branch and the detection branch are connected, the condensate water detection output voltage can be reduced, and the reduction amount is related to the resistance value presented by the condensate water. In combination with the circuit, the detection of the liquid level of condensate water with different components can be realized only by configuring different judgment thresholds at a receiving end, and the circuit has relatively high universality.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of circuit design, and in particular relates to a liquid level detection circuit, a liquid level detection device and a liquid level detection method. BACKGROUND

[0002] In a gas water heater, the condensing gas water heater and the gas wall-hanging stove have higher combustion efficiency. The main difference between the two and the ordinary gas boiler is that they are equipped with a condenser, which is the core component for improving thermal efficiency. The main function is to recover the waste heat in the high-temperature flue gas, reduce heat waste, and thus reduce gas consumption.

[0003] When the flue gas passes through the condenser, it exchanges heat with the low-temperature water in the condenser, the flue gas temperature decreases, and the cold water temperature increases. At the same time, the water vapor in the flue gas will also condense into liquid water and release heat. The condensate needs to be discharged to the outside of the machine in a timely manner through a special pipeline to prevent corrosion of the machine.

[0004] At present, most manufacturers detect the liquid level in the condensate cup according to the circuit as shown in Figure 1 When the water is full, a signal is sent for timely discharge. In this circuit, the two pins of terminal CN1 are respectively connected to two electrodes in the condensate cup (the two electrodes are arranged at the highest liquid level in the condensate cup), the water level signal is connected to the MCU. When the condensate cup is not full, the circuit between the two electrodes is broken and presents high resistance, the open circuit between terminals CN1, and the transistor T20 is not turned on, the water level signal is high. When the condensate cup is full, the circuit between the two electrodes is short-circuited and presents impedance, the transistor T20 is turned on, and the water level signal is low.

[0005] However, due to the difference in types of gas, the composition of the condensate produced will also be different, and the conductivity will also be different, resulting in different resistance values of the condensate. When the resistance value is relatively large, it may cause the transistor T20 to be unable to turn on, thereby failing to accurately output the water level signal. In order to make the circuit suitable for different working conditions, the resistance value of the resistor R148 is important, and even in order to adapt to the needs of different regions, different resistance values of R148 need to be replaced for different regional orders, resulting in low stability and universality of the water level detection circuit. SUMMARY

[0006] In order to overcome the problem of low universality and stability of the existing condensate detection circuit, the present application provides a liquid level detection circuit, device and method suitable for different condensate compositions. The liquid level detection circuit outputs different detection voltages according to different condensate compositions, and the receiving party only needs to change the detection threshold to realize the detection of the liquid level of the condensate cup, that is, the detection sensitivity is adjustable, without the need to change the circuit elements, thereby improving the stability and universality of the condensate liquid level detection circuit.

[0007] The application is implemented by adopting the following technical solutions: The application provides a liquid level detection circuit. The PWM signal generation circuit is composed of a PWM generator and a switching tube Q1; the first input end of the switching tube Q1 is connected to the output of the PWM generator, the second input end of the switching tube Q1 is connected to the power supply input V1 through a pull-up resistor R1, and the output end of the switching tube Q1 is grounded. The condensate cup electrode connection branch is composed of a first capacitor C1, a second resistor R2 and a terminal CN2; the 1 and 2 pins of the terminal CN2 are respectively connected to two detection electrodes in the condensate cup, and the 1 pin is grounded; one end of the first capacitor C1 is connected to the second input end of the switching tube Q1, and the other end is connected to the second resistor R2; the other end of the second resistor R2 is connected to the 2 pin of the terminal CN2. The detection branch is composed of a diode D1, a third resistor R3 and a fourth resistor R4, a voltage division circuit and a second capacitor C2 connected in parallel to the fourth resistor R4; the connection end of the third resistor R3 and the fourth resistor R4 is led out as a condensate detection output.

[0008] Compared with the prior art, the application has the following advantages and positive effects: the liquid level detection circuit generates a PWM wave through the PWM signal generation circuit; when the PWM wave is at a high level, the switching tube Q1 is turned on, so that the left side of the first capacitor C1 is at a low level, the diode D1 is not turned on, and the detection branch has no output; when the PWM wave is at a low level, the switching tube Q1 is not turned on, the left side of the first capacitor C1 is at a high level, the diode D1 is turned on, and the detection branch is turned on to form a circuit of the power supply input V1-pull-up resistor R1-diode D1-third resistor R3-fourth resistor R4-ground, so that the second capacitor C2 is charged, and the charging voltage is related to the anode voltage of the diode D1; if the condensate cup is not filled with water, the two detection electrodes are open, and the electrodes are in a high resistance state, so that the circuit of the power supply input V1-pull-up resistor R1-first capacitor C1-second resistor R2-condensate-ground is not connected, only the detection branch is connected, and the condensate detection output voltage is (V1-V D1R4 / (R1+R3+R4); when the water in the condensate cup is full (when the highest liquid level is reached), the two electrodes in the condensate cup contact the condensate water, and an electric resistance with a resistance value determined by the composition of the condensate water is formed between the two electrodes. Since the input at the left end of the first capacitor C1 is a square wave signal consistent with the PWM wave, the current will pass through the first capacitor C1, so that the circuit of the power supply input V1-the pull-up resistor R1-the first capacitor C1-the second resistor R2-the condensate water-the ground is connected. When the circuit of the power supply input V1-the pull-up resistor R1-the diode D1-the third resistor R3-the fourth resistor R4-the ground is also connected, the voltage at the anode of the diode D1 is lower than when the condensate water is not full, and the condensate water detection output voltage of the detection branch is also lowered. The amount of reduction is related to the resistance value presented by the condensate water. In combination with the circuit, the condensate water detection output voltage is different for different condensate water resistance values. It is only necessary to configure different judgment threshold values at the receiving end (such as an MCU or other receiving circuit) to realize the detection of the condensate water level. It can be seen that, compared with the prior art which needs to replace components to adjust the detection sensitivity, the condensate water level detection circuit provided in the present application has strong versatility.

[0009] Further, when a hysteresis comparison voltage is added at the receiving end, the stability of the detection signal can also be improved.

[0010] In some embodiments of the present application, a zener diode ZD1 is connected in parallel with the fourth resistor R4 in the detection branch, to limit the minimum value of the condensate water detection output.

[0011] In some embodiments of the present application, a third capacitor C3 is connected in parallel with the fourth resistor in the detection branch.

[0012] In some embodiments of the present application, the liquid level detection circuit further comprises: A master control chip, which is applied as a PWM generator of the PWM signal generation circuit.

[0013] In some embodiments of the present application, the condensate water detection output of the detection branch is connected to an I / O pin of the master control chip. The master control chip can adapt to different compositions of condensate water by configuring different judgment threshold values.

[0014] In other embodiments of the present application, the condensate water detection output can also be output to the inverting input end of a comparator, and an adapted voltage is loaded at the non-inverting input end of the comparator as a judgment threshold value. The output of the comparator reflects the detection result of different compositions of condensate water.

[0015] A liquid level detection device is provided, which comprises a condensate cup and two detection electrodes arranged at a specified liquid level of the condensate cup, and further comprises: A liquid level detection circuit composed of a PWM signal generation circuit, a condensate cup electrode connection branch, and a detection branch; wherein, The PWM signal generating circuit is composed of a PWM generator and a switch tube Q1; a first input end of the switch tube Q1 is connected with an output of the PWM generator, a second input end of the switch tube Q1 is connected with a power supply input V1 through a pull-up resistor R1, and an output end of the switch tube Q1 is grounded; The condensate cup electrode connection branch is composed of a first capacitor C1, a second resistor R2 and a terminal CN2; 1 and 2 pins of the terminal CN2 are respectively connected with two detection electrodes in the condensate cup, and the 1 pin is grounded; one end of the first capacitor C1 is connected with the second input end of the switch tube Q1, and the other end is connected with the second resistor R2; the other end of the second resistor R2 is connected with the 2 pin of the terminal CN2; The detection branch is composed of a diode D1, a third resistor R3 and a fourth resistor R4, a voltage division circuit composed of the third resistor R3 and the fourth resistor R4, and a second capacitor C2 connected in parallel at two ends of the fourth resistor R4; a connection end of the third resistor R3 and the fourth resistor R4 is led out as a condensate detection output.

[0016] Compared with the prior art, the liquid level detection device provided by the application is composed of a liquid level detection circuit, a condensate cup and two detection electrodes arranged at a specified liquid level of the condensate cup; the liquid level detection circuit is composed of a PWM signal generating circuit, a condensate cup electrode connection branch and a detection branch; the PWM signal generating circuit generates a PWM wave; when the PWM wave is at a high level, the switch tube Q1 is turned on, so that the left side of the first capacitor C1 is at a low level, the diode D1 is not turned on, and the detection branch has no output; when the PWM wave is at a low level, the switch tube Q1 is not turned on, the left side of the first capacitor C1 is at a high level, the diode D1 is turned on, a circuit of the power supply input V1-pull-up resistor R1-diode D1-third resistor R3-fourth resistor R4-ground is formed, so that the second capacitor C2 is charged, and the charging voltage is related to the anode voltage of the diode D1; if the condensate cup is not filled with water, the two detection electrodes are open, a high resistance state is formed between the electrodes, the circuit of the power supply input V1-pull-up resistor R1-first capacitor C1-second resistor R2-condensate-ground is not connected, only the detection branch is connected, and the condensate detection output voltage is (V1-V D1R4 / (R1+R3+R4); when the water in the condensate cup is full (when the highest liquid level is reached), the two electrodes in the condensate cup contact the condensate water, and an electric resistance with a resistance value determined by the composition of the condensate water is formed between the two electrodes. Since the input at the left end of the first capacitor C1 is a square wave signal consistent with the PWM wave, the current will pass through the first capacitor C1, so that the circuit of the power supply input V1-the pull-up resistor R1-the first capacitor C1-the second resistor R2-the condensate water-the ground is connected. When the circuit of the power supply input V1-the pull-up resistor R1-the diode D1-the third resistor R3-the fourth resistor R4-the ground is also connected, the voltage at the anode of the diode D1 is lower than when the condensate water is not full, and the condensate water detection output voltage of the detection branch is also lowered. The amount of reduction is related to the resistance value presented by the condensate water. In combination with the circuit, the condensate water detection output voltage is different for different condensate water resistance values. It is only necessary to configure different judgment thresholds at the receiving end (such as an MCU or other receiving circuit) to realize the detection of the condensate water level. It can be seen that, compared with the prior art which needs to replace components to adjust the detection sensitivity, the condensate water detection device has strong versatility.

[0017] Further, when the hysteresis comparison voltage is increased at the receiving end, the stability of the detection signal can also be improved In some embodiments of the present application, a zener diode ZD1 is connected in parallel with the fourth resistor R4 in the detection branch.

[0018] In some embodiments of the present application, a third capacitor C3 is connected in parallel with the fourth resistor in the detection branch.

[0019] In some embodiments of the present application, the liquid level detection circuit further comprises: A master control chip, which is applied as a PWM generator of the PWM signal generation circuit.

[0020] In some embodiments of the present application, the condensate water detection output of the detection branch is connected to an I / O pin of the master control chip.

[0021] A liquid level detection method is proposed, which is applied in the liquid level detection device as described above, and comprises: Determining the impedance value presented by the condensate water between the detection electrodes; Setting a water full threshold value based on the impedance value; the water full threshold value is configured based on the electrode spacing and the composition of the condensate water; Receiving the condensate water detection output signal output by the liquid level detection device; Comparing the condensate water detection output signal with the water full threshold value, and judging whether the condensate cup is full based on the comparison result.

[0022] Other features and advantages of the present application will become more apparent after reading the detailed description of the embodiments of the present application in combination with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort based on these drawings.

[0024] Figure 1 For the existing condensate water detection circuit; Figure 2 For the composition structure of the condensate water detection device proposed in the present application; Figure 3 For the circuit structure of the condensate water detection circuit proposed in the present application; Figure 4 For the embodiment of the condensate water detection circuit proposed in the present application; Figure 5 For the embodiment of the condensate water detection circuit proposed in the present application; Figure 6 For the embodiment of the condensate water detection circuit proposed in the present application; Figure 7 For the embodiment of the condensate water detection circuit proposed in the present application; Figure 8 For the condensate water detection method proposed in the present application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the scope of protection of the present application.

[0026] In the description of the present application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0027] In the description of the present application, it is necessary to point out that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected. For those skilled in the art, the specific meaning of the above terms in the present application can be understood in specific circumstances. In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0028] The terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise stated, the meaning of "multiple" is two or more.

[0029] In the embodiments of the present application, a condensate water detection device is provided for gas water heaters, gas wall-mounted boilers, gas / oil boilers, etc., which has adjustable sensitivity, strong versatility and stability. As shown in Figure 2 The liquid level detection device is composed of a condensate cup C (or a condensate container), a first detection electrode A, a second detection electrode B and a condensate detection circuit U; the first detection electrode A and the second detection electrode B are arranged at the same height at the specified liquid level of the condensate cup, which is usually the highest liquid level that the condensate cup C can carry condensate water. The first detection electrode A and the second detection electrode B are connected to the liquid level detection circuit through pins or connecting wires.

[0030] The liquid level detection circuit, as shown in Figure 3 includes: The PWM signal generation circuit 1 is composed of a PWM generator U1 and a switching tube Q1; the first input end of the switching tube Q1 is connected to the output of the PWM generator, the second input end of the switching tube Q1 is connected to the power supply input V1 through the pull-up resistor R1, and the output end of the switching tube Q1 is grounded. The switching tube Q1 is, for example, an NPN triode, the first input end of which is the base of the triode, the second input end of which is the collector of the triode, and the output end of which is the emitter of the triode; the switching tube Q1 is, for example, an NMOS tube, the first input end of which is the gate of the NMOS tube, the second input end of which is the source of the NMOS tube, and the output end of which is the drain of the NMOS tube.

[0031] The condensate cup electrode connection branch 2 is composed of a first capacitor C1, a second resistor R2 and a terminal CN2; the 1 and 2 pins of the terminal CN2 are respectively connected to the two detection electrodes in the condensate cup, and the 1 pin is grounded; one end of the first capacitor C1 is connected to the second input end of the switching tube Q1, and the other end is connected to the second resistor R2; the other end of the second resistor R2 is connected to the 2 pin of the terminal CN2.

[0032] The detection branch 3 consists of a voltage divider circuit composed of diode D1, third resistor R3 and fourth resistor R4, and second capacitor C2 connected in parallel across the fourth resistor R4; the connection point of the third resistor R3 and the fourth resistor R4 is led out as the condensate detection output.

[0033] In the above liquid level detection circuit, the PWM signal generation circuit 1 generates a 1kHz PWM wave. When the PWM wave is high, the switching transistor Q1 is turned on, making the left side of the first capacitor C1 low. Then, the diode D1 is not turned on, and the detection branch 3 has no output.

[0034] When the PWM wave is low, the switch Q1 is not turned on, and the left side of the first capacitor C1 is high, causing the diode D1 to turn on. This connects detection branch 3, forming a circuit: power input V1 - pull-up resistor R1 - diode D1 - third resistor R3 - fourth resistor R4 - ground. Therefore, the second capacitor C2 is charged, and the charging voltage is related to the positive terminal voltage of the switch D1. At this time, if the condensate cup is not full, the two detection electrodes are open, and there is a high resistance state between them (R0 is infinite). This prevents the circuit of power input V1 - pull-up resistor R1 - first capacitor C1 - second resistor R2 - condensate - ground from being connected. In other words, condensate cup connection branch 2 is not connected, and only detection branch 3 is connected. The condensate detection output voltage is (V1 - V...). D1 R4 / (R1+R3+R4); When the condensate cup is full (reaching the specified liquid level), the two detection electrodes in the condensate cup contact the condensate, forming a resistor between the two electrodes whose resistance value is determined by the composition of the condensate (R0 is KΩ or MΩ). Since the input at the left end of the first capacitor C1 is a square wave signal consistent with the PWM wave, the current will pass through the first capacitor C1, making the circuit of power supply input V1-pull-up resistor R1-first capacitor C1-second resistor R2-condensate-ground connected. When the circuit of power supply input V1-pull-up resistor R1-diode D1-third resistor R3-fourth resistor R4-ground is also connected, the positive voltage of diode D1 is lower than when the condensate is not full, and the output voltage of the condensate detection in detection branch 3 will also decrease. The amount of decrease is related to the resistance value of the condensate.

[0035] With this circuit, the output voltage of the condensate detection will be different for different condensate resistance values. Therefore, it is only necessary to configure different judgment thresholds at the receiving end (such as MCU or other receiving circuit) to realize the detection of condensate level. It can be seen that compared with the existing technology that requires changing components to adjust the detection sensitivity, the condensate detection circuit provided in this application has strong versatility.

[0036] In this embodiment, a hysteresis comparison voltage can be added to the receiving end to improve the stability of the detection signal through the hysteresis comparison function.

[0037] As Figure 4 shown in the embodiment, in the detection branch 3, a voltage stabilizing diode ZD1 is connected in parallel with the fourth resistor R4, which is used to define the minimum value of the condensed water detection output, and if the value is lower than the minimum value, the detection circuit is considered as a fault or invalid detection.

[0038] As Figure 5 shown in the embodiment, a filter capacitor C3 is arranged at the condensed water detection output end of the detection branch 3, which is used to stabilize the output detection signal.

[0039] As Figure 6 shown in the embodiment, the main control chip MCU of the gas water heater, gas wall-hanging stove, gas / oil boiler, etc. is used as the PWM generator to generate the PWM signal of the specified frequency, and the condensed water detection output of the detection branch 3 is connected to an I / O port of the MCU, and the MCU is configured with different judgment thresholds to adapt to the condensed water of different components.

[0040] As Figure 7 shown in the embodiment, the condensed water detection output of the detection branch 3 is connected to the inverting terminal of the comparator U1, and the non-inverting terminal of the comparator U1 is loaded with the adaptive reference voltage V0 as the judgment threshold through the power supply circuit or the MCU scheduling, and then the output of the comparator U1 reflects the comparison result with the judgment threshold, and then the water level of the condensed water cup can be judged according to the output of the comparator U1.

[0041] In the embodiment of the present application, the receiving end runs the liquid level detection method as Figure 8 shown, and by setting different water full thresholds, the liquid level detection of the condensed water of different components is realized, the detection sensitivity can be adjusted without replacing the components, the universality of the liquid level detection circuit is improved, including: S1: Determine the impedance value of the condensed water between the detection electrodes.

[0042] In actual design, the impedance value of the condensed water of different components corresponding to different gas types can be counted, and the corresponding impedance value is recorded. When the gas equipment is sold, the gas type can be determined through the boot detection and manual confirmation, and then the actual impedance value of the condensed water is determined.

[0043] S2: Set the water full threshold based on the impedance value.

[0044] The water full threshold is configured based on the electrode spacing and the condensed water component.

[0045] S3: Receive the condensed water detection output signal output by the liquid level detection device, compare the condensed water detection output signal with the water full threshold, and judge whether the condensed water cup is full based on the comparison result.

[0046] When the condensate is not full, the condensate detection output voltage is (V1-V D1 )R4 / (R1+R3+R4); when the condensate is full, the condensate detection output signal is consistent with the water full threshold, and S4 is executed: a water full prompt is sent out.

[0047] It should be noted that the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present application should also be within the scope of the present application.

Claims

1. A liquid level detection circuit, characterized by, The circuit comprises: A PWM signal generation circuit composed of a PWM generator and a switching tube Q1; a first input end of the switching tube Q1 is connected to an output of the PWM generator, a second input end of the switching tube Q1 is connected to a power supply input V1 through a pull-up resistor R1, and an output end of the switching tube Q1 is grounded; A condensate cup electrode connection branch composed of a first capacitor C1, a second resistor R2 and a terminal CN2; 1 and 2 pins of the terminal CN2 are respectively connected to two detection electrodes in a condensate cup, and the 1 pin is grounded; one end of the first capacitor C1 is connected to the second input end of the switching tube Q1, and the other end is connected to the second resistor R2; the other end of the second resistor R2 is connected to the 2 pin of the terminal CN2; A detection branch composed of a diode D1, a third resistor R3 and a fourth resistor R4, a voltage division circuit composed of the diode D1, the third resistor R3 and the fourth resistor R4, and a second capacitor C2 connected in parallel to the fourth resistor R4; a connection end of the third resistor R3 and the fourth resistor R4 is led out as a condensate detection output.

2. The liquid level detection circuit according to claim 1, characterized in that, In the detection branch, a voltage stabilizing diode ZD1 is connected in parallel to the fourth resistor R4.

3. The liquid level detection circuit according to claim 1, characterized in that, In the detection branch, a third capacitor C3 is connected in parallel to the fourth resistor.

4. The liquid level detection circuit of claim 1, wherein The circuit further comprises: A main control chip applied as the PWM generator of the PWM signal generation circuit; The condensate detection output of the detection branch is connected to an I / O pin of the main control chip.

5. A liquid level detecting device comprising a condensate cup and two detecting electrodes provided at a specified liquid level of the condensate cup, characterized in that, Further comprising: A liquid level detection circuit composed of the PWM signal generation circuit, the condensate cup electrode connection branch and the detection branch; wherein, The PWM signal generation circuit is composed of a PWM generator and a switching tube Q1; a first input end of the switching tube Q1 is connected to an output of the PWM generator, a second input end of the switching tube Q1 is connected to a power supply input V1 through a pull-up resistor R1, and an output end of the switching tube Q1 is grounded; The condensate cup electrode connection branch is composed of a first capacitor C1, a second resistor R2 and a terminal CN2; 1 and 2 pins of the terminal CN2 are respectively connected to two detection electrodes in a condensate cup, and the 1 pin is grounded; one end of the first capacitor C1 is connected to the second input end of the switching tube Q1, and the other end is connected to the second resistor R2; the other end of the second resistor R2 is connected to the 2 pin of the terminal CN2; The detection branch is composed of a diode D1, a third resistor R3 and a fourth resistor R4, a voltage division circuit composed of the diode D1, the third resistor R3 and the fourth resistor R4, and a second capacitor C2 connected in parallel to the fourth resistor R4; a connection end of the third resistor R3 and the fourth resistor R4 is led out as a condensate detection output.

6. The liquid level detection device according to claim 5, characterized in that In the detection branch, a voltage stabilizing diode ZD1 is connected in parallel to the fourth resistor R4.

7. The liquid level detection device according to claim 5, characterized in that In the detection branch, a third capacitor C3 is connected in parallel to the fourth resistor.

8. The liquid level detection device according to claim 5, characterized in that The liquid level detection circuit further comprises: A main control chip applied as the PWM generator of the PWM signal generation circuit.

9. The liquid level detection device according to claim 8, characterized in that The condensate detection output of the detection branch is connected to an I / O pin of the main control chip.

10. A liquid level detecting method applied to the liquid level detecting apparatus according to claim 5, characterized by, Comprise: Determine the impedance value presented by the condensate between the detection electrodes; Set a water full threshold value based on the impedance value; The water full threshold value is configured based on the electrode spacing and the condensate composition; Receive the condensate detection output signal output by the liquid level detection device; Compare the condensate detection output signal with the water full threshold value, and determine whether the condensate cup is full based on the comparison result.

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