Water level monitoring device, water injection control method and micro-steaming and baking all-in-one machine

Abstract

The invention provides a water level monitoring device, a water injection control method and a micro-steaming and baking all-in-one machine. The water level monitoring device comprises a pressure sensor, an electromagnetic valve and a main controller. The pressure sensor is arranged at the bottom of a water tank of the micro-steaming-baking all-in-one machine; the electromagnetic valve is arranged at one end of a water inlet pipe of the micro-steaming-baking all-in-one machine away from the water tank; the pressure sensor and the electromagnetic valve are electrically connected with a main controller of the micro-steaming and baking all-in-one machine; the main controller comprises a microcontroller and an acquisition module; the pressure sensor is in communication connection with the acquisition module, and the electromagnetic valve is connected with the microcontroller; according to the water level monitoring device, the water injection control method and the micro-steaming and baking all-in-one machine, the structure of the water level monitoring device can be optimized, the monitoring precision of the device is improved, the anti-interference performance of the monitoring process of the device is improved, and the accuracy of a monitoring result is guaranteed. In addition, through the arrangement of the water injection control method, the control complexity can be simplified, and the control cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of embedded microwave-steam-grill combination appliances in the field of household appliances, and more specifically, to a water level monitoring device and water injection control method, and a microwave-steam-grill combination appliance. Background Technology

[0002] With the diversification of user needs, the application of embedded microwave-steam-oven combos has become increasingly common. Water level monitoring and water filling control in the water tank are crucial aspects of their use. Currently available water level monitoring methods are mostly float-type and photoelectric type, which suffer from low accuracy and susceptibility to interference. Float-type sensors are prone to jamming due to scale buildup and water flow fluctuations, affecting monitoring accuracy; photoelectric sensors may be affected by water vapor condensation and contamination of the water tank's inner wall, reducing monitoring effectiveness. Therefore, researching how to improve the accuracy of water level monitoring in the water tank of an embedded microwave-steam-oven combo and avoid the impact of external interference on detection accuracy is of great significance.

[0003] Currently, pressure sensors have certain advantages in water level measurement, as they can indirectly calculate water level by measuring the pressure at the bottom of the liquid. However, in the application of microwave-steam-grill combos, the use of pressure sensors is easily affected by factors such as temperature and pressure fluctuations in the water tank, which can impact measurement accuracy. Furthermore, there is no effective solution to the problem of how to achieve coordinated control between the pressure sensor and the solenoid valve to achieve precise water injection.

[0004] Patent CN112754270B discloses a cooking inner pot structure, a steam oven, and a method for controlling residual water. The cooking inner pot structure includes an inner pot and a heating plate disposed at the bottom of the inner pot. A pressure sensor is installed at the bottom of the heating plate. The method for controlling residual water includes: (1) When cooking begins, water is pumped into the inner pot through a water pump outside the inner pot. The water pump operates for t1 seconds, and the heating plate operates continuously at high power, causing the temperature of the inner pot to rise continuously; (2) When the temperature of the inner pot reaches 100°C, the heating plate switches to low power intermittent operation. The NTC temperature T1 at the bottom of the heating plate is recorded every t2 seconds. When the NTC sensing temperature jumps, the pressure sensor value is cleared. (3) After the pressure sensor value is cleared to zero, the water pump continues to pump water for t3 seconds, and the pressure sensor value m1 is recorded. The heating plate continues to heat intermittently at low power. When the pressure sensor value is less than m2, it is considered that the remaining water in the inner pot has evaporated. (4) The water pump continues to pump water for t3 seconds. Based on m1-m2 and the time t4 required for the heating plate to evaporate this water during the inner pot heat preservation stage, the water consumption rate Q1 = (m1-m2) / t4 can be calculated. (5) When the pressure sensor value is greater than m2 and the remaining cooking time is less than t5, it is considered that the cooking is about to end. The water pump works according to the calculated water inlet time. When the cooking ends, zero water remains in the inner pot. The above method can improve the service life of the heating plate, but it does not solve the problem that the water level monitoring of the internal water tank of the microwave steam oven is prone to low detection accuracy and the monitoring results are easily interfered with. Summary of the Invention

[0005] In view of this, the present invention aims to propose a water level monitoring device and a water injection control method, as well as a microwave-steam-oven integrated appliance, to solve the problems of low accuracy and susceptibility to interference in existing water level monitoring methods for internal water tanks in microwave-steam-oven integrated appliances. This achieves optimized structure of the water level monitoring device, improved monitoring accuracy, enhanced anti-interference capabilities during monitoring, and ensures accurate monitoring results. Furthermore, the water injection control method simplifies control complexity and reduces control costs.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] This invention relates to a water level monitoring device and water injection control method, and a microwave-steam-oven combo. The water level monitoring device includes a pressure sensor, a solenoid valve, and a main controller. The pressure sensor is located at the bottom of the water tank of the microwave-steam-oven combo, and the solenoid valve is located at the end of the water inlet pipe of the microwave-steam-oven combo away from the water tank. Both the pressure sensor and the solenoid valve are electrically connected to the main controller of the microwave-steam-oven combo. The main controller includes a microcontroller and a data acquisition module. The pressure sensor and the data acquisition module are communicatively connected, and the solenoid valve is connected to the microcontroller.

[0008] Furthermore, the pressure sensor is a resistance strain gauge pressure sensor.

[0009] Furthermore, the pressure sensor includes a full-bridge circuit and a temperature sensor; both the full-bridge circuit and the temperature sensor are located inside the pressure sensor; one end of the full-bridge circuit is connected to the positive and negative terminals of the input power supply through the temperature sensor, respectively; the other two ends of the full-bridge circuit are connected to the two ends of other required loads, respectively.

[0010] Furthermore, the temperature sensor can be a thermistor Rm.

[0011] Furthermore, the main controller also includes a calibration module, a fault alarm module, a comparison module, and a pressure signal processing module; the microcontroller is connected to the solenoid valve, the calibration module, the fault alarm module, the comparison module, and the pressure signal processing module respectively; the end of the pressure signal processing module furthest from the microcontroller is connected to the acquisition module.

[0012] A water injection control method for a water level monitoring device, the method being applied to the aforementioned water level monitoring device, the method comprising the following steps:

[0013] Step 1, Calibration: Calibrate the pressure sensor and temperature sensor separately;

[0014] Step 2, Initialization: Initialize the parameters required for the water level calculation algorithm and the water injection control algorithm;

[0015] Step 3: Real-time detection and calculation of water level height h;

[0016] Step 4, Water Injection Control: The calculated water level height h is compared with the set lower limit hmin and upper limit hmax. Based on the comparison results, the microcontroller controls the water injection into the tank through the solenoid valve.

[0017] Furthermore, in step two, the required parameters in the water level calculation algorithm and the water injection control algorithm include the gravitational acceleration g, the standard density value of water ρ0, the water temperature influence coefficient β, the ambient temperature compensation coefficient γ, the lower limit of water level hmin, and the upper limit of water level hmax.

[0018] Furthermore, step three includes:

[0019] Step S31: The microcontroller periodically reads the pressure data P of the water at the bottom of the water tank in the pressure sensor, the temperature data Tw detected by the built-in temperature sensor, and the cavity temperature Ta measured by the cavity temperature sensor in the microwave-steam-grill combo.

[0020] Step S32: The pressure signal is amplified and filtered by the pressure signal processing module;

[0021] Step S33: Obtain the density ρ(T) of the water in the tank at the current temperature using the temperature compensation formula, and calculate the water level height h using the water level calculation formula;

[0022] Step S34: Initially determine whether h < 0 mm or h > water tank volume V1 mm. If yes, trigger the pressure sensor fault alarm, and the microcontroller transmits fault prompt information to the user through the fault alarm module; otherwise, proceed to step four.

[0023] Furthermore, the temperature compensation formula is: ρ(T)=ρ0×[1-β(Tw-T0)-γ(Tw-T0)], where T0 is the standard temperature value, ρ0 is the standard density value of water, Tw is the water temperature value, β is the water temperature influence coefficient, and γ is the ambient temperature compensation coefficient.

[0024] A microwave-steam-oven combo appliance includes a water level monitoring device, which is installed inside the microwave-steam-oven combo appliance.

[0025] Compared with existing technologies, the water level monitoring device, water injection control method, and microwave-steam-oven combo machine described in this invention have the following beneficial effects:

[0026] By incorporating the aforementioned device into the microwave-steam-oven combo, the structure of the water level monitoring device can be optimized, improving monitoring accuracy, enhancing the anti-interference capability of the monitoring process, and ensuring the accuracy of monitoring results. Furthermore, the water injection control method simplifies control complexity and reduces control costs. Attached Figure Description

[0027] The accompanying drawings, which constitute a part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 This is a schematic diagram of the overall structure of the device after installation on the water tank.

[0029] Figure 2 This is a first-person view of the overall structure of the device mounted on the water tank.

[0030] Figure 3 This is a first-person view of the overall structure of the device mounted on the water tank, with a schematic diagram of a cross-section at point AA.

[0031] Figure 4 This is a second-view schematic diagram of the overall structure of the device mounted on the water tank.

[0032] Figure 5 This is a schematic diagram of the internal main controller structure of the device;

[0033] Figure 6This is a schematic diagram illustrating the connection method between a full-bridge circuit and a thermistor Rm.

[0034] Figure 7 This is a schematic flowchart of the water injection control method.

[0035] Explanation of reference numerals in the attached diagram: 1. Pressure sensor; 2. Solenoid valve; 3. Main controller; 31. Microcontroller; 32. Acquisition module; 33. Calibration module; 34. Fault alarm module; 35. Comparison module; 36. Pressure signal processing module; 4. Water tank; 40. Inlet pipe; 41. Outlet pipe. Detailed Implementation

[0036] The inventive concepts of this disclosure will be described below using terminology commonly used by those skilled in the art to communicate the essence of their work to others skilled in the art. However, these inventive concepts may be embodied in many different forms and should not be construed as limited to the embodiments described herein.

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0038] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] This embodiment is for a microwave-steam-grill combo. Similar to conventional microwave-steam-grill combos, the overall structure consists of a water tank, an inlet pipe, and an outlet pipe.

[0040] To address the issues of low accuracy and susceptibility to interference in existing water level monitoring methods for microwave-steam-grill combos, this embodiment proposes a water level monitoring device and water injection control method, specifically an embedded water level monitoring and water injection control system for a microwave-steam-grill combo based on a pressure sensor. The water level monitoring device includes a pressure sensor 1, a solenoid valve 2, and a main controller 3. The pressure sensor 1 is located at the bottom of the water tank 4 of the microwave-steam-grill combo, and the solenoid valve 2 is located at the end of the water inlet pipe 40 of the microwave-steam-grill combo away from the water tank 4. It is used to control the water injection process. Both the pressure sensor 1 and the solenoid valve 2 are electrically connected to the main controller 3 of the microwave-steam-grill combo. The main controller 3 includes a microcontroller 31 and a data acquisition module 32. The pressure sensor 1 and the data acquisition module 32 are communicatively connected, and the solenoid valve 2 is connected to the microcontroller 31. Under the action of the microcontroller 31, the system uses the pressure sensor 1 and the solenoid valve 2 to achieve real-time monitoring of the water level in the water tank 4 and precise water injection control. In this embodiment, "bottom" refers to the direction shown in the diagram below.

[0041] The water level is calculated by measuring the pressure at the bottom of water tank 4 using pressure sensor 1, and the water filling process is precisely controlled by solenoid valve 2, which improves the ease of use and reliability of the microwave-steam-oven combo. It also optimizes the structure of the water level monitoring device, improves the monitoring accuracy, enhances the anti-interference capability of the monitoring process, and ensures the accuracy of the monitoring results.

[0042] Pressure sensor 1 is a resistance strain gauge pressure sensor. This resistance strain gauge sensor mainly works based on the resistance strain effect. Assuming the initial resistance of the resistance strain gauge is R, there is an approximately linear relationship between the change in resistance ΔR and the strain ε: ΔR / R = Kε. Here, K is the sensitivity coefficient of the resistance strain gauge, and the strain ε is proportional to the pressure P acting on the elastic sensitive element. Therefore, by measuring the change in resistance ΔR of the resistance strain gauge, the magnitude of the pressure P can be indirectly measured, and thus the pressure of the water in water tank 4 can be measured in real time.

[0043] Pressure sensor 1 includes a full-bridge circuit and a temperature sensor. Both the full-bridge circuit and the temperature sensor are housed inside pressure sensor 1. Two terminals of the full-bridge circuit are connected to the positive and negative terminals of the input power supply via the temperature sensor, respectively; the other two terminals of the full-bridge circuit are connected to the terminals of other required loads. The temperature sensor can be a thermistor Rm. At least one thermistor Rm is provided. Preferably, two thermistors Rm are provided.

[0044] By employing temperature compensation technology in pressure sensor 1, a temperature sensor is installed inside to correct for pressure measurement errors caused by temperature changes. This solves the problem that the resistance value of the strain gauge changes with temperature, thus affecting the measurement results and improving measurement accuracy.

[0045] Specifically, the full-bridge circuit includes a first resistor r1, a second resistor r2, a third resistor r3, and a fourth resistor r4. These resistors are connected end-to-end to form a closed-loop circuit. One end of the first resistor r1 and the fourth resistor r4, and one end of the second resistor r2 and the third resistor r3, are connected to the positive and negative terminals of the input power supply respectively via a thermistor Rm. The other ends of the first resistor r1 and the second resistor r2, and the third resistor r3 and the fourth resistor r4, are connected to the two ends of other required loads. Where r1 = R1 + ΔR1; r2 = R2 + ΔR2; r3 = R3 + ΔR3; r4 = R4 + ΔR4; R1, R2, R3, and R4 are the standard resistance values ​​of each resistor, and ΔR1, ΔR2, ΔR3, and ΔR4 are the corresponding variable resistance values ​​for each resistor. The specific values ​​of R1, R2, R3, R4, ΔR1, ΔR2, ΔR3, and ΔR4 shall be determined based on actual measurements. The output voltage of the full bridge is Uo = (ΔR / R)Ui; Uo is... Figure 6 The point pressure values ​​at both ends of V are shown in the diagram. Ui is as follows. Figure 6 The input voltage value at both ends of e is shown in the figure.

[0046] By combining the full-bridge circuit with the thermistor Rm, the resistance change ΔR of the strain gauge can be converted into a voltage signal for subsequent measurement and processing, greatly facilitating the measurement and processing of voltage signals by the microcontroller 31.

[0047] The main controller 3 also includes a calibration module 33, a fault alarm module 34, a comparison module 35, and a pressure signal processing module 36. The microcontroller 31 is connected to the solenoid valve 2, calibration module 33, fault alarm module 34, comparison module 35, and pressure signal processing module 36, respectively. Under the action of the microcontroller 31, it controls each module, thereby achieving precise control of water level detection and water injection. The end of the pressure signal processing module 36 furthest from the microcontroller 31 is connected to the acquisition module 32; it amplifies and filters the pressure signal to remove noise interference.

[0048] Controlled by the microcontroller 31, the solenoid valve 2 can precisely open and close the water inlet pipe 40 based on water level monitoring results, thus achieving precise control over the water filling of the water tank 4. Furthermore, the coordinated design of the modules within the main controller 3 effectively enhances its rapid operation, reducing the delay in the microcontroller 31's control of the solenoid valve 2. This improves the accuracy and safety of the device's water level control.

[0049] The device also includes a cavity temperature sensor, which is located outside the cavity of the microwave-steam-grill combo oven and is used to measure the temperature inside the cavity. The cavity temperature sensor is connected to the microcontroller 31 to facilitate the transmission of the cavity temperature to the microcontroller 31.

[0050] A water injection control method for a water level monitoring device, the method being applied to the aforementioned water level monitoring device, the method comprising the following steps:

[0051] Step 1, Calibration: Calibrate both pressure sensor 1 and temperature sensor to ensure the accuracy of measurement data.

[0052] Step 2, Initialization: Initialize the parameters required for the water level calculation algorithm and the water injection control algorithm;

[0053] Step 3: Real-time detection and calculation of water level height h.

[0054] Step 4, Water Injection Control: The calculated water level height h is compared with the set lower limit hmin and upper limit hmax respectively. Based on the comparison results, the microcontroller 31 controls the water injection of the water tank 4 through the solenoid valve 2.

[0055] By implementing the aforementioned method, the complexity of control can be simplified, and the cost of control can be reduced. Furthermore, the accuracy of water level control within water tank 4 can be improved.

[0056] Step one includes:

[0057] Step S11: Calibration: Zero-point calibration of pressure sensor 1: After stabilizing pressure sensor 1 for 5 minutes under standard atmospheric pressure, record the measured air pressure value P output by pressure sensor 1. 测量 Calculate the zero-point offset ΔP0 = P 实际 -P 测量 Then the compensation value P 补偿 =P 测量 +△P0.

[0058] Step S12: Perform multi-point calibration of the cavity temperature sensor: Take 7 temperature points within the range of 20°C-80°C, and perform linear fitting of T. 实际 = aT 测量 +b. a is the temperature fitting coefficient. b is the temperature fitting deviation value. In this embodiment, the built-in temperature sensor of pressure sensor 1 can be calibrated using a multi-point calibration method.

[0059] By calibrating the pressure sensor 1 and the temperature sensor in different ways, the inherent errors of the sensors can be eliminated, and the measurement accuracy of each sensor can be improved.

[0060] In step two, the required parameters for the water level calculation algorithm and the water injection control algorithm include gravitational acceleration g, the standard density value of water ρ0, the water temperature influence coefficient β, the ambient temperature compensation coefficient γ, the lower limit of water level hmin, and the upper limit of water level hmax. Specifically, the initial value of gravitational acceleration g is 9.81 m / s²; the initial value of the standard density value of water ρ0 is 1000 kg / m³; the initial value of the water temperature influence coefficient β is 0.00021 / ℃; the initial value of the ambient temperature compensation coefficient γ is 0.0005 / ℃; the initial value of the lower limit of water level hmin is 30 mm; and the initial value of the upper limit of water level hmax is 150 mm.

[0061] The initial settings help configure the constants and thresholds required for the core algorithm to run, which lays the foundation for subsequent calculations and also helps improve the speed of calculations.

[0062] Step three includes:

[0063] Step S31: The microcontroller 31 periodically reads the pressure data P of the water at the bottom of the water tank 4 in the pressure sensor 1, the temperature data Tw detected by the built-in temperature sensor, and the cavity temperature Ta measured by the cavity temperature sensor in the microwave-steam-grill combo oven through the acquisition module 32.

[0064] Step S32: The pressure signal is amplified and filtered by the pressure signal processing module 36; the ADC value is converted into a pressure value.

[0065] Step S33: Perform temperature compensation on the current water temperature based on the measured temperature data, obtain the density ρ(T) of the water in tank 4 at the current temperature through the temperature compensation formula, and calculate the water level height h using the water level calculation formula;

[0066] Step S34: Initially determine whether h < 0 mm or h > water tank 4 volume V1 mm. If yes, trigger pressure sensor 1 fault alarm, and microcontroller 31 transmits fault prompt information to the user through fault alarm module 34; otherwise, proceed to step four. In this embodiment, V1 is set to 200, but the specific value can be set according to requirements.

[0067] In step S31, pressure sensor 1 is a resistance strain gauge type with a range of 0-100 kPa and an output signal of 0V-5V. A temperature sensor for measuring water temperature is integrated inside pressure sensor 1. A cavity temperature sensor for measuring the temperature inside the microwave-steam-grill combo is located outside the cavity. When the user triggers the relevant functions of water tank 4, the liquid bottom pressure P, water temperature Tw, and cavity temperature Ta are simultaneously sampled, triggering the sampling signal and initiating ADC conversion.

[0068] In step S32, the pressure signal processing module 36 converts the acquired pressure signal into a pressure value by amplifying the signal, offset correction, and filtering.

[0069] In step S33, the temperature compensation formula is: ρ(T)=ρ0×[1-β(Tw-T0)-γ(Tw-T0)], where T0 is the standard temperature value, ρ0 is the standard density value of water, and Tw is the water temperature value, which is measured by the temperature sensor built into pressure sensor 1. β is the water temperature influence coefficient; γ is the ambient temperature compensation coefficient. The water level calculation formula is: h=[P / (ρ(T)*g)]×1000mm.

[0070] The water level is calculated based on the pressure value sampled by pressure sensor 1 using temperature compensation and water level calculation formulas. Microcontroller 31 calculates the water level based on the pressure value measured by pressure sensor 1, using the liquid pressure formula: P=ρgh; where P is the pressure of the water at the bottom of tank 4, ρ is the liquid density, g is the acceleration due to gravity, and h is the liquid level. Simultaneously, the influence of temperature on water density is considered; water density typically decreases as temperature rises; changes in ambient temperature also indirectly affect water density through heat transfer. Temperature compensation technology is used to correct the water density based on the temperature data measured by the temperature sensor, effectively improving the accuracy of water level calculation and thus ensuring the precision of the device's water level measurement.

[0071] Step four includes:

[0072] Step S41: Water injection control: Compare the calculated water level height h with the set lower limit hmin and upper limit hmax respectively;

[0073] Step S42: Determine whether h < hmin - Δh, where Δh is the water level deviation value; if yes, it is determined that water needs to be injected, and the microcontroller 31 controls the solenoid valve 2 on the water inlet pipe 40 to enter the water injection control process and execute step S43; if no, execute step S44.

[0074] Step S43: The microcontroller 31 controls the solenoid valve 2 on the water inlet pipe 40 to open, and the water injection process begins. Step S45 is then executed.

[0075] Step S44: Determine if h < hmax + Δh. If yes, hmin - Δh ≤ h < hmax + Δh, maintain the current state, that is, if it is in the water injection state, continue to maintain the water injection state; if it is in the water injection stop state, keep the solenoid valve 2 closed, no other action is required; and execute step S46; if no, h ≥ hmax, after water injection the water level reaches above hmax, the microcontroller 31 controls the solenoid valve 2 on the water inlet pipe 40 to close, and stop water injection.

[0076] Step S45: Store the calculated water level height h, return to step three, and continue to monitor the water level changes in water tank 4.

[0077] When the conditions for water injection or water injection are met, a 5-second confirmation is required to prevent misjudgment of the water level due to instantaneous fluctuations.

[0078] The microcontroller 31 monitors the water level in the water tank 4 in real time according to the set upper and lower limits. When the water level is below the lower limit, the microcontroller 31 sends a command to open the solenoid valve 2 to start water injection; when the water level reaches the upper limit, the microcontroller 31 sends a command to close the solenoid valve 2 to stop water injection; when the water level is between the upper and lower limits, the current state is maintained. Combined with the setting of the water injection condition confirmation time, the accuracy and efficiency of water injection control can be greatly improved, preventing misjudgment and also helping to improve the anti-interference capability of the device.

[0079] A microwave-steam-oven combo appliance includes the aforementioned water level monitoring device, which is installed inside the appliance. The appliance also includes a water outlet pipe 41. One end of both the water inlet pipe 40 and the water outlet pipe 41 is connected to a water tank 4, and the other end of the water inlet pipe 40 is connected to a solenoid valve 2. The other end of the water outlet pipe 41 is connected to a drainage device.

[0080] By installing a pressure sensor 1 at the bottom of the water tank 4 of the integrated machine, and under the control of the main controller 3, the information from the pressure sensor 1 is collected in real time, and the solenoid valve 2 is precisely controlled. This optimizes the device, reduces the space occupied by the device within the embedded microwave-steam-grill integrated machine, facilitates the embedded setup of the integrated microwave-steam-grill integrated machine, extends its service life, and reduces the maintenance cost of the integrated microwave-steam-grill integrated machine.

[0081] In this invention, any microwave-steam-grill combination appliance can include the water level monitoring device structure described in this embodiment. Based on the relevant structure and assembly relationship of the pressure sensor 1 and the thermistor Rm provided in this embodiment, the microwave-steam-grill combination appliance also includes conventional components such as water tank 4, water inlet pipe 40, and water outlet pipe 41. Since these are all prior art, they will not be described in detail here.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A water level monitoring device, characterized in that, It includes a pressure sensor (1), a solenoid valve (2), and a main controller (3); the pressure sensor (1) is located at the bottom of the water tank (4) of the microwave-steam-grill combo, and the solenoid valve (2) is located at the end of the water inlet pipe (40) of the microwave-steam-grill combo away from the water tank (4); the pressure sensor (1) and the solenoid valve (2) are both electrically connected to the main controller (3) of the microwave-steam-grill combo; the main controller (3) includes a microcontroller (31) and a data acquisition module (32); the pressure sensor (1) and the data acquisition module (32) are connected in communication, and the solenoid valve (2) is connected to the microcontroller (31).

2. The water level monitoring device according to claim 1, characterized in that, The pressure sensor (1) is a resistance strain gauge pressure sensor.

3. The water level monitoring device according to claim 1, characterized in that, The pressure sensor (1) includes a full-bridge circuit and a temperature sensor; both the full-bridge circuit and the temperature sensor are located inside the pressure sensor (1); one end of the full-bridge circuit is connected to the positive and negative terminals of the input power supply through the temperature sensor; the other end of the full-bridge circuit is connected to the two ends of other required loads.

4. The water level monitoring device according to claim 3, characterized in that, The temperature sensor can be a thermistor Rm.

5. A water level monitoring device according to claim 1, characterized in that, The main controller (3) also includes a calibration module (33), a fault alarm module (34), a comparison module (35), and a pressure signal processing module (36); the microcontroller (31) is connected to the solenoid valve (2), the calibration module (33), the fault alarm module (34), the comparison module (35), and the pressure signal processing module (36) respectively; the end of the pressure signal processing module (36) away from the microcontroller (31) is connected to the acquisition module (32).

6. A water injection control method for a water level monitoring device, the method being applied to a water level monitoring device according to any one of claims 1-5, the method comprising the following steps: Step 1, Calibration: Calibrate the pressure sensor (1) and the temperature sensor respectively; Step 2, Initialization: Initialize the parameters required for the water level calculation algorithm and the water injection control algorithm; Step 3: Real-time detection and calculation of water level height h; Step 4, Water Injection Control: The calculated water level height h is compared with the set lower limit hmin and upper limit hmax respectively. Based on the comparison results, the microcontroller (31) controls the water injection of the water tank (4) through the solenoid valve (2).

7. The water injection control method for a water level monitoring device according to claim 6, characterized in that, In step two, the required parameters in the water level calculation algorithm and the water injection control algorithm include gravitational acceleration g, standard density value of water ρ0, water temperature influence coefficient β, ambient temperature compensation coefficient γ, lower limit of water level hmin, and upper limit of water level hmax.

8. The water injection control method for a water level monitoring device according to claim 7, characterized in that, Step three includes: Step S31: The microcontroller (31) reads the pressure data P of the water at the bottom of the water tank (4) in the pressure sensor (1) and the temperature data Tw detected by the built-in temperature sensor and the cavity temperature Ta measured by the cavity temperature sensor in the microwave steam oven through the acquisition module (32) at regular intervals. Step S32: The pressure signal is amplified and filtered by the pressure signal processing module (36); Step S33: Obtain the density ρ(T) of the water in the tank (4) at the current temperature using the temperature compensation formula, and calculate the water level height h using the water level calculation formula; Step S34: Initially determine whether h < 0 mm or h > water tank (4) volume V1 mm. If yes, trigger pressure sensor (1) fault alarm, and microcontroller (31) transmits fault prompt information to user through fault alarm module (34); otherwise, execute step four.

9. The water injection control method for a water level monitoring device according to claim 8, characterized in that, The temperature compensation formula is: ρ(T)=ρ0×[1-β(Tw-T0)-γ(Tw-T0)], where T0 is the standard temperature value, ρ0 is the standard density value of water, Tw is the water temperature value, β is the water temperature influence coefficient, and γ is the ambient temperature compensation coefficient.

10. A microwave-steam-oven combo appliance, comprising a water level monitoring device according to any one of claims 1-5, wherein the device is installed inside the microwave-steam-oven combo appliance.

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