Liquid level detection system for inhibiting electrolysis of probe and control method
By using the self-learning and judgment function of three probes and the MCU in the liquid level detection system, combining the voltage divider circuit and filter capacitor, the probe current is reduced, and the problem of electrolytic corrosion of electronic liquid level probes is solved, achieving high accuracy and low cost liquid level detection.
Patent Information
- Application Number
- CN202411478521.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-22
- Publication Date
- 2024-12-31
AI Technical Summary
In liquid level detection, existing electronic level probes are prone to reduced detection accuracy and system failure due to electrolytic corrosion, and the existing mitigation solutions are costly and complex, making them difficult to popularize.
The liquid level detection system with three different probes is adopted to realize self-learning and judgment through the MCU of the microcontroller, reduce the liquid level detection time and reduce the probe current, and control the current using components such as voltage divider circuits and filter capacitors to reduce electrolytic corrosion.
Effectively reduce the degree of probe electrolysis, improve the accuracy of liquid level detection and system reliability, reduce costs, and is suitable for heating systems of hot tanks.
Smart Images
Figure CN119223393A_ABST
Abstract
Description
[Technical field] The present invention relates to the technical field of liquid level detection in drinking water supply equipment, and in particular to a liquid level detection system capable of suppressing the electrolysis degree of a probe and a suppression control method adopted by the system. [Background technology] In heating water tanks, heating water dispensers or hot water supply equipment, it is a very basic and conventional technical means to detect the water level and control the water replenishment according to the water temperature. At present, there are basically only four types of liquid level detection methods used in the industry: the first is the float type, but the disadvantages of the float type are that the mechanical structure is inconvenient to assemble and the contacts are easily misplaced, so this method is rarely used; the second is the capacitance detection type, which has the defects of being easily affected by external interference and low precision; the third is ultrasonic liquid level detection, which is more accurate and less susceptible to interference, but its cost is high, basically several times or dozens of times that of other methods, so it is not suitable for large-scale popularization and promotion; the fourth is the electronic probe, which has the advantages of relatively simple structure, easy installation, no mechanical structure and high temperature resistance, and the application solution of the electronic probe is relatively mature, and it has a wide range of use cases in hot tank heating systems in the industry.
[0001] However, the biggest disadvantage of this electronic probe is determined by its principle. The principle of the electronic probe is that the pin of the microcontroller is connected to the probe through an extension line, and the common terminal is connected to the negative terminal of the microcontroller. When the probe detects water, current flows through the water tank, making the potential of the microcontroller pin end lower, thereby achieving the purpose of liquid level detection. Therefore, all the probes for electronic liquid level detection are made of metal, which can be conductive through water flow and form the conditions for electrolysis. Such a circuit structure principle determines that even if stainless steel is used for detection, there will be a weak current passing through it, such as a weak current of several milliamperes. Such a weak current will also affect the probe, and electrolytic corrosion will soon occur. Electrolytic corrosion brings about scaling of the electrolyte, which will become thicker and thicker after long-term use, causing the resistance between water and the probe to increase, thereby affecting the accuracy of the detection results, causing detection deviations and errors. Moreover, the problems caused by electrolysis are not only the impact on the test results, but may even cause the probe to be severely corroded by electrolysis, resulting in the electrolysis products containing heavy metal pollutants. Finally, the accumulation of electrolysis effects will cause the probe to become shorter and shorter, resulting in the failure of liquid level detection, and then causing the entire system to malfunction.
[0002] There are also related technologies in the industry to alleviate or reduce the degree of probe electrolysis, such as the public patent CN202321632562.9, which discloses an electronic probe anti-electrolysis circuit, which discloses that the circuit includes a current conversion circuit, a signal isolation circuit, a signal enhancement circuit, a signal processing circuit and a liquid level probe circuit. This circuit uses a low-voltage AC signal to send a signal to the probe, and the signal is completely isolated to alleviate the degree of electrolysis. The solution is relatively complicated and requires complete isolation of the signal, which is costly and has limited application. It is necessary to further improve and optimize the technology and adopt a simpler and more economical way to improve the degree of electrolysis of the probe. [Summary of the invention] In view of the problems existing in the prior art, the present invention provides a liquid level detection system for suppressing probe electrolysis, and a control method suitable for the system to suppress electrolysis. The MCU in the detection system can realize self-learning and judgment. Under the premise of satisfying the normal operation of hot tank heating system products, the liquid level detection time is reduced and the current flowing through the probe is reduced, thereby reducing the degree of probe electrolysis.
[0003] The present invention relates to a liquid level detection system for suppressing probe electrolysis, characterized in that the detection system comprises: Probe: It contains three different probes, including high liquid level, low liquid level and common end probes; Connecting harness: the connecting harness connects the probe and the liquid level detection unit; Control unit: includes single-chip microcomputer MCU, in which MCU-AD detection 1 and MCU-AD detection 2 are input to MCU as input signals. The internal program of MCU uses the input signal as the basis for logic judgment, and outputs MCU-liquid level detection control as the output control signal. The input signal, output signal and program run; And liquid level detection unit: MCU-liquid level detection control is the MCU general input and output port, MCU-AD detection 1 and MCU-AD detection 2 are MCU-AD detection input and push-pull output ports; the third interface CN3 at the probe is connected to the first interface CN1 through a connecting harness, CN1 is a high and low liquid level probe connection terminal, wherein CN1 branches into three pins, pin 1 is composed of a voltage divider resistor R5 and an equivalent resistor R9 to form a voltage divider circuit for detecting a high liquid level; pin 2 is composed of a voltage divider resistor R7 and an equivalent resistor R10 to form a voltage divider circuit for detecting a low liquid level, and the voltage divider circuit composed of a voltage divider resistor R7 and an equivalent resistor R10 is powered by a transistor Q1 to control +3.3V, and the pull-up resistor R1, the voltage divider current limiting resistor R2, the transistor Q1 and the filter capacitor C1 form a switch circuit for controlling the power supply VCC; The switch circuit of the control power supply VCC is connected in series to the high and low liquid level detection circuit; the filter capacitors C1, C2, and C3 play the role of filtering out clutter interference. When detecting the liquid level, VCC-R5-C2-GND and VCC-R7-C3-GND form an RC charging circuit, and the current limiting resistors R6 and R8 limit the current of the flow line; pin 3 is connected to GND, and +3.3V and GND are the positive and negative terminals of the detection system respectively.
[0004] The detection system further comprises a water taking action detection unit, the driving action detection unit comprises a driving action signal receiver, and the water taking action signal comprises but is not limited to a serial port command signal, a Hall sensor signal, and a key level signal.
[0005] The pull-up resistor R1 is connected to the base of the transistor Q1, so that the base of the transistor Q1 is pulled up to a high level state when there is no control signal to prevent external interference from generating uncertain levels. When there is a control signal, the control signal is controlled to a low level state, so that the back-stage transistor is in a saturated conduction state. It is usually 10K The voltage-dividing and current-limiting resistor R2, +3.3V-transistor Q1 emitter-transistor Q1 base-resistor R2-MCU liquid level detection control-GND form a closed loop. The current in the loop is limited by the maximum input current of the MCU pin and must satisfy the resistance value of R2 ≥ (+3.3V-Vbe) / Imax, where (+3.3V-Vbe) is the voltage difference between the base and emitter of the transistor Q1 and Imax is the maximum input current of the MCU pin.
[0006] The resistance value of R2 is ≥ (the voltage difference between the base and emitter of transistor Q1) / Imax (the maximum input current of the MCU pin), where the voltage difference between the base and emitter of transistor Q1 is generally 0.7V, and the maximum input current of the MCU pin is usually 20 mA.
[0007] The transistor Q1 is a PNP transistor, which works as a switch and operates in a saturation state. S8550 is usually selected.
[0008] The C1 is a filter capacitor, which filters out the clutter interference in the +3.3V power supply, and is usually 100 nanofarads.
[0009] When the high liquid level probe contacts the measured liquid, the voltage divider resistor R5 and the high liquid level probe equivalent resistor R9 form a closed loop through +3.3V-R5-R9-GND.
[0010] When the low liquid level probe contacts the measured liquid, the voltage divider resistor R7 and the low liquid level probe equivalent resistor R10 form a closed loop through +3.3V-R7-R10-GND.
[0011] The C2 is a filter capacitor. When the transistor Q1 is turned on, a charging loop is formed by +3.3V-R5-C2-GND.
[0012] The C3 is a filter capacitor. When the transistor Q1 is turned on, a charging loop is formed by +3.3V-R7-C3-GND.
[0013] The R6 and R8 are current limiting resistors, which prevent the interference signal of the resistor stage from entering the MCU. The R6 and R8 are much smaller than the equivalent R9 and R10. Generally speaking, R6 and R8 are 1K ohms, while R9 and R10 are usually 200K ohms.
[0014] Furthermore, the resistance value of the voltage-dividing resistor R5 is close to the equivalent resistor R9, and the resistance value of the voltage-dividing resistor R7 is close to R10.
[0015] The RC is charged and refluxed, and the charging time is shorter than the time for detecting the liquid level.
[0016] A control method for a liquid level detection system, characterized in that the control method includes the following steps: S1: MCU-liquid level detection control output pulse signal of single-chip microcomputer MCU, 20ms low level 200ms high level mode to control the power supply of liquid level detection end; S2: When the output is low level, transistor Q1 is turned on, and the power supply is turned on after the filter capacitor C1 of CN1 is charged. The power supply voltage is equal to +3.3V; at this time, there is a voltage drop between MCU-AD detection 1 and MCU-AD detection 2, and the voltage drop value depends on the resistance value between the high liquid level probe and the common probe / the low liquid level probe and the common probe. If there is no water between MCU-AD detection 1 and MCU-AD detection 2 and the common probe, the voltage drop value at this time is 3.3V. If there is water, the voltage at this time is <3.3V, which depends on the conductivity of water. The liquid level is determined by this voltage drop value; When the output is low, transistor Q1 is turned off, and pins 1 and 2 of CN1 are connected to the ground after the discharge of the filter capacitor C1 is completed, and the voltage is equal to 0V; at this time, there is no need to read the voltage drop of MCU-AD detection 1 and MCU-AD detection 2, and there is no electrolysis between the probes; S3: At the initial power-on, liquid level detection is activated. The MCU-AD detection 1 and MCU-AD detection 2 pins are configured as analog inputs and used as ADC detection functions to detect voltage values. When the liquid levels do not reach the high level state at the same time, water replenishment is started. After the water replenishment is completed, both the high and low liquid levels have been reached. At this time, liquid level detection is turned off. The MCU-AD detection 1 and MCU-AD detection 2 pins are configured as push-to-complete outputs and output a low level. At this time, the C1, C3, and C7 capacitors can be quickly discharged to ensure that the probe will not drop in voltage and electrolysis will occur; when there is a water extraction action sensing, the liquid level detection function is reactivated; after the water replenishment is completed, the liquid level detection function is turned off.
[0017] The liquid level detection system for inhibiting electrolysis involved in the present invention has intelligent control: the system makes liquid level detection control according to the water intake action and the high and low liquid level states, thereby ensuring that the system realizes the liquid level detection function while reducing the time the system is in the detection state, and finally achieving the effect of reducing the electrolysis degree of the probe. Accurate detection: by selecting appropriate resistance and capacitance values, controlling the RC charging and discharging time, and detecting the internal state in real time through the system, adjusting and controlling the liquid level detection switch, real-time and accurate detection can be achieved.
Brief Description of the Drawings
[0018] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.
[0019] Please refer to the attached Figure 1, which shows a liquid level detection system for inhibiting probe electrolysis according to the present invention, characterized in that the detection system comprises: Probe: It contains three different probes, including high liquid level, low liquid level and common end probes; Wherein R9 is the equivalent resistance between the high liquid level probe and the common end probe. When the high liquid level probe leaves the measured liquid, the equivalent resistance R9 tends to infinity. When the high liquid level probe contacts the measured liquid, the equivalent resistance R9 can be obtained based on actual measurement and is usually taken as 200K ohms.
[0020] Wherein R10 is the equivalent resistance between the low liquid level probe and the common end probe. When the low liquid level probe leaves the measured liquid, the equivalent resistance R10 tends to infinity. When the low liquid level probe contacts the measured liquid, the equivalent resistance R10 can be obtained based on actual measurement and is usually taken as 200K ohms.
[0021] Connection harness: The connection harness connects the probe and the liquid level detection unit; the connection harness is a physical connection wire, including three wires connected to the high liquid level probe, the low liquid level probe, and the common end probe, which plays the role of physical connection and transmission of electrical signals.
[0022] Control unit: includes single-chip microcomputer MCU, in which MCU-AD detection 1 and MCU-AD detection 2 are input to MCU as input signals. The internal program of MCU uses the input signal as the basis for logical judgment, and outputs MCU-liquid level detection control as the output control signal. The input signal, output signal and program run.
[0023] The control unit makes logical judgments based on the input signals of MCU-AD detection 1, MCU-AD detection 2, and water intake action detection, and outputs the output signals of MCU-liquid level detection control, MCU-AD detection 1, and MCU-AD detection 2 in combination with the program algorithm, thereby realizing real-time monitoring and real-time control, thereby achieving the purpose of reducing the power-on time of the liquid level probe.
[0024] MCU-liquid level detection control is configured as the level output port of MCU. Outputting low level allows detection current to flow through the high and low liquid level probes, providing the necessary conditions for liquid level detection. If low level is not output, no detection current flows through the high and low liquid level probes, and liquid level detection is not performed.
[0025] MCU-AD detection 1 is configured as the AD detection input port and low-level output port of the MCU as needed. When configured as the AD detection input port of the MCU, by reading the voltage value of the port, it can be determined whether the high liquid level probe is in contact with the liquid to be detected, and then the high liquid level state can be calculated according to the algorithm. When configured as the low-level output port of the MCU, the voltage of the high liquid level probe can be quickly lowered.
[0026] MCU-AD detection 2 is configured as the AD detection input port and low-level output port of the MCU as needed. When configured as the AD detection input port of the MCU, by reading the voltage value of the port, it can be determined whether the high liquid level probe is in contact with the liquid to be detected, and then the high liquid level state can be calculated according to the algorithm. When configured as the low-level output port of the MCU, the voltage of the low liquid level probe can be quickly lowered.
[0027] And liquid level detection unit: MCU-liquid level detection control is the MCU general input and output port, MCU-AD detection 1 and MCU-AD detection 2 are MCU-AD detection input and push-pull output ports; the third interface CN3 at the probe is connected to the first interface CN1 through a connecting harness, CN1 is a high and low liquid level probe connection terminal, wherein CN1 branches into three pins, pin 1 is composed of a voltage divider resistor R5 and an equivalent resistor R9 to form a voltage divider circuit for detecting a high liquid level; pin 2 is composed of a voltage divider resistor R7 and an equivalent resistor R10 to form a voltage divider circuit for detecting a low liquid level, and the voltage divider circuit composed of a voltage divider resistor R7 and an equivalent resistor R10 is powered by a transistor Q1 to control +3.3V, and the pull-up resistor R1, the voltage divider current limiting resistor R2, the transistor Q1 and the filter capacitor C1 form a switch circuit for controlling the power supply VCC; The switch circuit of the control power supply VCC is connected in series to the high and low liquid level detection circuit; the filter capacitors C1, C2, and C3 play the role of filtering out clutter interference. When detecting the liquid level, VCC-R5-C2-GND and VCC-R7-C3-GND form an RC charging circuit, and the current limiting resistors R6 and R8 limit the current of the flow line; pin 3 is connected to GND, and +3.3V and GND are the positive and negative terminals of the detection system respectively.
[0028] The detection system further comprises a water taking action detection unit, the driving action detection unit comprises a driving action signal receiver, and the water taking action signal comprises but is not limited to a serial port command signal, a Hall sensor signal, and a key level signal.
[0029] The pull-up resistor R1 is connected to the base of the transistor Q1, so that the base of the transistor Q1 is pulled up to a high level state when there is no control signal to prevent external interference from generating uncertain levels. When there is a control signal, the control signal is controlled to a low level state, so that the back-stage transistor is in a saturated conduction state. It is usually 10K The voltage-dividing current-limiting resistor R2, +3.3V-transistor Q1 emitter-transistor Q1 base-resistor R2-MCU liquid level detection control-GND form a closed loop. The current in the loop is limited by the maximum input current of the MCU pin and must satisfy the resistance value of R2 ≥ (+3.3V-Vbe) / Imax, where (+3.3V-Vbe) is the voltage difference between the base and emitter of the transistor Q1 and Imax is the maximum input current of the MCU pin. The resistance value of R2 is ≥ (the voltage difference between the base and emitter of transistor Q1) / Imax (the maximum input current of the MCU pin), where the voltage difference between the base and emitter of transistor Q1 is generally 0.7V, and the maximum input current of the MCU pin is generally 20 mA. The resistance value of R2 is generally 1K ohms.
[0030] The transistor Q1 is a PNP transistor, which works as a switch and is in a saturated state. The selection mainly considers the current flowing through, the base control voltage, the system power supply voltage, and the cost of the device itself. S8550 is usually selected.
[0031] The C1 is a filter capacitor, which filters out the clutter interference in the +3.3V power supply, and is usually 100 nanofarads.
[0032] When the high liquid level probe contacts the measured liquid, the voltage divider resistor R5 and the high liquid level probe equivalent resistor R9 form a closed loop through +3.3V-R5-R9-GND.
[0033] When R5=R9=200K ohms, Vad1 (the voltage value detected by MCU-AD detection 1) is half of +3.3V. When R5 decreases relative to R9, Vad1 will decrease accordingly. When R5 increases relative to R9, the detection current flowing through the high liquid level probe will decrease accordingly. In summary, R5 takes a value of 200K ohms, and the voltage value sampled by MCU-AD detection 1 is optimal.
[0034] When the low liquid level probe contacts the measured liquid, the voltage divider resistor R7 and the low liquid level probe equivalent resistor R10 form a closed loop through +3.3V-R7-R10-GND.
[0035] When R7=R10=200K ohms, Vad2 (the voltage value detected by MCU-AD detection 2) is half of +3.3V. When R7 decreases relative to R10, Vad1 will decrease accordingly. When R7 increases relative to R10, the detection current flowing through the low liquid level probe will decrease accordingly. In summary, R7 takes a value of 200K ohms, and the voltage value sampled by MCU-AD detection 2 is optimal.
[0036] The C2 is a filter capacitor. When the transistor Q1 is turned on, +3.3V-R5-C2-GND forms a charging circuit. The charging time τ=R5 (the value of the resistor R5) C2 (the capacitance of the capacitor C2). This system uses a program control method of 20 milliseconds low level and 200 milliseconds high level, so τ needs to be less than 20 milliseconds. If C2 is too small, the filtering effect will be poor. According to the commonly used capacitance of the chip capacitor, the C2 value of this system is 10 nanofarads.
[0037] The C3 is a filter capacitor. When the transistor Q1 is turned on, a charging loop is formed by +3.3V-R7-C3-GND.
[0038] Charging time τ=R7 (the value of resistor R7) C3 (the capacitance of capacitor C3). This system adopts a program control method of 20 milliseconds low level and 200 milliseconds high level, so τ needs to be less than 20 milliseconds. If C3 is too small, the filtering effect will be poor. According to the commonly used capacitance of chip capacitors, the value of C3 in this system is 10 nanofarads.
[0039] The R6 and R8 are current limiting resistors, which prevent the interference signal of the resistor stage from entering the MCU. The R6 and R8 are much smaller than the equivalent R9 and R10. Generally speaking, R6 and R8 are 1K ohms, while R9 and R10 are usually 200K ohms.
[0040] When the high liquid level probe contacts the detected liquid, the filter capacitor C2 is fully charged, and the transistor Q1 is turned off when the detection is completed, in order to reduce the power-on time of the high liquid level probe, the microcontroller MCU needs to control the MCU-AD detection port 1 to a low level. At this time, C2-R6-GND forms a discharge loop. The smaller the R6 value, the faster the discharge. Combined with the need to block interference signals (the larger the resistance value, the better the resistance interference effect), R6 is usually 1K.
[0041] When the high liquid level probe contacts the detected liquid, the filter capacitor C3 is fully charged, and the transistor Q1 is turned off at the end of the detection, in order to reduce the power-on time of the low liquid level probe, the single-chip microcomputer MCU needs to control the MCU-AD detection port 2 to be low. At this time, C3-R8-GND forms a discharge loop. The smaller the R8 value, the faster the discharge. Combined with the need to block interference signals (the larger the resistance value, the better the resistance interference effect), R8 is usually 1K.
[0042] Furthermore, the resistance value of the voltage-dividing resistor R5 is close to the equivalent resistor R9, and the resistance value of the voltage-dividing resistor R7 is close to R10.
[0043] The RC is charged and refluxed, and the charging time is shorter than the time for detecting the liquid level.
[0044] A control method for a liquid level detection system, characterized in that the control method includes the following steps: S1: MCU-liquid level detection control output pulse signal of single-chip microcomputer MCU, 20ms low level 200ms high level mode to control the power supply of liquid level detection end; S2: When the output is low level, transistor Q1 is turned on, and pin 1 and pin 2 of CN1 R7-200K are connected to the power supply after the filter capacitor C1 is charged, and the power supply voltage is equal to +3.3V; at this time, there is a voltage drop between MCU-AD detection 1 and MCU-AD detection 2, and the voltage drop value depends on the resistance value between the high liquid level probe and the common probe / the low liquid level probe and the common probe. If there is no water between MCU-AD detection 1 and MCU-AD detection 2 and the common probe, the voltage drop value at this time is 3.3V. If there is water, the voltage at this time is <3.3V, which depends on the conductivity of water. The liquid level is determined by this voltage drop value; When the output is low, transistor Q1 is turned off, and pins 1 and 2 of CN1 are connected to the ground after the discharge of the filter capacitor C1 is completed, and the voltage is equal to 0V; at this time, there is no need to read the voltage drop of MCU-AD detection 1 and MCU-AD detection 2, and there is no electrolysis between the probes; S3: At the initial power-on, liquid level detection is activated. The MCU-AD detection 1 and MCU-AD detection 2 pins are configured as analog inputs and used as ADC detection functions to detect voltage values. When the liquid levels do not reach the high level state at the same time, water replenishment is started. After the water replenishment is completed, both the high and low liquid levels have been reached. At this time, liquid level detection is turned off. The MCU-AD detection 1 and MCU-AD detection 2 pins are configured as push-to-complete outputs and output a low level. At this time, the C1, C3, and C7 capacitors can be quickly discharged to ensure that the probe will not drop in voltage and electrolysis will occur; when there is a water extraction action sensing, the liquid level detection function is reactivated; after the water replenishment is completed, the liquid level detection function is turned off.
[0045] The liquid level detection system for inhibiting electrolysis involved in the present invention has intelligent control: the system makes liquid level detection control according to the water intake action and the high and low liquid level states, thereby ensuring that the system realizes the liquid level detection function while reducing the time the system is in the detection state, and finally achieving the effect of reducing the electrolysis degree of the probe. Accurate detection: by selecting appropriate resistance and capacitance values, controlling the RC charging and discharging time, and detecting the internal state in real time through the system, adjusting and controlling the liquid level detection switch, real-time and accurate detection can be achieved.
[0046] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention is disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent changes and modifications made to the above embodiments according to the technology of the present invention are within the scope of the technical solution of the present invention without departing from the content of the technical solution of the present invention.
Claims
1. A liquid level detection system for suppressing probe electrolysis, characterized in that: The detection system includes: Probe: It includes three different probes, which are divided into three probes of high liquid level, low liquid level and common end; Connection harness: The connection harness connects the probe and the liquid level detection unit; Control unit: includes single-chip microcomputer MCU, in which MCU-AD detection 1 and MCU-AD detection 2 are input to MCU as input signals. The internal program of MCU uses the input signal as the basis for logic judgment, and outputs MCU-liquid level detection control as the output control signal. The input signal, output signal and program run; And liquid level detection unit: MCU-liquid level detection control is the MCU general input and output port, MCU-AD detection 1 and MCU-AD detection 2 are MCU-AD detection input and push-pull output ports; the third interface CN3 at the probe is connected to the first interface CN1 through a connecting harness, CN1 is a high and low liquid level probe connection terminal, wherein CN1 branches into three pins, pin 1 is composed of a voltage divider resistor R5 and an equivalent resistor R9 to form a voltage divider circuit for detecting a high liquid level; pin 2 is composed of a voltage divider resistor R7 and an equivalent resistor R10 to form a voltage divider circuit for detecting a low liquid level, and the +3.3V voltage divider circuit is controlled by the transistor Q1 to respectively The voltage divider circuit composed of resistor R7 and equivalent resistor R10 is used for power supply, and the pull-up resistor R1, the voltage divider current limiting resistor R2, the transistor Q1 and the filter capacitor C1 constitute the switch circuit of the control power supply VCC; the switch circuit of the control power supply VCC is connected in series to the high and low liquid level detection circuit; the filter capacitors C1, C2, and C3 play the role of filtering out clutter interference. When detecting the liquid level, VCC-R5-C2-GND and VCC-R7-C3-GND form an RC charging loop, and the current limiting resistors R6 and R8 limit the current of the circulation line; pin 3 is connected to GND, and +3.3V and GND are the positive and negative ends of the detection system respectively.
2. The liquid level detection system for suppressing probe electrolysis according to claim 1, characterized in that: The detection system further comprises a water taking action detection unit, the driving action detection unit comprises a driving action signal receiver, and the water taking action signal comprises but is not limited to a serial port command signal, a Hall sensor signal, and a key level signal.
3. The liquid level detection system for suppressing probe electrolysis according to claim 1, characterized in that: The pull-up resistor R1 is connected to the base of the transistor Q1, so that the base of the transistor Q1 is pulled up to a high level state when there is no control signal to prevent external interference from generating an uncertain level. When there is a control signal, the base is controlled to a low level state by the control signal, so that the rear transistor is in a saturated conduction state, usually 10K.
4. The liquid level detection system for suppressing probe electrolysis according to claim 1, characterized in that: The voltage-dividing and current-limiting resistor R2, +3.3V-transistor Q1 emitter-transistor Q1 base-resistor R2-MCU liquid level detection control-GND form a closed loop. The current in the loop is limited by the maximum input current of the MCU pin and must satisfy the resistance value of R2 ≥ (+3.3V-Vbe) / Imax, where (+3.3V-Vbe) is the voltage difference between the base and emitter of the transistor Q1, and Imax is the maximum input current of the MCU pin.
5. The liquid level detection system for suppressing probe electrolysis according to claim 1, characterized in that: The transistor Q1 is a PNP transistor, which acts as a switch and works in a saturation state.
6. The liquid level detection system for suppressing probe electrolysis according to claim 1, characterized in that: The C1 is a filter capacitor, which filters out the clutter interference in the +3.3V power supply and has a capacitance of 100 nanofarads.
7. The liquid level detection system for suppressing probe electrolysis according to claim 1, characterized in that: When the high liquid level probe contacts the measured liquid, the voltage divider resistor R5 and the high liquid level probe equivalent resistor R9 form a closed loop through +3.3V-R5-R9-GND; when the low liquid level probe contacts the measured liquid, the voltage divider resistor R7 and the low liquid level probe equivalent resistor R10 form a closed loop through +3.3V-R7-R10-GND.
8. The liquid level detection system for suppressing probe electrolysis according to claim 1, characterized in that: The C2 is a filter capacitor. When the transistor Q1 is turned on, +3.3V-R5-C2-GND forms a charging loop. The C3 is a filter capacitor. When the transistor Q1 is turned on, +3.3V-R7-C3-GND forms a charging loop.
9. The liquid level detection system for suppressing probe electrolysis according to claim 1, characterized in that: R6 and R8 are current limiting resistors, which prevent the interference signal of the resistor stage from entering the MCU. R6 and R8 are smaller than the equivalent R9 and R10; the resistance value of the voltage divider resistor R5 is close to the equivalent resistor R9, and the resistance value of the voltage divider resistor R7 is close to R10.
10. A control method for a liquid level detection system, characterized in that: The control method includes The following steps are involved: S1: MCU-liquid level detection control output pulse signal of single-chip microcomputer MCU, 20ms low level 200ms high level mode to control the power supply of liquid level detection end; S2: When the output is low level, transistor Q1 is turned on, and pin 1 and pin 2 of CN1 R7-200K are connected to the power supply after the filter capacitor C1 is charged, and the power supply voltage is equal to +3.3V; at this time, there is a voltage drop between MCU-AD detection 1 and MCU-AD detection 2, and the voltage drop value depends on the resistance value between the high liquid level probe and the common probe / the low liquid level probe and the common probe. If there is no water between MCU-AD detection 1 and MCU-AD detection 2 and the common probe, the voltage drop value at this time is 3.3V. If there is water, the voltage at this time is <3.3V, which depends on the conductivity of water. The liquid level is determined by this voltage drop value; When the output is low level, transistor Q1 is cut off, and pin 1 and pin 2 of CN1 R7-200K are connected to ground after the filter capacitor C1 is discharged, and the voltage is equal to 0V; At this time, there is no need to read the voltage drop of MCU-AD detection 1 and MCU-AD detection 2, and there is no electrolysis between the probes; S3: At the initial power-on, liquid level detection is activated. The MCU-AD detection 1 and MCU-AD detection 2 pins are configured as analog inputs and used as ADC detection functions to detect voltage values. When the liquid levels do not reach the high level state at the same time, water replenishment is started. After the water replenishment is completed, both the high and low liquid levels have been reached. At this time, liquid level detection is turned off. The MCU-AD detection 1 and MCU-AD detection 2 pins are configured as push-to-complete outputs and output a low level. At this time, the C1, C3, and C7 capacitors can be quickly discharged to ensure that the probe will not drop in voltage and electrolysis will occur; when there is a water extraction action sensing, the liquid level detection function is reactivated; after the water replenishment is completed, the liquid level detection function is turned off.