Liquid level detection circuit and device and liquid level detector

Abstract

The utility model discloses a liquid level detection circuit and device and a liquid level detector, and relates to the field of detection.The liquid level detection circuit comprises a first controllable switch, a second controllable switch and a third controllable switch, the input end of the boosting module is connected with the power supply, the output end of the boosting module is connected with the power supply end of the detection module, and the boosting module is used for boosting the voltage output by the power supply and supplying power to the detection module when the first controllable switch is switched on; a detection end of the detection module is connected with the probe, an output module of the detection module is connected with the controller, and the detection module is used for increasing the frequency of square waves output by the detection module when the probe detects the liquid, so that the controller determines the contact liquid level. Characterization of the contacted liquid level is achieved by changing the frequency of the square wave output by the device, analog-to-digital conversion is not needed, and the accuracy of liquid level detection is improved. The first controllable switch is used for controlling the boosting module, so that the influence of noise on the boosting module can be avoided.

Description

TECHNICAL FIELD

[0001] The utility model relates to the field of detection, especially to a liquid level detection circuit, device and liquid level detector. BACKGROUND

[0002] The current liquid level detection scheme is analog circuit collection needle end resistance and capacitance change voltage signal, after amplification, analog-digital conversion quantization into digital quantity, through detecting quantization data jump situation to judge whether to reach liquid level. This scheme has high requirement to environment and electric characteristic of pipeline, is easily affected by pipeline, needle and ground, leading to liquid level detection failure or false triggering. SUMMARY

[0003] The purpose of the present application is to provide a liquid level detection circuit, device and liquid level detector, which realizes the representation of contacting liquid surface by changing the frequency of the output square wave, without analog-digital conversion, improving the accuracy of liquid level detection. Using the first controllable switch to control the boost module can avoid the influence of power supply noise on the boost module.

[0004] To solve the above technical problems, the present application provides a liquid level detection circuit, comprising:

[0005] A first controllable switch, a first end connected with the control end of the boost module, a second end grounded, a control end connected with the input signal, for turning on or turning off based on the input signal of the control end, to control the working of the boost module;

[0006] The boost module, the input end of the boost module connected with the power supply, the output end connected with the power supply end of the detection module, for boosting the voltage output by the power supply to power the detection module when the first controllable switch is turned on;

[0007] The detection module, the detection end of the detection module connected with the detection needle, the output module of the detection module connected with the controller, for increasing the frequency of the output square wave when the detection needle detects liquid, so that the controller determines the liquid surface.

[0008] On the other hand, the boost module includes a boost circuit, and the boost circuit includes a second controllable switch;

[0009] The control end of the second controllable switch is used as the control end of the boost circuit, the first end of the second controllable switch is connected with the power supply, the second end of the second controllable switch is grounded, and the second controllable switch is used for turning on when the first controllable switch is turned on, and turning off when the first controllable switch is turned off, to realize the voltage boosting of the power supply output.

[0010] In another aspect, the liquid level detection circuit further comprises a first base resistor, and the voltage boosting module further comprises a second base resistor, a first inductor, a first diode and a first capacitor;

[0011] A first end of the first base resistor is connected with an input signal, a second end of the first base resistor is connected with a control end of the first controllable switch, a first end of the second base resistor is connected with the power supply, a second end of the second base resistor is connected with a control end of the second controllable switch, a first end of the first inductor is connected with the power supply, a second end of the first inductor is connected with a first end of the second controllable switch and an anode of the first diode respectively, a second end of the second controllable switch is grounded, a second end of the first diode is connected with a first end of the first capacitor, and a common end connected with the first end of the first capacitor is used as an output end of the voltage boosting circuit, and a second end of the first capacitor is grounded.

[0012] In another aspect, the voltage boosting module further comprises a current limiting resistor;

[0013] A first end of the current limiting resistor is connected with the first end of the first base resistor, and a second end of the current limiting resistor is connected with the first end of the second base resistor.

[0014] The current limiting resistor is used for current limiting.

[0015] In another aspect, the detection module comprises a 555 timer, a second inductor, a fourth resistor, a fifth resistor, a sixth resistor and a seventh resistor;

[0016] A first end of the second inductor is connected with the detection needle, a second end of the second inductor is connected with a THR end of the 555 timer, a first end of the fifth resistor, a second end of the fourth resistor and a second end of the seventh resistor respectively, a first end of the fourth resistor is connected with a CON end of the 555 timer, a second end of the fifth resistor is grounded, a first end of the sixth resistor is connected with an output end of the voltage boosting module, a second end of the sixth resistor is connected with a first end of the seventh resistor, and a common end connected with the first end of the seventh resistor is connected with a DIS end of the 555 timer, and an OUT end of the 555 timer is connected with the controller as an output end.

[0017] The 555 timer is used for increasing a frequency of an output square wave when the detection needle contacts the liquid level.

[0018] In another aspect, an eighth resistor, a ninth resistor and a tenth resistor are further included;

[0019] A first end of the eighth resistor is connected with the OUT end of the 555 timer, a second end of the eighth resistor is connected with a first end of the ninth resistor and a first end of the tenth resistor, a second end of the ninth resistor and a second end of the tenth resistor are both grounded.

[0020] The eighth resistor, the ninth resistor, and the tenth resistor are used for voltage division.

[0021] On the other hand, it also includes a clamping module;

[0022] The first terminal of the clamping module is connected to the output terminal of the boost module, the second terminal of the clamping module is connected to the protective ground of the liquid level detection circuit, and the third terminal of the clamping module is grounded.

[0023] The clamping module is used to stabilize the voltage of the protective ground.

[0024] On the other hand, the clamping module includes an eleventh resistor, a twelfth resistor, and a third controllable switch;

[0025] The first end of the eleventh resistor is connected to the output end of the boost module and the first end of the third controllable switch. The second end of the eleventh resistor is connected to the first end of the twelfth resistor, and the common end of the connection is connected to the control end of the third controllable switch. The second end of the twelfth resistor is grounded, and the second end of the third controllable switch is connected to the protective ground.

[0026] The eleventh and twelfth resistors are used for voltage division, and the third controllable switch is used for voltage following.

[0027] To address the aforementioned technical problems, this application also provides a liquid level detection device, including the aforementioned liquid level detection circuit and a detection needle, wherein the detection needle is connected to the detection end of the detection module of the liquid level detection circuit.

[0028] To address the aforementioned technical problems, this application also provides a liquid level detector, including the aforementioned liquid level detection device, and further including a housing, which serves as a protective layer for the liquid level detection device.

[0029] This application provides a liquid level detection circuit, device, and detector, relating to the field of detection. It includes a first controllable switch, with its first terminal connected to the control terminal of a boost module and its second terminal grounded. The control terminal is connected to an input signal for controlling the operation of the boost module. The boost module has its input terminal connected to a power supply and its output terminal connected to the power supply terminal of a detection module. When the first controllable switch is turned on, it boosts the voltage output by the power supply to power the detection module. The detection module has its detection terminal connected to a probe, and its output module connected to a controller. When the probe detects liquid, the output module increases the frequency of its own output square wave to help the controller determine the contact liquid surface. By changing the frequency of its own output square wave, the contact liquid surface is characterized without analog-to-digital conversion, improving the accuracy of liquid level detection. Using the first controllable switch to control the boost module avoids the influence of noise on the boost module. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the prior art and embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This application provides a schematic diagram of the structure of a liquid level detection circuit;

[0032] Figure 2 A schematic diagram of a boost module provided in this application;

[0033] Figure 3 A schematic diagram of the structure of a detection module provided in this application;

[0034] Figure 4 This is a schematic diagram of a clamping module provided in this application. Detailed Implementation

[0035] The core of this application is to provide a liquid level detection circuit, device, and detector. By changing the frequency of its output square wave, it characterizes the contact with the liquid surface without analog-to-digital conversion, thus improving the accuracy of liquid level detection. Using a first controllable switch to control the boost module avoids the influence of power supply noise on the boost module.

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0037] Figure 1 This application provides a schematic diagram of a liquid level detection circuit, which includes:

[0038] The first controllable switch Q1 has its first terminal connected to the control terminal of the boost module 1, its second terminal grounded, and its control terminal connected to the input signal. It is used to turn the boost module 1 on or off based on the input signal from its own control terminal to control the operation of the boost module 1.

[0039] The input terminal of the boost module 1 is connected to the power supply, and the output terminal is connected to the power supply terminal of the detection module 2. It is used to boost the voltage output by the power supply to power the detection module 2 when the first controllable switch Q1 is turned on.

[0040] The detection module 2 has its detection end connected to the probe needle, and its output module connected to the controller. When the probe needle detects liquid, it increases the frequency of its output square wave so that the controller can determine the contact liquid surface.

[0041] Existing liquid level detection technologies often use a "positive voltage phase shift" method to detect the liquid level in reagent needles. This method is significantly affected by static electricity, noise, and current surges; it suffers from low sensitivity, susceptibility to false triggering, and low reliability. This application aims to solve these problems, reduce equipment production and maintenance costs, improve the sensitivity of liquid level detection, and increase response speed. This application also provides a novel method for measuring small-capacity capacitors. Current liquid level detection schemes use analog circuits to collect the voltage signal of resistance-capacitance changes at the needle tip, amplify it, and then quantize it into a digital quantity through AD conversion. The liquid level is determined by detecting the jump in the quantized data. This scheme has very high requirements for the environment and the electrical characteristics of the pipeline, and is easily affected by the pipeline, needle, and grounding, leading to liquid level detection failure or false triggering. The root cause is that the circuit detection system introduces impedance factors along with capacitance, and impedance changes are more sensitive. To address this phenomenon, the detection scheme needs to be optimized to reduce or eliminate the influence of impedance factors.

[0042] To avoid noise issues, this application sets up a first controllable switch Q1 to control the operation of the boost module 1. When the first controllable switch Q1 is turned on, the boost module 1 starts to work, increasing the voltage output by the power supply and then outputting it to the detection module 2. The detection module 2 is different from existing technologies. It detects liquid by changing its own output square wave. The controller can then determine whether it has come into contact with the liquid surface based on the frequency of the square wave.

[0043] Specifically, when the probe comes into contact with the liquid, the liquid causes the capacitance to increase. After the capacitance increases, the detection module 2 will increase the frequency of its output square wave, so that the controller can determine that it is currently in contact with the liquid.

[0044] It should be noted that the detection module 2 is a hardware device. The change in capacitance affects the frequency of the output square wave due to the device's own structure and does not require software algorithm improvements. The controller's counter monitors changes in the output frequency in real time, and the controller determines whether the square wave frequency has changed—a conventional technique in this field.

[0045] The application provides a liquid level detection circuit, and relates to the field of detection.

[0046] On the basis of the above embodiments:

[0047] In some embodiments, the voltage boosting module 1 comprises a voltage boosting circuit, and the voltage boosting circuit comprises a second controllable switch Q2.

[0048] The control end of the second controllable switch Q2 serves as the control end of the voltage boosting circuit, the first end of the second controllable switch Q2 is connected to the power supply, and the second end of the second controllable switch Q2 is grounded.

[0049] The controller drives the first controllable switch Q1 to drive the second controllable switch Q2, the second controllable switch Q2 is turned on when the first controllable switch Q1 is turned on, the voltage boosting circuit starts to work, the second controllable switch Q2 is turned off when the first controllable switch Q1 is turned off, and the voltage boosting circuit stops working.

[0050] In some embodiments, the liquid level detection circuit further comprises a first base resistor R1, and the voltage boosting module 1 further comprises a second base resistor R2, a first inductor L1, a first diode D1 and a first capacitor C1.

[0051] The first end of the first base resistor R1 is connected with an input signal, the second end of the first base resistor R1 is connected with the control end of the first controllable switch Q1, the first end of the second base resistor R2 is connected with a power supply, the second end of the second base resistor R2 is connected with the control end of the second controllable switch Q2, the first end of the first inductor L1 is connected with the power supply, the second end of the first inductor L1 is connected with the first end of the second controllable switch Q2 and the anode of the first diode D1 respectively, the second end of the second controllable switch Q2 is grounded, the second end of the first diode D1 is connected with the first end of the first capacitor C1, and the common end connected with the first end of the first capacitor C1 is used as an output end of a boost circuit, and the second end of the first capacitor C1 is grounded.

[0052] The controller drives the first controllable switch Q1 through a pulse, and then drives the second controllable switch Q2 to charge the first inductor L1, and the voltage in the first capacitor C1 is raised through the boost of the first inductor L1, so that a voltage output of 15V is generated at the point Vx. It should be noted that the boost module 1 constitutes a boost circuit.

[0053] The boost module 1 is converted from the energy stored by the inductor. When the pulse signal output by the controller is a high pulse: the first controllable switch Q1 and the second controllable switch Q2 are turned on, and the first inductor L1 stores energy. When the pulse signal output by the controller is a low pulse: the first controllable switch Q1 and the second controllable switch Q2 are cut off. Due to the hysteresis of the inductor current, D1 is turned on, and a boost effect is generated. C3 retains a part of the charge to continuously drive the load to work, so the current flows from Vx to GND through the 555 timer U1.

[0054] In some embodiments, the boost module 1 further comprises a current limiting resistor R3;

[0055] The first end of the current limiting resistor R3 is connected with the first end of the first base resistor R1, and the second end of the current limiting resistor R3 is connected with the first end of the second base resistor R2.

[0056] The current limiting resistor R3 is used for current limiting.

[0057] The current limiting resistor R3 is connected with the first base resistor R1 and the second base resistor R2 respectively, and is used for limiting the current input to the first controllable switch Q1 and the second controllable switch Q2.

[0058] In some embodiments, the detection module 2 comprises a 555 timer U1, a second inductor L2, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7.

[0059] The first end of the second inductor L2 is connected with the probe needle, the second end of the second inductor L2 is connected with the THR end of the 555 timer U1, the first end of the fifth resistor R5, the second end of the fourth resistor R4 and the second end of the seventh resistor R7 respectively, the first end of the fourth resistor R4 is connected with the CON end of the 555 timer U1, the second end of the fifth resistor R5 is grounded, the first end of the sixth resistor R6 is connected with the output end of the boost module 1, the second end of the sixth resistor R6 is connected with the first end of the seventh resistor R7, and the common end connected with the DIS end of the 555 timer U1, the OUT end of the 555 timer U1 is connected with the controller as an output end;

[0060] The 555 timer U1 is used to increase the frequency of the output square wave when the probe needle contacts the liquid surface.

[0061] The adjusting capacitor of the 555 timer U1 is equivalent to the input end of the probe capacitor. The frequency of the output square wave of the 555 timer U1 constitutes a pulse output to the controller. The controller monitors the frequency of the pulse in real time to determine the position of the liquid surface detection point. The fifth resistor R5 belongs to a single-point grounding function, which can reduce the interference of ripple conduction.

[0062] The pin function of the 555 timer U1 is relatively well-known. The GND pin represents the ground, which is used for grounding as a low level (0V). The TRIG pin represents the trigger, which is used for the output end to give a high level when the pin voltage drops to 1 / 3VCC. The OUT pin represents the output, which is used for outputting a high level or a low level. The RST pin represents the reset, which is used for the 555 timer U1 to work when a high level is connected. When this pin is grounded, the chip is reset, and the output is low. The CTRL pin represents the control, which is used for controlling the threshold voltage of the chip. When it is empty, the default two threshold voltages are 1 / 3VCC and 2 / 3VCC. The THR pin represents the threshold, which is used for the output end to give a low level when the pin voltage rises to 2 / 3VCC (or the threshold voltage determined by the control end). The DIS pin represents the discharge, which is connected with the OC gate inside, and is used for discharging the capacitor. The VCC pin represents the power supply, which is used for providing a high level and powering the chip.

[0063] The 555 timer U1 is started, and interacts with the liquid surface detection parasitic capacitor to produce different frequencies. According to the generated frequency, the capacity of the parasitic capacitor acting on the height of the liquid surface can be equivalent to be solved; the frequency output circuit: uses the resistor voltage division mechanism, so that the 555 timer U1 outputs the same frequency square wave.

[0064] In some embodiments, the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10 are further included.

[0065] The first end of the eighth resistor R8 is connected with the OUT end of the 555 timer U1, the second end of the eighth resistor R8 is connected with the first end of the ninth resistor R9 and the first end of the tenth resistor R10, and the second end of the ninth resistor R9 and the second end of the tenth resistor R10 are grounded.

[0066] The eighth resistor R8, the ninth resistor R9 and the tenth resistor R10 are used for voltage division.

[0067] The frequency of the output square wave of the 555 timer U1 is divided by the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10, and then the pulse is output to the controller.

[0068] In some embodiments, a clamping module is further included.

[0069] The first end of the clamping module is connected with the output end of the boost module 1, the second end of the clamping module is connected with the protection ground of the liquid level detection circuit, and the third end of the clamping module is grounded.

[0070] The clamping module is used for stabilizing the voltage of the protection ground.

[0071] In order to make the needle and the protection ground PGND potential basically consistent, a clamping circuit is introduced, and the voltage of the protection ground and the detection needle is equalized through the clamping circuit. It should be noted that the protection ground can be a shell.

[0072] In some embodiments, the clamping module includes an eleventh resistor R11, a twelfth resistor R12 and a third controllable switch Q3.

[0073] The first end of the eleventh resistor R11 is connected with the output end of the boost module 1 and the first end of the third controllable switch Q3, the second end of the eleventh resistor R11 is connected with the first end of the twelfth resistor R12, and the common end connected with the control end of the third controllable switch Q3, the second end of the twelfth resistor R12 is grounded, and the second end of the third controllable switch Q3 is connected with the protection ground.

[0074] The eleventh resistor R11 and the twelfth resistor R12 are used for voltage division, and the third controllable switch Q3 is used for voltage following.

[0075] After being divided by two resistors, in order to achieve the target voltage value, the resistance value of the resistor can be set according to actual needs, and then the third controllable switch Q3 is followed, so that the clamping voltage function is realized.

[0076] The application also provides a liquid level detection device, which includes the above-mentioned liquid level detection circuit and a detection needle, and the detection needle is connected with the detection end of the detection module of the liquid level detection circuit.

[0077] The liquid level detection device provided by the application is introduced in the above-mentioned embodiments, and will not be described here.

[0078] The application also provides a liquid level detector, comprising the liquid level detecting device, and further comprising a shell which serves as a protection for the liquid level detecting device.

[0079] The liquid level detector provided by the application is introduced in the above-mentioned embodiments, and will not be described here again.

[0080] It should be further noted that the terms such as first and second, etc. are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In addition, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, article or equipment. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, article or equipment including the element.

[0081] The skilled person can further realize that the units and algorithm steps of the examples described in conjunction with the disclosed embodiments herein can be realized in electronic hardware, computer software or a combination of both. In order to clearly illustrate the interchangeability of hardware and software, the components and steps of the examples have been described in the above description in general terms. Whether the functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. The skilled person can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the application.

[0082] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A liquid level detection circuit, characterized by comprising: The liquid level detection circuit comprises a first controllable switch, a boost module, a detection module and a controller. The first controllable switch is connected with the control end of the boost module at the first end, connected with the ground at the second end, and connected with the input signal at the control end, and is used for being turned on or turned off based on the input signal of the control end to control the working of the boost module. The input end of the boost module is connected with the power supply, and the output end is connected with the power supply end of the detection module, and is used for boosting the voltage output by the power supply to supply power to the detection module when the first controllable switch is turned on. The detection end of the detection module is connected with the detection needle, and the output module of the detection module is connected with the controller, and is used for increasing the frequency of the output square wave when the detection needle detects the liquid to determine the contact liquid level by the controller.

2. The liquid level detection circuit of claim 1, wherein The boost module comprises a boost circuit, and the boost circuit comprises a second controllable switch. The control end of the second controllable switch is used as the control end of the boost circuit, the first end of the second controllable switch is connected with the power supply, the second end of the second controllable switch is connected with the ground, and the second controllable switch is used for being turned on when the first controllable switch is turned on and being turned off when the first controllable switch is turned off to boost the voltage output by the power supply.

3. The liquid level detection circuit of claim 2, wherein, The liquid level detection circuit further comprises a first base resistance, and the boost module further comprises a second base resistance, a first inductor, a first diode and a first capacitor. The first end of the first base resistance is connected with the input signal, the second end of the first base resistance is connected with the control end of the first controllable switch, the first end of the second base resistance is connected with the power supply, the second end of the second base resistance is connected with the control end of the second controllable switch, the first end of the first inductor is connected with the power supply, the second end of the first inductor is connected with the first end of the second controllable switch and the anode of the first diode respectively, the second end of the second controllable switch is connected with the ground, the second end of the first diode is connected with the first end of the first capacitor, and the common end connected with the first end of the first capacitor is used as the output end of the boost circuit.

4. The liquid level detection circuit of claim 3, wherein the first and second resistors are connected in series between the first and second nodes. The boost module further comprises a current-limiting resistance. The first end of the current-limiting resistance is connected with the first end of the first base resistance, and the second end of the current-limiting resistance is connected with the first end of the second base resistance. The current-limiting resistance is used for current limiting.

5. The liquid level detection circuit of claim 1, wherein, The detection module comprises a 555 timer, a second inductor, a fourth resistance, a fifth resistance, a sixth resistance and a seventh resistance. The first end of the second inductor is connected with the detection needle, the second end of the second inductor is connected with the THR end of the 555 timer, the first end of the fifth resistance, the second end of the fourth resistance and the second end of the seventh resistance respectively, the first end of the fourth resistance is connected with the CON end of the 555 timer, the second end of the fifth resistance is connected with the ground, the first end of the sixth resistance is connected with the output end of the boost module, the second end of the sixth resistance is connected with the first end of the seventh resistance, and the common end connected with the first end of the seventh resistance is connected with the DIS end of the 555 timer, and the OUT end of the 555 timer is connected with the controller as the output end. The 555 timer is used to increase the frequency of the output square wave when the probe contacts the liquid surface.

6. The liquid level detection circuit of claim 5, wherein the first and second resistors are connected in series between the first and second nodes. An eighth resistor, a ninth resistor and a tenth resistor are further included; The first end of the eighth resistor is connected with the OUT end of the 555 timer, the second end of the eighth resistor is connected with the first end of the ninth resistor and the first end of the tenth resistor, and the second end of the ninth resistor and the second end of the tenth resistor are both grounded. The eighth resistor, the ninth resistor and the tenth resistor are used for voltage division.

7. A liquid level detection circuit as claimed in any one of claims 1 to 6, characterized in that A clamping module is further included; The first end of the clamping module is connected with the output end of the voltage boosting module, the second end of the clamping module is connected with the protection ground of the liquid surface detection circuit, and the third end of the clamping module is grounded. The clamping module is used to stabilize the voltage of the protection ground.

8. The liquid level detection circuit of claim 7, wherein the first and second resistors are connected in series between the first and second nodes. The clamping module includes an eleventh resistor, a twelfth resistor and a third controllable switch. The first end of the eleventh resistor is connected with the output end of the voltage boosting module and the first end of the third controllable switch, the second end of the eleventh resistor is connected with the first end of the twelfth resistor, the common end of the connection is connected with the control end of the third controllable switch, the second end of the twelfth resistor is grounded, and the second end of the third controllable switch is connected with the protection ground. The eleventh resistor and the twelfth resistor are used for voltage division, and the third controllable switch is used for voltage following.

9. A liquid level detection device, characterized by The liquid surface detection circuit includes the liquid surface detection circuit according to any one of claims 1 to 8, and further includes a probe, the probe being connected with the detection end of the detection module of the liquid surface detection circuit.

10. A level probe, characterized in that The liquid surface detection device includes the liquid surface detection device according to claim 9, and further includes a shell, the shell serving as the protection ground of the liquid surface detection device.

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