CN211554340U - Liquid detection circuit - Google Patents
Liquid detection circuit Download PDFInfo
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- CN211554340U CN211554340U CN202020144159.1U CN202020144159U CN211554340U CN 211554340 U CN211554340 U CN 211554340U CN 202020144159 U CN202020144159 U CN 202020144159U CN 211554340 U CN211554340 U CN 211554340U
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Abstract
A liquid detection circuit comprising: the liquid sensing circuit comprises an oscillating resistor, an oscillating capacitor, a liquid sensing capacitor and an oscillation amplifying unit; the oscillation resistor, the oscillation capacitor and the liquid sensing capacitor are connected in parallel to form a parallel structure; the input end of the oscillation amplifying unit is connected with the first end of the parallel structure; the common end of the oscillation amplification unit is connected with the positive electrode of the power supply; the liquid sensing capacitor is disposed proximate to a liquid container of the product. The liquid detection circuit can quickly detect the existence of liquid in the corresponding liquid container.
Description
Technical Field
The utility model relates to a liquid detection area especially relates to a liquid detection circuitry.
Background
At present, in various small household appliances or industrial production products, a plurality of products need to detect whether water exists in a water tank in the products in real time. For example, in small household appliances, a household hot (boiling) kettle, a water purifier, a water heater or a humidifier has a need for detecting whether water exists in a water tank in a product in real time. In industry, the water tank or other water storage (using) container of the corresponding equipment is more required to detect whether water exists in real time.
Since these devices using water products often need to be tested, these products usually need to have corresponding liquid testing functions. Therefore, many solutions have been proposed.
Among them, the liquid detection sensor is a module frequently used for such products. Liquid detection sensors typically employ various active signal generating devices that emit an active signal to sense the presence of water in a tank (container) of the corresponding product. However, this solution using a liquid detection sensor needs a dedicated sensor, is still susceptible to the change of ambient temperature and humidity (causing sensor failure), and has complex circuitry and increased cost.
SUMMERY OF THE UTILITY MODEL
The utility model provides a problem provide a liquid detection circuitry to whether have liquid to exist in being used for the corresponding liquid container of short-term test, and the price reduction circuit cost improves economic benefits.
In order to solve the above problems, the utility model provides a liquid detection circuit, include: the liquid sensing circuit comprises an oscillating resistor, an oscillating capacitor, a liquid sensing capacitor and an oscillation amplifying unit; the oscillation resistor, the oscillation capacitor and the liquid sensing capacitor are connected in parallel to form a parallel structure; the input end of the oscillation amplifying unit is connected with the first end of the parallel structure; the common end of the oscillation amplification unit is connected with the positive electrode of the power supply; the liquid sensing capacitor is disposed proximate to a liquid container of the product.
Optionally, the liquid sensing capacitor includes two copper foils, and the two copper foils are separated by a PCB.
Optionally, the liquid sensing circuit further includes a first adjusting resistor, a second adjusting resistor, an oscillation adjusting capacitor, and an oscillation feedback resistor; the first adjusting resistor, the second adjusting resistor and the oscillation feedback resistor are connected between the first end and the second end of the parallel structure, and the second adjusting resistor is located between the first adjusting resistor and the oscillation feedback resistor; the first pole of the oscillation adjusting capacitor is connected between the output end of the oscillation amplifying unit and the oscillation feedback resistor, and the second pole of the oscillation adjusting capacitor is connected between the first adjusting resistor and the second adjusting resistor.
Optionally, the liquid sensing circuit further includes an external amplifying unit and an external bias resistor; the common end of the external amplification unit is connected with the positive electrode of a power supply; the input end of the external amplification unit is connected with the common end of the oscillation amplification unit; and the output end of the external amplifying unit is connected with the second end of the parallel structure.
Optionally, the oscillation amplifying unit is an NPN triode or an NMOS transistor; the external amplifying unit is an NPN triode or an NMOS tube.
Optionally, the liquid detection circuit further includes a state judgment circuit, where the state judgment circuit includes a rectification unit, a filtering unit, an operational amplifier, and an output adjustment unit; the input end of the rectifying unit is connected with the output end of the liquid induction circuit, and the output end of the rectifying unit is connected with the inverting input end of the operational amplifier; the positive phase input end of the operational amplifier is connected with a reference voltage; the output end of the operational amplifier is connected with the output adjusting unit, and the output end of the output adjusting unit is connected with the micro-processing unit.
Optionally, the output adjusting unit includes a first switch unit and a second switch unit; the first switch unit is a PNP triode, the second switch unit is an NPN triode, and the output end of the operational amplifier is connected with the base electrode of the PNP triode and the base electrode of the NPN triode; the emitting electrode of the PNP triode is connected with the emitting electrode of the NPN triode; the collector of the PNP triode is connected with the positive electrode of the power supply; the collector of the NPN triode is connected with the negative electrode of the power supply; and the emitter of the PNP triode and the emitter of the NPN triode are connected with the output end of the state judgment circuit.
Optionally, the state determination circuit further includes a filtering capacitor, and the filtering capacitor is connected to an output end of the external amplification unit.
Optionally, the rectifying unit includes a first rectifying diode and a second rectifying diode; the cathode of the first rectifying diode is connected with the filtering capacitor, and the anode of the first rectifying diode is used as the output end of the rectifying unit; the cathode of the second rectifier diode is connected with the negative electrode of the power supply, and the anode of the second rectifier diode is connected with the filter direct capacitor; the filtering unit comprises a filtering resistor and a filtering capacitor; the first pole of the filter capacitor is connected with the output end of the rectifying unit and the inverting input end of the operational amplifier, and the second pole of the filter capacitor is connected with the negative pole of the power supply; one end of the filter resistor is connected with the output end of the rectifying unit and the inverting input end of the operational amplifier, and the other end of the filter resistor is connected with the negative electrode of the power supply.
Optionally, the state determination circuit further includes a first voltage-dividing resistor, a second voltage-dividing resistor, an operational amplifier feedback resistor, and a pull-up resistor; the first end of the first voltage-dividing resistor is connected with the positive electrode of a power supply, the second end of the first voltage-dividing resistor is connected with the first end of the second voltage-dividing resistor, and the second end of the second voltage-dividing resistor is connected with the negative electrode of the power supply; a reference voltage output point serving as the reference voltage is arranged between the first voltage-dividing resistor and the second voltage-dividing resistor; the operational amplifier feedback resistor is connected between the reference voltage output point and the output end of the operational amplifier; the pull-up resistor is connected between the positive electrode of the power supply and the output end of the operational amplifier.
The utility model discloses in one of them aspect of technical scheme, provide a liquid detection circuitry, liquid detection circuitry includes liquid induction circuit and state judgement circuit. The liquid detection circuit is a composite circuit of a liquid sensing circuit and a state judgment circuit, and can detect whether liquid exists or not. The liquid sensing circuit can be used for rapidly detecting whether liquid exists or not in real time, so that the liquid existence or not can be confirmed under the condition of not using a special sensor, and the liquid sensing circuit can be used in a plurality of consumer electronic products, such as small household appliances or other products.
Drawings
FIG. 1 is a block circuit diagram of a liquid detection circuit in an embodiment;
FIG. 2 is a diagram showing the relationship between the liquid detection capacitor and the water tank in the liquid detection circuit according to the embodiment.
Detailed Description
For the detection of the existence of liquid, the conventional solution is realized by using a special liquid sensor, which increases the cost, and most of the special liquid sensors are easily influenced by the environment and have limited application range, thereby increasing the difficulty of development and design of the whole product.
The utility model relates to an utilize the liquid detection circuitry that passive component (passive component does not initiatively emit the component of signals such as laser or ultrasonic wave promptly) is constituteed, can effectively reduce circuit complexity, reduce product design cost.
For a clearer illustration, the present invention will be described in detail with reference to the accompanying drawings.
An embodiment of the present invention provides a liquid detection circuit, please refer to fig. 1 and fig. 2 in combination.
As shown in fig. 1, the liquid detection circuit includes: the liquid sensing circuit, as shown on the right side of the dashed line in FIG. 1.
The liquid sensing circuit comprises a liquid sensing circuit, such as the circuit enclosed by the dashed box inside the liquid sensing circuit in fig. 1.
The liquid induction circuit comprises an oscillation resistor R11, an oscillation capacitor C11, a liquid sensing capacitor C10 and an oscillation amplifying unit Q11. The oscillating resistor R11, the oscillating capacitor C11 and the liquid sensing capacitor C10 are connected in parallel to form a parallel structure (not labeled). The input end of the oscillation amplifying unit Q11 is connected with the first end of the parallel structure. The common terminal of the oscillation amplification unit Q11 is connected to the positive terminal of the power supply DC. The output end of the oscillation amplifying unit Q11 is indirectly connected to the second end of the parallel structure, and the indirect connection means that the oscillation amplifying unit Q11 and the second end of the parallel structure have corresponding structures such as capacitance and resistance, etc., as shown in fig. 1.
Referring to fig. 2 in conjunction, the liquid sensing capacitor C10 is disposed proximate to the liquid container of the product (water tank 20 in fig. 2).
In this embodiment, the liquid sensing capacitor C10 is implemented by two copper foils. The copper foil serves as a capacitor plate of the capacitor, i.e., the liquid sensing capacitor C10 includes two copper foils. And the two copper foils are separated by the PCB board. This PCB may be the PCB on which the entire liquid detection circuit is located, shown in fig. 2 as detection circuit PCBA board 11.
In this embodiment, the entire liquid sensing capacitor C10 is implemented by two copper foils on the upper surface (first surface) and the lower surface (second surface) of the PCB. Only one of the copper foils 10 is shown in fig. 2, which is on one side of a detection circuit PCBA board 11. The other copper foil is not shown because it is located on the other side of the detection circuit PCBA board 11. The mode of using two copper foils reduces the required size of the PCB.
Fig. 2 also shows that the liquid container is embodied as a water tank 20, and that the water tank 20 has a liquid 21 therein (the liquid 21 may be water or another liquid).
Fig. 2 shows that the detection circuit PCBA board 11 and the copper foil 10 are both arranged in close proximity to the water tank 20. The detection circuit PCBA board 11 and the copper foil 10 may be glued or otherwise abutted against the side of the water tank 20.
In addition, fig. 2 also shows that the detection circuit PCBA board 11 is connected to a corresponding main control unit 12, which main control unit 12 typically employs a micro-processing unit (MCU).
In this embodiment, the copper foil 10 may have a thickness of one Ounce (OZ), which is approximately equal to 35 μm, i.e., 0.035 mm. The area of the copper foil 10 may be 30mm × 35 mm.
The spacing between the two copper foils may be 1.6 mm. The space between the two copper foils is formed by separating PCBA (detection circuit PCBA 11), and the PCBA 11 can be made of FR-4 material.
It should be noted that, in a specific product (e.g., a small household electrical appliance), the value of the oscillating resistor R11 of the circuit shown in fig. 1 may be selected to be 47K Ω, and the capacitance value of the oscillating capacitor C11 may be selected to be 15 pF.
With reference to fig. 1, the liquid sensing circuit further includes a first adjusting resistor R13, a second adjusting resistor R14, an oscillation adjusting capacitor C12, and an oscillation feedback resistor R12.
The first adjusting resistor R13, the second adjusting resistor R14 and the oscillation feedback resistor R12 are connected between the first end and the second end of the parallel structure, and the second adjusting resistor R14 is located between the first adjusting resistor R13 and the oscillation feedback resistor R12.
A first pole of the oscillation adjusting capacitor C12 is connected between the output terminal of the oscillation amplifying unit Q11 and the oscillation feedback resistor R12, and a second pole of the oscillation adjusting capacitor C12 is connected between the first adjusting resistor R13 and the second adjusting resistor R14.
With continued reference to fig. 1, the liquid sensing circuit further includes an external amplifying unit Q12 and an external bias resistor R15. The common terminal of the external amplifying unit Q12 is connected to the positive pole of the power supply DC. An input terminal of the external amplifying unit Q12 is connected to the common terminal of the oscillation amplifying unit Q11. The output terminal of the external amplifying unit Q12 is connected to the second terminal of the parallel structure. Meanwhile, the amplifying unit is also a feedback loop of the liquid sensing circuit.
In this embodiment, the oscillation amplifying unit Q11 is an NPN transistor. In other embodiments, the oscillation amplifying unit may also adopt an NMOS transistor.
In this embodiment, the external amplifying unit Q12 is an NPN transistor. In other embodiments, the external amplifying unit may also adopt an NMOS transistor.
Referring to fig. 1, the liquid detection circuit provided in this embodiment further includes a state determination circuit, which is a circuit shown on the left of the dashed line in fig. 1.
The state judging circuit comprises a rectifying unit U20, a filtering unit U21, an operational amplifier U22 and an output adjusting unit U23. The input end of the rectifying unit U20 is connected with the output end of the liquid sensing circuit, and the output end of the rectifying unit U20 is connected with the inverting input end of the operational amplifier U22. The non-inverting input of the operational amplifier U22 is connected to a reference voltage. The output end of the operational amplifier U22 is connected with the output adjusting unit U23, and the output end of the output adjusting unit U23 is connected with the micro-processing unit.
Referring to fig. 1, the state determination circuit further includes a filtering capacitor C13, and the filtering capacitor C13 is connected to the output terminal of the external amplifying unit Q12.
In the present embodiment, the rectifying unit U20 includes a first rectifying diode D11 and a second rectifying diode D12. The cathode of the first rectifying diode D11 is connected with the filtering capacitor C13, and the anode of the first rectifying diode D11 is used as the output end of the rectifying unit U20; the cathode of the second rectifying diode D12 is connected with the negative pole of the power supply DC, and the anode of the second rectifying diode D12 is connected with the smoothing capacitor C13.
In this embodiment, the filter unit U21 includes a filter resistor R25 and a filter capacitor C21. A first pole of the filter capacitor C21 is connected with the output end of the rectifying unit U20 and the inverting input end of the operational amplifier U22, and a second pole of the filter capacitor C21 is connected with the negative pole of the power supply DC. One end of the filter resistor R25 is connected with the output end of the rectifying unit U20 and the inverting input end of the operational amplifier U22, and the other end of the filter resistor R25 is connected with the negative pole of the power supply DC.
In the present embodiment, the output adjusting unit U23 includes a first switching unit Q21 and a second switching unit Q22. The first switch unit Q21 is a PNP triode, the second switch unit Q22 is an NPN triode, and the output end of the operational amplifier U22 is connected to the base of the PNP triode and the base of the NPN triode. And the emitter of the PNP triode is connected with the emitter of the NPN triode. And the collector of the PNP triode is connected with the positive pole of the power supply DC. And the collector of the NPN triode is connected with the negative pole of the power supply DC. And the emitter of the PNP triode and the emitter of the NPN triode are connected with the output end of the state judgment circuit.
In other embodiments, the first switching unit Q21 may be a PMOS transistor.
In other embodiments, the second switching unit Q22 may be an NMOS transistor.
In this embodiment, the state determining circuit further includes a first voltage dividing resistor R21, a second voltage dividing resistor R22, an operational amplifier feedback resistor R23, and a pull-up resistor R24. The first end of the first voltage-dividing resistor R21 is connected with the positive pole of the power DC, the second end of the first voltage-dividing resistor R21 is connected with the first end of the second voltage-dividing resistor R22, and the second end of the second voltage-dividing resistor R22 is connected with the negative pole of the power DC. And a reference voltage output point P1 serving as a reference voltage is arranged between the first voltage-dividing resistor R21 and the second voltage-dividing resistor R22. The operational amplifier feedback resistor R23 is connected between the reference voltage output point P1 and the output terminal of the operational amplifier U22. A pull-up resistor R24 is connected between the positive DC supply and the output of operational amplifier U22.
The utility model discloses a liquid detection circuit is based on RC self-excited oscillation principle, changes the capacitance value of parallelly connected structure through having or not liquid to reach and let the oscillating circuit start the purpose whether or not vibrate. The change in capacitance is accomplished using copper foil 10 disposed on a PCBA board 11 (i.e., a PCB board) (i.e., using liquid sensing capacitance C10).
The oscillation capacitor C11 can be used for capacitance compensation of the liquid sensing circuit. The first adjusting resistor R13, the second adjusting resistor R14 and the oscillation adjusting capacitor C12 are used for adjusting oscillation starting parameters. The first regulating resistor R13 and the second regulating resistor R14 are multiplexed with the feedback function of the oscillation feedback resistor R12, namely the first regulating resistor R13 and the second regulating resistor R14 also have the feedback function.
After the liquid sensing circuit starts oscillation by using the self-excited oscillation principle, a small signal output by the liquid sensing circuit is amplified by an external amplifying unit Q12, a direct current component in the signal is filtered by a filtering direct current capacitor C13, and then the direct current component is rectified by a first rectifying diode D11 and a second rectifying diode D12, so that alternating current output by the liquid detection circuit is converted into variable direct current level. Then, the changing dc level output from the first rectifying diode D11 is applied to one input terminal (inverting input terminal) of the operational amplifier U22 by obtaining a stable dc voltage through the filter capacitor C21 and the filter resistor R25. In the state decision circuit, the power supply DC supplies a DC bias voltage to the other input terminal (non-inverting input terminal) of the operational amplifier U22 by voltage division of the first voltage dividing resistor R21 and the second voltage dividing resistor R22 for comparison with the inverting output terminal voltage, thereby changing the state of the output terminal of the operational amplifier U22.
Meanwhile, the operational amplifier feedback resistor R23 forms an operational amplifier feedback loop. The first switching unit Q21 and the second switching unit Q22 are used to adjust the output of the state decision circuit to output different interrupt signals (level states) to the micro processing unit (MCU) at the output terminal P2.
In the circuit provided in this embodiment, by using the arrangement of the circuit, one of the operation principles may be as follows:
when water (liquid) is present in the corresponding liquid container shown in fig. 2, the liquid sensing circuit shown in fig. 1 starts to vibrate; the oscillation starting causes a signal to exist in the liquid sensing circuit, the signal is amplified, filtered, rectified and filtered to serve as an output signal of the liquid sensing circuit and is sent to the state judgment circuit, namely, at the moment, the voltage accessed by the inverting input end of the operational amplifier U22 is higher than the reference voltage accessed by the positive input end, so that the operational amplifier U22 outputs low voltage, and the whole liquid detection circuit outputs a low voltage signal to the micro control unit;
when no water (liquid) exists in the corresponding liquid container shown in fig. 2, the liquid sensing circuit does not start to vibrate, and therefore, no signal is sent to the state judgment circuit by the liquid sensing circuit, that is, at this time, the voltage accessed by the inverting input terminal of the operational amplifier U22 is lower than the reference voltage accessed by the non-inverting input terminal, so that the operational amplifier U22 outputs a high voltage, and the whole liquid detection circuit outputs a high voltage signal to the micro control unit to remind the user that no water (liquid) exists in the corresponding liquid container.
It can also be known from the above principle that, in this embodiment, the liquid sensing circuit is used to collect corresponding analog signals, and then the state judgment circuit is used to convert the corresponding analog signals into digital signals and send the digital signals to the micro-processing unit, thereby realizing the quick and effective judgment of whether liquid exists or not.
It should be noted that the above is only one principle that can be realized by the circuit of this embodiment, and in the above circuit structure, other detection principles, such as outputting a low voltage signal when no water exists, outputting a high level signal when water exists, and the like, can also be realized.
Therefore, in the liquid detection circuit of the embodiment, the liquid sensing circuit can be used for judging whether liquid exists or not, and the state judgment circuit can be used for converting the signal output by the liquid sensing circuit into a signal which can be identified by a Micro Control Unit (MCU), so that the purpose of detecting whether liquid exists or not with high sensitivity by using a simple element can be realized, and the function of quickly judging liquid is realized.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the scope or spirit of the present invention, and the scope of the present invention is defined by the appended claims.
Claims (10)
1. A liquid detection circuit, comprising:
the liquid sensing circuit comprises an oscillating resistor, an oscillating capacitor, a liquid sensing capacitor and an oscillation amplifying unit;
the oscillation resistor, the oscillation capacitor and the liquid sensing capacitor are connected in parallel to form a parallel structure; the input end of the oscillation amplifying unit is connected with the first end of the parallel structure; the common end of the oscillation amplification unit is connected with the positive electrode of the power supply;
the liquid sensing capacitor is disposed proximate to a liquid container of the product.
2. The liquid detection circuit of claim 1, wherein the liquid sensing capacitor comprises two copper foils separated by a PCB.
3. The liquid detection circuit of claim 1, wherein the liquid sensing circuit further comprises a first tuning resistor, a second tuning resistor, an oscillation tuning capacitor, and an oscillation feedback resistor;
the first adjusting resistor, the second adjusting resistor and the oscillation feedback resistor are connected between the first end and the second end of the parallel structure, and the second adjusting resistor is located between the first adjusting resistor and the oscillation feedback resistor;
the first pole of the oscillation adjusting capacitor is connected between the output end of the oscillation amplifying unit and the oscillation feedback resistor, and the second pole of the oscillation adjusting capacitor is connected between the first adjusting resistor and the second adjusting resistor.
4. The liquid detection circuit of claim 1, wherein the liquid sensing circuit further comprises an external amplification unit and an external bias resistor; the common end of the external amplification unit is connected with the positive electrode of a power supply; the input end of the external amplification unit is connected with the common end of the oscillation amplification unit; and the output end of the external amplifying unit is connected with the second end of the parallel structure.
5. The liquid detection circuit of claim 4, wherein the oscillation amplification unit is an NPN transistor or an NMOS tube; the external amplifying unit is an NPN triode or an NMOS tube.
6. The liquid detection circuit according to claim 5, further comprising a state judgment circuit including a rectifying unit, a filtering unit, an operational amplifier, and an output adjusting unit; the input end of the rectifying unit is connected with the output end of the liquid induction circuit, and the output end of the rectifying unit is connected with the inverting input end of the operational amplifier; the positive phase input end of the operational amplifier is connected with a reference voltage; the output end of the operational amplifier is connected with the output adjusting unit, and the output end of the output adjusting unit is connected with the micro-processing unit.
7. The liquid detection circuit according to claim 6, wherein the output adjustment unit includes a first switching unit and a second switching unit;
the first switch unit is a PNP triode, the second switch unit is an NPN triode, and the output end of the operational amplifier is connected with the base electrode of the PNP triode and the base electrode of the NPN triode;
the emitting electrode of the PNP triode is connected with the emitting electrode of the NPN triode;
the collector of the PNP triode is connected with the positive electrode of the power supply;
the collector of the NPN triode is connected with the negative electrode of the power supply;
and the emitter of the PNP triode and the emitter of the NPN triode are connected with the output end of the state judgment circuit.
8. The liquid detection circuit of claim 6, wherein the state decision circuit further comprises a smoothing capacitor connected to an output of the external amplification unit.
9. The liquid detection circuit of claim 8,
the rectifying unit comprises a first rectifying diode and a second rectifying diode; the cathode of the first rectifying diode is connected with the filtering capacitor, and the anode of the first rectifying diode is used as the output end of the rectifying unit; the cathode of the second rectifier diode is connected with the negative electrode of the power supply, and the anode of the second rectifier diode is connected with the filter direct capacitor;
the filtering unit comprises a filtering resistor and a filtering capacitor; the first pole of the filter capacitor is connected with the output end of the rectifying unit and the inverting input end of the operational amplifier, and the second pole of the filter capacitor is connected with the negative pole of the power supply; one end of the filter resistor is connected with the output end of the rectifying unit and the inverting input end of the operational amplifier, and the other end of the filter resistor is connected with the negative electrode of the power supply.
10. The liquid detection circuit of claim 9, wherein the state decision circuit further comprises a first voltage divider resistor, a second voltage divider resistor, an operational amplifier feedback resistor, and a pull-up resistor; the first end of the first voltage-dividing resistor is connected with the positive electrode of a power supply, the second end of the first voltage-dividing resistor is connected with the first end of the second voltage-dividing resistor, and the second end of the second voltage-dividing resistor is connected with the negative electrode of the power supply;
a reference voltage output point serving as the reference voltage is arranged between the first voltage-dividing resistor and the second voltage-dividing resistor;
the operational amplifier feedback resistor is connected between the reference voltage output point and the output end of the operational amplifier;
the pull-up resistor is connected between the positive electrode of the power supply and the output end of the operational amplifier.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202020144159.1U CN211554340U (en) | 2020-01-22 | 2020-01-22 | Liquid detection circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202020144159.1U CN211554340U (en) | 2020-01-22 | 2020-01-22 | Liquid detection circuit |
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| CN211554340U true CN211554340U (en) | 2020-09-22 |
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| CN202020144159.1U Active CN211554340U (en) | 2020-01-22 | 2020-01-22 | Liquid detection circuit |
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