A high-frequency oscillation self-feedback variable capacitance circuit and proximity switch for liquid level detection

Abstract

The present invention proposes a high-frequency oscillation self-feedback variable capacitance circuit for liquid level detection, comprising a microcontroller (MCU); a sensing plate for receiving a conductivity signal of a liquid medium; a high-frequency automatic feedback circuit connected to the sensing plate and configured to convert the high-frequency conductivity signal into a stable voltage signal; and a power supply and output module electrically connected to the MCU control module and the high-frequency automatic feedback circuit, respectively, for outputting control signals required by a user terminal. The present invention can detect liquid level information without contacting the liquid medium, while avoiding errors and eliminating interference from foam, liquid film, and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid level detection, and in particular to a high-frequency oscillation self-feedback variable capacitance circuit and a proximity switch for liquid level detection. Background Art

[0002] In many industrial production processes, it is often necessary to detect the height of the liquid and whether there is any change in the liquid state in order to provide an effective prompt signal and notify the host to take corresponding measures to protect some peripherals of the equipment to operate effectively, reduce energy loss, and extend the service life of some peripherals, etc.

[0003] There are many types of liquid level sensors currently used in the market, including float type, photoelectric type, capacitive type, ultrasonic type, etc., each with its own advantages and disadvantages. Any object has capacitance, and the capacitance is related to the dielectric constant and volume. The liquid level sensor determines the height of the liquid or the presence of liquid by detecting the change in the capacitance of the object. When the liquid level sensor is placed close to the container wall, a capacitor similar to parallel plates is formed between it and the liquid.

[0004] In the prior art, proximity switches often receive inaccurate conductivity information due to the liquid film and foam of the liquid medium in the container and the moisture outside the container, thereby causing inaccurate liquid level information. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention proposes a high-frequency oscillation self-feedback variable capacitance circuit for liquid level detection, which can detect the liquid level and send corresponding control signals without contacting the liquid medium, while avoiding errors and eliminating interference from liquid films, foam, etc.

[0006] The technical solution of the present invention is achieved as follows:

[0007] A high-frequency oscillation self-feedback variable capacitance circuit for liquid level detection, comprising:

[0008] a sensing plate for receiving conductivity information of a liquid medium;

[0009] A high-frequency automatic feedback circuit, wherein the T0 terminal and the T1 terminal of the high-frequency automatic feedback circuit are respectively connected to two induction plates, and are used to convert the high-frequency signal into a stable phase voltage difference signal;

[0010] A microcontroller MCU is used to apply a high-frequency signal to the T0 terminal and the T1 terminal of the sensing board;

[0011] A power supply and output module, the power supply and output module are electrically connected to the microcontroller MCU and the high-frequency automatic feedback circuit respectively, and are used to output the control signals required by the machine equipment;

[0012] The microcontroller MCU applies a high-frequency signal to the TO terminal and the TI terminal respectively. When the liquid level approaches the sensing plate, the high-frequency signal forms a stable phase voltage difference signal through the high-frequency automatic feedback circuit and is transmitted to the microcontroller MCU. The microcontroller MCU sends a control signal to enable the power supply and output module to send an adjustment signal.

[0013] Furthermore, the high-frequency automatic feedback circuit includes a first detection voltage circuit, a second detection voltage circuit, a varactor diode D1, a transistor Q2, and a transistor Q3; the two ends of the first detection voltage circuit are respectively connected to the C1 end of the microcontroller MCU and the collector of the transistor Q2, the base of the transistor Q2 is electrically connected to the T0 end of the sensing plate, and the emitter of the transistor Q2 is connected to a 5V power supply; the two ends of the second detection voltage circuit are respectively connected to the C2 end of the microcontroller MCU and the collector of the transistor Q3, the base of the transistor Q3 is electrically connected to the T1 end of the sensing plate, and the emitter of the transistor Q3 is connected to a 5V power supply; the positive electrode of the varactor diode D1 is connected to the T0 end of the sensing plate, and its negative electrode is connected to the T1 end of the sensing plate.

[0014] Furthermore, the first detection voltage circuit includes a varactor diode D2, a resistor R12, a capacitor C13, a capacitor C14 and a resistor R13, the positive electrode of the varactor diode D2 is connected to the collector of the transistor Q2, the negative electrode of the varactor diode D2 is connected to the resistor R12, the resistor R12 is electrically connected to the microcontroller MCU, the capacitor C14 and the resistor R13 respectively, and the other ends of the capacitor C14 and the resistor R13 are grounded; the second detection circuit includes a varactor diode D3, a resistor R14, a capacitor C16 and a resistor R15, the positive electrode of the varactor diode D3 is connected to the collector of the transistor Q3, the negative electrode of the varactor diode D3 is connected to the resistor R14, the resistor R14 is electrically connected to the microcontroller MCU, the capacitor C16 and the resistor R15 respectively, and the other ends of the capacitor C16 and the resistor R15 are grounded.

[0015] Furthermore, the power supply and output module includes an amplifier, a first transistor and a second transistor; the output end of the comparator is connected to an input end of the amplifier, the output end of the amplifier is respectively connected to the bases of the two transistors, and the emitter of the first transistor is connected to the power regulator.

[0016] Furthermore, it also includes a temperature compensation circuit electrically connected to the microcontroller MCU, the temperature compensation circuit electrically connected to the microcontroller MCU, and is used to compensate the received voltage signal according to the temperature. The temperature compensation circuit includes a resistor R11, a thermistor NT and a capacitor C11. One end of the resistor R11 is connected to a 3.3V power supply, and the other end is electrically connected to the microcontroller MCU, the thermistor NT, and the capacitor C11 respectively; the other end of the thermistor NT is electrically connected to the microcontroller MCU and a common end respectively; the other end of the capacitor C11 is electrically connected to the microcontroller MCU and a common end respectively.

[0017] Furthermore, it also includes an LED display circuit electrically connected to the microcontroller MCU, the LED display circuit is connected to the output end of the microcontroller MCU, and is used to indicate the working status of the microcontroller MCU; the LED display circuit includes a first light-emitting diode LED1, a second light-emitting diode LED2, a resistor R2, and a resistor R3; the two ends of the first light-emitting diode are respectively connected to the G-end output pin of the microcontroller MCU and the resistor R2, and the two ends of the second light-emitting diode are respectively connected to the O-end output pin of the microcontroller MCU and the resistor R3, and the resistors R2 and R3 are connected to a 5V power supply.

[0018] Furthermore, it also includes a calibration circuit electrically connected to the microcontroller MCU, the calibration circuit electrically connected to the microcontroller MCU, and is used to perform full calibration and / or empty calibration on the microcontroller MCU; the calibration circuit includes a burning chip H1, a reset circuit, a transistor Q1, a resistor R4, and a resistor R5, the reset end of the reset circuit is electrically connected to the burning chip H1, and the burning chip H1 is connected to the microcontroller MCU; the collector of the transistor Q1 is electrically connected to the microcontroller MCU, the two ends of the resistor R5 are respectively connected to the base and the common end of the transistor Q1, the emitter of the transistor Q1 is connected to the common end, one end of the resistor R4 is connected to the base of the transistor Q1, and the other end is connected to the debugging calibration signal output end.

[0019] The present invention further provides a proximity switch comprising the high-frequency oscillation self-feedback varactor circuit for liquid level detection as described in any one of the above items.

[0020] Compared with the prior art, the present invention has the following advantages.

[0021] The sensor plate forms parallel electrodes with the liquid medium to detect whether the liquid medium has reached the specified level. It can automatically adapt to the wall thickness of various non-metallic containers such as plastic and glass, and can detect the liquid level of water-based media in non-metallic containers or pipes without direct contact with the medium itself. The phase voltage difference circuit in the high-frequency automatic feedback circuit can compensate for the conductivity of the internal and external walls (up to 50ms / cm), avoiding errors caused by residual liquid film, moisture, or foam accumulation formed by the water-based medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0023] Figure 1 This is a system block diagram of a high-frequency oscillation self-feedback variable capacitance circuit for liquid level detection according to the present invention;

[0024] Figure 2 This is a structural diagram of a high-frequency oscillation self-feedback variable capacitance circuit for liquid level detection according to the present invention;

[0025] Figure 3 1 is a circuit structure diagram of the high-frequency automatic feedback circuit of the present invention;

[0026] Figure 4 This is a circuit structure diagram of the output processing module in the present invention;

[0027] Figure 5 This is a circuit structure diagram of the calibration module in the present invention;

[0028] Figure 6 1 is a circuit structure diagram of the microcontroller MCU in the present invention;

[0029] Figure 7 This is a circuit structure diagram of the temperature compensation module in the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0031] See also Figures 1 to 7The embodiment of the present invention discloses a high-frequency oscillation self-feedback varactor circuit for liquid level detection, which is characterized by comprising:

[0032] a sensing plate for receiving conductivity information of a liquid medium;

[0033] A high-frequency automatic feedback circuit, wherein the T0 terminal and the T1 terminal of the high-frequency automatic feedback circuit are respectively connected to two induction plates, and are used to convert the high-frequency signal into a stable phase voltage difference signal;

[0034] A microcontroller MCU is used to apply a high-frequency signal to the T0 terminal and the T1 terminal of the sensing board;

[0035] A power supply and output module, the power supply and output module are electrically connected to the microcontroller MCU and the high-frequency automatic feedback circuit respectively, and are used to output the control signals required by the machine equipment;

[0036] The microcontroller MCU applies a high-frequency signal to the TO terminal and the TI terminal respectively. When the liquid level approaches the sensing plate, the high-frequency signal forms a stable phase voltage difference signal through the high-frequency automatic feedback circuit and is transmitted to the microcontroller MCU. The microcontroller MCU sends a control signal to enable the power supply and output module to send an adjustment signal.

[0037] Specifically, when the high-frequency signal strength at the T0 and T1 ends of the sensing plate changes, it is converted into a stable voltage signal through the first and second detection voltage circuits. The voltage signal is input into the C1 and C2 ends of the microcontroller MCU to obtain a phase voltage difference signal. After the phase voltage difference signal is transmitted to the microcontroller MCU, it is compared with the internal calibrated value. If the detected value is greater than or equal to the calibration value, the microcontroller MCU outputs a control signal, which controls the power output module, and the output module outputs a signal to the external machine equipment.

[0038] Furthermore, the high-frequency automatic feedback circuit includes a first detection voltage circuit, a second detection voltage circuit, a varactor diode D1, a transistor Q2, and a transistor Q3; the first detection voltage circuit has two ends connected to the C1 end of the microcontroller MCU and the collector of the transistor Q2, respectively; the base of the transistor Q2 is electrically connected to the T0 end of the sensing plate, and the emitter of the transistor Q2 is connected to a 5V power supply; the second detection voltage circuit has two ends connected to the C2 end of the microcontroller MCU and the collector of the transistor Q3, respectively; the base of the transistor Q3 is electrically connected to the T1 end of the sensing plate, and the emitter of the transistor Q3 is connected to a 5V power supply; the positive electrode of the varactor diode D1 is connected to the T0 end of the sensing plate, and the negative electrode is connected to the T1 end of the sensing plate. The varactor diode is a semiconductor device made using the principle of variable capacitance between PN junctions, and is used as a variable capacitor in the high-frequency tuning circuit.

[0039] Specifically, transistor Q1 and transistor Q2 are respectively connected to two sets of detection voltage circuits, which generate output voltage signals with the same phase. When there is external interference, the two sets of output voltage signals change simultaneously, but the potential difference between the two output voltage signals remains unchanged. When the sensor plate detects a dielectric object, the liquid medium will weaken the high-frequency signal in the high-frequency automatic feedback module, thereby changing the varactor diode, resulting in a phase voltage change, and thus a phase voltage difference.

[0040] Further embodiments, such as Figure 3 As shown, the first detection voltage circuit includes a varactor diode D2, a resistor R12, a capacitor C13, a capacitor C14, and a resistor R13. The positive electrode of the varactor diode D2 is connected to the collector of the transistor Q2, the negative electrode of the varactor diode D2 is connected to the resistor R12, the resistor R12 is electrically connected to the microcontroller MCU, the capacitor C14, and the resistor R13, respectively. The other ends of the capacitor C14 and the resistor R13 are grounded. The high-frequency signal is detected by the varactor diode D2 and filtered by the RC low-pass filter to obtain a stable output voltage, which is input into the microcontroller MCU through the C1 terminal.

[0041] The second detection voltage circuit includes a varactor diode D3, a resistor R14, a capacitor C16, and a resistor R15. The anode of the varactor diode D3 is connected to the collector of the transistor Q3, and the cathode of the varactor diode D3 is connected to the resistor R14. The resistor R14 is electrically connected to the microcontroller MCU, the capacitor C16, and the resistor R15, respectively. The other ends of the capacitor C16 and the resistor R15 are grounded. The principle of the second detection voltage circuit is similar to that of the first detection voltage circuit. The output voltage signal is input to the microcontroller MCU through the C2 terminal.

[0042] Furthermore, the LED display circuit includes a first light-emitting diode LED1, a second light-emitting diode LED2, a resistor R2, and a resistor R3; the two ends of the first light-emitting diode are respectively connected to the G-end output pin of the microcontroller MCU and the resistor R2, and the two ends of the second light-emitting diode are respectively connected to the O-end output pin of the microcontroller MCU and the resistor R3, and the resistors R2 and R3 are connected to a 5V power supply; specifically, the first light-emitting diode LED1 is a power indicator light, and when power is turned on, LED1 lights up, and the second light-emitting diode LED2 is an indication when liquid is sensed and an output overload and short-circuit protection indication. When the product senses liquid or an object, the second light-emitting diode LED2 lights up; when the current at the output end exceeds the rated value or is short-circuited, the second light-emitting diode LED2 will flash.

[0043] Furthermore, the calibration circuit includes a programming chip H1, a reset circuit, a transistor Q1, a resistor R4, and a resistor R5. The reset end of the reset circuit is electrically connected to the programming chip H1, and the programming chip H1 is connected to the microcontroller MCU.

[0044] The collector of the transistor Q1 is electrically connected to the microcontroller MCU, the two ends of the resistor R5 are respectively connected to the base and the common end of the transistor Q1, the emitter of the transistor Q1 is connected to the common end, one end of the resistor R4 is connected to the base of the transistor Q1, and the other end is connected to the debugging and calibration signal output end;

[0045] Furthermore, the temperature compensation circuit includes a resistor R11, a thermistor NT and a capacitor C11, one end of the resistor R11 is connected to a 3.3V power supply, and the other end is electrically connected to the microcontroller MCU, the thermistor NT and the capacitor C11 respectively; the other end of the thermistor NT is electrically connected to the microcontroller MCU and a common end respectively; the other end of the capacitor C11 is electrically connected to the microcontroller MCU and a common end respectively.

[0046] Preferably, if Figure 4 As shown, the power supply and signal output module includes a processing module U1, which includes an amplifier, a first transistor, and a second transistor. The output of the comparator is connected to one input of the amplifier, and the output of the amplifier is connected to the bases of the two transistors. The emitter of the first transistor is connected to a power regulator. The N-type and P-type outputs of the power supply and output module refer to the electrical signals output by the power supply and output module. The N-type output refers to the output of an NPN-type electrical signal, and the P-type refers to the output of a PNP-type electrical signal. These N-type or P-type signals are provided to the user terminal.

[0047] Working method: The microcontroller MCU sends a high-frequency signal through the high-frequency automatic feedback circuit, and applies a high-frequency signal to the TO terminal and the TI terminal respectively. When the liquid medium rises to the other side of the sensing plate, parallel plates are formed between the sensing plate and the liquid medium, and the high-frequency signal intensity changes. The high-frequency signal is shaped by the high-frequency automatic feedback circuit to generate a phase voltage difference. The phase voltage difference signal is transmitted to the microcontroller MCU and compared with the internal calibrated value. If the detected value is greater than or equal to the calibration value, the MCU outputs a control signal, and the control signal controls the power output module, and the output module outputs a signal to the external machine equipment.

[0048] Beneficial effects of the present invention:

[0049] 1. The sensor plate forms a parallel electrode with the liquid medium to detect whether the liquid medium has reached the specified liquid level. It can automatically adapt to the wall thickness of various non-metallic containers such as plastic or glass. It can detect the liquid level information of water-based media in non-metallic containers or pipes without direct contact with the medium itself.

[0050] 2. The phase voltage difference circuit in the high-frequency automatic feedback circuit can compensate for the conductivity inside and outside the wall (up to 50ms / cm), avoiding the error caused by residual liquid film, moisture or foam accumulation formed by water-based media.

[0051] The present invention further provides a proximity switch, comprising the high-frequency oscillation self-feedback variable capacitance circuit for liquid level detection as described above, thereby being able to bring about all the above-mentioned beneficial effects, which will not be described in detail here.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-frequency oscillation self-feedback variable capacitance circuit for liquid level detection, characterized in that: include: a sensing plate for receiving conductivity information of a liquid medium; A high-frequency automatic feedback circuit, wherein the T0 terminal and the T1 terminal of the high-frequency automatic feedback circuit are respectively connected to two induction plates, and are used to convert the high-frequency signal into a stable phase voltage difference signal; A microcontroller MCU is used to apply a high-frequency signal to the T0 terminal and the T1 terminal of the sensing board; A power supply and output module, the power supply and output module are electrically connected to the microcontroller MCU and the high-frequency automatic feedback circuit respectively, and are used to output the control signals required by the machine equipment; The microcontroller MCU applies a high-frequency signal to the TO terminal and the TI terminal respectively. When the liquid level approaches the sensing plate, the high-frequency signal is converted into a stable phase voltage difference signal through the high-frequency automatic feedback circuit and transmitted to the microcontroller MCU. The microcontroller MCU sends a control signal to enable the power supply and output module to send an adjustment signal. The high-frequency automatic feedback circuit includes a first detection voltage circuit, a second detection voltage circuit, a varactor diode D1, a transistor Q2 and a transistor Q3; The two ends of the first detection voltage circuit are respectively connected to the C1 terminal of the microcontroller MCU and the collector of the transistor Q2, the base of the transistor Q2 is electrically connected to the T0 terminal of the induction plate, and the emitter of the transistor Q2 is connected to a 5V power supply; The two ends of the second detection voltage circuit are respectively connected to the C2 terminal of the microcontroller MCU and the collector of the transistor Q3, the base of the transistor Q3 is electrically connected to the T1 terminal of the induction plate, and the emitter of the transistor Q3 is connected to a 5V power supply; The positive electrode of the varactor diode D1 is connected to the T0 terminal of the sensing plate, and the negative electrode thereof is connected to the T1 terminal of the sensing plate; The power supply and output module includes an amplifier, a first transistor and a second transistor; the output end of the comparator is connected to an input end of the amplifier, the output end of the amplifier is respectively connected to the bases of the two transistors, and the emitter of the first transistor is connected to the power regulator.

2. The high-frequency oscillation self-feedback varactor circuit for liquid level detection according to claim 1, characterized in that: The first detection voltage circuit includes a varactor diode D2, a resistor R12, a capacitor C13, a capacitor C14, and a resistor R13, wherein the positive electrode of the varactor diode D2 is connected to the collector of the transistor Q2, the negative electrode of the varactor diode D2 is connected to the resistor R12, the resistor R12 is electrically connected to the microcontroller MCU, the capacitor C14, and the resistor R13, respectively, and the other ends of the capacitor C14 and the resistor R13 are grounded; The second detection voltage circuit includes a varactor diode D3, a resistor R14, a capacitor C16 and a resistor R15. The positive electrode of the varactor diode D3 is connected to the collector of the transistor Q3, and the negative electrode of the varactor diode D3 is connected to the resistor R14. The resistor R14 is electrically connected to the microcontroller MCU, the capacitor C16 and the resistor R15 respectively. The other ends of the capacitor C16 and the resistor R15 are grounded.

3. The high-frequency oscillation self-feedback varactor circuit for liquid level detection according to claim 1, characterized in that: Also included is a temperature compensation circuit electrically connected to the microcontroller MCU, the temperature compensation circuit being electrically connected to the microcontroller MCU and configured to compensate a received voltage signal according to temperature, the temperature compensation circuit comprising a resistor R11, a thermistor NT, and a capacitor C11, one end of the resistor R11 being connected to a 3.3V power supply, and the other end being electrically connected to the microcontroller MCU, the thermistor NT, and the capacitor C11, respectively; The other end of the thermistor NT is electrically connected to the microcontroller MCU and the common end respectively; The other end of the capacitor C11 is electrically connected to the microcontroller MCU and a common end respectively.

4. The high-frequency oscillation self-feedback varactor circuit for liquid level detection according to claim 1, characterized in that: It also includes an LED display circuit electrically connected to the microcontroller MCU, and the LED display circuit is connected to the output end of the microcontroller MCU, for indicating the working status of the microcontroller MCU; the LED display circuit includes a first light-emitting diode LED1, a second light-emitting diode LED2, a resistor R2, and a resistor R3; the two ends of the first light-emitting diode are respectively connected to the G-end output pin of the microcontroller MCU and the resistor R2, and the two ends of the second light-emitting diode are respectively connected to the O-end output pin of the microcontroller MCU and the resistor R3, and the resistors R2 and R3 are connected to a 5V power supply.

5. The high-frequency oscillation self-feedback varactor circuit for liquid level detection according to claim 1, characterized in that: The device further includes a calibration circuit electrically connected to the microcontroller MCU, the calibration circuit being electrically connected to the microcontroller MCU and configured to perform full calibration and / or empty calibration on the microcontroller MCU; the calibration circuit comprising a programming chip H1, a reset circuit, a transistor Q1, a resistor R4, and a resistor R5; a reset terminal of the reset circuit being electrically connected to the programming chip H1, and the programming chip H1 being connected to the microcontroller MCU; The collector of the transistor Q1 is electrically connected to the microcontroller MCU, the two ends of the resistor R5 are respectively connected to the base and common end of the transistor Q1, the emitter of the transistor Q1 is connected to the common end, one end of the resistor R4 is connected to the base of the transistor Q1, and the other end is connected to the debugging and calibration signal output end.

6. A proximity switch, characterized in that: The invention comprises a high-frequency oscillation self-feedback variable capacitance circuit for liquid level detection as claimed in any one of claims 1 to 5.

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