Multi-step contact type liquid level detection device

Abstract

The application discloses a multi-gear contact type liquid level detection device, which comprises a controller, a liquid level detection circuit, liquid level detection probes installed on a container cover, a display and a voltage stabilizing power supply VIN; the liquid level detection probes at least comprise first liquid level detection probes and second liquid level detection probes, which are respectively connected with a signal input end of the liquid level detection circuit; a signal input end of the controller is connected with a signal output end of the liquid level detection circuit, so as to obtain a liquid level state of a detected liquid; and a data input end of the display is connected with a data output end of the controller through a communication interface, so as to display the liquid level state of the detected liquid. The application realizes multi-gear contact type liquid level detection; the liquid level detection probes are fixed when working, so that the reliability and stability of liquid level detection are ensured. Meanwhile, the Schmitt trigger effect of the liquid level detection circuit can effectively prevent the output signal oscillation problem caused by the matching resistance fluctuation between the detection probes, and the liquid level detection precision is high.

Description

Technical Field

[0001] This invention relates to a contact-type liquid level detection device, and more particularly to a multi-level contact-type liquid level detection device. Background Technology

[0002] Currently, in the medical device field, the liquid level detection method for purified water tanks, alkaline washing tanks, and BF automatic proportioning tanks mostly involves installing a float-type level switch on the tank lid. Float-type level switches primarily utilize the Hall effect, where the rise and fall of a float floating on the liquid inside the tank causes a high / low level change in the switch. When the liquid level reaches the set lower limit, the float falls, triggering the level switch to send a low-level signal, thereby activating the machine alarm or opening the pump valve to replenish the liquid in the tank. When the liquid level reaches the set upper limit, the float rises, triggering the level switch to send a high-level signal to close the pump valve. However, prolonged immersion of the float in liquid can lead to float corrosion, Hall sensor malfunction, float jamming, and other inactive phenomena, resulting in potential risks such as water leakage, failed level detection, or even instrument failure. Furthermore, float-type level switches can only detect the upper and lower limits of the liquid level, and cannot detect multiple levels.

[0003] For liquid-containing containers, in addition to the float-type level switch mentioned above, there are also non-contact level switches such as photoelectric (through-beam) level switches and capacitive level switches for liquid level detection. Photoelectric level switches are only suitable for transparent containers, relying on the difference in refractive index of light in air and liquid to determine whether the liquid level is below a set value. When the container is opaque, a through-beam hole must be made in the container wall, and sealing measures must be taken to install the photoelectric sensor, resulting in high manufacturing costs and a risk of leakage during container use. Capacitive level switches are implemented through a capacitance value detection circuit, which has high manufacturing costs and is easily affected by factors such as temperature, humidity, static electricity, and liquid concentration, leading to abnormal liquid level detection. Summary of the Invention

[0004] The purpose of this invention is to provide a small, low-cost, stable and reliable multi-level contact liquid level detection device to achieve multi-level liquid level detection.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The multi-level contact liquid level detection device of the present invention includes a controller, a liquid level detection circuit, a liquid level detection probe mounted downwards on a container lid, a display, and a regulated power supply VIN. The regulated power supply VIN is connected to the power input terminals of the controller and the liquid level detection circuit, respectively, to provide a stable voltage to the controller and the liquid level detection circuit. The liquid level detection probe includes at least a first liquid level detection probe and a second liquid level detection probe, each connected to a corresponding signal input terminal of the liquid level detection circuit. The signal input terminal of the controller is connected to the signal output terminal of the liquid level detection circuit to obtain the liquid level status of the detected liquid. The data input terminal of the display is connected to the data output terminal of the controller via a communication interface to display the liquid level status of the detected liquid.

[0007] Alternatively, the liquid level detection circuit includes a first signal input terminal and a second signal input terminal;

[0008] The first signal input terminal is connected to the first liquid level detection probe, and is connected to the non-inverting input terminal of the first integrated operational amplifier U1 via a series circuit of resistors R1, R2, and R4. A capacitor C1 is connected between the first signal input terminal and ground. The connection point of resistors R1 and R2 is connected to the regulated power supply VIN and one end of capacitor C2, and the other end of capacitor C2 is grounded. Resistor R1 and capacitor C1 form a first RC filter circuit. The connection point of resistors R2 and R4 is connected to one end of resistor R3 and capacitor C4, and the other end of resistor R3 and capacitor C4 is grounded. Resistor R2 and R3 form a voltage divider circuit. A capacitor C5 is connected between the non-inverting input terminal of the first integrated operational amplifier U1 and ground. Resistor R4 and capacitor C4 form a second RC filter circuit. A resistor R7 is connected between the non-inverting input terminal and the output terminal OUT1 of the first integrated operational amplifier U1 to form a positive feedback circuit. The output terminal OUT1 of the first integrated operational amplifier U1 is connected to the controller signal input terminal.

[0009] The second signal input terminal is connected to the second liquid level detection probe; a capacitor C3 is connected between the second signal input terminal and ground, and is connected to the inverting input terminal of the first integrated operational amplifier U1 through a resistor R5; a parallel circuit consisting of a resistor R6 and a capacitor C6 is connected between the inverting input terminal of the first integrated operational amplifier U1 and ground; the resistors R5 and R6 form a voltage divider circuit.

[0010] Furthermore, it also includes a second integrated operational amplifier U2, a third liquid level detection probe, and a third signal input terminal;

[0011] The inverting input of the second integrated operational amplifier U2 is connected to the inverting input of the first integrated operational amplifier U1 via resistor R13; the third signal input is connected to the third liquid level detection probe, and is connected to the non-inverting input of the second integrated operational amplifier U2 via a series circuit of resistors R10, R9, and R8; a capacitor C10 is connected between the third signal input and ground; the connection point of resistors R10 and R9 is connected to the regulated power supply VIN and one end of capacitor C8, and the other end of capacitor C8 is grounded; resistor R10 and capacitor C8 form a third RC filter circuit. The circuit consists of: a voltage divider circuit formed by resistors R9 and R8 connected to one end of resistor R12 and capacitor C9, with the other end of resistor R12 and capacitor C9 grounded; a capacitor C7 connected between the non-inverting input of the second integrated operational amplifier U2 and ground; and resistors R8 and capacitor C7 forming a fourth RC filter circuit. A resistor R11 is connected between the non-inverting input and output OUT2 of the second integrated operational amplifier U2 to form a positive feedback circuit. The output OUT2 of the second integrated operational amplifier U2 is connected to the controller signal input.

[0012] Furthermore, the surfaces of the first, second, and third liquid level detection probes are provided with a nickel plating layer, which serves to prevent corrosion and conduct electricity; the length of the first liquid level detection probe is greater than that of the second liquid level detection probe, and the length of the third liquid level detection probe is less than that of the second liquid level detection probe; the first and second liquid level detection probes are used to detect the 50% liquid level, and the first and third liquid level detection probes are used to detect the upper limit of the liquid level.

[0013] This invention achieves multi-level contact-type liquid level detection through a liquid level detection probe and circuit mounted on a container lid. The liquid level detection probe remains stationary during operation, ensuring reliable and stable liquid level detection. The analog signal collected by the liquid level detection probe is output to an integrated operational amplifier after multi-stage filtering, comparison, and feedback circuitry. The integrated operational amplifier outputs high and low level signals to the controller, which obtains the current liquid level status by running an embedded program. The liquid level detection circuit and probe have a simple structure and low manufacturing cost. Furthermore, the Schmitt trigger effect of the liquid level detection circuit effectively prevents output signal oscillation caused by fluctuations in the matching resistance between the detection probes, resulting in high liquid level detection accuracy. Attached Figure Description

[0014] Figure 1 This is a circuit block diagram of the present invention.

[0015] Figure 2 This is a schematic diagram of the liquid level detection circuit of the present invention, including a first signal input terminal and a second signal input terminal.

[0016] Figure 3This is a schematic diagram of the liquid level detection circuit of the present invention, which includes a first signal input terminal, a second signal input terminal, and a third signal input terminal.

[0017] Figure 4 This is a schematic diagram showing the usage state of the first liquid level detection probe, the second liquid level detection probe, and the third liquid level detection probe of the present invention installed on the container lid. Detailed Implementation

[0018] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the scope of protection of the present invention is not limited to the following embodiments.

[0019] It should be noted that, in this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] like Figure 1 , 4 As shown, the multi-level contact liquid level detection device of the present invention includes a controller (MCU), a liquid level detection circuit, liquid level detection probes mounted downwards on the container cover 4, a display, and a regulated power supply VIN. The regulated power supply VIN is connected to the power input terminals of the controller and the liquid level detection circuit, respectively, to provide a stable voltage to the controller and the liquid level detection circuit. The liquid level detection probes include a first liquid level detection probe 1 and a second liquid level detection probe 2, which are respectively connected to a corresponding signal input terminal of the liquid level detection circuit. The signal input terminal of the controller is connected to the signal output terminal of the liquid level detection circuit to obtain the liquid level status of the detected liquid. The data input terminal of the display is connected to the data output terminal of the controller via a communication interface to display the liquid level status of the detected liquid.

[0021] Beneficial or exemplary, such as Figure 2 , 4 As shown, the liquid level detection circuit includes a first signal input terminal 1.1 and a second signal input terminal 2.1;

[0022] The first signal input terminal 1.1 is connected to the first liquid level detection probe 1, and is connected to the non-inverting input terminal of the first integrated operational amplifier U1 through a series circuit of resistors R1, R2, and R4. A capacitor C1 is connected between the first signal input terminal 1.1 and ground. The bottom of the first liquid level detection probe 1 is located at the set lower liquid level limit L. The connection point of resistors R1 and R2 is connected to the regulated power supply VIN and one end of capacitor C2, and the other end of capacitor C2 is grounded. Resistor R1 and capacitor C1 form a first RC filter circuit. The connection point of resistors R2 and R4 is connected to one end of resistor R3 and capacitor C4, and the other end of resistor R3 and capacitor C4 is grounded. Resistor R2 and R3 form a voltage divider circuit. A capacitor C5 is connected between the non-inverting input terminal of the first integrated operational amplifier U1 and ground. Resistor R4 and capacitor C4 form a second RC filter circuit. A resistor R7 is connected between the non-inverting input terminal and the output terminal OUT1 of the first integrated operational amplifier U1 to form a positive feedback circuit. The output terminal OUT1 of the first integrated operational amplifier U1 is connected to the controller signal input terminal.

[0023] The second signal input terminal 2.1 is connected to the second liquid level detection probe 2, and the bottom of the second liquid level detection probe 2 is located at 50% of the set liquid level; a capacitor C3 is connected between the second signal input terminal and ground, and is connected to the inverting input terminal of the first integrated operational amplifier U1 through a resistor R5; a parallel circuit consisting of a resistor R6 and a capacitor C6 is connected between the inverting input terminal of the first integrated operational amplifier U1 and ground; resistors R5 and R6 form a voltage divider circuit.

[0024] Beneficial or exemplary, such as Figure 3 , 4 As shown, it also includes a second integrated operational amplifier U2, a third liquid level detection probe 3, and a third signal input terminal 3.1; the bottom of the third liquid level detection probe 3 is located at the set upper limit of the liquid level T.

[0025] The inverting input of the second integrated operational amplifier U2 is connected to the inverting input of the first integrated operational amplifier U1 via resistor R13; the third signal input 3.1 is connected to the third liquid level detection probe 3, and is connected to the non-inverting input of the second integrated operational amplifier U2 via a series circuit of resistors R10, R9, and R8; a capacitor C10 is connected between the third signal input 3.1 and ground; the connection point of resistors R10 and R9 is connected to the regulated power supply VIN and one end of capacitor C8, and the other end of capacitor C8 is grounded; resistor R10 and capacitor C8 form a third RC filter. The circuit consists of: the connection point of resistors R9 and R8 is connected to one end of resistor R12 and capacitor C9, and the other end of resistor R12 and capacitor C9 is grounded; resistors R9 and R12 form a voltage divider circuit; capacitor C7 is connected between the non-inverting input of the second integrated operational amplifier U2 and ground; resistors R8 and capacitor C7 form a fourth RC filter circuit; resistor R11 is connected between the non-inverting input and output OUT2 of the second integrated operational amplifier U2 to form a positive feedback circuit; the output OUT2 of the second integrated operational amplifier U2 is connected to the controller signal input.

[0026] Beneficial or exemplary, such as Figure 4 As shown, the surfaces of the first liquid level detection probe 1, the second liquid level detection probe 2, and the third liquid level detection probe 3 are provided with a nickel plating layer, which serves to prevent corrosion and conduct electricity; the length of the first liquid level detection probe 1 is greater than that of the second liquid level detection probe 2, and the length of the third liquid level detection probe 3 is less than that of the second liquid level detection probe 2; the first liquid level detection probe 1 and the second liquid level detection probe 2 are used to detect the 50% liquid level, and the first liquid level detection probe 1 and the third liquid level detection probe 3 are used to detect the upper limit T of the liquid level.

[0027] Of course, the present invention can be extended by adding third and fourth integrated operational amplifiers, fourth and fifth liquid level detection probes and fourth and fifth signal input terminals; for detecting liquid level states such as 25% and 75%.

[0028] The circuit principle of this invention is briefly described as follows:

[0029] One or two liquid level detection probe circuits, such as Figure 2 As shown:

[0030] When the first liquid level detection probe 1 and the second liquid level detection probe 2 are in the container 5 and neither probe is in contact with the liquid, or only one probe is in contact with the liquid, a high resistance state exists between the first liquid level detection probe 1 and the second liquid level detection probe 2. Therefore, the voltage of the second liquid level detection probe 2 is 0V. After passing through the voltage divider circuit composed of filter capacitor C3, resistor R5, and resistor R6, and then through filter capacitor C6, the voltage is output to the inverting input terminal of the first integrated operational amplifier U1. At this time, the voltage at the inverting input terminal of the first integrated operational amplifier U1 is U. 30 =0V; The regulated power supply VIN is filtered by the filter capacitor C2, and then by the RC circuit composed of resistor R1 and capacitor C1 before being connected to one end of the first liquid level detection probe 1. Since there is no loop between the first liquid level detection probe 1 and the second liquid level detection probe 2, the voltage on the first liquid level detection probe 1 is close to the voltage of the regulated power supply VIN. The regulated power supply VIN is then filtered by the voltage divider circuit composed of resistors R2 and R3.

[0031] The voltage after voltage division is VIN is the regulated power supply voltage;

[0032] After passing through capacitor C4 for filtering and an RC filter circuit consisting of resistor R4 and capacitor C5, the output is given to the non-inverting input of the first integrated operational amplifier U1. At this time, the initial state voltage of the non-inverting input of the first integrated operational amplifier U1 is... At this time, the voltage U at the non-inverting input terminal of the first integrated operational amplifier U1 is... 20 Greater than the inverting input voltage U 30 ,Right now The voltage U output from the output terminal of the first integrated operational amplifier U1 is...OUT The power supply voltage U of the first integrated operational amplifier U1 VIN ,Right now .

[0033] Voltage U OUT1 The voltage is fed back to the non-inverting input of the first operational amplifier U1 through feedback resistor R7. Therefore, the voltage at the non-inverting input of the first operational amplifier U1 is approximately:

[0034] However, due to the inverting input terminal U of the first integrated operational amplifier U1 30 If the voltage is 0V, the output of the first integrated operational amplifier U1 will remain unchanged. .

[0035] When both the first liquid level detection probe 1 and the second liquid level detection probe 2 are in contact with the liquid, an equivalent resistance will be formed between the first liquid level detection probe 1 and the second liquid level detection probe 2 due to the equivalent resistance of the liquid. For ease of analysis, this can be considered equivalent to a megawatt-level resistor connecting the first liquid level detection probe 1 and the second liquid level detection probe 2. At this time, due to the existence of the equivalent resistance, the voltage VIN of the regulated power supply passes through resistor R1, the first liquid level detection probe 1, and the liquid to the second liquid level detection probe 2. After being filtered by filter capacitor C3, it is connected to the inverting input terminal of the first integrated operational amplifier U1 through a voltage divider circuit composed of resistors R5 and R6.

[0036] After actual testing, when resistors R5 and R6 are selected as megawatt-level resistors to match the equivalent resistance between the first liquid level detection probe 1 and the second liquid level detection probe 2, the voltage at the inverting input terminal of the first integrated operational amplifier U1 is:

[0037] ;

[0038] Therefore, simply adjusting the values ​​of resistors R5 and R6 will achieve the desired result. This results in the voltage at the non-inverting input terminal of the first integrated operational amplifier U1 being less than the voltage at the inverting input terminal, thereby causing the output voltage U of the first integrated operational amplifier U1 to be less than the voltage at the inverting input terminal. OUT1 It is close to 0V.

[0039] Due to the presence of the positive feedback resistor R7, the voltage at the non-inverting input terminal of the first operational amplifier U1 is as follows:

[0040] ;

[0041] Therefore, by simply adjusting the resistance ratio of resistors R2 and R3, the voltage U at the non-inverting input of the first operational amplifier U1 can be adjusted. 20The voltage is lower than the non-inverting input voltage of the liquid level detection probe when it is in air, thus creating a Schmitt trigger effect. This effectively prevents output signal oscillation caused by fluctuations in the matching resistance between the first liquid level detection probe 1 and the second liquid level detection probe 2. Connecting the output terminal OUT1 of the first integrated operational amplifier U1 to the controller signal allows the voltage U to be controlled. OUT1 Determine whether the liquid level is higher than 50% of the set liquid level.

[0042] II. Three liquid level detection probe circuits, such as Figure 3 As shown:

[0043] When none of the first liquid level detection probe 1, the second liquid level detection probe 2, and the third liquid level detection probe 3 are in contact with liquid in container 5, or only one of them is in contact with liquid, U 30 = U 40 =0V, for the second integrated operational amplifier U2, since the voltage at the inverting input terminal U... 40 0, Non-inverting input voltage U 50 for:

[0044] At this time, the voltage at the output terminal OUT2 of the second integrated operational amplifier U2 is VIN; when the first liquid level detection probe 1 and the second liquid level detection probe 2 are in contact with the liquid but the third liquid level detection probe 3 is not in contact, for the second integrated operational amplifier U2, since a circuit is formed between the first liquid level detection probe 1 and the second liquid level detection probe 2, and

[0045] ,

[0046] Therefore, for the two input voltages of the second integrated operational amplifier U2, as long as the appropriate values ​​of resistors R9, R12, R8 and R11 are selected, U50>U40 can be achieved, and at this time, the output OUT2 of the second integrated operational amplifier U2 will be VIN.

[0047] When liquid simultaneously contacts the first liquid level detection probe 1, the second liquid level detection probe 2, and the third liquid level detection probe 3, since the first liquid level detection probe 1 and the second liquid level detection probe 2 are both charged probes, they form two equivalent resistances in parallel with the second liquid level detection probe 3. Therefore, the voltage U at the inverting input terminal of the first integrated operational amplifier U1 will... 30 for:

[0048]

[0049] in, The equivalent resistance between the first liquid level detection probe 1 and the second liquid level detection probe 2; The equivalent resistance between the third liquid level detection probe 3 and the second liquid level detection probe 2;

[0050] At this time, U30 = U40, and the voltage value increases compared to when there are only the first liquid level detection probe 1 and the second liquid level detection probe 2. Therefore, U50 < U40, which causes the level at the output terminal OUT2 of the second integrated operational amplifier U2 to flip. Connecting this signal to the controller determines that the liquid in the container 5 has reached the upper liquid level limit, and corresponding action processing can be performed, such as controlling the liquid addition pump to stop working and prompting that the liquid is full, etc.

[0051] It should be noted that the controller described in the present invention can be a PID controller U1, a general-purpose processor, a special-purpose processor, a conventional processor, a digital signal processor (DSP), a microprocessor associated with the DSP core, a microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) circuit, and any other type of integrated circuit (IC) and state machine, etc.

Claims

1. A multi-position contact liquid level detection device, characterized in that: The system includes a controller, a liquid level detection circuit, a liquid level detection probe, a display, and a regulated power supply VIN. The regulated power supply VIN is connected to the power input terminals of the controller and the liquid level detection circuit, respectively, to provide a stable voltage to the controller and the liquid level detection circuit. The liquid level detection probe includes at least a first liquid level detection probe and a second liquid level detection probe, each connected to a corresponding signal input terminal of the liquid level detection circuit. The controller signal input terminal is connected to the signal output terminal of the liquid level detection circuit to obtain the liquid level status of the detected liquid. The display data input terminal is connected to the controller data output terminal via a communication interface to display the liquid level status of the detected liquid. The liquid level detection circuit includes a first signal input terminal and a second signal input terminal. The first signal input terminal is connected to the first liquid level detection probe and is connected to the non-inverting input terminal of the first integrated operational amplifier U1 via a series circuit of resistors R1, R2, and R4. A capacitor C1 is connected between the first signal input terminal and ground. The connection point of resistors R1 and R2 is connected to one end of the regulated power supply VIN and capacitor C2, and the other end of capacitor C2 is grounded. The connection point of resistors R2 and R4 is connected to one end of resistor R3 and capacitor C4, and the other end of resistor R3 and capacitor C4 is grounded. A capacitor C5 is connected between the non-inverting input terminal of the first operational amplifier U1 and ground. A resistor R7 is connected between the non-inverting input terminal and the output terminal OUT1 of the first operational amplifier U1 to form a positive feedback circuit. The output terminal OUT1 of the first operational amplifier U1 is connected to the controller signal input terminal. The second signal input terminal is connected to the second liquid level detection probe. A capacitor C3 is connected between the second signal input terminal and ground, and is connected to the inverting input terminal of the first operational amplifier U1 through a resistor R5. A parallel circuit consisting of a resistor R6 and a capacitor C6 is connected between the inverting input terminal of the first operational amplifier U1 and ground.

2. The multi-position contact liquid level detection device according to claim 1, characterized in that: It also includes a second integrated operational amplifier U2, a third liquid level detection probe, and a third signal input terminal; the inverting input terminal of the second integrated operational amplifier U2 is connected to the inverting input terminal of the first integrated operational amplifier U1 via resistor R13; the third signal input terminal is connected to the third liquid level detection probe, and is connected to the non-inverting input terminal of the second integrated operational amplifier U2 via a series circuit of resistors R10, R9, and R8; a capacitor C10 is connected between the third signal input terminal and ground; the connection point of resistors R10 and R9 is connected to the regulated power supply VIN and one end of capacitor C8, and the other end of capacitor C8 is grounded; the connection point of resistors R9 and R8 is connected to one end of resistor R12 and capacitor C9, and the other end of resistor R12 and capacitor C9 is grounded; a capacitor C7 is connected between the non-inverting input terminal of the second integrated operational amplifier U2 and ground; a resistor R11 is connected between the non-inverting input terminal and the output terminal OUT2 of the second integrated operational amplifier U2 to form a positive feedback circuit; the output terminal OUT2 of the second integrated operational amplifier U2 is connected to the controller signal input terminal.

3. The multi-position contact liquid level detection device according to claim 2, characterized in that: The surfaces of the first liquid level detection probe, the second liquid level detection probe, and the third liquid level detection probe are provided with a nickel plating layer.

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