Threshold self-adaptive liquid level detection device

Abstract

The utility model discloses a threshold value self-adaption liquid level detection device which comprises a control panel, a single chip microcomputer arranged on the control panel, an excitation probe interface, a detection probe interface, an excitation circuit and a detection adjusting circuit. According to the utility model, the detection threshold value is automatically adjusted according to the solution characteristics, the hysteresis interval problem which lags behind the input quantity change when the output quantity changes is eliminated, the accurate judgment is realized, and the stability is high; meanwhile, an analog circuit design is adopted, and the manufacturing cost is low.

Description

Technical Field

[0001] This utility model relates to a liquid level detection device, and more particularly to a threshold adaptive liquid level detection device. Background Technology

[0002] Currently, liquid level detection is mostly achieved using capacitive methods, and threshold judgment is often used to improve accuracy. However, in applications such as microbial culture instruments and chemical analyzers, solvents are often added to the solutions used, such as purified water, as needed. Since the resistivity of different solvents varies greatly, the capacitance measurement value fluctuates greatly, leading to misjudgments. At the same time, capacitive detection is expensive and easily affected by the environment, causing large fluctuations in the acquired signal, which also reduces the accuracy of liquid level detection. Summary of the Invention

[0003] In view of this, the present invention provides a threshold adaptive liquid level detection device, which achieves accurate judgment and high stability; at the same time, it adopts analog circuit design, resulting in low manufacturing cost.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] The threshold adaptive liquid level detection device of this utility model includes a control board, a microcontroller, an excitation probe interface, a detection probe interface, an excitation circuit, and a detection adjustment circuit, which are mounted on the control board.

[0006] The excitation circuit consists of a diode D1 and a resistor R9. The positive terminal of the diode D1 is connected to the power supply Vcc, and the negative terminal of the diode D1 is connected to the excitation probe interface via the current-limiting resistor R9. The excitation probe interface is used to connect the excitation probe of an external device.

[0007] The detection and adjustment circuit includes a filter protection circuit, a feedback hysteresis circuit, an optocoupler isolation circuit, an ADC acquisition circuit, and an adjustable reference circuit.

[0008] The filter protection circuit includes a resistor R5. The high potential end of the resistor R5 is connected to the detection probe interface and is connected to the ground terminal GND via a clamping diode D2. The low potential end of the resistor R5 is connected to the feedback hysteresis circuit and the ADC acquisition circuit and is connected to the ground terminal GND via a parallel circuit composed of capacitors C1, C2 and resistor R6.

[0009] The feedback hysteresis circuit includes an integrated operational amplifier U1. The inverting input terminal of the integrated operational amplifier U1 is connected to the high potential terminal of the resistor R5. The non-inverting input terminal of the integrated operational amplifier U1 is connected to the adjustable reference circuit via the resistor R3. A feedback resistor R4 is connected between the non-inverting input terminal and the output terminal of the integrated operational amplifier U1. The output terminal of the integrated operational amplifier U1 is connected to the optocoupler isolation circuit.

[0010] The optocoupler isolation circuit includes an optocoupler U2. The positive terminal of the LED at the input end of the optocoupler U2 is connected to the power supply Vcc via a current-limiting resistor R8. The negative terminal of the LED at the input end of the optocoupler U2 is connected to the output end of the integrated operational amplifier U1. The emitter of the transistor at the output end of the optocoupler U2 is connected to the ground terminal GND. The collector of the transistor at the output end of the optocoupler U2 is connected to the signal acquisition interface GPIO of the microcontroller.

[0011] The ADC acquisition circuit includes an integrated operational amplifier U3. The non-inverting input terminal of the integrated operational amplifier U3 is connected to the low potential terminal of the resistor R5. A feedback resistor R7 is connected between the inverting input terminal and the output terminal of the integrated operational amplifier U3. The output terminal of the integrated operational amplifier U3 is connected to the ADC acquisition interface of the microcontroller.

[0012] The adjustable reference circuit includes an integrated operational amplifier U4. The inverting input terminal of the integrated operational amplifier U4 is connected to the ground terminal GND via a resistor R1, and is connected to the output terminal of the integrated operational amplifier U4 via a feedback resistor R2. The output terminal of the integrated operational amplifier U4 is connected to the non-inverting input terminal of the integrated operational amplifier U3 via a resistor R3. The non-inverting input terminal of the integrated operational amplifier U4 is connected to the DAC output interface of the microcontroller.

[0013] Optionally, several detection and adjustment circuits can be provided on the control board, each detection and adjustment circuit being connected to a corresponding detection probe interface; the number of detection and adjustment circuits depends on the number of liquid levels to be detected.

[0014] This invention automatically adjusts the detection threshold based on the solution characteristics, eliminating the hysteresis problem where the output changes lag behind the input changes, thus achieving accurate judgment and high stability; at the same time, it adopts an analog circuit design, resulting in low manufacturing cost. Attached Figure Description

[0015] Figure 1 These are structural schematic diagrams and circuit diagrams of embodiments of this utility model.

[0016] Figure 2 This is a schematic diagram illustrating the generation of the hysteresis interval as described in an embodiment of this utility model. Detailed Implementation

[0017] The embodiments of this utility model will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solution of this utility model and provide detailed implementation methods and specific operation processes. However, the protection scope of this utility model is not limited to the following embodiments.

[0018] It should be noted that, in the description of this utility model, unless otherwise explicitly specified and limited, the terms "connected" and "linked" 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 utility model based on the specific circumstances.

[0019] like Figure 1 As shown, the threshold adaptive liquid level detection device of this utility model includes a control board 1, a microcontroller, an excitation probe interface 2, a detection probe interface 3, an excitation circuit, and a detection adjustment circuit, all mounted on the control board 1.

[0020] The excitation circuit consists of diode D1 and resistor R9. The positive terminal of diode D1 is connected to the power supply Vcc, and the negative terminal of diode D1 is connected to excitation probe interface 2 through current limiting resistor R9. Excitation probe interface 2 is used to connect the excitation probe of the peripheral device.

[0021] The detection and adjustment circuit includes a filter protection circuit, a feedback hysteresis circuit, an optocoupler isolation circuit, an ADC acquisition circuit, and an adjustable reference circuit.

[0022] The filter protection circuit includes resistor R5. The high potential end of resistor R5 is connected to the detection probe interface 3 and is connected to the ground terminal GND through clamping diode D2 (transient suppression diode). The low potential end of resistor R5 is connected to the feedback hysteresis circuit and ADC acquisition circuit and is connected to the ground terminal GND through a parallel circuit composed of capacitors C1, C2 and resistor R6. The filter protection circuit is used for overvoltage protection and to improve interference capability.

[0023] The feedback hysteresis circuit includes an integrated operational amplifier U1. The inverting input of the integrated operational amplifier U1 is connected to the low potential end of the resistor R5, and the non-inverting input of the integrated operational amplifier U1 is connected to the adjustable reference circuit via the resistor R3. A feedback resistor R4 is connected between the non-inverting input and the output of the integrated operational amplifier U1, and the output of the integrated operational amplifier U1 is connected to the optocoupler isolation circuit. The feedback hysteresis circuit is used to eliminate the hysteresis problem that exists when the output changes behind the input changes, thereby realizing the control of the hysteresis range.

[0024] The optocoupler isolation circuit includes an optocoupler U2. The positive terminal of the LED at the input of the optocoupler U2 is connected to the power supply Vcc via a current-limiting resistor R8. The negative terminal of the LED at the input of the optocoupler U2 is connected to the output of the integrated operational amplifier U1. The emitter of the transistor at the output of the optocoupler U2 is connected to the ground terminal GND. The collector of the transistor at the output of the optocoupler U2 is connected to the signal acquisition interface GPIO of the microcontroller.

[0025] The ADC acquisition circuit includes an integrated operational amplifier U3. The non-inverting input terminal of the integrated operational amplifier U3 is connected to the low-potential terminal of a resistor R5. A feedback resistor R7 is connected between the inverting input terminal and the output terminal of the integrated operational amplifier U3. The output terminal of the integrated operational amplifier U3 is connected to the ADC (analog-to-digital converter) acquisition interface of the single-chip microcomputer.

[0026] The adjustable reference circuit includes an integrated operational amplifier U4. The inverting input terminal of the integrated operational amplifier U4 is connected to the ground terminal GND through a resistor R1 and is connected to the output terminal of the integrated operational amplifier U4 through a feedback resistor R2. The output terminal of the integrated operational amplifier U4 is connected to the non-inverting input terminal of the integrated operational amplifier U3 through a resistor R3. The non-inverting input terminal of the integrated operational amplifier U4 is connected to the DAC (digital-to-analog converter) acquisition interface of the single-chip microcomputer.

[0027] Exemplarily, there are several detection and adjustment circuits provided on the control board, and each detection and adjustment circuit is respectively connected to a corresponding detection probe interface; the number of detection and adjustment circuits is determined according to the number of liquid levels to be detected.

[0028] As Figure 1 、 2 shown, the working principle of the present invention is briefly described as follows:

[0029] The excitation signal provided by the excitation circuit to the peripheral excitation probe forms a loop through the solution in the container (such as a reaction dish) and supplies the excitation signal to the detection probe; when the liquid level does not reach the specified detection height, the loop cannot be formed, and the excitation signal cannot reach the detection probe, so the detection and adjustment circuit does not receive the signal and outputs a high-level signal.

[0030] When the liquid level reaches the detection probe, the excitation signal reaches the detection probe through the solution, and reaches the feedback hysteresis circuit through the detection probe interface 3 and the filtering and protection circuit; the excitation signal generates a voltage VOUT through the filtering and protection circuit and is compared with the Vref_A voltage value output by the current adjustable reference circuit. If VOUT > Vref_A, it means that the current liquid level has reached, and the integrated operational amplifier U1 changes its output state and outputs a low level; at the same time, due to the change in the output state of the integrated operational amplifier U1, according to the series-parallel voltage division principle, this value changes to Vref_B,

[0031] and ref_B < Vref_A. At this time, Vref_A and Vref_B generate a hysteresis interval, as Figure 2 shown; finally, it is triggered when VOUT > Vref_A and must become non-triggered when VOUT < Vref_B.

[0032] From the above, it can be known that:

[0033] When the detection unit is not triggered, it means that the current liquid level height has not reached the detection position of the detection probe;

[0034] When the detection unit is triggered, it indicates that the current liquid level has reached the detection position of the detection probe.

[0035] The threshold adaptive liquid level detection principle of this utility model is as follows:

[0036] Different solutions have different electrical conductivity, which is reflected in their different resistivity values. During the experiment, the following factors can affect the liquid level detection value, causing fluctuations in the measurement results:

[0037] 1. The depth of the probe inserted into the liquid surface, i.e. the change in the effective cross-sectional area of ​​the probe electrode, is determined by the formula: R=ρ×L / S. The length L of the liquid between the excitation probe and the detection probe remains constant. The change in the depth of the probe immersed in the liquid surface will affect the cross-sectional area S, resulting in a change in resistance.

[0038] Note:

[0039] ρ: Liquid resistivity (unit: Ω·m)

[0040] L: Length of the liquid between the two electrodes (unit: m)

[0041] S: Effective cross-sectional area of ​​the probe electrode (unit: m²)

[0042] Second, changes in liquid resistivity ρ are commonly caused by the addition of solutions such as antibacterial and phosphorus-free solutions or external contamination during instrument operation, as well as the addition of purified water to mixed solutions. All of these changes alter the value of liquid resistivity ρ, resulting in significant resistance variations.

[0043] Third, the presence of a small number of air bubbles in the solution, which adhere to the probe, affects the detection.

[0044] Fourth, if the probe is immersed in water for a long time, it is prone to electrolysis, which can lead to rust or contamination and affect the resistivity ρ. This situation is a long-term gradual change, while the first three are short-term fluctuations.

[0045] The above-mentioned changes ultimately manifest as variations in the voltage value VOUT at the output of the filter protection circuit. To address the interference of these changes on the output results, this invention performs an initial calibration of the peripheral detection probes before starting the liquid level detection process, such as... Figure 2 As shown:

[0046] The microcontroller acquires the voltage value VOUT at the output of the filter protection circuit in real time through the ADC acquisition circuit. When the height of the liquid being detected reaches the set height of the detection probe, the microcontroller uses the acquired calibration reference voltage value VOUT at this time. ref The control reference voltage value VDAC is calculated through the embedded program. ref And will regulate the reference voltage value VDAC ref and calibration reference voltage value VOUT refsave;

[0047] VDAC ref ={ VOUT ref ⅹ80%ⅹ(R3+R4)-Vcc} / {R4ⅹ(R1+R2)},Formula (1);

[0048] After the liquid level detection begins, the microcontroller acquires the voltage value VOUT at the output of the filter protection circuit in real time through the ADC acquisition circuit and compares it with VOUT. ref In comparison, the trend of change is calculated using a sliding algorithm, when VOUT and VOUT ref When the deviation exceeds ±5%, the microcontroller readjusts the VDAC value output to the adjustable reference circuit according to the formula (1) to ensure adaptive threshold adjustment and hysteresis range adjustment for different solutions, thereby achieving accurate liquid level detection.

[0049] Finally, it should be emphasized that the above description is merely a preferred embodiment of this utility model and is not intended to limit this utility model. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make modifications to the technical solutions described in the foregoing embodiments without creative effort, or make equivalent substitutions for some of the technical features. Therefore, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A threshold adaptive liquid level detection device, characterized in that: Includes a control board, a microcontroller, an excitation probe interface, a detection probe interface, an excitation circuit, and a detection adjustment circuit mounted on the control board; The excitation circuit consists of a diode D1 and a resistor R9. The positive terminal of the diode D1 is connected to the power supply Vcc, and the negative terminal of the diode D1 is connected to the excitation probe interface via the current-limiting resistor R9. The detection and adjustment circuit includes a filter protection circuit, a feedback hysteresis circuit, an optocoupler isolation circuit, an ADC acquisition circuit, and an adjustable reference circuit. The filter protection circuit includes a resistor R5, the high potential end of which is connected to the detection probe interface and connected to the ground terminal GND via a clamping diode D2. The low-potential end of resistor R5 is connected to the feedback hysteresis circuit and the ADC acquisition circuit, and is connected to the ground terminal GND through a parallel circuit composed of capacitors C1, C2 and resistor R6. The feedback hysteresis circuit includes an integrated operational amplifier U1. The inverting input terminal of the integrated operational amplifier U1 is connected to the high potential terminal of the resistor R5. The non-inverting input terminal of the integrated operational amplifier U1 is connected to the adjustable reference circuit via the resistor R3. A feedback resistor R4 is connected between the non-inverting input terminal and the output terminal of the integrated operational amplifier U1. The output terminal of the integrated operational amplifier U1 is connected to the optocoupler isolation circuit. The optocoupler isolation circuit includes an optocoupler U2. The positive terminal of the LED at the input end of the optocoupler U2 is connected to the power supply Vcc via a current-limiting resistor R8. The negative terminal of the LED at the input end of the optocoupler U2 is connected to the output end of the integrated operational amplifier U1. The emitter of the transistor at the output end of the optocoupler U2 is connected to the ground terminal GND. The collector of the transistor at the output end of the optocoupler U2 is connected to the signal acquisition interface GPIO of the microcontroller. The ADC acquisition circuit includes an integrated operational amplifier U3. The non-inverting input terminal of the integrated operational amplifier U3 is connected to the low potential terminal of the resistor R5. A feedback resistor R7 is connected between the inverting input terminal and the output terminal of the integrated operational amplifier U3. The output terminal of the integrated operational amplifier U3 is connected to the ADC acquisition interface of the microcontroller. The adjustable reference circuit includes an integrated operational amplifier U4. The inverting input terminal of the integrated operational amplifier U4 is connected to the ground terminal GND via a resistor R1, and is connected to the output terminal of the integrated operational amplifier U4 via a feedback resistor R2. The output terminal of the integrated operational amplifier U4 is connected to the non-inverting input terminal of the integrated operational amplifier U3 via a resistor R3. The non-inverting input terminal of the integrated operational amplifier U4 is connected to the DAC output interface of the microcontroller.

2. The threshold adaptive liquid level detection device according to claim 1, characterized in that: The control board has several detection and adjustment circuits, each of which is connected to a corresponding detection probe interface.

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