A conductivity sensor and its automatic sizing method

Abstract

This invention relates to the field of sensor technology, specifically to a conductivity sensor and its automatic ranging method. The conductivity sensor includes a sensor body and a conductivity detection circuit. The sensor body includes an excitation signal terminal and a detection signal terminal. The conductivity detection circuit includes a conductivity excitation drive circuit and an automatic ranging circuit. The automatic ranging circuit includes a first operational amplifier circuit, a second operational amplifier circuit, a third operational amplifier circuit, and a fourth operational amplifier circuit connected in parallel. The detection ranges of the first, second, third, and fourth operational amplifier circuits are different and proportional. This invention solves the technical problems existing in the prior art, such as untimely range switching when measuring solution conductivity, data errors during range switching affecting measurement accuracy, and time delay in output conductivity data.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and more specifically, to a conductivity sensor and its automatic range measurement method. Background Technology

[0002] A conductivity sensor is a specialized sensor for measuring changes in the conductivity of a solution. It is mainly used to detect the presence and concentration of ionic substances in a solution and can sensitively detect changes in the total concentration of charged ions in the solution.

[0003] The working principle of a conductivity sensor: The conductivity of a solution is the reciprocal of its resistance, reflecting the solution's ability to conduct current. Higher ion concentrations result in more mobile charge carriers and thus higher conductivity. The core component of the sensor is one or more pairs of parallel electrodes made of inert metal, fixed within a conductivity cell. The conductivity cell allows the solution to flow continuously across the electrode surfaces. A stable low-frequency sinusoidal or square wave AC voltage is applied between the electrodes. When the ion-containing solution flows through the conductivity cell, the ions migrate directionally under the influence of the AC electric field, forming a current. The conductivity of the solution can be obtained by measuring the current flowing through the solution or by directly measuring the conductivity across the conductivity cell.

[0004] Since the conductivity of a solution is related to the concentration of charged ions in the solution, and the conductivity of a solution has a linear relationship with the ion concentration within a certain range, conductivity sensors can be used to quantitatively determine the concentration of target ions for quantitative analysis. Solutions of different concentrations have different total concentrations of charged ions, and conductivity sensors also have a maximum limit on the conductivity signal they can detect. When the total concentration of charged ions in the solution exceeds the maximum detection limit of the conductivity sensor, the conductivity collected by the sensor will be a flat line, and it is no longer suitable for measurement and analysis.

[0005] Currently, there are two methods for handling conductivity exceeding the limit with existing conductivity sensors: one is to manually switch the range of the conductivity sensor by turning a mechanical button, so that the detection range of the conductivity sensor can be increased; the other is to control the automatic switching of the range through analog switches and digital signals, without the need for human intervention. The first approach has the following drawbacks: the total ion concentration in the solution system changes dynamically and continuously. When the total ion concentration exceeds the current range, if the range is not manually switched in time, the output conductivity data will be distorted due to range mismatch. The second approach has the following drawbacks: the analog switch has an internal on-resistance when it is turned on and off. The resistance of this on-resistance is generally between 20 ohms and 100 ohms. When switching ranges, this on-resistance will introduce systematic errors, affecting the accuracy and precision of conductivity measurement. In addition, since the acquired data needs to be filtered by software, the output conductivity data has a certain delay. Finally, the automatic range switching is controlled by a digital signal. When the digital signal output by the microcontroller is interfered with, the analog switch may switch ranges randomly or incorrectly, resulting in abnormal values ​​in the output conductivity data. Summary of the Invention

[0006] The purpose of this application is to provide a conductivity sensor and its automatic range implementation method, which solves the technical problems existing in the prior art, such as untimely range switching when measuring the conductivity of a solution, data errors during range switching affecting measurement accuracy, and time delay in output conductivity data.

[0007] To solve the above-mentioned technical problems, the solution adopted in this application is as follows:

[0008] A conductivity sensor is used to detect the conductivity of a solution in a conductivity cell, comprising a conductivity sensor body and a conductivity detection circuit; the conductivity sensor body includes an excitation signal terminal and a detection signal terminal, and the conductivity detection circuit includes a conductivity excitation drive circuit and an automatic sizing circuit;

[0009] The conductivity excitation drive circuit generates an excitation signal, which is connected to the first electrode of the conductivity cell through the excitation signal terminal. The excitation signal is applied to the first electrode, and the automatic sizing circuit collects the conductivity value of the solution to be tested in the conductivity cell from the second electrode through the detection signal terminal.

[0010] The conductivity excitation drive circuit includes a digital driver, an oscillator, a frequency divider, and a conductivity excitation drive connection circuit. The oscillator is electrically connected to the digital driver through the connection circuit, the frequency divider, and the digital driver. The automatic scouring circuit includes a first operational amplifier circuit, a second operational amplifier circuit, a third operational amplifier circuit, and a fourth operational amplifier circuit connected in parallel.

[0011] The first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit have different detection ranges and are proportional to each other.

[0012] Preferably, the conductivity excitation drive connection circuit includes an energy storage element, a filter source element, and a coupling element;

[0013] The power input terminal of the oscillator U2 is connected to the first DC source through the energy storage element and grounded through the first filter element;

[0014] The signal output terminal of the oscillator U2 is connected to the signal input terminal of the frequency divider U1;

[0015] The power input terminal of the frequency divider U1 is connected to the first DC source and grounded through the second filter element;

[0016] The signal output terminal of the frequency divider U1 is connected to the signal input terminal of the digital driver U3 through the coupling element;

[0017] The positive power input terminal of the digital driver U3 is connected to the second DC power supply and grounded through the third filter element;

[0018] The negative power input terminal of the digital driver U3 is connected to a third DC power supply and grounded through the fourth filter element.

[0019] Preferably, the first operational amplifier circuit includes a first operational amplifier and a first feedback network; the feedback input terminal of the first feedback network is connected to the output terminal of the first operational amplifier; the feedback output terminal of the first feedback network is connected to the inverting input terminal of the first operational amplifier; and the non-inverting input terminal of the first operational amplifier is grounded.

[0020] The second operational amplifier circuit includes a second operational amplifier and a second feedback network; the feedback input terminal of the second feedback network is connected to the output terminal of the second operational amplifier; the feedback output terminal of the second feedback network is connected to the inverting input terminal of the second operational amplifier; the non-inverting input terminal of the second operational amplifier is grounded.

[0021] The third operational amplifier circuit includes a third operational amplifier and a third feedback network; the feedback input terminal of the third feedback network is connected to the output terminal of the third operational amplifier; the feedback output terminal of the third feedback network is connected to the inverting input terminal of the third operational amplifier; the non-inverting input terminal of the third operational amplifier is grounded.

[0022] The fourth operational amplifier circuit includes a fourth operational amplifier and a fourth feedback network; the feedback input terminal of the fourth feedback network is connected to the output terminal of the fourth operational amplifier; the feedback output terminal of the fourth feedback network is connected to the inverting input terminal of the fourth operational amplifier; the non-inverting input terminal of the fourth operational amplifier is grounded.

[0023] The inverting input terminals of the first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit are connected in parallel to serve as the detection terminal for the conductivity of the solution to be tested in the conductivity cell.

[0024] Preferably, the first feedback network includes a first feedback resistor; the second feedback network includes a second feedback resistor; the third feedback network includes a third feedback resistor; and the fourth feedback network includes a fourth feedback resistor.

[0025] The ratio of the resistance values ​​of the first feedback resistor, the second feedback resistor, the third feedback resistor, and the fourth feedback resistor is 1:10:100:1000.

[0026] Preferably, the analog conductance voltage signals output by the first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit are... , , , The proportional relationship is as follows:

[0027] ;

[0028] The detection range of the second operational amplifier circuit is 10 times that of the first operational amplifier circuit; the detection range of the third operational amplifier circuit is 100 times that of the first operational amplifier circuit; and the detection range of the fourth operational amplifier circuit is 1000 times that of the first operational amplifier circuit.

[0029] Preferably, the conductivity detection circuit is further connected to an analog-to-digital conversion circuit;

[0030] The analog-to-digital conversion circuit includes an analog-to-digital converter U8 and a filter capacitor network and a pull-up resistor network electrically connected to it.

[0031] The power input terminal and reference power input terminal of the analog-to-digital converter U8 are connected to the input power supply and reference power supply respectively through the filter capacitor network;

[0032] The chip select signal input terminal, clock signal input terminal, serial data input terminal, serial data output terminal, and logic output terminal of the analog-to-digital converter U8 are respectively connected to a 3.3V positive power supply through the pull-up resistor network;

[0033] The first positive analog signal input terminal of the analog-to-digital converter U8 is electrically connected to the output terminal of the first operational amplifier; the first negative analog signal input terminal of the analog-to-digital converter U8 is electrically connected to the output terminal of the second operational amplifier; the second positive analog signal input terminal of the analog-to-digital converter U8 is electrically connected to the output terminal of the third operational amplifier; and the second negative analog signal input terminal of the analog-to-digital converter U8 is electrically connected to the output terminal of the fourth operational amplifier.

[0034] Preferably, the analog-to-digital conversion circuit is further connected to a microcontroller;

[0035] The analog-to-digital converter circuit is electrically connected to the microcontroller via an analog-to-digital converter U8; the chip select signal input terminal of the analog-to-digital converter U8 is electrically connected to the chip select signal output terminal of the microcontroller, the clock signal input terminal of the analog-to-digital converter U8 is electrically connected to the clock signal output terminal of the microcontroller, the serial data input terminal of the analog-to-digital converter U8 is electrically connected to the serial data output terminal of the microcontroller, the serial data output terminal of the analog-to-digital converter U8 is electrically connected to the serial data input terminal of the microcontroller, and the logic output terminal of the analog-to-digital converter U8 is electrically connected to the logic input terminal of the microcontroller.

[0036] A method for automatic sizing of a conductivity sensor, characterized by comprising the following steps:

[0037] S1: The electrode that generates an AC excitation signal and applies it to the conductivity cell;

[0038] S2: Acquire the conductivity signal of the solution to be tested in the conductivity cell, input the conductivity signal into several parallel operational amplifiers proportional to the feedback resistors, and output several analog conductivity voltage signals; the several parallel operational amplifiers proportional to the feedback resistors are used to realize several detection ranges without the need for range switching operation.

[0039] S3: Perform analog-to-digital conversion on several analog conductance voltage signals to obtain several digital conductance voltage signals with different ranges;

[0040] S4: Based on the digital conductance voltage signal, the feedback resistor value of the operational amplifier that generates the digital conductance voltage signal, and the amplitude of the input AC excitation signal, calculate several conductance values, and select the conductance value closest to the midpoint of the range as the final value.

[0041] Preferably, the relationship between the output analog conductance voltage signal and the feedback resistor of the operational amplifier that outputs the analog conductance voltage signal is as follows:

[0042]

[0043] in, This represents the output analog conductance voltage signal value, in volts (V). This indicates the resistance value of the feedback resistor, in ohms (Ω). The conductivity of the solution being tested in the conductivity cell is expressed in Siemens (S). It represents the voltage amplitude of the AC excitation signal applied to the two electrodes, and the unit is volt (V).

[0044] Preferably, the feedback resistor values ​​of the plurality of operational amplifiers in S2 are approximately equal to the values ​​of the feedback resistors. The proportional relationship is given by a factor of n, where n is an integer; the amplitude relationships of the several output analog voltage signals are also proportional. A proportional relationship, where n is an integer.

[0045] The technical solution of this application has at least the following advantages and beneficial effects:

[0046] 1. This invention employs a multi-channel detection method. Each channel has a different detection range (detection scale) for the conductivity of the solution to be tested in the conductivity cell, and the ranges are linearly proportional to each other. There is no need for manual control of range switching via buttons, nor for analog switches or other control switches to manage the conductivity detection range switching. Multiple ranges are detected simultaneously, resulting in multiple simulated conductivity voltage signal values. These simulated conductivity voltages are processed, and the conductivity is calculated based on the relationship between the input excitation signal amplitude, the output simulated conductivity voltage signal value, the conductivity, and the feedback resistor value. The conductivity value closest to the midpoint of the range is selected as the final detection result.

[0047] In response to the above conductivity detection methods, the conductivity sensor disclosed in this invention is equipped with an automatic range circuit. The automatic range circuit includes a first operational amplifier circuit, a second operational amplifier circuit, a third operational amplifier circuit, and a fourth operational amplifier circuit connected in parallel. The detection ranges of the first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit are different and proportional. The automatic range circuit can realize multi-channel detection of conductivity.

[0048] Therefore, through the above method and the corresponding settings of the conductivity sensor, there is no need to manually determine whether the current solution conductivity exceeds the current measurement range, thus easily avoiding the problem of untimely manual range switching when the solution conductivity exceeds the detection range. In addition, multiple operational amplifier circuits with different detection ranges work simultaneously, directly detecting analog conductivity voltage signals within multiple measurement ranges, without the need to set up analog switches to switch ranges. This avoids the impact of system errors caused by analog switches on measurement accuracy, and also avoids the problem of incorrect / random range switching caused by interference with the digital signal controlling the analog switch. Based on this, the system errors caused by analog switches are avoided, eliminating the need for software processing of system errors and solving the technical problem of output delay. Attached Figure Description

[0049] Figure 1 This is a circuit block diagram of a conductivity sensor that uses mechanical buttons to switch measurement ranges.

[0050] Figure 2 The circuit block diagram of a conductivity sensor that uses an analog switch to switch the measurement range;

[0051] Figure 3 This is a circuit structure block diagram of the present invention;

[0052] Figure 4 This is a flowchart of the automatic range setting method of the present invention;

[0053] Figure 5 This is a schematic diagram of the conductivity-driven excitation circuit of the present invention;

[0054] Figure 6 This is a schematic diagram of the automatic ranging circuit of the present invention;

[0055] Figure 7 This is a schematic diagram of the analog-to-digital converter circuit of the present invention. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. The terms "center," "upper," "lower," "inner," and "outer," indicating orientation or positional relationships based on the orientation or positional relationships shown in the figures, or the orientation or positional relationships commonly used when the product is in use, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed or operated in a specific orientation, and therefore should not be construed as a limitation on this application. It should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0058] The following section provides a more detailed introduction to the existing range switching technologies mentioned in the background section.

[0059] See Figure 1 , Figure 1 This is a circuit block diagram of a conductivity sensor that uses mechanical buttons for range switching, where operators manually switch ranges. The circuit includes a driver, conductivity cell, pre-amplifier signal conditioning module, button range switching module, temperature acquisition module, A / D converter, microcontroller, and LCD screen. The driver generates a stable AC voltage, which is applied to the two electrodes used to measure the ion concentration in the conductivity cell. The conductivity cell is where ions in the solution migrate directionally under the influence of an AC electric field. The pre-amplifier signal conditioning module converts the current flowing through the solution at the two ends of the conductivity cell or the conductivity at the two ends of the electrodes into an analog voltage signal output. The button range switching module... The module allows adjustment of the detection range of the pre-amplifier signal conditioning module, enabling conductivity measurements at different settings by toggling different buttons. The temperature acquisition module detects the temperature in the solution, thereby compensating for the conductivity readings to ensure stability and accuracy. The A / D converter converts the measured conductivity analog voltage signal into a first digital signal and outputs it to the microcontroller, and also converts the temperature analog signal detected by the temperature acquisition module into a second digital signal and outputs it to the microcontroller. The first and second digital signals are processed by the microcontroller and finally displayed on the LCD screen used to display the conductivity.

[0060] When measuring conductivity using this technical solution, since each range switch requires manual operation, there are technical problems such as range mismatch and measurement errors caused by untimely switching when the ion concentration in the solution changes beyond the current range.

[0061] Based on this, see Figure 2 , Figure 2 The circuit block diagram for a conductivity sensor that uses an analog switch to switch measurement ranges is shown below. Improvements were made to the aforementioned technical solution, including a driver source, conductivity cell, pre-amplifier signal conditioning module, analog switch switching module, A / D converter, microcontroller, and LCD screen. The manually controlled button switching module was replaced with an analog switch switching module. When the ion concentration in the solution reaches a set threshold within the current measurement range, the microcontroller outputs a digital signal to control the analog switch. The analog switch then controls the switching of the detection range of the pre-amplifier signal conditioning module. This allows the conductivity sensor's measurement range to be completely controlled by the microcontroller, eliminating the need for manual switching.

[0062] This technical solution solves the problem of untimely range switching caused by manual button range switching, leading to range mismatch and measurement errors, by replacing the manual button range switching module with an analog switch range switching module. However, using an analog switch range switching module for range switching also presents some technical problems and drawbacks: The analog switch has an internal resistance when it is on or off, typically between 20Ω and 100Ω. This internal resistance affects the amplification factor of the operational amplifier in the pre-amplifier signal conditioning module. Therefore, when the analog switch range switching module controls the pre-amplifier signal conditioning module to switch ranges, a systematic error is introduced, further affecting the accuracy of the final conductivity data. Furthermore, when measuring conductivity using this solution, the output conductivity data needs to be filtered by software to remove systematic errors, resulting in a certain delay. Finally, the digital signal output by the microcontroller is susceptible to interference, which can cause the analog switch range switching module to switch ranges arbitrarily or incorrectly, leading to abnormal conductivity data.

[0063] See Figures 3-4 This invention discloses an automatic range measurement method for a conductivity sensor. By detecting the conductivity value of the solution to be measured in a conductivity cell, multiple analog conductivity voltage signals at multiple ranges are obtained. These analog conductivity voltages are then digitized to obtain multiple digital conductivity voltage signals. Finally, a microcontroller processes these digital conductivity voltage signals to obtain the final conductivity. This method solves technical problems such as untimely range switching, data errors during range switching affecting measurement accuracy, and time delays in output conductivity data. The method includes the following steps:

[0064] S1: The electrode that generates an AC excitation signal and applies it to the conductivity cell;

[0065] S2: Acquire the conductivity signal of the solution to be tested in the conductivity cell, input the conductivity signal into several parallel operational amplifiers proportional to the feedback resistors, and output several analog conductivity voltage signals; the several parallel operational amplifiers proportional to the feedback resistors are used to realize several detection ranges without the need for range switching operation.

[0066] S3: Perform analog-to-digital conversion on several analog conductance voltage signals to obtain several digital conductance voltage signals with different ranges;

[0067] S4: Based on the digital conductance voltage signal, the feedback resistor value of the operational amplifier that generates the digital conductance voltage signal, and the amplitude of the input AC excitation signal, calculate several conductance values, and select the conductance value closest to the midpoint of the range as the final value.

[0068] In some embodiments, in S2, the relationship between the output analog conductance voltage signal and the feedback resistor of the operational amplifier that outputs the analog conductance voltage signal is as follows:

[0069]

[0070] in, This represents the output analog conductance voltage signal value, in volts (V). This indicates the resistance value of the feedback resistor, in ohms (Ω). The conductivity of the solution being tested in the conductivity cell is expressed in Siemens (S). It represents the voltage amplitude of the AC excitation signal applied to the two electrodes, and the unit is volt (V).

[0071] In some embodiments, the feedback resistor values ​​of the plurality of operational amplifiers in S2 are approximately equal to the resistance values ​​of each other. The proportional relationship is given by a factor of n, where n is an integer; the amplitude relationships of the several output analog voltage signals are also proportional. A proportional relationship, where n is an integer;

[0072] For example, in a feasible embodiment of the present invention, the operational amplifier circuit is configured with four channels, wherein the feedback resistor values ​​of the four operational amplifier circuits are 200Ω, 2kΩ, 20kΩ, and 200kΩ, respectively, and their corresponding ratios are 1:10:100:1000. The voltage signal relationship output by the four operational amplifier circuits is also 1:10:100:1000. That is, the detection range of the second operational amplifier circuit is 10 times that of the first operational amplifier circuit; the detection range of the third operational amplifier circuit is 100 times that of the first operational amplifier circuit; and the detection range of the fourth operational amplifier circuit is 1000 times that of the first operational amplifier circuit.

[0073] This invention discloses a conductivity sensor applicable to the aforementioned automatic sizing method for conductivity sensors, used to detect the conductivity of a solution to be tested in a conductivity cell, comprising a conductivity sensor body and a conductivity detection circuit; the conductivity sensor body includes an excitation signal terminal and a detection signal terminal, and the conductivity detection circuit includes a conductivity excitation drive circuit and an automatic sizing circuit;

[0074] The conductivity excitation drive circuit generates an excitation signal, which is connected to the first electrode of the conductivity cell through the excitation signal terminal. The excitation signal is applied to the first electrode, and the automatic sizing circuit collects the conductivity value of the solution to be tested in the conductivity cell from the second electrode through the detection signal terminal.

[0075] The conductivity excitation drive circuit includes a digital driver, an oscillator, a frequency divider, and a conductivity excitation drive connection circuit. The oscillator is electrically connected to the digital driver through the connection circuit, the frequency divider, and the digital driver. The automatic scouring circuit includes a first operational amplifier circuit, a second operational amplifier circuit, a third operational amplifier circuit, and a fourth operational amplifier circuit connected in parallel.

[0076] The first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit have different detection ranges and are proportional to each other.

[0077] In this embodiment, see Figure 5The conduction-driven connection circuit includes inductor L1, capacitors C1 and C2, resistors R1 and R2, capacitors C3, C4, and C5. The power input terminal of oscillator U2 is electrically connected to one end of inductor L1 and one end of capacitor C1, respectively. The other end of inductor L1 is connected to a 5V positive power supply, and the other end of capacitor C1 is grounded. The signal output terminal of oscillator U2 is connected to the signal input terminal of frequency divider U1. The power input terminal of frequency divider U1 is connected to a 5V positive power supply and is also electrically connected to one end of capacitor C2, with the other end of capacitor C2 grounded. The Q9 pin of frequency divider U1 is electrically connected to one end of resistor R2. The other end is electrically connected to one end of capacitor C5; the other end of capacitor C5 is electrically connected to the signal input terminal of digital driver U3; the power input terminal of digital driver U3 is electrically connected to one end of capacitor C3, and the power input terminal of digital driver U3 is connected to a 12V positive power supply, while the other end of capacitor C3 is grounded; the ground pin of digital driver U3 is electrically connected to one end of capacitor C4, and the ground pin of digital driver U3 is connected to a 12V negative power supply, while the other end of capacitor C4 is grounded; through the above components and their electrical connections, the conduction excitation drive circuit and its conduction excitation drive connection circuit in this embodiment are constituted.

[0078] Specifically, the oscillator U2 generates the original high-frequency signal, which is then down-divided by the frequency divider U1 to obtain a logic level signal, which is then input to the digital driver U3. The digital driver U3 is powered by a dual ±12V power supply and converts the input logic level signal into an excitation signal with a ±12V swing.

[0079] More specifically, the excitation signal generated by the conductivity excitation drive circuit is applied to the first electrode, forming a conductivity cell loop of excitation signal-first electrode-test solution-second electrode-detection signal. At this time, the ions in the test solution inside the conductivity cell move in a directional manner to generate current, which in turn causes the ion concentration at both ends of the first and second electrodes of the conductivity cell to change. At the same time, the conductivity value of the test solution in the conductivity cell also changes with the change of ion concentration.

[0080] In this embodiment, see Figure 6 The first operational amplifier circuit includes operational amplifier U7, a first feedback resistor, and a feedback capacitor C13. The non-inverting input terminal of operational amplifier U7 is grounded. The first common node of the first feedback resistor and the feedback capacitor C13, after being connected in parallel, is electrically connected to the inverting input terminal of operational amplifier U7, and its second common node is electrically connected to the output terminal of operational amplifier U7. The positive power supply input terminal of operational amplifier U7 is connected to a 12V positive power supply, and the negative power supply input terminal is connected to a 12V negative power supply.

[0081] In this embodiment, the second operational amplifier circuit includes an operational amplifier U6, a second feedback resistor, and a feedback capacitor C12. The non-inverting input terminal of the operational amplifier U6 is grounded. The first common node of the second feedback resistor and the feedback capacitor C12 connected in parallel is electrically connected to the inverting input terminal of the operational amplifier U6, and the second common node is electrically connected to the output terminal of the operational amplifier U6. The positive power supply input terminal of the operational amplifier U6 is connected to a 12V positive power supply, and the negative power supply input terminal is connected to a 12V negative power supply.

[0082] In this embodiment, the third operational amplifier circuit includes operational amplifier U5, a third feedback resistor, and a feedback capacitor C11; the non-inverting input terminal of operational amplifier U5 is grounded, and the first common node of the third feedback resistor and the feedback capacitor C11 connected in parallel is electrically connected to the inverting input terminal of operational amplifier U5, and the second common node is electrically connected to the output terminal of operational amplifier U4; the positive power supply input terminal of operational amplifier U4 is connected to a 12V positive power supply, and the negative power supply input terminal is connected to a 12V negative power supply.

[0083] In this embodiment, the fourth operational amplifier circuit includes operational amplifier U4, a fourth feedback resistor, a feedback capacitor C10, a filter capacitor C8, and a filter capacitor C9. The non-inverting input terminal of operational amplifier U4 is grounded. The first common node of the fourth feedback resistor and the feedback capacitor C10 connected in parallel is electrically connected to the inverting input terminal of operational amplifier U4, and the second common node is electrically connected to the output terminal of operational amplifier U4. The positive power supply input terminal of operational amplifier U4 is connected to a 12V positive power supply and one end of the filter capacitor C8, and the other end of the filter capacitor C8 is grounded. The negative power supply input terminal of operational amplifier U4 is connected to a 12V negative power supply and one end of the filter capacitor C9, and the other end of the filter capacitor C9 is grounded.

[0084] Specifically, the inverting input terminals of the first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit are connected in parallel to serve as the detection terminals for conductivity in the conductivity cell. At the same time, the conductivity values ​​of the solution to be tested in the conductivity cell are collected, and the collected conductivity values ​​are processed to output four voltage signals.

[0085] The first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit have different detection ranges and are proportional to each other.

[0086] In this embodiment, the resistance values ​​of the four feedback resistors in the aforementioned four-channel operational amplifier circuit—the first feedback resistor, the second feedback resistor, the third feedback resistor, and the fourth feedback resistor—are proportionally 1:10:100:1000. Correspondingly, the voltage signal output by the four-channel operational amplifier circuit is... , , , The voltage signal relationship of the output of the 4-channel operational amplifier circuit is as follows:

[0087]

[0088] This proportional constraint allows for the following: the detection range of the second operational amplifier circuit is 10 times that of the first operational amplifier circuit; the detection range of the third operational amplifier circuit is 100 times that of the first operational amplifier circuit; and the detection range of the fourth operational amplifier circuit is 1000 times that of the first operational amplifier circuit. Therefore, by using four operational amplifier circuits, range switching for detecting conductance / current values ​​can be achieved.

[0089] Specifically, in this embodiment, the resistance values ​​of the first feedback resistor, the second feedback resistor, the third feedback resistor, and the fourth feedback resistor are 200Ω, 2kΩ, 20kΩ, and 200kΩ, respectively.

[0090] In this embodiment, see Figure 7 The conductivity detection circuit is also connected to an analog-to-digital converter (ADC) circuit. The ADC circuit includes an ADC U8 and an external connection circuit electrically connected to it. The external connection circuit includes capacitors C14, C15, and C16, and resistors R8, R9, R10, R11, and R12. The power input pin AVDD of the ADC U8 is connected to a 5V positive power supply and is also connected to one end of capacitor C15, with the other end of capacitor C15 grounded. The power input pin DVDD of the ADC U8 is connected to a 3.3V positive power supply and is also connected to one end of capacitor C16, with the other end of capacitor C16 grounded. The reference power input terminal of the ADC U8 is connected to a 2.5V positive reference power supply and is also connected to one end of capacitor C14, with the other end of capacitor C14 grounded.

[0091] The chip select signal input terminal of the analog-to-digital converter U8 is connected to a 3.3V positive power supply through resistor R8; the clock signal input terminal of the analog-to-digital converter U8 is connected to a 3.3V positive power supply through resistor R9; the serial data input terminal of the analog-to-digital converter U8 is connected to a 3.3V positive power supply through resistor R10; the serial data output terminal of the analog-to-digital converter U8 is connected to a 3.3V positive power supply through resistor R11; and the logic output terminal of the analog-to-digital converter U8 is connected to a 3.3V positive power supply through resistor R12.

[0092] The first positive analog signal input terminal of analog-to-digital converter U8 is electrically connected to the output terminal of operational amplifier U4; the first negative analog signal input terminal of analog-to-digital converter U8 is electrically connected to the output terminal of operational amplifier U5; the second positive analog signal input terminal of analog-to-digital converter U8 is electrically connected to the output terminal of operational amplifier U6; and the second negative analog signal input terminal of analog-to-digital converter U8 is electrically connected to the output terminal of operational amplifier U7.

[0093] In this embodiment, the analog-to-digital converter circuit is also connected to a microcontroller; the analog-to-digital converter circuit is electrically connected to the microcontroller through an analog-to-digital converter U8; the chip select signal input terminal of the analog-to-digital converter U8 is electrically connected to the chip select signal output terminal of the microcontroller, the clock signal input terminal of the analog-to-digital converter U8 is electrically connected to the clock signal output terminal of the microcontroller, the serial data input terminal of the analog-to-digital converter U8 is electrically connected to the serial data output terminal of the microcontroller, the serial data output terminal of the analog-to-digital converter U8 is electrically connected to the serial data input terminal of the microcontroller, and the logic output terminal of the analog-to-digital converter U8 is electrically connected to the logic input terminal of the microcontroller.

[0094] In this embodiment, the conductivity detection circuit also includes a temperature acquisition circuit, which is used to acquire the temperature of the solution to be tested in the conductivity cell, and then perform temperature compensation on the acquired conductivity value of the solution to be tested; however, the setting of the temperature acquisition circuit is very common in existing conductivity sensor technology and is existing technology, so it will not be described in detail here, and those skilled in the art will understand.

[0095] Through the electrical connection between the circuit and the microcontroller, the analog-to-digital converter circuit converts the received four analog voltage signals into corresponding digital voltage signals and outputs them to the microcontroller, which then displays them on a computer or LCD screen.

[0096] It should be noted that all the electronic devices mentioned in the above embodiments are available in domestic and international markets.

[0097] The various embodiments of the present invention have now been described in detail. To avoid obscuring the concept of the invention, some details known in the art have not been described. Those skilled in the art will fully understand how to implement the technical solutions of this invention based on the above description, and the scope of the invention is defined by the appended claims.

Claims

1. A conductivity sensor, characterized in that, This device is used to detect the conductivity of a solution in a conductivity cell. It includes a conductivity sensor body and a conductivity detection circuit. The conductivity sensor body includes an excitation signal terminal and a detection signal terminal. The conductivity detection circuit includes a conductivity excitation drive circuit, an automatic sizing circuit, an analog-to-digital conversion circuit, and a microcontroller. The conductivity excitation drive circuit generates an excitation signal, which is connected to the first electrode of the conductivity cell through the excitation signal terminal. The excitation signal is applied to the first electrode, and the automatic sizing circuit collects the conductivity value of the solution to be tested in the conductivity cell from the second electrode through the detection signal terminal. The conductivity excitation drive circuit includes a digital driver, an oscillator, a frequency divider, and a conductivity excitation drive connection circuit. The oscillator is electrically connected to the digital driver through the connection circuit, the frequency divider, and the digital driver. The automatic scouring circuit includes a first operational amplifier circuit, a second operational amplifier circuit, a third operational amplifier circuit, and a fourth operational amplifier circuit connected in parallel. The first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit include a first feedback network, a second feedback network, a third feedback network, and a fourth feedback network; The feedback input terminal of each feedback network is connected to the output terminal of its corresponding operational amplifier; the feedback output terminal of each feedback network is connected to the inverting input terminal of its corresponding operational amplifier. The first feedback network includes a first feedback resistor, the second feedback network includes a second feedback resistor, the third feedback network includes a third feedback resistor, and the fourth feedback network includes a fourth feedback resistor; the resistance values ​​of the first feedback resistor, the second feedback resistor, the third feedback resistor, and the fourth feedback resistor are different and proportional to each other. The first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit have different detection ranges and are proportional to each other; the output terminals of the first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit output analog conductance voltage signals. The output of the automatic tracing circuit is connected to the input of the analog-to-digital converter circuit. The analog-to-digital converter circuit receives the analog conductance voltage signal output by the automatic tracing circuit and converts it into a digital conductance voltage signal. The analog-to-digital conversion circuit is electrically connected to the microcontroller through the analog-to-digital converter. The microcontroller calculates several conductivity values ​​based on the digital conductivity voltage signal, the feedback resistor value of the operational amplifier that generates the digital conductivity voltage signal, and the amplitude of the input excitation signal, and selects the conductivity value closest to the midpoint of the range as the final value.

2. The conductivity sensor according to claim 1, characterized in that, The conductivity excitation drive connection circuit includes an energy storage element, a filter element, and a coupling element; The power input terminal of the oscillator is connected to a first DC source through the energy storage element and grounded through the first filter element; The signal output terminal of the oscillator is connected to the signal input terminal of the frequency divider; The power input terminal of the frequency divider is connected to the first DC source and grounded through the second filter element; The signal output terminal of the frequency divider is connected to the signal input terminal of the digital driver through the coupling element; The positive power input terminal of the digital driver is connected to a second DC power supply and grounded through a third filter element; The negative power input terminal of the digital driver is connected to a third DC power supply and grounded through a fourth filter element.

3. The conductivity sensor according to claim 1, characterized in that, The first operational amplifier circuit includes a first operational amplifier and a first feedback network; the feedback input terminal of the first feedback network is connected to the output terminal of the first operational amplifier; the feedback output terminal of the first feedback network is connected to the inverting input terminal of the first operational amplifier; and the non-inverting input terminal of the first operational amplifier is grounded. The second operational amplifier circuit includes a second operational amplifier and a second feedback network; the feedback input terminal of the second feedback network is connected to the output terminal of the second operational amplifier; the feedback output terminal of the second feedback network is connected to the inverting input terminal of the second operational amplifier; the non-inverting input terminal of the second operational amplifier is grounded. The third operational amplifier circuit includes a third operational amplifier and a third feedback network; the feedback input terminal of the third feedback network is connected to the output terminal of the third operational amplifier; the feedback output terminal of the third feedback network is connected to the inverting input terminal of the third operational amplifier; the non-inverting input terminal of the third operational amplifier is grounded. The fourth operational amplifier circuit includes a fourth operational amplifier and a fourth feedback network; the feedback input terminal of the fourth feedback network is connected to the output terminal of the fourth operational amplifier; the feedback output terminal of the fourth feedback network is connected to the inverting input terminal of the fourth operational amplifier; the non-inverting input terminal of the fourth operational amplifier is grounded. The inverting input terminals of the first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit are connected in parallel to serve as the detection terminal for the conductivity of the solution to be tested in the conductivity cell.

4. A conductivity sensor according to claim 3, characterized in that, The first feedback network includes a first feedback resistor; the second feedback network includes a second feedback resistor; the third feedback network includes a third feedback resistor; and the fourth feedback network includes a fourth feedback resistor. The ratio of the resistance values ​​of the first feedback resistor, the second feedback resistor, the third feedback resistor, and the fourth feedback resistor is 1:10:100:1000.

5. A conductivity sensor according to claim 1, characterized in that, The analog conductance voltage signals output by the first operational amplifier circuit, the second operational amplifier circuit, the third operational amplifier circuit, and the fourth operational amplifier circuit are: , , , The proportional relationship is as follows: ； The detection range of the second operational amplifier circuit is 10 times that of the first operational amplifier circuit; the detection range of the third operational amplifier circuit is 100 times that of the first operational amplifier circuit; and the detection range of the fourth operational amplifier circuit is 1000 times that of the first operational amplifier circuit.

6. A conductivity sensor according to claim 1, characterized in that, The conductivity detection circuit is also connected to an analog-to-digital conversion circuit; The analog-to-digital conversion circuit includes an analog-to-digital converter and a filter capacitor network and a pull-up resistor network electrically connected to it. The power input terminal and reference power input terminal of the analog-to-digital converter are respectively connected to the input power supply and the reference power supply through the filter capacitor network; The chip select signal input terminal, clock signal input terminal, serial data input terminal, serial data output terminal, and logic output terminal of the analog-to-digital converter are respectively connected to a 3.3V positive power supply through the pull-up resistor network; The first positive analog signal input terminal of the analog-to-digital converter (ADC) is electrically connected to the output terminal of the first operational amplifier; the first negative analog signal input terminal of the ADC is electrically connected to the output terminal of the second operational amplifier; the second positive analog signal input terminal of the ADC is electrically connected to the output terminal of the third operational amplifier; and the second negative analog signal input terminal of the ADC is electrically connected to the output terminal of the fourth operational amplifier.

7. A conductivity sensor according to claim 6, characterized in that, The analog-to-digital conversion circuit is also connected to a microcontroller; The analog-to-digital converter (ADC) circuit is electrically connected to the microcontroller via the ADC; the chip select signal input terminal of the ADC is electrically connected to the chip select signal output terminal of the microcontroller; the clock signal input terminal of the ADC is electrically connected to the clock signal output terminal of the microcontroller; the serial data input terminal of the ADC is electrically connected to the serial data output terminal of the microcontroller; the serial data output terminal of the ADC is electrically connected to the serial data input terminal of the microcontroller; and the logic output terminal of the ADC is electrically connected to the logic input terminal of the microcontroller.

8. A method for implementing automatic sizing of a conductivity sensor, characterized in that, Includes the following steps: S1: The electrode that generates an AC excitation signal and applies it to the conductivity cell; S2: Acquire the conductivity signal of the solution to be tested in the conductivity cell, input the conductivity signal into several parallel operational amplifiers proportional to the feedback resistors, and output several analog conductivity voltage signals; the several parallel operational amplifiers proportional to the feedback resistors are used to realize several detection ranges without the need for range switching operation. S3: Perform analog-to-digital conversion on several analog conductance voltage signals to obtain several digital conductance voltage signals with different ranges; S4: Based on the digital conductance voltage signal, the feedback resistor value of the operational amplifier that generates the digital conductance voltage signal, and the amplitude of the input AC excitation signal, calculate several conductance values, and select the conductance value closest to the midpoint of the range as the final value.

9. The method for automatic sizing of a conductivity sensor according to claim 8, characterized in that, The relationship between the output analog conductance voltage signal and the feedback resistor of the operational amplifier that outputs the analog conductance voltage signal is as follows: ； in, This represents the output analog conductance voltage signal value, in volts. This indicates the resistance value of the feedback resistor, in ohms. The conductivity of the solution being tested in the conductivity cell is expressed in Siemens units. It represents the voltage amplitude of the AC excitation signal applied to the two electrodes, and the unit is volts.

10. The method for automatic sizing of a conductivity sensor according to claim 8, characterized in that, The feedback resistor values ​​of the several operational amplifiers in S2 are related as follows: The proportional relationship is given by a factor of n, where n is an integer; the amplitude relationships of the several output analog voltage signals are also proportional. A proportional relationship, where n is an integer.

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