A circuit structure for measuring conductivity of pure water with automatic adjustment of excitation

Abstract

The utility model provides a kind of circuit structure of pure water conductivity of measurement that can automatically adjust excitation, it is related to conductivity measurement technical field.The structure includes: controllable excitation circuit module, for modulating the peak-peak value of excitation square wave circuit module output;Excitation square wave circuit module, for generating alternating signal on electrode in conductivity cell;Two electrodes, set in the conductivity cell containing pure water;Signal conversion circuit module, for amplifying conversion to the signal received by electrode in conductivity cell;Gear switching module, for cooperating with the signal from signal conversion circuit module collected by the analog-digital converter of single-chip microcomputer to modulate digital-analog converter to change excitation signal size, so that the analog-digital converter of final single-chip microcomputer collects signal within preset range.The present scheme acquires signal in current solution by single-chip microcomputer, then changes excitation signal by digital-analog converter, so that current measurement signal is in suitable range, and measurement precision is significantly improved.

Description

Technical Field

[0001] This utility model relates to the field of conductivity measurement technology, specifically to a circuit structure for measuring the conductivity of pure water that can automatically adjust the excitation. Background Technology

[0002] The conductivity of pure water refers to its ability to conduct electric current, and its value depends on the concentration of ions in the water. Ultrapure water has extremely low conductivity because it contains almost no ions. However, in practical applications, trace impurities in the water (such as dissolved salts, gases, or organic matter) can introduce ions, thus affecting conductivity. Therefore, conductivity testing has become a key indicator for assessing water purity, especially in industries requiring high-purity water, such as biopharmaceuticals, electronics manufacturing, and food and beverage. By monitoring conductivity, it is possible to quickly determine whether water quality meets standards, avoiding product defects or production failures caused by water quality issues.

[0003] Current pure water conductivity testing primarily relies on electrode-type conductivity meters, which calculate conductivity by measuring the resistance between two electrodes. While this technology is low-cost and easy to operate, it has some limitations. For example, the electrodes are susceptible to contamination or aging, leading to reading drift; the testing range is limited, making it difficult to measure ultra-low conductivity (e.g., below 0.1 μS / cm); furthermore, temperature variations significantly affect the results, requiring manual compensation. These drawbacks have spurred technological improvements to meet the demand for higher accuracy. Utility Model Content

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a circuit structure for measuring the conductivity of pure water that can automatically adjust the excitation, thereby solving the problem of improving the accuracy of conductivity measurement.

[0005] To achieve the above objectives, the technical solution adopted by this utility model is as follows: This invention provides a circuit structure for measuring the conductivity of pure water with automatically adjustable excitation. The circuit structure includes: A controllable excitation circuit module, which is controlled by a digital-to-analog converter of a microcontroller, is used to modulate the peak-to-peak value of the output of the excitation square wave circuit module; An excitation square wave circuit module is provided, which generates a square wave with a duty cycle of 50% through pulse width modulation of a microcontroller, and is used to generate an alternating signal on the electrodes in the conductivity cell. Two electrodes are placed in a conductivity cell containing pure water; A signal conversion circuit module, which is used to amplify and convert the signal received by the electrodes in the conductivity cell; The range switching module switches the measurement range by modulating the amplification resistor. The range switching module is used to work with the analog-to-digital converter of the microcontroller to modulate the digital-to-analog converter to change the excitation signal magnitude, so that the analog-to-digital converter of the microcontroller finally acquires a signal within a preset range.

[0006] Optionally, the controllable excitation circuit module generates positive and negative excitation power supplies by using operational amplifiers to amplify in both forward and invert directions.

[0007] Optionally, the range switching module is a transimpedance amplifier circuit, which uses a microcontroller to control an analog switch for range switching.

[0008] Optionally, the output of the cross-group amplifier circuit is connected to an RC filter, and the output of the RC filter is directly connected to the analog-to-digital converter port of the microcontroller.

[0009] Optionally, the gear switching module includes the following three gears: 0-2uS / cm, 2-20uS / cm, and 20-200uS / cm.

[0010] The beneficial effects of this utility model include: The circuit structure for measuring the conductivity of pure water with automatically adjustable excitation provided by this utility model includes: a controllable excitation circuit module, which is controlled by a microcontroller's digital-to-analog converter (DAC) to modulate the peak-to-peak value of the excitation square wave circuit module output; an excitation square wave circuit module, which generates a square wave with a 50% duty cycle through pulse width modulation by the microcontroller to generate an alternating signal on the electrodes in the conductivity cell; two electrodes, which are placed in the conductivity cell containing pure water; a signal conversion circuit module, which amplifies and converts the signal received by the electrodes in the conductivity cell; and a range switching module, which switches the measurement range by modulating an amplifying resistor. The range switching module is used to coordinate with the DAC to modulate the DAC to change the excitation signal magnitude based on the signal from the signal conversion circuit module acquired by the DAC of the microcontroller, so that the DAC of the microcontroller ultimately acquires a signal within a preset range. The technical solution of this application acquires the signal in the current solution using a microcontroller, and then changes the excitation signal through a digital-to-analog converter to ensure that the current measurement signal is within a suitable range, significantly improving measurement accuracy. The excitation is generated by positive and negative power supplies, ensuring that the changed excitation is also positive and negative, thereby reducing polarization effects. After changing the excitation, the microcontroller uses signals from different ranges to determine whether the current solution is in the appropriate range, thus avoiding problems such as gaps in range or abnormal signal changes when switching between different ranges. Using different excitations, a wide range of conductivity can be measured, and the excitation can be switched according to the actual situation. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 A schematic diagram of a circuit structure for measuring the conductivity of pure water with automatically adjustable excitation, provided in an embodiment of the present invention, is shown. Figure 2 A circuit diagram of the DAC adjustment excitation circuit provided in an embodiment of the present invention is shown; Figure 3 A circuit diagram of the signal conversion circuit provided in an embodiment of the present invention is shown; Figure 4 A circuit diagram of the gear switching circuit provided in an embodiment of the present invention is shown; Figure 5 A circuit diagram of the RC filter provided in an embodiment of the present invention is shown; Figure 6 The flowchart of the microcontroller signal switching and automatic excitation change provided in the embodiment of this utility model is shown. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0014] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0015] It should be noted that similar labels 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.

[0016] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this utility model is in use. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0017] In the description of this utility model, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" 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.

[0018] Current pure water conductivity testing primarily relies on electrode-type conductivity meters, which calculate conductivity by measuring the resistance between two electrodes. While this technology is low-cost and easy to operate, it has some limitations. For example, the electrodes are susceptible to contamination or aging, leading to reading drift; the testing range is limited, making it difficult to measure ultra-low conductivity (e.g., below 0.1 μS / cm); furthermore, temperature variations significantly affect the results, requiring manual compensation. These drawbacks have spurred technological improvements to meet the demand for higher accuracy.

[0019] Figure 1 A schematic diagram of a circuit structure for measuring the conductivity of pure water with automatically adjustable excitation, provided by an embodiment of the present invention, is shown.

[0020] like Figure 1As shown, the circuit structure for measuring the conductivity of pure water with automatically adjustable excitation provided by this utility model includes: a controllable excitation circuit module 11, which is controlled by a digital-to-analog converter of a microcontroller 16 to modulate the peak-to-peak value VPP output of the excitation square wave circuit module 12; the excitation square wave circuit module 12, which generates a square wave with a duty cycle of 50% through pulse width modulation of the microcontroller 16, to generate an alternating signal on the electrodes in the conductivity cell 13 for subsequent signal sampling; and two electrodes, set with... In the conductivity cell 13 containing pure water; signal conversion circuit module 14, which amplifies and converts the signal received by the electrodes in the conductivity cell 13; range switching module 15, which switches the range by modulating the amplification resistor, and is used to coordinate with the analog-to-digital converter of the microcontroller 16 to modulate the digital-to-analog converter to change the excitation signal magnitude according to the signal from the signal conversion circuit module 14 collected by the analog-to-digital converter of the microcontroller 16, so that the analog-to-digital converter of the microcontroller 16 finally collects the signal within the preset range.

[0021] The controllable excitation circuit module 11 generates positive and negative excitation power supplies through forward and inverting amplification by an operational amplifier. The range switching module 15 is a transimpedance amplifier circuit, which controls the analog switch for range switching via a microcontroller 16. The output of the transimpedance amplifier circuit is connected to an RC filter, and the output of the RC filter is directly connected to the analog-to-digital converter port of the microcontroller 16.

[0022] The gear switching module 15 includes the following three gears: 0-2uS / cm, 2-20uS / cm, and 20-200uS / cm.

[0023] The technical solution of this application first acquires the signal in the current solution using a microcontroller, and then changes the excitation signal through a digital-to-analog converter (DAC) to ensure that the current measurement signal is within a suitable range, significantly improving the measurement accuracy of conductivity. The excitation is generated by positive and negative power supplies, ensuring that the changed excitation is also positive and negative, thereby reducing the polarization effect. After changing the excitation, the microcontroller uses signals at different levels to determine whether the current solution is in the appropriate range, thus avoiding problems such as gaps in the range or abnormal signal changes when switching between different ranges. This method of switching excitation is suitable for many contact electrodes on the market and can be driven by this solution without considering the limitations of electrode constants. A wide range of conductivity can be measured using different excitations, and the excitation can be switched according to the actual situation.

[0024] Figure 2 The circuit diagram of the DAC adjustment excitation circuit provided in the embodiment of this utility model is shown, as follows: Figure 2As shown, based on the initial default settings for the excitation and gain resistors, the ADC on the microcontroller acquires a signal. If this signal is too large (exceeding 80% of full scale) or too small (20% of full scale), the DAC on the microcontroller will automatically adjust its output. If the measured signal is too large, the DAC output will be reduced; conversely, the output will be increased. The selection of the back-end gain resistor follows the same principle. The excitation for the drive is generated by the positive and negative excitation power supplies through the forward and inverting amplification principles of operational amplifier U5. Since positive and negative excitation can greatly reduce the electrode polarization effect, this scheme can improve the ADC sampling range.

[0025] Figure 3 The circuit diagram of the signal conversion circuit provided in this embodiment of the present invention is shown. This circuit rectifies and amplifies the signal generated by excitation on the acquisition electrode, so that the ADC on the microcontroller can acquire the signal.

[0026] Figure 4 The circuit diagram of the gear switching circuit provided in this embodiment of the present invention is shown. The principle is a transimpedance amplifier circuit. The analog switch U14 is controlled by a microcontroller to switch the range. This part is to adjust the gain resistor according to the signal collected by the microcontroller ADC.

[0027] Figure 5 A circuit diagram of the RC filter provided in an embodiment of this utility model is shown. The signal passes through... Figure 4 After passing through a multi-group amplifier, the signal is then output through an RC filter. This signal is directly connected to the ADC port of the microcontroller for signal acquisition.

[0028] Figure 6 The flowchart illustrates the microcontroller signal switching and automatic excitation adjustment provided in this embodiment of the invention. Taking a maximum conductivity range of 200 μS / cm as an example, three ranges are set: 0-2 μS / cm, 2-20 μS / cm, and 20-200 μS / cm. The microcontroller internally judges whether the output data falls within the ranges of 2 μS / cm and 20 μS / cm, and switches and adjusts accordingly based on the specific signal.

[0029] In summary, this application utilizes positive and negative AC excitation, driven by a square wave with a 50% duty cycle generated by a microcontroller. This strictly controls the driving time of the positive and negative excitations within a single cycle to minimize electrode polarization effects caused by charge movement between electrodes. The excitation magnitude can be dynamically adjusted based on the conductivity of the solution being measured. The microcontroller adjusts the output DAC signal, which in turn adjusts the excitation output via an operational amplifier. In solutions with low conductivity, the effective conductivity is very small, resulting in a very large equivalent measured conductivity, necessitating a higher excitation signal amplitude. Conversely, in solutions with high conductivity, the equivalent conductivity is very small, requiring a lower excitation signal amplitude. The microcontroller automatically switches excitations based on the acquired signal magnitude, maximizing the measurement range and improving resolution and accuracy within a single range.

[0030] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. 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 circuit structure for measuring the conductivity of pure water with automatically adjustable excitation, characterized in that, The circuit structure includes: A controllable excitation circuit module, which is controlled by a digital-to-analog converter of a microcontroller, is used to modulate the peak-to-peak value of the output of the excitation square wave circuit module; An excitation square wave circuit module is provided, which generates a square wave with a duty cycle of 50% through pulse width modulation of a microcontroller, and is used to generate an alternating signal on the electrodes in the conductivity cell. Two electrodes are placed in a conductivity cell containing pure water; A signal conversion circuit module, which is used to amplify and convert the signal received by the electrodes in the conductivity cell; The range switching module switches the measurement range by modulating the amplification resistor. The range switching module is used to work with the analog-to-digital converter of the microcontroller to modulate the digital-to-analog converter to change the excitation signal magnitude, so that the analog-to-digital converter of the microcontroller finally acquires a signal within a preset range.

2. The circuit structure for measuring the conductivity of pure water with automatically adjustable excitation according to claim 1, characterized in that, The controllable excitation circuit module generates positive and negative excitation power supplies by using operational amplifiers to amplify in both forward and invert directions.

3. The circuit structure for measuring the conductivity of pure water with automatically adjustable excitation according to claim 1, characterized in that, The range switching module is a transimpedance amplifier circuit, which uses a microcontroller to control an analog switch for range switching.

4. The circuit structure for measuring the conductivity of pure water with automatically adjustable excitation according to claim 3, characterized in that, The output of the cross-group amplifier circuit is connected to an RC filter, and the output of the RC filter is directly connected to the analog-to-digital converter port of the microcontroller.

5. The circuit structure for measuring the conductivity of pure water with automatically adjustable excitation according to claim 3, characterized in that, The gear switching module includes the following three gears: 0-2uS / cm, 2-20uS / cm, and 20-200uS / cm.

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