Water quality detection system

Abstract

The utility model relates to the technical field of water quality detection, in particular to a water quality detection system. The system comprises a PH detection probe, a PH value signal amplification conditioning circuit and a processor, the PH detection probe adopts a PH composite glass electrode, and the PH value signal amplification conditioning circuit comprises a pre-amplification circuit and a post-stage translation circuit. The pH composite glass electrode is adopted, a high-performance operational amplifier CA3140 is matched to serve as a pre-amplifier, an operational amplifier LM741 serves as a post-amplifier, weak pH signals can be accurately amplified and processed, and therefore the detection precision is remarkably improved.

Description

Technical Field

[0001] The utility model relates to the technical field of water quality detection, in particular to a water quality detection system. Background Art

[0002] The pH value of water is a crucial parameter in aquaculture and in daily life. Changes in pH have significant impacts on the physiological processes of aquatic organisms and human health.

[0003] In aquaculture, maintaining an appropriate pH range is crucial for the growth, reproduction, and health of aquatic organisms such as fish and shellfish. An inappropriate pH value can lead to decreased immunity, slowed growth, and even disease and death, resulting in significant economic losses for the aquaculture industry. Therefore, accurate and timely testing of aquaculture water pH is crucial for optimizing the aquaculture environment and improving aquaculture profitability.

[0004] When it comes to drinking water, the pH value also affects its taste and potential health effects. Drinking water that is too acidic or too alkaline can have adverse effects on the digestive system and overall health. Therefore, ensuring the pH value of drinking water is within the appropriate range is crucial for maintaining public health.

[0005] However, traditional pH measurement methods often suffer from low precision, complex operation, and slow response speed, making them difficult to meet the water quality testing needs of modern aquaculture and daily life. Therefore, the development of a highly accurate, convenient, and reliable water pH measurement system has become an urgent need.

[0006] The present invention is based on such technical background and aims to provide a water quality detection system that can effectively solve the above problems, and provide a more accurate and convenient water quality pH detection method for aquaculture and people's daily life. Utility Model Content

[0007] In order to solve the above-mentioned problems, the utility model provides a water quality detection system.

[0008] In a first aspect, the present invention provides a water quality detection system, comprising a pH detection probe, a pH value signal amplification and conditioning circuit, and a processor, wherein the pH detection probe adopts a pH composite glass electrode, and the pH value signal amplification and conditioning circuit comprises a preamplifier circuit and a post-stage shift circuit.

[0009] Furthermore, the pH composite glass electrode includes an indicator electrode and a reference electrode, wherein the indicator electrode is a glass electrode and the reference electrode is a silver-silver chloride electrode.

[0010] Furthermore, the end of the pH composite glass electrode is connected to two output leads, the pH composite glass electrode and the solution to be tested form a primary battery, and the two output leads are respectively the positive electrode and the negative electrode of the primary battery.

[0011] Furthermore, the preamplifier circuit includes a preamplifier, and the preamplifier adopts an operational amplifier CA3140.

[0012] Furthermore, the post-stage shift circuit includes a post-stage amplifier, and the post-stage amplifier adopts an operational amplifier LM741.

[0013] Furthermore, the processor adopts the hc32l130 low-power processor.

[0014] Furthermore, the output end of the post-amplifier is connected to a signal converter, and the signal converter is connected to a hc32l130 low-power processor.

[0015] Furthermore, the signal converter adopts a 12-bit ADC converter.

[0016] Furthermore, a voltage stabilizing circuit is provided at the positive end of the post-amplifier, and the voltage stabilizing circuit includes a resistor R5, a voltage stabilizer D1, a circuit R6, a resistor R7 and an adjustable potentiometer R8.

[0017] Furthermore, a standard buffer solution is also included, wherein the standard buffer solution includes a phosphate standard solution with a pH value of 6.86 and a borax standard solution with a pH value of 9.18.

[0018] In summary, the present invention has the following beneficial technical effects:

[0019] Improve detection accuracy: The pH composite glass electrode is used, and is equipped with a high-performance operational amplifier CA3140 as a preamplifier and an operational amplifier LM741 as a post-amplifier, which can accurately amplify and process weak pH signals, thereby significantly improving detection accuracy.

[0020] Enhanced stability: Through the carefully designed signal amplification and conditioning circuit, including the pre-amplifier circuit and the post-stage shift circuit, the measurement noise is effectively reduced, the stability of the system is improved, and the reliability of the measurement results is ensured.

[0021] Adaptable to various environments: Equipped with a phosphate standard solution with a pH value of 6.86 and a borax standard solution with a pH value of 9.18 for two-point calibration, it can adapt to different water quality conditions and measurement environments, improving the accuracy and versatility of detection.

[0022] Low power operation: Using the hc32l130 low power processor and 3.3v lithium battery for power supply, the power consumption of the whole system is within 100uA, which enables the instrument to work stably for a long time and reduce energy consumption and maintenance costs.

[0023] Convenient and efficient: The 12-bit ADC converter can quickly convert analog signals into digital signals, which are processed and analyzed by the processor to achieve fast and accurate pH value detection and improve work efficiency.

[0024] Easy to operate and maintain: The overall system has a compact design, reasonable structure, and easy operation, which reduces the difficulty of use and maintenance and facilitates users to test water pH values ​​in different scenarios.

[0025] Ensure aquaculture and drinking water safety: By accurately testing the pH value of water quality, we provide optimized water environment parameters for aquaculture, ensure the healthy growth of aquatic products, and ensure the quality and safety of people's daily drinking water. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a circuit connection diagram of a water quality detection system according to an embodiment of the present utility model;

[0027] Figure 2 This is a structural diagram of a water quality detection system according to an embodiment of the present utility model;

[0028] Figure 3 This is a schematic diagram of an operational amplifier CA3140 according to an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of an operational amplifier LM741 according to an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram of a temperature compensation circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be described in further detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] Reference Figure 1A water quality testing system according to this embodiment includes a pH detection probe, a pH signal amplification and conditioning circuit, and a processor. The pH detection probe utilizes a pH composite glass electrode, and the pH signal amplification and conditioning circuit includes a preamplifier circuit and a post-stage shifting circuit. The pH composite glass electrode includes an indicator electrode and a reference electrode, wherein the indicator electrode is a glass electrode and the reference electrode is a silver-silver chloride electrode. Two output leads are connected to the end of the pH composite glass electrode. The pH composite glass electrode and the test solution form a primary battery, and the two output leads serve as the positive and negative electrodes of the primary battery, respectively. The preamplifier circuit includes a preamplifier, which utilizes a CA3140 operational amplifier. The post-stage shifting circuit includes a post-stage amplifier, which utilizes an LM741 operational amplifier. The processor utilizes the HC32L130 low-power processor. The output of the post-stage amplifier is connected to a signal converter, which is connected to the HC32L130 low-power processor. The signal converter utilizes a 12-bit ADC. The positive terminal of the post-amplifier is provided with a voltage stabilizing circuit, which includes a resistor R5, a voltage stabilizer D1, a circuit R6, a resistor R7, and an adjustable potentiometer R8. A standard buffer solution is also provided, which includes a phosphate standard solution with a pH value of 6.86 and a borax standard solution with a pH value of 9.18.

[0034] Specifically,

[0035] 1. pH signal amplification and conditioning circuit design

[0036] (1) The design uses a pH composite glass electrode. Due to the large internal resistance of the pH measurement electrode, the preamplifier is required to have a higher input impedance. The design uses the operational amplifier CA3140, which has the characteristics of high input impedance, low bias current, low noise, and high gain. It is mainly used to complete impedance matching, reduce measurement noise, and improve system stability. The pH value signal amplification circuit is as follows: Figure 1 .

[0037] (2) Since the pH value can be positive or negative, the amplifier LM741 is added in the subsequent stage to perform signal shifting, and the signal amplified by the pH electrode through CA3140 is shifted to above zero point to facilitate the conversion of the signal by the ADC converter.

[0038] 2. pH value measurement principle (two-point calibration method)

[0039] Potentiometric measurement of solution pH often uses a glass electrode as the indicator electrode and a silver-silver chloride electrode as the reference electrode. These two electrodes are packaged together to form a composite glass electrode. The electrodes are inserted into the solution to be measured. The composite glass electrode and the solution to be measured form a galvanic cell, with the two output leads of the composite glass electrode serving as the positive and negative electrodes of the galvanic cell, respectively. According to the Nernst equation, the relationship between the galvanic cell's output electromotive force, the absolute temperature of the solution being measured, and the pH value of the solution being measured satisfies the following equation:

[0040]

[0041] Where: E is the output electromotive force of the primary cell, mV; E0 is a constant, which is the potential difference related to the electrode material, internal reference solution, internal reference electrode and liquid junction potential, mV; K is a constant, which is the Nernst coefficient; T is the absolute temperature of the solution being measured, K; pHx is the pH value of the solution being measured; Ph0 is a constant, which is the pH value of the buffer solution in the composite glass electrode.

[0042] From formula (1), it can be seen that the pH value and temperature of the measured solution work together to generate the output electromotive force of the primary cell. Therefore, by measuring the output electromotive force of the primary cell and the solution temperature at the same time, the pH value of the measured solution can be calculated according to formula (1).

[0043] Due to the manufacturing process of the glass electrode and other reasons, the actual values ​​of the parameters E0 and K in formula (1) will differ from their theoretical values ​​and change as the electrode ages. Therefore, the electrode must be calibrated with a standard buffer solution with a known pH value. Since the aquaculture water environment is alkaline, a standard buffer solution of mixed phosphate (pH=6.86) and borax (pH=9.18) is used for calibration. The specific calibration method is as follows: Assume that the pH values ​​of the two standard buffer solutions are PH1 and pH2, and the output electromotive force is E1 and E2 respectively. Calibrate at the same temperature T. The relationship between the solution output electromotive force E and pH is obtained from formula (1) as shown below:

[0044]

[0045] The test formula for pH value is: PHx=(E-Eo) / KT+PHo;

[0046] 3. This product uses the HC32L130 low-power processor (with built-in segment LCD driver), a segment LCD, and a 3.3V lithium battery to keep the power consumption of the entire circuit below 100uA. Using the microcontroller's built-in 12-bit ADC converter can meet this requirement.

[0047] Example 2

[0048] This embodiment differs from Example 1 in that it provides a water quality detection system, wherein the water quality pH detector generally consists of two parts: a sensor and a secondary meter. The sensor mainly includes a glass electrode and a reference electrode, and the secondary meter is used to display and control the detection data.

[0049] Glass electrode: It is pH-sensitive and can react with the solution to be measured to generate a potential difference. It mainly consists of a glass stem, a glass membrane, an internal reference solution, an internal reference electrode, an electrode cap, and wires.

[0050] Reference electrode: It has a stable potential and serves as a reference for measuring various deviation potentials. The most commonly used reference electrode is the calomel electrode.

[0051] Secondary meter: Receives and processes the signal from the sensor, converts it into pH value, and displays it. The secondary meter may also have functions such as data storage, calibration, and temperature compensation.

[0052] Example 3

[0053] The water quality pH detection circuit implemented in this embodiment is generally composed of the following circuits:

[0054] 1. Measuring electrode circuit: This includes a glass electrode and a reference electrode. The glass electrode is the primary component of a pH electrode, typically made of a special glass that selectively responds to hydrogen ions (H⁺). The sensitive portion of the glass electrode is typically a thin-walled glass bulb, the interior of which is filled with a reference solution, typically a buffer solution with a pH of approximately 7. Ions are exchanged between the external solution and the internal buffer solution through the glass membrane.

[0055] Reference electrode: pH electrodes usually contain a reference electrode, such as a silver / silver chloride electrode. Its function is to provide a stable potential as a reference for measuring the activity of hydrogen ions in the solution.

[0056] Electrode body: The glass electrode and reference electrode are usually enclosed in the same electrode body, which is usually made of plastic or glass and has an interface that can be connected to the measuring instrument.

[0057] When the glass electrode comes into contact with the solution being measured, hydrogen ions in the solution exchange with sodium ions on the glass membrane. This exchange creates a potential difference between the inside and outside of the glass membrane, which is proportional to the pH value of the solution. The reference electrode provides a stable potential, allowing the change in potential of the glass electrode relative to the reference electrode to be measured, thereby inferring the pH value of the solution.

[0058] 2. Signal Amplification Circuit: An operational amplifier is used to amplify the weak pH signal. For the preamplifier, select an amplifier with an input impedance greater than that of the electrode to capture the extremely weak signal generated by the pH probe. The amplifier is connected to form a proportional amplifier circuit, and the amplification factor can be adjusted as needed.

[0059] 3. Filter Circuit: To filter out noise interference, either passive or active filter circuits can be used. Conventional low-pass filter circuits can meet this requirement, but care must be taken to filter out 50Hz power frequency interference. This embodiment uses a passive filter circuit, consisting of passive components such as resistors, capacitors, and inductors. These are categorized as RC and LC filter circuits. In RC filter circuits, capacitors pass AC and block DC, while resistors act as voltage dividers. When the input signal contains high-frequency noise, the capacitors present a low impedance to the high-frequency signal, shunting the high-frequency noise to ground, thereby achieving filtering.

[0060] For example, in a simple RC low-pass filter circuit, if a signal containing high-frequency components is input, the capacitor will short-circuit the high-frequency part to the ground, greatly reducing the high-frequency components in the output signal.

[0061] LC filter circuit: Inductors have the characteristic of passing DC but blocking AC, presenting high impedance to high-frequency signals, while capacitors present low impedance to high-frequency signals. When high-frequency noise passes through, the inductor blocks it, while the capacitor short-circuits it to ground, thus filtering out the high-frequency noise.

[0062] For example, in an LC filter circuit, for high-frequency interference signals, the inductor will produce a large inductive reactance to prevent it from passing through, while the capacitor will bypass it to the ground to achieve a filtering effect.

[0063] 4. Temperature Compensation Circuit: Because pH is sensitive to temperature, a resistor with a positive temperature coefficient is required to offset the temperature coefficient of the pH probe. pH measurement is based on the Nernst equation, which describes the relationship between electrode potential and solution pH. Temperature is a critical parameter that affects the electrode potential. Therefore, temperature compensation circuits typically use temperature sensors, such as thermistors or thermocouples, to detect changes in ambient temperature.

[0064] Based on the output signal of the temperature sensor, the compensation circuit adjusts the parameters of the measurement circuit to offset the effect of temperature on the electrode potential. The compensation circuit calculates the corresponding conversion coefficient based on the Nernst equation and the current temperature to convert the electrode potential into the correct pH value. By adjusting the conversion coefficient, the temperature compensation circuit can enable the pH meter to provide relatively accurate pH value measurement results at different temperatures. Figure 5 shown.

[0065] In this way, even if the temperature of the solution changes, the temperature compensation circuit can automatically adjust, thereby improving the accuracy of pH measurement.

[0066] 5. Analog-to-digital conversion circuit (ADC): converts the analog pH signal into a digital signal for subsequent processing.

[0067] Structural components: (1) Analog input port: used to receive the analog voltage signal from the detection circuit, that is, the voltage signal corresponding to the pH value. (2) Sample and hold circuit (S / H): maintains the stability of the input signal during the ADC conversion to ensure accurate conversion. (3) Quantization and encoding circuit: converts the continuous analog voltage value into a discrete digital value. (4) Digital output port: outputs the converted digital signal to subsequent processing circuits, such as a microcontroller or digital signal processor.

[0068] Working principle:

[0069] (1) Analog signal input: The analog voltage signal from the water quality pH detection part is connected to the analog input port of the ADC.

[0070] (2) Sampling: Sample the input analog signal at a certain sampling frequency to obtain the instantaneous voltage value.

[0071] (3) Hold: During the conversion process, the sampled voltage value is kept unchanged through the sample-and-hold circuit.

[0072] (4) Quantization: Divide the sampled analog voltage value into several quantization levels.

[0073] (5) Coding: Assign a unique digital code to each quantization level.

[0074] (6) Output: After quantization encoding, the obtained digital signal is output from the digital output port.

[0075] For example, assume the ADC resolution is 8 bits and the input analog voltage range is 0-5V. Then, 5V is divided equally into 2^8 = 256 quantization levels, each representing 5V / 256 ≈ 0.0195V. If the sampled analog voltage value is 2.5V, after quantization encoding, the corresponding digital value is 2.5V / 0.0195V ≈ 128.

[0076] Microcontroller (MCU): Such as a single-chip microcomputer, used to control the operation of the entire detection circuit, process digital signals, and perform calculations and displays.

[0077] Among them, the potential difference generated by the glass electrode and the reference electrode is input into the signal amplification circuit. The amplified signal is filtered by the filter circuit and then sent to the ADC for analog-to-digital conversion. The converted digital signal is transmitted to the MCU for further processing and calculation, and finally the pH value is obtained and displayed through the display module.

[0078] Working principle:

[0079] When the glass electrode and reference electrode are inserted into the water sample to be tested, a different potential difference is generated between the electrodes due to the varying pH values ​​of the water samples. This potential difference is very weak and requires amplification by a signal amplifier circuit. The amplified signal may contain noise and interference, which is filtered by a filter circuit to obtain a purer signal. After the ADC converts the digital signal into a digital signal, the MCU processes and calculates it according to a preset algorithm, converting it into a corresponding pH value. For example, the pH value of the current water sample can be calculated using a pre-calibrated curve or formula that shows the relationship between potential difference and pH value.

[0080] Consider a water pH measurement circuit using a glass electrode that produces a potential difference of 0 mV at a pH of 7 and a potential difference of -177 mV at a pH of 4. After amplification and filtering, the ADC converts the signal into a digital signal. Calibration data stored in the MCU indicates that every 59 mV change in potential difference corresponds to a change of 1 pH unit. Therefore, when the detected potential difference is -177 mV, the pH of the water sample is approximately 4, calculated as (-177 / 59 = -3).

[0081] The above are all preferred embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A water quality detection system, characterized in that: It includes a pH detection probe, a pH value signal amplification and conditioning circuit and a processor, wherein the pH detection probe adopts a pH composite glass electrode, and the pH value signal amplification and conditioning circuit includes a pre-amplifier circuit and a post-stage translation circuit; The pH composite glass electrode includes an indicator electrode and a reference electrode, wherein the indicator electrode is a glass electrode and the reference electrode is a silver-silver chloride electrode; The end of the pH composite glass electrode is connected to two output leads, the pH composite glass electrode and the solution to be tested form a primary battery, and the two output leads are respectively the positive electrode and the negative electrode of the primary battery; The preamplifier circuit includes a preamplifier, and the preamplifier adopts an operational amplifier CA3140; The post-stage shift circuit includes a post-stage amplifier, and the post-stage amplifier adopts an operational amplifier LM741; The processor adopts hc32l130 low-power processor; The output end of the post-amplifier is connected to a signal converter, and the signal converter is connected to a hc32l130 low-power processor; The signal converter adopts a 12-bit ADC converter; A voltage stabilizing circuit is provided at the positive end of the post-stage amplifier, and the voltage stabilizing circuit includes a resistor R5, a voltage stabilizer D1, a circuit R6, a resistor R7 and an adjustable potentiometer R8.

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