Automatic monitoring device and evaluation method suitable for drum-type filter screen cathodic protection system

Abstract

The application discloses an automatic monitoring device of a cathodic protection system suitable for a drum-shaped filter screen, which comprises a data transmission module and a sensor, the sensor is arranged on the drum-shaped filter screen and is used for collecting the cathodic protection potential, the protection current density and the residual chlorine concentration below the water surface of the drum-shaped filter screen, the sensor comprises a data acquisition unit, a data sending unit, a working electrode, a silver / silver chloride reference electrode, a residual chlorine measuring electrode and a first power supply battery, and the data transmission module comprises a data receiving unit, a data storage unit, a 4G-DTU data transmission unit and a second power supply battery. The automatic monitoring device and the evaluation method can collect the cathodic protection potential, the current density and the residual chlorine concentration and other parameters below the water surface of the drum-shaped filter screen in situ and on line, and utilize the Internet of Things technology to remotely and wirelessly transmit the data of the multi-point corrosion sensor to a background server, so that the health index of the cathodic protection system can be automatically evaluated in real time.

Description

Technical Field

[0001] This invention relates to the field of automated monitoring of cathodic protection systems, and in particular to an in-situ automated multi-parameter monitoring device for the status of a nuclear power plant drum filter cathodic protection system, as well as an evaluation method based on the monitoring device. Background Technology

[0002] Nuclear power plant drum filters use cathodic protection technology for corrosion protection. To periodically inspect the reliability of the cathodic protection system, the current method mainly relies on manual inspection of the cathodic protection potential on the main shaft platform of the drum filter, which has problems such as low efficiency, large error and high risk.

[0003] To address this issue, utility model patent CN2022216698210 discloses a monitoring device for cathodic protection of a drum-shaped rotating filter in a nuclear power plant. This device includes a clamp for mounting on the spoke channel steel of the drum-shaped rotating filter, and a data acquisition module mounted on the clamp and connected to the data acquisition object on the spoke channel steel. This monitoring device solves the problem of monitoring cathodic protection of the drum-shaped filter in nuclear power plants due to environmental and spatial constraints, improving the management level of cathodic protection for the drum-shaped filter. It provides assurance for preventative corrosion management, stable equipment operation, and extended service life, without affecting the normal rotation of the drum-shaped filter. This device fundamentally solves the problems and risks associated with previous manual underwater measurements, such as inaccuracy, lack of timeliness, personal injury, drowning, and falls. It also saves labor costs, ensures personnel safety, and improves the reliability of the unit's cathodic protection system.

[0004] For example, Chinese invention patent CN2021116216203 discloses a method for monitoring the corrosion status of drum-shaped filters in nuclear power plants, including the following steps: electrically connecting the positive electrode of the monitoring module to the drum-shaped filter, and electrically connecting the negative electrode of the monitoring module to a potential sensor; controlling the potential sensor to move to different measurement points to measure the potential between the drum-shaped filter and the measurement points at different locations; and / or, controlling the measurement point position of the potential sensor to be fixed to measure the potential between different locations of the drum-shaped filter and the measurement points; and determining the corrosion status of the drum-shaped filter based on the measured potential. This invention's method for monitoring the corrosion status of drum-shaped filters in nuclear power plants can solve the safety and time problems of detecting the corrosion status of drum-shaped filter cylinders in nuclear power plants, improve detection and evaluation efficiency, and simultaneously perform precise regional monitoring and evaluation; it can quickly, efficiently, and safely complete on-site detection and evaluation.

[0005] Both patents mentioned above are based on the operation and maintenance needs of the cathodic protection system at nuclear power plant sites, and have developed a drum-shaped rotating filter cathodic protection potential monitoring device. The difference is that the clamp and acquisition module described in patent CN2022216698210 are installed on the spoke channel steel and rotate with the drum screen, so that the cathodic protection potential at different positions can be obtained through multi-point installation; while the monitoring module described in patent CN2021116216203 is installed on a movable device on the concrete wall between the drum screens, and the cathodic protection potential at different positions can be monitored by moving the mechanical device.

[0006] Because the cathodic protection mesh is electrically conductive with the reinforcing steel in the concrete structure, leakage of cathodic protection current can occur. The magnitude of this leakage is related to the condition of the reinforced concrete; when the concrete cracks or falls apart, the water resistance between the reinforcing steel and seawater decreases, increasing the leakage current. If the leakage current gradually increases, the cathodic protection system may become insufficient in capacity, leading to under-protection and equipment corrosion. Therefore, it is necessary to monitor the three key parameters—cathodic protection potential, current density, and residual chlorine concentration—over a long-term basis and calculate the actual cathodic protection current and leakage value to automatically assess the health index of the cathodic protection system. While the two patents mentioned above can achieve real-time on-site monitoring and data storage of cathodic protection potential, they suffer from the problem of monitoring only a single parameter and cannot achieve multi-dimensional monitoring of cathodic protection system operating parameters and automated health diagnosis. Summary of the Invention

[0007] In view of this, in order to overcome the shortcomings of the prior art, the object of the present invention is to provide an automated monitoring device suitable for a cathodic protection system of a drum filter.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] An automated monitoring device for a cathodic protection system suitable for a drum-shaped filter screen includes a data transmission module and a sensor. The sensor is installed on the drum-shaped filter screen and is used to collect the cathodic protection potential, protection current density, and ambient residual chlorine concentration below the water surface of the drum-shaped filter screen. The sensor includes a data acquisition unit, a data transmission unit, a working electrode, a silver / silver chloride reference electrode, a residual chlorine measuring electrode, and a first power supply battery. The data transmission module includes a data receiving unit, a data storage unit, a 4G-DTU data transmission unit, and a second power supply battery.

[0010] According to some preferred embodiments of the present invention, the cathodic protection potential is measured in the range of -10V to +10V with an accuracy of 1mV; the protection current density is expressed in terms of an area of ​​1cm². 2 The working electrode is made of 316L stainless steel, with a current measurement range of 1μA to 100μA and an accuracy of 0.1μA; the residual chlorine concentration is measured in the range of 0 to 20mg / L with an accuracy of 0.01mg / L.

[0011] According to some preferred embodiments of the present invention, the drum-shaped filter screen includes a rotating shaft, spokes, and a mesh sheet located in the circumferential direction; the drum-shaped filter screen is provided with multiple sets of sensors, including a first set of sensors disposed on one end of the spokes near the end of the mesh sheet, a second set of sensors disposed at the middle position of the spokes, and a third set of sensors located at the end of the rotating shaft, each set including multiple sensors.

[0012] According to some preferred embodiments of the invention, the first group of sensors and the second group of sensors are located on different spokes.

[0013] According to some preferred embodiments of the present invention, the second group of sensors is correspondingly distributed between adjacent first groups of sensors.

[0014] According to some preferred embodiments of the present invention, the first group of sensors includes 4-8 sensors arranged symmetrically, the second group of sensors includes 4-8 sensors arranged symmetrically, and the third group of sensors includes 2-4 sensors corresponding to the ends of the rotating shaft.

[0015] According to some preferred embodiments of the present invention, the sensor includes a base and a housing disposed on the base, the working electrode, the silver / silver chloride reference electrode, and the residual chlorine measuring electrode are disposed on the housing, and the housing contains a low-power ARM module, a low-power Bluetooth module, an LDO voltage converter, a FLASH data memory, an ADC acquisition circuit, a gyroscope, a resistor, and a lithium-ion battery.

[0016] The present invention also provides a method for evaluating a cathodic protection system based on the above-mentioned automated monitoring device, comprising the following steps:

[0017] Sensors were installed at 10 locations on the drum-shaped filter screen to collect online, in-situ data on the cathodic protection potential, protection current density, and residual chlorine concentration. The cathodic protection potential values ​​of the corresponding areas were monitored in real time, and the actual cathodic protection current and leakage values ​​were calculated. Then, based on the cathodic protection potential distribution and cathodic protection current leakage values, an algorithm model was used to automatically assess the health index of the cathodic protection system.

[0018] According to some preferred embodiments of the present invention, the actual value of the cathodic protection current is calculated according to the following steps: based on the drum filter current density collected online in situ by 10 sensors, using the residual chlorine concentration-cathode protection current density change curve, the influence value i of each current density value is obtained through the measured residual chlorine concentration. 余氯影响值 Then, the current density measurement values ​​i of each sensor are... 测量值 Subtract i 余氯影响值 The actual current density value of the corresponding region is calculated, i. 实际值 =i测量值 -i 余氯影响值 Then multiply by the area of ​​the corresponding region to obtain the actual value of the cathodic protection current.

[0019] According to some preferred embodiments of the present invention, the cathodic protection current leakage value is calculated by the following steps: subtracting the actual value of the cathodic protection current from the output current of the cathodic protection power supply device to obtain the cathodic protection current leakage value, i.e., I. 泄漏值 =I 输出值 -I 实际值 .

[0020] According to some preferred embodiments of the present invention, the algorithm model is as follows: the cathodic protection potential health index measured by 10 sensors is defined as K. E1 ~K E10 The weighting is 80%; the cathodic protection current leakage value health index is defined as K. I The weight is 20%. That is:

[0021]

[0022] According to some preferred embodiments of the present invention, the health index is:

[0023] 1) Using silver / silver chloride as the reference electrode, the standard potential protection range is -0.80V to -1.05V, with an average value of -0.925V. If the average value is scored out of 100, and -0.80V and -1.05V are scored out of 60, then:

[0024]

[0025] 2) The output current of the cathodic protection power supply is designed to have a redundancy of 25% of the rated value. Therefore, a score of 0 is given if the leakage current reaches 25% of the rated output current, and a score of 100 is given if the leakage current is 0.

[0026]

[0027] Compared to existing technologies, the advantages of this invention, due to the adoption of the above technical solutions, are as follows: The automated monitoring device for the cathodic protection system of the drum-shaped filter screen includes a multifunctional corrosion monitoring sensor and a remote wireless data transmission module. By fixing multiple multifunctional corrosion sensors to the drum screen body, it can collect parameters such as cathodic protection potential, current density, and residual chlorine concentration below the seawater surface of the drum-shaped filter screen online and in situ. The data from the multi-point corrosion sensors is then remotely and wirelessly transmitted to a backend server using Internet of Things (IoT) technology. Then, based on the cathodic protection potential distribution and cathodic protection current leakage value, an algorithm model is used to automatically assess the health index of the cathodic protection system. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram showing the installation position of the sensor on the drum-shaped filter screen in a preferred embodiment of the present invention;

[0030] Figure 2 This is a curve showing the relationship between cathodic protection current density and residual chlorine concentration in a preferred embodiment of the present invention;

[0031] Figure 3 This is a three-dimensional structural diagram of the sensor in a preferred embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the internal structure of the sensor in a preferred embodiment of the present invention;

[0033] Figure 5 This is a schematic diagram of the internal structure of the data transmission module in a preferred embodiment of the present invention;

[0034] In the attached diagram: 1. Sealing shell; 2. Working electrode; 3. Reference electrode; 4. Residual chlorine electrode; 5. Mounting base; 6. Cathode grounding. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions of the present invention, 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 should fall within the scope of protection of the present invention.

[0036] For drum-shaped filters in nuclear power plants, this invention designs and develops an in-situ automated monitoring device for cathodic protection systems based on Internet of Things (IoT) remote transmission technology. The technical problems it addresses include: 1) how to accurately monitor three key parameters below the seawater surface of the drum-shaped filter: cathodic protection potential, current density, and residual chlorine concentration; 2) how to wirelessly transmit monitoring data in real-time to a backend server using IoT technology for automated health diagnosis. The key focus is on calculating the cathodic protection leakage current and actual current density based on the cathodic protection potential, current density, and residual chlorine concentration data, thereby evaluating the status of the cathodic protection system, i.e., the corrosion protection effect achieved by the drum-shaped filter. Specifically, the automated monitoring device for the cathodic protection system of drum-shaped filters is shown in Example 1, and the evaluation method for the cathodic protection system of drum-shaped filters is shown in Example 2.

[0037] Example 1: Automated Monitoring Device

[0038] like Figure 1 As shown, the drum-shaped filter screen includes a rotating shaft, spokes, and mesh sheets located in the circumferential direction. The automated monitoring device for the cathodic protection system of the drum-shaped filter screen in this embodiment includes a data transmission module and a sensor. The sensor is installed on the drum-shaped filter screen and is used to collect the cathodic protection potential, current density, and residual chlorine concentration below the water surface of the drum-shaped filter screen.

[0039] Specifically, the drum-shaped filter screen is equipped with multiple sets of sensors, including a first set of sensors located at one end of the spokes near the screen, a second set of sensors located in the middle of the spokes, and a third set of sensors located at the end of the rotating shaft. Each set includes multiple sensors. Preferably, the first and second sets of sensors are located on different spokes, and the second set of sensors are distributed between adjacent first sets of sensors. This allows for uniform measurement of values ​​in each area, resulting in a more accurate evaluation of the cathodic protection system status.

[0040] In this embodiment, the first group of sensors includes four symmetrically arranged sensors (A1, A2, A3, A4), the second group of sensors includes four symmetrically arranged sensors (B1, B2, B3, B4), and the third group of sensors includes two sensors (C1, C2) corresponding to the ends of the rotating shaft.

[0041] The sensor includes a data acquisition unit, a data transmission unit, a working electrode, a silver / silver chloride reference electrode, a residual chlorine measuring electrode, and a primary power supply battery. It employs low-power electronic components, and the lithium battery has a designed capacity of 20Ah and a continuous operating period of 2 years. Specifically, such as... Figure 3 and 4As shown, the sensor includes a base and a housing mounted on the base. The working electrode, silver / silver chloride reference electrode, and residual chlorine measuring electrode are mounted on the housing. Inside the housing are a low-power ARM module, a low-power Bluetooth module, an LDO voltage converter, a FLASH data storage device, an ADC acquisition circuit, a gyroscope, resistors, and a lithium-ion battery. The low-power ARM module acts as the system controller, responsible for controlling the system's operation. The low-power Bluetooth module enables communication between the sensor and the data transmission module. The LDO voltage converter converts the +24V lithium battery voltage to a suitable voltage (+3.3V and +5V) for the current circuit. The FLASH data storage device stores the sensor's acquired data locally. The ADC acquisition circuit acquires voltage and current signals. The gyroscope senses the angle of rotation of the sensor with the drum mesh, triggering data transmission. The resistors are low-temperature drift, high-precision resistors used for converting voltage and current signals. This embodiment of the sensor enables multi-data fusion, real-time measurement, convenient installation, and its wireless design allows for use with rotating equipment.

[0042] like Figure 5 As shown, the data transmission module includes a data receiving unit, a data storage unit, a 4G-DTU data transmission unit, and a second power supply battery. The Bluetooth data receiving unit is used to form a Bluetooth mesh network with multiple multi-functional corrosion monitoring sensors, enabling data communication, data collection, and management of the Bluetooth mesh network. After receiving data, the remote wireless data transmission module temporarily stores it in the FLASH data storage unit and periodically transmits it to the backend server via the 4G-DTU data transmission unit.

[0043] In this embodiment, the sensor's cathode protection potential measurement range is -10V to +10V, with an accuracy of 1mV; the protection current density is measured over an area of ​​1cm². 2 The working electrode is made of 316L stainless steel. The current measurement range is 1μA to 100μA with an accuracy of 0.1μA; the residual chlorine concentration measurement range is 0 to 20mg / L with an accuracy of 0.01mg / L. The protective current is measured by the working electrode, which has an area of ​​1cm². 2 The current density is obtained by dividing the measured current by the area.

[0044] Example 2 Evaluation Method

[0045] The method for evaluating a cathodic protection system based on the aforementioned automated monitoring device in this embodiment includes the following steps:

[0046] Step 1: Install sensors at 10 locations on the drum-shaped filter screen and collect the cathodic protection potential, protection current density, and residual chlorine concentration of the drum-shaped filter screen in situ online. Monitor the cathodic protection potential values ​​of the corresponding areas (different areas of the drum-shaped filter screen structure, such as the outer mesh A1 / A2 / A3 / A4, the middle spokes B1 / B2 / B3 / B4, and the inner shafts C1 / C2) in real time.

[0047] Step 2: Calculate the actual value of the cathodic protection current and the leakage value.

[0048] The actual value of the cathodic protection current is calculated according to the following steps:

[0049] Based on the drum filter current density collected online in situ by 10 sensors, the residual chlorine concentration-cathode protection current density change curve was used, as shown in... Figure 2 As shown, the influence value i of each current density value is obtained by measuring the residual chlorine concentration. 余氯影响值 Then, the current density measurement values ​​i of each sensor are... 测量值 Subtract i 余氯影响值 The actual current density value of the corresponding region is calculated, i. 实际值 =i 测量值 -i 余氯影响值 Then multiply by the area of ​​the corresponding region to obtain the actual value of the cathodic protection current.

[0050] According to the principle of cathodic protection, the actual current density value is related to the coating condition of the drum filter surface. That is, when the actual current density value of a certain sensor increases significantly, it indicates that the coating condition of the corresponding area of ​​the sensor is poor. Attention should be paid to this area, and the coating in this area should be checked for defects such as blistering and damage during the power plant overhaul.

[0051] The cathodic protection current leakage value is calculated according to the following steps:

[0052] Subtracting the actual value of the cathodic protection current from the output current of the cathodic protection power supply device yields the cathodic protection current leakage value, i.e., I. 泄漏值 =I 输出值 -I 实际值 This value is related to the deterioration of reinforced concrete and can be used to assess the health status of the cathodic protection system. When it increases significantly, it should be closely monitored, and the system should be inspected and addressed during a major power plant overhaul.

[0053] Step 3: Based on the cathodic protection potential distribution and cathodic protection current leakage value, an algorithm model is used to automatically assess the health index of the cathodic protection system.

[0054] The algorithm model is as follows: the cathodic protection potential health index measured by 10 sensors is defined as K. E1 ~K E10The weighting is 80%; the cathodic protection current leakage value health index is defined as K. I The weight is 20%. That is:

[0055]

[0056] The health index is:

[0057] 1) Using silver / silver chloride as the reference electrode, the standard potential protection range is -0.80V to -1.05V, with an average value of -0.925V. If the average value is scored out of 100, and -0.80V and -1.05V are scored out of 60, then:

[0058]

[0059] 2) The output current of the cathodic protection power supply is designed to have a redundancy of 25% of the rated value. Therefore, a score of 0 is given if the leakage current reaches 25% of the rated output current, and a score of 100 is given if the leakage current is 0.

[0060]

[0061] The automated monitoring device and evaluation method for the cathodic protection system of a drum-shaped filter described in this invention are applied to drum-shaped filters in nuclear power plants. During monitoring, ten multifunctional corrosion sensors are evenly distributed and installed on the drum-shaped filter. Specifically, sensors A1, A2, A3, and A4 are installed near the mesh; sensors B1, B2, B3, and B4 are installed in the middle of the spokes; and sensors C1 and C2 are installed on both sides of the main shaft. Based on the online in-situ acquisition of cathodic protection potential, current density, and residual chlorine concentration of the drum-shaped filter by these ten multifunctional corrosion sensors, the cathodic protection potential values ​​of different areas can be obtained in real time. The actual cathodic protection current and leakage value can be calculated, and then an algorithm model is used to automatically evaluate the health index of the cathodic protection system.

[0062] The automated monitoring device for the cathodic protection system of nuclear power plants of the present invention has the following advantages: 1) By fixing multi-point, multi-functional corrosion sensors on the drum filter body, parameters such as cathodic protection potential, current density, and residual chlorine concentration below the seawater surface of the drum filter can be collected online in situ, with strong anti-interference ability and high measurement accuracy; 2) Compared with the manual measurement of cathodic protection potential currently used in power plants, the fixed in-situ measurement results are more reliable, while avoiding industrial safety risks during manual operation; 3) By multiplying the current density value measured by the multi-point sensors by the surface area of ​​the drum filter area, the actual value of the cathodic protection current can be calculated, and then the cathodic protection power supply device can be used. Subtracting this value from the total output current yields the cathodic protection current leakage value, thereby assessing the health status of the cathodic protection system; 4) By measuring the residual chlorine concentration in the environment, the current density measurement value is corrected to eliminate the influence of environmental factors, thus obtaining the actual current density value, thereby assessing the coating status of the drum filter surface; 5) Using low-power Bluetooth modules, FLASH memory, automatic sleep CPUs, and other electronic components, the 20Ah lithium battery can be used continuously for 2 years, meeting the power plant's 1.5-year overhaul replacement requirements; 6) Based on the cathodic protection potential distribution and the cathodic protection current leakage value, an algorithm model is used to automatically assess the health index of the cathodic protection system.

[0063] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for evaluating a cathodic protection system using an automated monitoring device suitable for a drum-type filter cathodic protection system, characterized in that, The automated monitoring device includes a data transmission module and sensors. The sensors are installed on the drum-shaped filter screen and are used to collect the cathodic protection potential, protection current density, and residual chlorine concentration below the water surface of the drum-shaped filter screen. The sensors include a data acquisition unit, a data transmission unit, a working electrode, a silver / silver chloride reference electrode, a residual chlorine measuring electrode, and a first power supply battery. The data transmission module includes a data receiving unit, a data storage unit, a 4G-DTU data transmission unit, and a second power supply battery. The drum-shaped filter screen includes a rotating shaft, spokes, and a mesh sheet located in the circumferential direction. Multiple sets of sensors are installed on the drum-shaped filter screen, including a first set of sensors installed on one end of the spokes near the mesh sheet, a second set of sensors installed in the middle of the spokes, and a third set of sensors located at the end of the rotating shaft, each set including multiple sensors. The evaluation method includes the following steps: installing multiple sensors on the drum-shaped filter screen, collecting the cathodic protection potential, protection current density, and residual chlorine concentration of the drum-shaped filter screen online in situ, monitoring the cathodic protection potential value of the corresponding area in real time, and obtaining the actual value of the cathodic protection current and the leakage value through calculation; then, based on the cathodic protection potential distribution and the cathodic protection current leakage value, using an algorithm model to realize the automated evaluation of the cathodic protection system health index; The actual value of the cathodic protection current is calculated according to the following steps: Based on the drum filter current density collected online in situ by multiple sensors, the influence value i of each current density value is obtained by using the residual chlorine concentration-cathode protection current density change curve and the measured residual chlorine concentration. 余氯影响值 Then, the current density measurement values ​​i of each sensor are... 测量值 Subtract i 余氯影响值 The actual current density value of the corresponding region is calculated, i. 实际值 =i 测量值 -i 余氯影响值 Then multiply by the area of ​​the corresponding region to obtain the actual value of the cathodic protection current; The cathodic protection current leakage value is calculated as follows: The output current of the cathodic protection power supply is subtracted from the actual value of the cathodic protection current to obtain the cathodic protection current leakage value, i.e., Ic. 泄漏值 =I 输出值 -I 实际值 ; The algorithm model is as follows: The cathodic protection potential health index measured by multiple sensors is defined as K. E1 ~K E10 The weighting is 80%; the cathodic protection current leakage value health index is defined as K. I Weight 20%; that is: ； The health index is: Using silver / silver chloride as the reference electrode, the standard potential protection range is -0.80V to -1.05V, with an average value of -0.925V. If the average value is scored out of 100, and -0.80V and -1.05V are scored out of 60, then: ； The output current of the cathodic protection power supply is designed to have a redundancy of 25% of the rated value. Therefore, a score of 0 is given if the leakage current reaches 25% of the rated output current, and a score of 100 is given if the leakage current is 0. 。 2. The evaluation method according to claim 1, characterized in that, The measurement range of the cathode protection potential is -10V to +10V; the protection current density is measured in an area of ​​1cm². 2 The working electrode is made of stainless steel, and the current measurement range is 1μA~100μA; the residual chlorine concentration measurement range is 0~20mg / L.

3. The evaluation method according to claim 1, characterized in that, The first group of sensors includes 4-6 sensors arranged symmetrically, the second group of sensors includes 4-6 sensors arranged symmetrically, and the third group of sensors includes 2-4 sensors corresponding to the end of the rotating shaft.

4. The evaluation method according to claim 1, characterized in that, The sensor includes a base and a housing mounted on the base. The working electrode, silver / silver chloride reference electrode, and residual chlorine measuring electrode are mounted on the housing. The housing contains an ARM module, a Bluetooth module, an LDO voltage converter, a FLASH data storage device, an ADC acquisition circuit, a gyroscope, a resistor, and a battery.

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