Online pH meter stability testing device and method

Abstract

The invention particularly relates to an online pH meter stability testing device and method, and belongs to the field of pH meter stability testing. The testing device comprises an instrument detection device which forms a testing loop and is used for testing the stability of the pH meter; the dosing device is used for injecting a reagent into the sample water in the test loop and adjusting the pH value of the sample water; the constant temperature device is used for controlling the sample water in the test loop to be at a set temperature; the data acquisition system is used for acquiring output signals of the instrument detection device, the dosing device and the constant temperature device; and controlling the instrument detection device, the dosing device and the constant temperature device to operate. The testing method is carried out by using the testing device. According to the invention, the long-term stability test of the on-line pH meter under different temperature and solution environments is realized.

Description

Technical Field

[0001] This invention relates to the field of pH meter stability testing technology, and in particular to an online pH meter stability testing device and method. Background Technology

[0002] As a crucial component of chemical instrumentation in nuclear power plants, online pH meters play a vital role in monitoring water chemistry. However, currently available online pH meters lack reliable stability assessment methods before being deployed in nuclear power plants. Due to the unique nature of nuclear power process systems, it is impossible to directly install unverified pH meters on-site for long-term stability testing, and conventional accelerated testing methods are insufficient to accurately simulate actual operating conditions and scientifically evaluate their long-term stability. Summary of the Invention

[0003] The purpose of this invention is to provide an online pH meter stability testing device and method that simulates the pure water operating environment of a nuclear power plant, enables long-term stability testing of the online pH meter under different temperatures and solution environments, and displays the stability test data of the online pH meter in an intuitive form, allowing users to more intuitively and comprehensively judge the stability of the online pH meter, and providing a basis for the actual use of the online pH meter in nuclear power plants.

[0004] To achieve the above objectives, in one aspect, the present invention provides an online pH meter stability testing device, comprising:

[0005] The instrument testing device forms a test circuit for pH meter stability testing.

[0006] The dosing device is used to inject reagents into the sample water in the test circuit to adjust the pH value of the sample water;

[0007] Thermostat is used to control the sample water in the test circuit at a set temperature;

[0008] The data acquisition system is used to collect output signals from the instrument detection device, the dosing device, and the temperature control device; and to control the operation of the instrument detection device, the dosing device, and the temperature control device.

[0009] As one possible implementation, the test loop includes a water tank, a circulating water pump, and multiple test branches; the inlet of the water tank is connected to the outlet pipe of each test branch, the outlet of the water tank is connected to the inlet pipe of the circulating water pump, and the outlet of the circulating water pump is connected to the inlet pipe of each test branch, thus forming a test loop.

[0010] As one possible implementation, the constant temperature device includes a constant temperature water tank, a heating unit for heating the medium in the constant temperature water tank, and a cooling unit for cooling the medium in the constant temperature water tank; the test circuit passes through the constant temperature water tank, and the medium in the constant temperature water tank exchanges heat with the sample water in the test circuit to achieve heating or cooling of the sample water in the test circuit.

[0011] As one possible implementation, the dosing device includes a solution tank and a dosing pump. The solution tank is connected to the test circuit between the circulating water pump and the test branch via the dosing pump. An anti-reverse device is installed on the pipeline connecting the dosing pump and the test circuit.

[0012] One possible approach is to connect multiple test branches in parallel. Each test branch includes a throttle valve, a filter, a flow meter, and a flow cell connected in sequence. The pH meter electrode is installed in the flow cell, and the electrode transmits the measurement signal to the secondary meter of the pH meter.

[0013] As one possible approach, a data acquisition system includes a PLC, a host computer, and monitoring software.

[0014] The PLC is connected to the secondary meter signal of the pH meter to acquire the analog signal output by the secondary meter of the pH meter.

[0015] The constant temperature water tank is equipped with a temperature sensor; the PLC is connected to the temperature sensor signal to collect the temperature sensor signal of the constant temperature device.

[0016] Monitoring software is installed on the host computer to receive data collected by the PLC and display, store, query historical data, and export reports in real time, as well as to perform closed-loop control of the temperature control device and the dosing device through the PID algorithm.

[0017] One feasible approach involves a temperature sensor inside the constant-temperature water tank monitoring the temperature of the medium within the tank in real time; the PLC collects the temperature of the medium from the temperature sensor and uploads it to the monitoring software on the host computer; the monitoring software uses a PID algorithm to perform closed-loop control of the temperature control device, including the following steps:

[0018] The monitoring software compares the temperature of the medium in the constant temperature water tank with the target temperature set by the user.

[0019] When the temperature of the medium in the constant temperature water tank is lower than the target temperature, the monitoring software issues a heating command through the PLC to start the heating unit and heat the medium in the constant temperature water tank.

[0020] When the temperature of the medium in the constant temperature water tank is higher than the target temperature, the monitoring software issues a cooling command through the PLC to start the cooling unit, which then absorbs heat from the medium in the constant temperature water tank.

[0021] When the temperature of the medium in the constant temperature water tank reaches the target temperature, the heating unit and the cooling unit stop heating and cooling the medium in the constant temperature water tank, and the medium in the constant temperature water tank remains at a constant temperature.

[0022] As one feasible approach, monitoring software uses a PID algorithm to perform closed-loop control of the dosing device, including the following steps:

[0023] Receives the target pH value set by the user and the actual pH value fed back by the pH meter;

[0024] Calculate the deviation between the target pH value and the actual pH value;

[0025] Based on the deviation, a PID control algorithm is executed to generate a control command for controlling the speed of the dosing pump.

[0026] Control commands are sent to the PLC to drive the dosing pump, thus forming a closed-loop control circuit.

[0027] As one possible approach, the online pH meter stability testing device also includes a water circulation ion exchange column, which is connected to the test loop after the outlet of the circulating water pump via a bypass and valve.

[0028] As one possible approach, the front panel of the testing device is equipped with multiple standardized instrument mounting holes and an electrode mounting system corresponding to multiple test branches.

[0029] On the other hand, the present invention also provides an online pH meter stability testing method, which uses the above-mentioned online pH meter stability testing device and includes the following steps:

[0030] S1. Install the pH meter to be tested and the standard pH meter on the flow cell of different test branches respectively; start the circulating water pump and adjust the sample water flow rate through the throttle valve of each test branch;

[0031] S2. Open the bypass valve of the water circulation ion exchange column to allow the sample water to pass through the water circulation ion exchange column to prepare pure water. After confirming that the water quality is qualified, close the bypass valve of the water circulation ion exchange column to bypass the water circulation ion exchange column.

[0032] S3. Set the target temperature of the sample water through the monitoring software, and the data acquisition system controls the thermostat to start and control the sample water temperature at the target temperature.

[0033] S4. Set the target pH value through the monitoring software, and the data acquisition system will automatically control the dosing pump to start and control the pH value of the sample water at the target pH value.

[0034] S5. After the pH readings of the pH meter to be tested and the standard pH meter have stabilized, perform initial calibration on the pH meter to be tested and the standard pH meter respectively.

[0035] S6. Run the pH meter under test and the standard pH meter continuously for a set time, and continuously record the pH readings of the pH meter under test and the standard pH meter through the data acquisition system;

[0036] S7. During the test, calibrate the pH meter under test and the standard pH meter regularly using a standard buffer solution and check their drift rate.

[0037] S8. By setting the disturbance program through the monitoring software, the data acquisition system automatically controls the constant temperature device to change the sample water temperature, and / or controls the dosing device to change the type of reagent, and records the data fluctuation of the pH meter to be tested.

[0038] S9. Based on the data recorded by the data acquisition system, evaluate the drift rate, repeatability, and overall error of the pH meter under test.

[0039] Beneficial technical effects of the present invention:

[0040] The online pH meter stability testing device and method of this invention successfully constructs a closed-loop circulation testing system that can highly simulate the chemical characteristics of secondary loop water in a nuclear power plant by integrating a constant temperature device, a dosing device, and a water circulation ion exchange column. This system can accurately control key parameters of the water sample, such as temperature, pH value, and conductivity, and can actively simulate actual operating conditions such as temperature fluctuations and water quality changes, providing a near-field, reproducible experimental environment for the stability testing of online pH meters.

[0041] The online pH meter stability testing device and method of this invention fills the gap in the lack of effective stability verification methods for online pH meters before their use in nuclear power plants. Through long-term automatic operation and data recording, the long-term drift, short-term repeatability, and response to changes in operating conditions of the pH meter can be quantitatively evaluated. Combined with comparison with a standard pH meter, the overall error of the device can be calculated, thus providing a multi-dimensional and comprehensive stability evaluation system with scientifically reliable evaluation conclusions.

[0042] The present invention relates to an online pH meter stability testing device and method. The device adopts a modular design and a multi-channel parallel testing scheme. The standardized layout of the front panel supports the simultaneous installation and testing of multiple pH meters, which greatly improves testing efficiency and equipment utilization. At the same time, the bypass design of the water circulation ion exchange column and the closed-loop operation of the system effectively reduce reagent consumption and resin regeneration frequency, thereby reducing long-term maintenance costs.

[0043] The online pH meter stability testing device and method of this invention, based on a data acquisition system composed of a PLC, a host computer, and monitoring software, achieves full automation from operating condition setting, process control, data acquisition to result analysis. This not only significantly reduces manual operation and avoids human error, but also ensures the standardization and consistency of the testing process and the integrity and reliability of the data. The test data can be displayed in intuitive forms such as curves and reports, providing a strong basis for judging the performance of the instrument. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the internal structure of an embodiment of the online pH meter stability testing device of the present invention;

[0045] Figure 2 This is a schematic diagram of the external structure of an embodiment of the online pH meter stability testing device of the present invention;

[0046] Figure 3 for Figure 2 A sectional view along the AA direction;

[0047] Figure 4 for Figure 2 Cross-sectional view along the BB direction;

[0048] Figure 5 This is a schematic diagram of the rear structure of an embodiment of the online pH meter stability testing device of the present invention.

[0049] In the diagram, 1. Throttling valve; 2. Filter; 3. Flow meter; 4. Cation exchange column; 5. Water sample inlet; 6. Reagent inlet; 7. Low-pressure drain outlet; 8. Thermostatic device; 9. Water circulation ion exchange column; 10. Water tank; 11. Circulating water pump; 12. Dosing pump; 13. Solution tank; 14. Cooling water inlet; 15. Cooling water outlet. Detailed Implementation

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “equivalent to”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0051] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0052] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments.

[0053] like Figures 1 to 5 As shown, this embodiment provides an online pH meter stability testing device, including:

[0054] The instrument testing device forms a test circuit for pH meter stability testing.

[0055] The dosing device is used to inject reagents into the sample water in the test circuit to adjust the pH value of the sample water;

[0056] Thermostat is used to control the sample water in the test circuit at a set temperature;

[0057] The data acquisition system is used to acquire analog signals output by the instrument detection device, the dosing device, and the temperature control device; and to control the operation of the instrument detection device, the dosing device, and the temperature control device.

[0058] In this embodiment, the test circuit includes a water tank 10, a circulating water pump 11, and multiple test branches; the inlet of the water tank 10 is connected to the outlet pipe of each test branch, the outlet of the water tank 10 is connected to the inlet pipe of the circulating water pump 11, and the outlet of the circulating water pump 11 is connected to the inlet pipe of each test branch, thus forming a test circuit.

[0059] In this embodiment, the water tank 10 is provided with a water sample filling port 5 on its side for adding sample water or rinsing water.

[0060] In this embodiment, the constant temperature device 8 includes a constant temperature water tank, a heating unit for heating the medium in the constant temperature water tank, and a cooling unit for cooling the medium in the constant temperature water tank; the test circuit passes through the constant temperature water tank, and the medium in the constant temperature water tank exchanges heat with the sample water in the test circuit to achieve heating or cooling of the sample water in the test circuit.

[0061] In this embodiment, the heating unit is a heat exchange coil, which is immersed in a constant temperature water tank.

[0062] In this embodiment, the lower part of the constant temperature water tank is provided with a cooling water inlet 14 and a cooling water outlet 15, which are used to exchange heat with the cooling unit when the cooling unit is working.

[0063] In this embodiment, the dosing device includes a solution tank 13 and a dosing pump 12. The solution tank 13 is connected to the test circuit between the circulating water pump 11 and the test branch through the dosing pump 12. An anti-reverse device is provided on the pipeline connecting the dosing pump 12 and the test circuit.

[0064] In this embodiment, the solution tank 13 is provided with a reagent filling port 6 on its side for adding different reagents.

[0065] In this embodiment, multiple test branches are connected in parallel; each test branch includes a throttle valve 1, a filter 2, a flow meter 3, and a flow tank connected in sequence by pipelines. The electrodes of a pH meter are installed in the flow tank, and the electrodes transmit the measurement signal to the secondary meter of the pH meter; the sample water returns to the water tank 10 after passing through the test branch.

[0066] In this embodiment, the data acquisition system includes a PLC, a host computer, and monitoring software;

[0067] The PLC is connected to the secondary meter signal of the pH meter to acquire the 4-20mA analog signal output by the secondary meter of the pH meter.

[0068] The constant temperature water tank is equipped with a temperature sensor; the PLC is connected to the temperature sensor signal to collect the temperature sensor signal of the constant temperature device.

[0069] Monitoring software is installed on the host computer to receive data collected by the PLC and display, store, query historical data and export reports in real time. It also performs closed-loop control of the constant temperature device 8 and the dosing device through PID algorithm to achieve automatic control and data recording of the testing process.

[0070] In this embodiment, a temperature sensor inside the constant temperature water tank monitors the temperature of the medium inside the tank in real time; the PLC collects the temperature of the medium inside the constant temperature water tank through the temperature sensor and further uploads it to the monitoring software on the host computer; the monitoring software performs closed-loop control of the constant temperature device 8 through a PID algorithm, including the following steps:

[0071] The monitoring software compares the temperature of the medium in the constant temperature water tank with the target temperature set by the user.

[0072] When the temperature of the medium in the constant temperature water tank is lower than the target temperature, the monitoring software issues a heating command through the PLC to start the heating unit and heat the medium in the constant temperature water tank.

[0073] When the temperature of the medium in the constant temperature water tank is higher than the target temperature, the monitoring software issues a cooling command through the PLC to start the cooling unit, which then absorbs heat from the medium in the constant temperature water tank.

[0074] When the temperature of the medium in the constant temperature water tank reaches the target temperature, the heating unit and the cooling unit stop heating and cooling the medium in the constant temperature water tank, and the medium in the constant temperature water tank remains at a constant temperature.

[0075] The medium inside the constant temperature water tank heats or cools the sample water in the test circuit by exchanging heat with it. During the entire heat exchange process, the sample water in the test circuit and the medium inside the constant temperature water tank exchange heat efficiently through the pipe wall, but are physically completely isolated and do not mix. This ensures the purity of the sample water and achieves precise temperature control.

[0076] In this embodiment, the monitoring software performs closed-loop control of the dosing device using a PID algorithm, including the following steps:

[0077] Receives the target pH value set by the user and the actual pH value fed back by the pH meter;

[0078] Calculate the deviation between the target pH value and the actual pH value;

[0079] Based on the deviation, a PID control algorithm is executed to generate a control command for controlling the rotation speed of the dosing pump 12.

[0080] Control commands are sent to the PLC to drive the dosing pump 12, thus forming a closed-loop control circuit to achieve automatic and precise adjustment and stabilization of the pH value of the sample water.

[0081] In this embodiment, the online pH meter stability testing device also includes a water circulation ion exchange column 9, which is connected to the test circuit after the outlet of the circulating water pump 11 via a bypass and valve, and is used to prepare pure water.

[0082] In this embodiment, a conductivity meter is installed on the test circuit to confirm whether the conductivity of the sample water in the test circuit meets the test requirements.

[0083] In this embodiment, the online pH meter stability testing device also includes a cation exchange column 4, which is installed on the pipeline between the conductivity meter flow meter and the inlet of the conductivity meter flow cell, and is used to measure hydrogen conductivity.

[0084] In this embodiment, a low-pressure drain outlet 7 is provided at the lower rear of the testing device for discharging sample water.

[0085] In this embodiment, the main structure of the testing device is made of S30408 ​​stainless steel, which has strong corrosion resistance; the dimensions of the testing device are 2.5 meters long * 1.2 meters wide * 2 meters high; the interior of the testing device is divided into different areas according to function.

[0086] In this embodiment, the constant temperature device is located at the rear of the testing device; the throttle valve 1, filter 2, flow meter 3, flow cell of the instrument detection device, as well as the electrodes, secondary meters, and electrode cables of the pH meter are all located on the front panel of the testing device; the water tank 10, circulating water pump 11, and water circulation ion exchange column 9 are all located at the rear of the testing device; eight 138mm*138mm instrument mounting holes and corresponding pipelines and electrode installation systems are reserved above the front panel of the testing device, which can adapt to the installation conditions of the secondary meters of most pH meters on the market, and can realize the simultaneous testing of multiple online pH meters.

[0087] This embodiment also provides an online pH meter stability testing method, using the above-mentioned online pH meter stability testing device, including the following steps:

[0088] S1. Install the pH meter to be tested and the standard pH meter on the flow cell of different test branches respectively; turn on the power, start the circulating water pump 11, and adjust the sample water flow rate within the allowable range of the pH meter through the throttle valve 1 of each test branch, and keep the water sample pressure stable.

[0089] S2. Open the bypass valve of the water circulation ion exchange column 9 to allow the sample water to pass through the water circulation ion exchange column 9 to prepare pure water. After confirming that the water conductivity is qualified, close the bypass valve of the water circulation ion exchange column 9 to bypass the water circulation ion exchange column 9.

[0090] S3. Set the target temperature of the sample water to 25℃ through the monitoring software, and the data acquisition system controls the thermostat 8 to start and control the sample water temperature at the target temperature.

[0091] S4. Set the target pH value to 9.6-9.8 through the monitoring software, and the data acquisition system will automatically control the dosing pump 12 to start and control the pH value of the sample water to the target pH value;

[0092] S5. After the pH readings of the pH meter to be tested and the standard pH meter have stabilized, that is, after the pH value changes by no more than 0.02 per minute, perform initial calibration on the pH meter and the standard pH meter respectively.

[0093] S6. Run the pH meter under test and the standard pH meter continuously for 3 months and continuously record the pH readings of the pH meter under test and the standard pH meter through the data acquisition system;

[0094] S7. During the test, after calibrating the pH meter to be tested and the standard pH meter with standard buffer solutions of pH 7.00 and pH 10.01, immerse the electrodes of the pH meter to be tested and the standard pH meter in the same standard buffer solution for 24 hours, keep the temperature stable and avoid vibration, and check their drift rate.

[0095] S8. By setting the disturbance program through the monitoring software, the data acquisition system automatically controls the constant temperature device to change the sample water temperature and records the data fluctuation of the pH meter to be tested.

[0096] S9. By setting a disturbance program through monitoring software, the data acquisition system automatically controls the dosing device to change the type of reagent and records the data fluctuation of the pH meter to be tested.

[0097] S10. Based on the data recorded by the data acquisition system, evaluate the drift rate, repeatability, and overall error of the pH meter under test.

[0098] In this embodiment, in step S8, the reagents include ammonia and ethanolamine.

[0099] In this embodiment, in S10, the drift rate of the pH meter to be tested is the 24-hour reading deviation of the pH meter.

[0100] In this embodiment, in S10, the drift rate of the pH meter to be tested is calculated using the following formula:

[0101]

[0102] Among them, S py The pH value represents the drift rate of the pH meter being measured. f The pH reading is the pH value at the final time. i The initial pH reading of the pH meter to be tested, t f For the final time, t i Let the initial time be t f -t i It is 24 hours.

[0103] In this embodiment, in S10, if the drift rate of the pH meter to be tested is <0.1 within 24 hours, then the drift rate of the pH meter to be tested is deemed to meet the requirements; if the drift rate of the pH reading of the pH meter to be tested is ≥0.1 within 24 hours, then the drift rate of the pH meter to be tested is deemed to not meet the requirements.

[0104] In this embodiment, in S9, the repeatability of the pH meter under test is evaluated using the following formula:

[0105]

[0106] Among them, S pH To ensure the repeatability of the pH meter being tested, pH i Let i be the value of the i-th measurement. The average of six measurements of the same standard buffer solution.

[0107] In this embodiment, in S10, if the standard deviation of the pH meter reading is <0.03, the repeatability of the pH meter is deemed to meet the requirements; if the standard deviation of the pH meter reading is ≥0.03, the repeatability of the pH meter is deemed to fail to meet the requirements.

[0108] In this embodiment, in S10, the overall error of the pH meter under test is evaluated using the following formula:

[0109] δ G =pH-pH 标准

[0110] Where, δ G The total error of the pH meter being measured is denoted as pH, where pH is the pH reading of the pH meter being measured. 标准 This is the pH reading from a standard pH meter.

[0111] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. An online pH meter stability testing device, characterized in that, include: The instrument testing device forms a test circuit for pH meter stability testing. The dosing device is used to inject reagents into the sample water in the test circuit to adjust the pH value of the sample water; Thermostat is used to control the sample water in the test circuit at a set temperature; The data acquisition system is used to collect output signals from the instrument detection device, the dosing device, and the temperature control device; and to control the operation of the instrument detection device, the dosing device, and the temperature control device.

2. The online pH meter stability testing device according to claim 1, characterized in that, The test circuit includes a water tank (10), a circulating water pump (11), and multiple test branches; the inlet of the water tank (10) is connected to the outlet pipe of each test branch, the outlet of the water tank (10) is connected to the inlet pipe of the circulating water pump (11), and the outlet of the circulating water pump (11) is connected to the inlet pipe of each test branch, thus forming a test circuit.

3. The online pH meter stability testing device according to claim 2, characterized in that, The constant temperature device (8) includes a constant temperature water tank, a heating unit for heating the medium in the constant temperature water tank, and a cooling unit for cooling the medium in the constant temperature water tank; the test circuit passes through the constant temperature water tank, and the medium in the constant temperature water tank exchanges heat with the sample water in the test circuit to achieve heating or cooling of the sample water in the test circuit.

4. The online pH meter stability testing device according to claim 2, characterized in that, The dosing device includes a solution tank (13) and a dosing pump (12). The solution tank (13) is connected to the test circuit between the circulating water pump (11) and the test branch through the dosing pump (12). A reverse flow prevention device is provided on the pipeline connecting the dosing pump (12) and the test circuit.

5. The online pH meter stability testing device according to claim 2, characterized in that, Multiple test branches are set up in parallel; the test branch includes a throttle valve (1), a filter (2), a flow meter (3) and a flow cell connected in sequence by pipelines. The electrodes of the pH meter are installed in the flow cell and the electrodes transmit the measurement signal to the secondary meter of the pH meter.

6. The online pH meter stability testing device according to claim 5, characterized in that, The data acquisition system includes a PLC, a host computer, and monitoring software; The PLC is connected to the secondary meter signal of the pH meter to acquire the analog signal output by the secondary meter of the pH meter. The constant temperature water tank is equipped with a temperature sensor; the PLC is connected to the temperature sensor signal to collect the temperature sensor signal of the constant temperature device. The host computer is equipped with monitoring software to receive data collected by the PLC and display, store, query and export reports in real time, and perform closed-loop control of the constant temperature device (8) and the dosing device through PID algorithm.

7. The online pH meter stability testing device according to claim 6, characterized in that, The temperature sensor inside the constant temperature water tank monitors the temperature of the medium inside the tank in real time; the PLC collects the temperature of the medium inside the constant temperature water tank through the temperature sensor and further uploads it to the monitoring software of the host computer; the monitoring software performs closed-loop control of the constant temperature device (8) through the PID algorithm, including the following steps: The monitoring software compares the temperature of the medium in the constant temperature water tank with the target temperature set by the user. When the temperature of the medium in the constant temperature water tank is lower than the target temperature, the monitoring software issues a heating command through the PLC to start the heating unit and heat the medium in the constant temperature water tank. When the temperature of the medium in the constant temperature water tank is higher than the target temperature, the monitoring software issues a cooling command through the PLC to start the cooling unit, which then absorbs heat from the medium in the constant temperature water tank. When the temperature of the medium in the constant temperature water tank reaches the target temperature, the heating unit and the cooling unit stop heating and cooling the medium in the constant temperature water tank, and the medium in the constant temperature water tank remains at a constant temperature.

8. The online pH meter stability testing device according to claim 6, characterized in that, The monitoring software uses a PID algorithm to perform closed-loop control of the dosing device, including the following steps: Receives the target pH value set by the user and the actual pH value fed back by the pH meter; Calculate the deviation between the target pH value and the actual pH value; Based on the deviation, a PID control algorithm is executed to generate a control command for controlling the rotational speed of the dosing pump (12); The control command is sent to the PLC to drive the dosing pump (12) to operate, thus forming a closed-loop control circuit.

9. The online pH meter stability testing device according to claim 2, characterized in that, It also includes a water circulation ion exchange column (9), which is connected to the test circuit after the outlet of the circulating water pump (11) via a bypass and valve.

10. A method for testing the stability of an online pH meter, characterized in that, Using the online pH meter stability testing device according to any one of claims 1-9, the process includes the following steps: S1. Install the pH meter to be tested and the standard pH meter on the flow cell of different test branches respectively; start the circulating water pump (11) and adjust the sample water flow rate through the throttle valve (1) of each test branch; S2. Open the bypass valve of the water circulation ion exchange column (9) to allow the sample water to pass through the water circulation ion exchange column (9) to prepare pure water. After confirming that the water quality is qualified, close the bypass valve of the water circulation ion exchange column (9) to bypass the water circulation ion exchange column (9). S3. Set the target temperature of the sample water through the monitoring software, and the data acquisition system controls the thermostat (8) to start and control the sample water temperature at the target temperature. S4. The target pH value is set by the monitoring software, and the data acquisition system automatically controls the dosing pump (12) to start and control the pH value of the sample water at the target pH value. S5. After the pH readings of the pH meter to be tested and the standard pH meter have stabilized, perform initial calibration on the pH meter to be tested and the standard pH meter respectively. S6. Run the pH meter under test and the standard pH meter continuously for a set time, and continuously record the pH readings of the pH meter under test and the standard pH meter through the data acquisition system; S7. During the test, calibrate the pH meter under test and the standard pH meter regularly using a standard buffer solution and check their drift rate. S8. By setting the disturbance program through the monitoring software, the data acquisition system automatically controls the constant temperature device to change the sample water temperature, and / or controls the dosing device to change the type of reagent, and records the data fluctuation of the pH meter to be tested. S9. Based on the data recorded by the data acquisition system, evaluate the drift rate, repeatability, and overall error of the pH meter under test.

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