On-line analysis instrument anti-drift capacitance type pipeline liquid detection method and on-line analysis instrument anti-drift capacitance type pipeline liquid detection device

Abstract

The invention relates to an anti-drift capacitive pipeline liquid detection method and device for a water quality online analysis instrument. The method comprises the following steps: collecting a liquid inlet pipe analog signal in a liquid inlet pipe in real time through a first capacitive sensor; collecting an empty tube analog signal in the empty tube in real time through a second capacitive sensor; the hollow pipe is arranged beside the liquid inlet pipe; the liquid inlet pipe analog signal is converted into a liquid inlet pipe value, and the empty pipe analog signal is converted into an empty pipe value; subtracting the currently collected empty pipe value from the currently collected liquid inlet pipe value to obtain a real-time detection value; the real-time detection value is compared with an air threshold value, if the real-time detection value is larger than the air threshold value, it is judged that the current liquid inlet pipe state is that liquid exists in the pipe, and if the real-time detection value is smaller than the air threshold value, it is judged that the current liquid inlet pipe state is air. The device has the advantages that by arranging the hollow pipe and introducing the reference, the temperature and humidity drift of the liquid inlet pipe caused by environmental change can be counteracted to a great extent by a real-time detection value, and the accuracy of judging whether liquid exists in the pipeline or not is improved.

Description

Technical Field

[0001] The present invention relates to the field of on-line water quality analysis equipment, and particularly to an anti-drift capacitive pipeline liquid detection method and device for on-line water quality analysis instruments. Background Art

[0002] On-line water quality analysis equipment needs to periodically extract water samples and reagents, and then perform water quality detection to analyze whether the water quality parameters meet the standards. The on-line water quality analysis equipment is in an unattended working state. Therefore, during the extraction process, if the liquid extraction fails, or there is a long air section or a large number of bubbles in the liquid path but not detected in time, it will result in the actual extracted liquid volume or liquid volume not meeting the standard. However, the system will still calculate the water quality parameters according to the preset liquid extraction volume or liquid extraction amount, which will seriously affect the detection result and lead to misjudgment of the water quality. There are mainly two common existing pipeline liquid detection devices. One is to use a photoelectric sensor for detection. The photoelectric sensor is set on the pipe wall of the pipeline, and it detects whether there is liquid flowing through the pipeline through the photoelectric sensor. However, it cannot detect the air content in the liquid in the pipeline, which affects the accuracy of water quality parameter detection. At the same time, the extracted reagent or water sample with high turbidity is likely to cause dirt on the inner wall of the pipe, blocking the light path of the photoelectric sensor, which will also cause misjudgment. Therefore, it is necessary to spend manpower to maintain the pipeline regularly. The other is to use a capacitive sensor. However, the capacitive sensor is prone to measurement value drift due to changes in environmental temperature and humidity. Therefore, it is generally calibrated during installation and needs to be calibrated regularly later. However, no matter which calibration, it only removes the environmental background noise based on the environmental temperature and humidity at the time of calibration. However, during the actual use of the equipment, there may be a large drop in temperature and humidity in a day or before and after the change of seasons. Therefore, as an on-line detection device, the capacitive sensor cannot ensure the accuracy of real-time on-line detection only by manual regular calibration. In addition, detecting bubbles or air sections in the liquid requires a threshold (i.e., the air threshold of the present invention) that can accurately distinguish air and liquid as a reference, and then further judgment. However, the existing capacitive sensor has a large temperature drift, and there will be misjudgment of liquid and air due to the temperature drift being greater than the threshold, which leads to inaccurate identification of bubbles and inaccurate statistics of the air volume. Therefore, in the existing technical solutions for judging whether there is liquid in the pipeline through a capacitive sensor, there are few technical means for identifying the air content in the liquid in the pipeline. Summary of the Invention

[0003] In order to solve the above problems, the purpose of the present invention is to provide an anti-drift capacitive pipeline liquid detection method for on-line water quality analysis instruments. By setting an empty pipe and introducing a reference, the real-time detection value can largely offset the temperature and humidity drift of the liquid inlet pipe caused by environmental changes, improving the accuracy of judging whether there is liquid in the pipeline, and further realizing the accuracy of identifying small bubbles, large bubbles, air sections and statistics of air content.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] Technical solution one

[0006] An anti-drift capacitive pipeline liquid detection method for an on-line water quality analysis instrument, comprising the following steps: real-time collecting an inlet pipe analog signal in an inlet pipe through a first capacitance sensor; real-time collecting an empty pipe analog signal in an empty pipe through a second capacitance sensor; the empty pipe is arranged beside the inlet pipe; converting the inlet pipe analog signal into an inlet pipe value, and converting the empty pipe analog signal into an empty pipe value; subtracting the currently collected empty pipe value from the currently collected inlet pipe value to obtain a real-time detection value; performing a liquid and air determination step: comparing the real-time detection value with an air threshold, if it is greater than the air threshold, it is determined that the current state of the inlet pipe is that there is liquid in the pipe, and if it is less than the air threshold, it is determined that the current state of the inlet pipe is air.

[0007] More preferably, subtracting the previously collected detection value from the real-time detection value to calculate a real-time change amount;

[0008] If the real-time change amount is positive and > a bubble threshold, further judgment is made in combination with the real-time change amount. If the real-time change amount is negative, it is determined that the current state in the inlet pipe is air. If the real-time change amount is non-negative, the current state remains unchanged and is the same as the previously detected state;

[0009] If the real-time change amount is positive and ≤ the bubble threshold, perform the liquid and air determination step.

[0010] More preferably, during a single liquid extraction process, each time it is determined that there is air in the inlet pipe, the air collection times are accumulated and it is judged whether the accumulated air collection times are greater than a preset counting threshold for liquid extraction failure. If so, a liquid extraction failure prompt is output.

[0011] Based on the same invention object, the present invention also provides an anti-drift capacitive pipeline liquid detection device for an on-line water quality analysis instrument.

[0012] Technical solution two

[0013] An anti-drift capacitive pipeline liquid detection device for an on-line water quality analysis instrument, comprising a housing and a main control circuit board arranged in the housing. Two first through holes for passing through a liquid inlet pipe and two second through holes for passing through an empty pipe are formed in the housing. An MCU, a capacitance measurement chip, a first capacitance sensor and a second capacitance sensor are fixed on the main control circuit board. The liquid inlet pipe passes through the outer shell through the two first through holes and the liquid inlet pipe is in close contact with the first capacitance sensor. The empty pipe passes through the housing through the two second through holes and the empty pipe is in close contact with the second capacitance sensor. The first capacitance sensor real-time collects the liquid inlet pipe analog signal in the liquid inlet pipe, and the second capacitance sensor real-time collects the empty pipe analog signal in the empty pipe. The capacitance measurement chip converts the liquid inlet pipe analog signal into a liquid inlet pipe value and converts the empty pipe analog signal into an empty pipe value. The MCU executes a liquid and air determination step: comparing the real-time detection value with an air threshold value. If it is greater than the air threshold value, it is determined that there is liquid in the liquid inlet pipe. If it is less than the air threshold value, it is determined that there is air in the liquid inlet pipe.

[0014] Preferably, the MCU subtracts the detection value collected last time from the real-time detection value to calculate the real-time change amount;

[0015] If the real-time change amount is positive and greater than the bubble threshold value, further judgment is made in combination with the real-time change amount. If the real-time change amount is negative, it is determined that the current state in the liquid inlet pipe is air. If the real-time change amount is non-negative, the current state remains unchanged and is the same as the state detected last time;

[0016] If the real-time change amount is positive and less than or equal to the bubble threshold value, the liquid and air determination step is executed.

[0017] Preferably, during a single liquid extraction process, each time the MCU determines that there is air in the liquid inlet pipe, the air collection times are accumulated and it is judged whether the accumulated air collection times are greater than a preset counting threshold for liquid extraction failure. If so, a liquid extraction failure prompt is output.

[0018] The present invention has the following beneficial effects:

[0019] 1. The anti-drift capacitive pipeline liquid detection method for an on-line water quality analysis instrument of the present invention, by setting an empty pipe and real-time collecting the empty pipe value as a reference for the current liquid inlet pipe value, overcomes the drift of the empty pipe capacitance value caused by environmental changes, realizes real-time calibration and improves the detection accuracy, so that manual regular calibration and maintenance can be eliminated and misjudgment can be avoided.

[0020] 2. An anti-drift capacitive pipeline liquid detection method for on-line water quality analysis instruments according to the present invention combines the real-time change amount with the bubble threshold on the basis of strong anti-drift performance to achieve high-sensitivity bubble recognition. Further combining the real-time detection value and the air threshold can accurately judge the fluctuations of the subtle state in the pipeline, providing all-round high-accuracy monitoring of the pipeline liquid state for on-line water quality analysis instruments.

[0021] 3. An anti-drift capacitive pipeline liquid detection device for on-line water quality analysis instruments according to the present invention is a device that can resist temperature and humidity drift without potting in addition to the advantages of the detection method. At the same time, the detection device of the present invention also has the advantages of simple structure and convenient production and installation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic flow chart of Embodiment 1 of the present invention;

[0023] Figure 2 is a comparison chart of temperature drift with and without / in the reference state under constant humidity;

[0024] Figure 3 is a comparison chart of humidity drift with and without / in the reference state under constant temperature;

[0025] Figure 4 is a schematic flow chart of Embodiment 2 of the present invention;

[0026] Figure 5 is a waveform chart of the detection value when there are bubbles and air in the liquid after adopting the technical solution of the present invention;

[0027] Figure 6 is a schematic structural diagram of the detection device of the present invention;

[0028] Figure 7 is an exploded view of the detection device of the present invention;

[0029] Figure 8 is a cross-sectional view of the detection device of the present invention

[0030] Figure 9 is a schematic circuit structure diagram of the detection device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

[0032] Embodiment 1

[0033] Please refer to Figure 1 , an anti-drift capacitive pipeline liquid detection method for on-line water quality analysis instruments, comprising the following steps:

[0034] Step 1: Collect the analog signal of the liquid inlet pipe in real time through the first capacitance sensor;

[0035] Step 2: Collect the analog signal of the empty pipe in real time through the second capacitance sensor; the empty pipe is arranged beside the liquid inlet pipe;

[0036] Step 3: Convert the analog signal of the liquid inlet pipe into a liquid inlet pipe value, and convert the analog signal of the empty pipe into an empty pipe value;

[0037] Step 4: Subtract the currently collected empty pipe value from the currently collected liquid inlet pipe value to obtain a real-time detection value; then perform the liquid and air determination step: compare the real-time detection value with the air threshold. If it is greater than the air threshold, it is determined that the state of the liquid inlet pipe is that there is liquid in the pipe. If it is less than the air threshold, it is determined that there is air in the liquid inlet pipe.

[0038] The present invention uses two capacitance sensors for real-time measurement. One measures the empty pipe as a reference, and the other measures the liquid inlet pipe. Subtract the empty pipe value from the liquid inlet pipe value to obtain a real-time detection value, and combine the real-time detection value with the air threshold to judge the liquid state in the pipe, which largely offsets the temperature and humidity drift of the liquid inlet pipe caused by environmental changes. The specific experimental data is as follows:

[0039] First, please refer to Figure 2 , under the condition of temperature drift from 0°C to 50°C at a constant humidity of 1.5%, a comparative test with and without reference is carried out on three groups of pipelines. In the case of having a reference, the output value is the real-time detection value. In the case of without a reference, the output value is the sample injection pipe value. The three groups of pipelines are Group 1, Group 2, and Group 3 respectively. The test results are shown in Table 1, where the "sample injection pipe" column represents the values of the liquid inlet pipe collected when there is air in the liquid inlet pipe and the temperature changes from 0 to 50° at a constant humidity. The "sample injection pipe minus air pipe" column represents the real-time detection value obtained by using the empty pipe value as a reference. It can be seen from Table 1 that when the empty pipe value is not used as a reference, calculating the maximum temperature drift value of the sample injection pipe, all three groups are above 8000. When a reference is introduced, the temperature drift of the detection value is about 2000, which greatly reduces the drift of the output value caused by temperature changes, and there will be no situation where the output value is greater than the air threshold due to temperature drift and misjudging the liquid state in the pipe.

[0040] Table 1

[0041]

[0042] Then, please refer to Figure 3, at a constant temperature of 25°C and under the condition of 10% to 80% humidity drift, repeat the above test steps, and the test results are shown in Table 2. It can be seen from Table 2 that when the empty tube value is not used as a reference, the maximum humidity drift values are all above 2000. When a reference is introduced, the humidity drift of the detected value is about 500. Therefore, the technical solution of the present invention can also well reduce the drift amplitude caused by humidity.

[0043] Table 2

[0044]

[0045] Finally, in the state of the liquid inlet pipe sucking liquid, adopt the solution of the present invention to measure the difference between the liquid inlet pipe and the air pipe, that is, the real-time detection value, record the minimum difference, and then compare this difference with the maximum temperature drift with / without reference, as shown in Table 3.

[0046] Table 3:

[0047] Item Measurement Value No. 1 Measurement Value No. 2 Measurement Value No. 3 Minimum Difference of Liquid Air 7205 7542 7153 Maximum Drift of 0 - 50°C with Reference 2652 2225 2206 Maximum Drift of 0 - 50°C without Reference 8458 8450 8015

[0048] It can be concluded from the test data in Table 3 that the maximum temperature drift of the real-time detection value after adding a reference is between 2000 and 3000, while the minimum value of the real-time detection value is above 7000. Therefore, by adopting the technical solution of the present invention, misjudgment will not occur due to the temperature drift value being greater than the real-time detection value. For the solution without a reference, the maximum temperature drift of the liquid inlet pipe value is 8000 - 8500, which is close to the minimum real-time detection value, and misjudgment caused by temperature drift is likely to occur.

[0049] It can be concluded from the above experimental data that the value range of the air threshold of the present invention is relatively wide, and it can be preferably selected between 3500 and 6500. As Figure 5 shown, when the air threshold value is 4000, the liquid state in the pipeline can be accurately judged. However, for the solution without a reference, since the change amount caused by temperature drift may exceed the air threshold, it is very easy to misjudge.

[0050] Example 2

[0051] In the liquid inlet state, when small bubbles appear in the liquid, the inside of the tube is not in a completely empty tube state. The volume of the small bubbles is small, and most of the space inside the tube is still filled with liquid. Therefore, the real-time detection value often still exceeds the air threshold. Only by comparing the real-time detection value with the air threshold, the small bubbles cannot be accurately identified. In this embodiment, the real-time change amount and the bubble threshold are further used to accurately identify the small bubbles and count the air content. Please refer to Figure 4 , the specific process is as follows:

[0052] Step 10, please refer to Figure 5When there are bubbles or air in the liquid, for the waveform diagram, subtract the previously collected detection value from the real-time detection value to calculate the real-time change amount; if the real-time change amount is positive and > the bubble threshold, execute step 20, if the real-time change amount is positive and ≤ the bubble threshold, execute step 30; in this embodiment, the value range of the bubble threshold is 100 - 130;

[0053] Step 20: If the real-time change amount is negative, it is determined that the current state in the liquid inlet pipe is air. If the real-time change amount is non-negative, the current state remains unchanged, and only the previously detected state needs to be read; if the previously detected state is air, the current state is still air, and if the previously detected state is liquid, the current state is still liquid;

[0054] Step 30: Execute the liquid and air determination step, compare the real-time detection value with the air threshold. If it is greater than the air threshold, it is determined that the state of the liquid inlet pipe is that there is liquid in the pipe. If it is less than the air threshold, it is determined that there is air in the liquid inlet pipe.

[0055] Step 40: After the determination of the liquid state in the pipe is completed, the 485 command of the water quality on-line analysis device can be listened to obtain the big table action. If the start liquid extraction command is listened to, which means the start of a new round of liquid extraction, the air collection times are cleared. During a single liquid extraction process, every time there is air in the liquid inlet pipe, the air collection times are accumulated, and it is judged whether the accumulated air collection times are greater than the preset counting threshold for liquid extraction failure. If so, a liquid extraction failure prompt is output. More preferably, the presence of an air segment in the pipe can also be identified according to the continuous accumulation of the space collection times and the accumulation times reaching the preset threshold.

[0056] More preferably, in order to avoid the interference of instantaneous small fluctuations in the real-time detection value caused by the external environment, it can be set that when the difference is negative and the number of consecutive occurrences exceeds the preset number, the air collection count +1 is executed. In this way, the presence of small bubbles can be judged more accurately. For example, it can be set that when the difference is negative and greater than the bubble threshold for three consecutive times, the air collection times +1 is started at the fourth time, and +1 at the fifth time, and so on.

[0057] Adopting the solution of the present invention, the air content tests are carried out on three groups of pipelines, namely No. 1, No. 2, and No. 3. The test results are as follows:

[0058] Table 4: Air Content Test No. 1

[0059] True Value of Air Content uL Measured Value of Air Content uL Measurement Error 0 0 0.00％ 50 54 8.66％ 100 104 3.56％ 150 147 -1.67％ 200 189 -5.62％ 250 244 -2.33％ 300 305 1.74％ 350 346 -1.01％ 400 388 -2.99％ 450 459 2.09％ 500 506 1.13％

[0060] Table 5: Air Content Test No. 2

[0061] True Value of Air Content uL Measured Value of Air Content uL Measurement Error 0 0 0.00％ 50 58 13.79％ 100 108 7.41％ 150 152 1.32％ 200 195 -2.56％ 250 250 0.00％ 300 310 3.23％ 350 355 1.41％ 400 400 0.00％ 450 465 3.23％ 500 515 2.91％

[0062] Table 6: Air Content Test No. 3

[0063]

[0064]

[0065] As can be seen from the test results, the detection of the air content by the present invention also has good accuracy.

[0066] A drift-resistant capacitive pipeline liquid detection method for an on-line water quality analysis instrument according to the present invention, by setting an empty pipe, and collecting the empty pipe value in real time as a reference for the current liquid inlet pipe value, overcomes the drift of the empty pipe capacitance value caused by environmental changes, realizes real-time calibration and improves the detection accuracy, thereby enabling the exemption of manual regular calibration and maintenance and avoiding misjudgment. At the same time, on the basis of having strong anti-drift performance, the real-time change amount is combined with the bubble threshold to realize high-sensitivity bubble recognition, and further combined with the real-time detection value and the air threshold, it can accurately judge the fluctuations of the fine state in the pipe, providing all-round high-accuracy pipeline liquid state monitoring for the on-line water quality analysis instrument.

[0067] Based on the same inventive concept, the present invention also provides a detection device for implementing the methods described in Embodiment 1 and Embodiment 2.

[0068] Embodiment 3

[0069] Please refer to Figures 6 to 9 , a drift-resistant capacitive pipeline liquid detection device for an on-line water quality analysis instrument, comprising a housing 1 and a main control circuit board 2 disposed inside the housing 1. Two first through holes 11 for passing through a liquid inlet pipe 5 and two second through holes 12 for passing through an empty pipe 6 are formed on the housing 1. An MCU, a capacitance measurement chip, a first capacitance sensor 3 and a second capacitance sensor 4 are fixed on the main control circuit board 2. The liquid inlet pipe 5 passes through the outer housing 1 through the two first through holes 11 and the liquid inlet pipe 5 is in close contact with the first capacitance sensor 3, the empty pipe 6 passes through the housing 1 through the two second through holes 12 and the empty pipe 6 is in close contact with the second capacitance sensor 4. The first capacitance sensor 3 collects the liquid inlet pipe analog signal in the liquid inlet pipe 5 in real time, the second capacitance sensor 4 collects the empty pipe analog signal in the empty pipe 6 in real time, the capacitance measurement chip converts the liquid inlet pipe analog signal into a liquid inlet pipe value, converts the empty pipe analog signal into an empty pipe value, and the MCU subtracts the currently collected liquid inlet pipe value from the currently collected empty pipe value to obtain a real-time detection value, and then executes a liquid and air determination step: comparing the real-time detection value with an air threshold, if it is greater than the air threshold, it is determined that there is liquid in the liquid inlet pipe, and if it is less than the air threshold, it is determined that there is air in the liquid inlet pipe.

[0070] In this embodiment, the empty tube 6 is arranged beside the liquid inlet tube 5. The first capacitance sensor 3 and the second capacitance sensor 4 are both metal induction motors attached to the main control circuit board. A power supply module is also arranged on the main control circuit board 2 of the detection device of the present invention to supply power to components such as the MCU and the capacitance measurement chip. The capacitance measurement chip can adopt other capacitance-type sensing chips such as MDC02. A plurality of interfaces 7 are also arranged on the housing 1, for example, a power supply interface, a signal input / output interface, etc., for communicating with external devices.

[0071] When judging the state of the liquid in the tube, in order to further identify small bubbles, the MCU subtracts the detection value collected last time from the real-time detection value to calculate the real-time change amount; if the real-time change amount is positive > the bubble threshold, then further judge in combination with the real-time change amount. If the real-time change amount is negative, it is determined that the current state in the liquid inlet tube is air. If the real-time change amount is non-negative, the current state remains unchanged and is the same as the state detected last time; if the real-time change amount is positive ≤ the bubble threshold, then execute the liquid and air judgment step.

[0072] During a single liquid extraction process, every time the MCU determines that there is air in the liquid inlet tube, the air collection times are accumulated and it is judged whether the accumulated air collection times are greater than the preset counting threshold for liquid extraction failure. If so, a liquid extraction failure prompt is output.

[0073] The method steps described in Embodiment 1 and Embodiment 2 can both be applied to the detection device of this Embodiment 3.

[0074] Using the detection device of the present invention, the state of the liquid in the tube can be accurately judged without manual calibration, and temperature and humidity drift can be resisted without potting. At the same time, the detection device of the present invention has a simple structure and is convenient for production and installation.

[0075] Since the detection device introduced in Embodiment 3 of the present invention is a hardware carrier for implementing the methods of Embodiment 1 and Embodiment 2 of the present invention, based on the detection method introduced in the present invention, those skilled in the art can understand the specific implementation manner of the detection device, so it will not be elaborated here. All the methods adopted in Embodiment 1 of the present invention belong to the scope of protection of the present invention.

[0076] The above are only the specific implementation manners of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made by using the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A drift-resistant capacitive pipeline liquid detection method for an online water quality analyzer, characterized in that: The steps include: The first capacitance sensor is used to collect the liquid inlet pipe analog signal in real time in the liquid inlet pipe; The empty pipe simulation signal in the empty pipe is collected in real time by a second capacitance sensor; the empty pipe is arranged beside the liquid inlet pipe; Convert the liquid inlet pipe analog signal into the liquid inlet pipe value, and convert the empty pipe analog signal into the empty pipe value; The real-time detection value is obtained by subtracting the currently collected empty pipe value from the currently collected liquid inlet pipe value; Execute the liquid and air judgment step: compare the real-time detection value with the air threshold value. If it is greater than the air threshold value, it is determined that the current state of the liquid inlet pipe is that there is liquid in the pipe. If it is less than the air threshold value, it is determined that the current state of the liquid inlet pipe is air.

2. The anti-drift capacitive pipeline liquid detection method for an online water quality analyzer according to claim 1, characterized in that: Subtract the last collected detection value from the real-time detection value to calculate the real-time change; If the real-time change is positive and is greater than the bubble threshold, the real-time change is further combined for judgment. If the real-time change is negative, it is determined that the current state in the liquid inlet pipe is air. If the real-time change is non-negative, the current state remains unchanged and is the same as the state detected last time. If the real-time change is positive ≤ the bubble threshold, the liquid and air determination step is executed.

3. The anti-drift capacitive pipeline liquid detection method for an online water quality analyzer according to claim 2, characterized in that: During a single liquid extraction process, each time it is determined that there is air in the liquid inlet pipe, the number of air collection times is accumulated and a determination is made as to whether the accumulated number of air collection times is greater than a preset counting threshold for liquid extraction failure. If so, a liquid extraction failure prompt is output.

4. An anti-drift capacitive pipeline liquid detection device for an online water quality analyzer, characterized in that: The invention comprises a shell and a main control circuit board arranged in the shell, wherein the shell is provided with two first through holes for penetrating a liquid inlet pipe and two second through holes for penetrating an empty pipe, an MCU, a capacitance measurement chip, a first capacitance sensor and a second capacitance sensor are fixed on the main control circuit board, the liquid inlet pipe penetrates the shell through the two first through holes and the liquid inlet pipe is closely attached to the first capacitance sensor, the empty pipe penetrates the shell through the two second through holes and the empty pipe is closely attached to the second capacitance sensor, the first capacitance sensor collects the liquid inlet pipe analog signal in the liquid inlet pipe in real time, and the second capacitance sensor The empty pipe analog signal in the empty pipe is collected in real time, the capacitance measurement chip converts the liquid inlet pipe analog signal into the liquid inlet pipe value, and the empty pipe analog signal is converted into the empty pipe value. The MCU executes the liquid and air judgment step: the real-time detection value is compared with the air threshold value. If it is greater than the air threshold value, it is determined that there is liquid in the liquid inlet pipe. If it is less than the air threshold value, it is determined that there is air in the liquid inlet pipe.

5. The anti-drift capacitive pipeline liquid detection device for an online water quality analyzer according to claim 4, characterized in that: The MCU subtracts the detection value collected last time from the real-time detection value to calculate the real-time change; If the real-time change is positive and is greater than the bubble threshold, the real-time change is further combined for judgment. If the real-time change is negative, it is determined that the current state in the liquid inlet pipe is air. If the real-time change is non-negative, the current state remains unchanged and is the same as the state detected last time. If the real-time change is positive ≤ the bubble threshold, the liquid and air determination step is executed.

6. The anti-drift capacitive pipeline liquid detection method for an online water quality analyzer according to claim 5, characterized in that: During a single liquid extraction process, each time the MCU determines that there is air in the liquid inlet pipe, the air collection times are accumulated and a determination is made as to whether the accumulated air collection times are greater than the preset liquid extraction failure counting threshold. If so, a liquid extraction failure prompt is output.

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