Automatic flow monitoring method and device for open system

Abstract

An automatic flow monitoring method and device for an open system belong to the technical field of energy conservation and emission reduction, and mainly comprise the following steps: arranging a pressure sensor on a medium circulation pipeline of the open system; sampling the measured value of the pressure sensor according to a set period; a maximum likelihood estimation method is adopted to process the pressure values collected in all the periods, and the pressure value of the current pipeline is determined; measuring the height difference between the mounting position of the pressure sensor and the outlet end; calibrating the resistance from the mounting point position of the pressure sensor to the outlet end pipeline; and a pipeline flow calculation model is established, the current pressure is collected on line, and real-time calculation of the flow in the pipeline is completed. According to the method, the flow value is obtained by establishing the calculation processing model based on the pipeline pressure and resistance, expensive and complex flowmeter products are avoided, the cost is greatly reduced, and a solution which is low in cost, high in precision and easy to install and maintain is provided for open system flow measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of energy conservation and emission reduction, and in particular to a flow monitoring method and device for an open system. Background Art

[0002] In modern industry and construction, flow monitoring technology plays a vital role, especially in central air-conditioning systems. Accurate flow monitoring can not only ensure the stable operation of the system, but also effectively improve energy utilization efficiency and reduce operating costs.

[0003] However, traditional flow monitoring devices often have problems such as high cost, complex installation, requirements for installation pipes, and difficult maintenance: The price of many existing flow meters increases exponentially with the size of the pipe being measured. A flow sensor for a DN200 pipe costs at least 5,000 yuan. As a result, some open systems are not used in places with strong flow measurement requirements (such as open cooling towers) due to their low cost-effectiveness. As a result, energy efficiency monitoring and improvement of equipment cannot be implemented, control systems are crude, and energy saving effects are poor. The installation of existing flow meters requires a straight pipe section of at least 15 times D. That is, if the flow of a DN200 pipe needs to be measured on site, a straight pipe section of at least 3m is required. Many project sites do not have this condition. The installation is complex and difficult. According to the characteristics of the sensor, the broken tube flowmeter requires a broken tube flange connection, the rotor type vortex type sensor and other sensors are inserted, and there are strict insertion depth requirements. The external clamp type sensor requires grinding the tube and using coupling agent for fitting installation.

[0004] These problems have limited the widespread application of flow meters in central air-conditioning systems to a certain extent. Summary of the Invention

[0005] The present invention provides a low-cost, high-precision, easy-to-install and maintain open system automated flow monitoring method and device. This method avoids the use of expensive and complex flow meter products in the prior art and obtains pipeline flow through the collection and calculation of pressure data.

[0006] The method mainly includes the following steps: S0, install a pressure sensor on the medium flow pipeline of the open system, and the installation position of the pressure sensor should be at least 2 elbows away from the outlet end; S1, sampling the measured value of the pressure sensor according to the set period; S2, using the maximum likelihood estimation method to process the pressure values collected in each cycle to determine the current pipeline pressure value; S3, measuring the height difference between the installation position of the pressure sensor and the outlet end; S4, calibrate the resistance of the pipeline from the installation point of the pressure sensor to the outlet end; S5, establish a pipeline flow calculation model, collect the current pressure online, and complete the real-time calculation of the flow in the pipeline.

[0007] Furthermore, the step S2 specifically includes: If the pressure sensor is sampled every 1 millisecond, 1000 data points will be sampled per second. These 1000 observation values are recorded as P1, P2…Pn…P1000, with the unit being kPa. Each item in the observed numerical sequence is used as an estimated value, and the maximum likelihood estimation method is used to find a subset of the numerical sequence. The arithmetic mean of the values in the numerical sequence subset is used as the most reasonable sampling value, that is, the most probable sampling value. The specific steps include: S21, taking the observed value P1 as the estimated value and setting the sampling value within P1±a% as reasonable, find the values within the range of P1±a% in the sequence P1, P2…Pn…P1000, and count the number of values, recorded as N1; where a is the set value; S22, similarly, using P2, P3, ..., P1000 as estimated values, respectively, according to the method in step S21, find the number of statistical values corresponding to each estimated value, and record them as N2, N3, ..., N1000; S23, find the largest set of sequences Nm in the statistical sequences N1, N2...N1000, and find several values in the range of Pm±a% in the sequence of values to be observed P1...P1000. The arithmetic average of these values is recorded as P0, and P0 is used as the most reasonable sampling value for this time.

[0008] Furthermore, in step S4, the method for calibrating the pipeline resistance includes: Use a high-precision handheld flow meter with an accuracy of 0.5% or more to calibrate the pipeline on site, that is, measure the current flow rate of the pipeline under any circumstances, record it as Q0, in m³ / h; According to the relationship between pressure and flow, when the liquid flows through the throttling device, the pressure difference between the installation point of the pressure sensor and the outlet of the throttling device is proportional to the square of the flow rate, so

[0009] The resistance R0 from the pressure sensor installation point to the outlet pipe can be calculated according to the following formula:

[0010] Among them: P0 represents the current pressure value; h0, represents the height difference between the pressure sensor and the outlet end; , indicating the flow rate of the current pipeline during calibration.

[0011] Furthermore, in step S5, the flow rate in the pipeline is calculated in real time according to the following formula, that is, the pipeline flow rate calculation model is:

[0012] Where: P represents the currently measured pipeline pressure value; Q represents the current flow rate of the pipeline.

[0013] The open system automatic flow monitoring device using the above method mainly includes: Pressure sensor, used to collect pressure values of media flow pipelines in open systems; Flow measurement module, used to collect the value of the pressure sensor and calculate the flow rate; The pressure sensor should be installed at least 2 elbows away from the outlet; The system inlet is the medium inflow end, the outlet is the medium outflow end, and the outlet is in contact with the air, forming an open system.

[0014] Furthermore, the measurement accuracy of the pressure sensor is not less than 0.05%.

[0015] Furthermore, no switch valve component is provided between the installation position of the pressure sensor and the outlet end, or measurement is performed when the switch valve component is in an open state.

[0016] Furthermore, the flow measurement module calculates the flow in the pipeline according to the following formula:

[0017] Where: P represents the currently measured pipeline pressure value; h0, represents the height difference between the pressure sensor and the outlet end; R0 represents the resistance from the pressure sensor installation point to the outlet end; Q represents the current flow rate of the pipeline.

[0018] Compared with the existing technology, the beneficial effects of the present invention are: ① By establishing a calculation and processing model based on pipeline pressure and resistance to obtain flow values, the use of expensive and complex flow meters is avoided, the cost is greatly reduced, and the price can be reduced to hundreds of yuan; ② The pressure sensor is installed outside the pipeline, which is convenient for installation; ③ It has good versatility and promotion and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present disclosure.

[0020] Figure 1 is a flow chart of an exemplary embodiment according to the present disclosure; Figure 2 A schematic diagram of an application scenario for an exemplary embodiment is shown. DETAILED DESCRIPTION

[0021] The preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0022] The present disclosure provides a flow monitoring method and device for an open system. Figure 1 As shown. It mainly includes the following steps: 1. Install a pressure sensor on the medium flow pipeline of the open system The system inlet is where liquid (specifically clean water in this embodiment) flows in, and the outlet is where the liquid flows out. The outlet is in contact with the air, forming an open system.

[0023] The installation location of the pressure sensor must meet two conditions: first, the installation location of the pressure sensor must be at least 2 elbows away from the outlet end; second, there must be no valve components between the installation location of the pressure sensor and the outlet end, or the valve components must be in the normally open state during measurement.

[0024] In this solution, the height difference between the installation position of the pressure sensor and the outlet end needs to be measured. The unit is kPa, which is recorded as h0. Therefore, in order to facilitate the measurement of h0, when the pressure sensor meets the above conditions, the installation point should be installed as close to the outlet end as possible, such as the flow measurement of a split cooling tower.

[0025] 2. Sampling and processing of pressure sensor data The key issue of this solution is the acquisition accuracy of the pressure sensor. To this end, this embodiment adopts the maximum likelihood estimation algorithm to solve this problem. The main steps are as follows: The flow measurement device samples the input value of the pressure sensor every 1 millisecond, sampling 1000 data per second. These 1000 observation values are recorded as P1, P2...Pn...P1000, and the unit is kPa; Then, each item in the numerical sequence to be observed is used as the estimated value for observation, and the maximum likelihood estimation method is used to find a subset of the numerical sequence. The arithmetic mean of the values in the numerical sequence subset is used as the most reasonable (most probable) sampling value at the moment. An example is shown below: 1) Take the observed value P1 as the estimated value and stipulate that the sampling value within P1±a% (optional, the default is 10%) is reasonable. Find the values in the sequence P1, P2...Pn...P1000 that are within the range of P1±a%, and count the number of values, recorded as N1; 2) Similarly, using P2, P3, ..., P1000, follow the method in 1) above to find the number of statistical values corresponding to each estimated value, and record them as N2, N3, ..., N1000; 3) Find the largest set of sequences Nm in the statistical sequences N1, N2…N1000, and find several values within the range of Pm±a% in the sequence of values to be observed P1…P1000. Take the arithmetic mean of these values and record it as P0. Then P0 is taken as the most reasonable sampling value for this time.

[0026] 3. Calibration calculation of the resistance R0 from the installation point of the pressure sensor to the outlet pipe The resistance R0 is determined after the pipeline is determined. In this embodiment, the calibration is performed as follows: Use a high-precision (0.5% or more) handheld flow meter to calibrate the pipeline on site, that is, measure the current flow of the pipeline under any circumstances and record it as , unit: m³ / h; According to the relationship between pressure and flow, when the liquid flows through the throttling device, the pressure difference generated at both ends of the throttling device (equivalent to the pressure sensor installation point to the outlet end) is proportional to the square of the flow.

[0027] but:

[0028] Among them: P0 represents the current pressure value.

[0029] h0 represents the height difference between the pressure sensor and the outlet.

[0030] R0 represents the resistance from the pressure sensor installation point to the outlet end.

[0031] , indicating the flow rate of the current pipeline.

[0032] 4. Establish a flow calculation model based on pressure and resistance to collect pressure online and calculate and monitor flow in real time After calculating R0 according to the above method, the flow rate in the pipeline can be measured by the following formula: ; The current pressure is accurately sampled online , the real-time calculation and measurement of the flow in the pipeline can be completed.

[0033] An exemplary open system automatic flow monitoring device using the above method is shown in the attached Figure 2 As shown, it mainly includes: ① is a pressure sensor (preferably with a measurement accuracy of 0.05%), responsible for collecting the pressure value of the open system; ② is the flow measurement module (control module), which is responsible for collecting the value of the pressure sensor and calculating the flow rate through the above algorithm.

[0034] The flow measurement device in this embodiment mainly processes and calculates the flow rate by establishing a calculation model, processing the data of the pressure sensor, and calculating the flow rate. Therefore, the cost is greatly reduced, the price can be only a few hundred yuan, and the installation is convenient.

[0035] The above technical solutions are only exemplary embodiments of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the application methods and principles disclosed in the present invention, and are not limited to the methods described in the above specific embodiments of the present invention. Therefore, the methods described above are only preferred and do not have a restrictive meaning.

Claims

1. An open system automatic flow monitoring method, characterized in that: The following steps are involved: S0, install a pressure sensor on the medium flow pipeline of the open system, and the installation position of the pressure sensor should be at least 2 elbows away from the outlet end; S1, sampling the measured value of the pressure sensor according to the set period; S2, using the maximum likelihood estimation method to process the pressure values collected in each cycle to determine the current pipeline pressure value; S3, measuring the height difference between the installation position of the pressure sensor and the outlet end; S4, calibrate the resistance of the pipeline from the installation point of the pressure sensor to the outlet end; S5, establish a pipeline flow calculation model, collect the current pressure online, and complete the real-time calculation of the flow in the pipeline.

2. The method according to claim 1, characterized in that The step S2 specifically includes: If the pressure sensor is sampled every 1 millisecond, 1000 data points will be sampled per second. These 1000 observation values are recorded as P1, P2…Pn…P1000, with the unit being kPa. Each item in the observed numerical sequence is used as an estimated value, and the maximum likelihood estimation method is used to find a subset of the numerical sequence. The arithmetic mean of the values in the numerical sequence subset is used as the most reasonable sampling value, that is, the most probable sampling value. The specific steps include: S21, taking the observed value P1 as the estimated value and setting the sampling value within P1±a% as reasonable, find the values within the range of P1±a% in the sequence P1, P2…Pn…P1000, and count the number of values, recorded as N1; where a is the set value; S22, similarly, using P2, P3, ..., P1000 as estimated values, respectively, according to the method in step S21, find the number of statistical values corresponding to each estimated value, and record them as N2, N3, ..., N1000; S23, find the largest set of sequences Nm in the statistical sequences N1, N2...N1000, and find several values in the range of Pm±a% in the sequence of values to be observed P1...P1000. The arithmetic average of these values is recorded as P0, and P0 is used as the most reasonable sampling value for this time.

3. The method according to claim 1 or 2, characterized in that In step S4, the method for calibrating the pipeline resistance includes: Use a high-precision handheld flow meter with an accuracy of 0.5% or more to calibrate the pipeline on site, that is, measure the current flow rate of the pipeline under any circumstances, record it as Q0, in m³ / h; According to the relationship between pressure and flow, when the liquid flows through the throttling device, the pressure difference between the installation point of the pressure sensor and the outlet of the throttling device is proportional to the square of the flow rate, so The resistance R0 from the pressure sensor installation point to the outlet pipe can be calculated according to the following formula: Among them: P0 represents the current pressure value; h0, represents the height difference between the pressure sensor and the outlet end; , indicating the flow rate of the current pipeline during calibration.

4. The method according to claim 3, characterized in that In step S5, the flow rate in the pipeline is calculated in real time according to the following formula, that is, the pipeline flow rate calculation model is: Where: P represents the currently measured pipeline pressure value; Q represents the flow rate of the current pipeline.

5. An open system automatic flow monitoring device using the method according to any one of claims 1 to 4, characterized in that: include: Pressure sensor, used to collect pressure values of media flow pipelines in open systems; Flow measurement module, used to collect the value of the pressure sensor and calculate the flow rate; The pressure sensor should be installed at least 2 elbows away from the outlet; The system inlet is the medium inflow end, the outlet is the medium outflow end, and the outlet is in contact with the air, forming an open system.

6. The device according to claim 5, characterized in that The measurement accuracy of the pressure sensor is not less than 0.05%.

7. The device according to claim 6, characterized in that There is no switch valve component between the installation position of the pressure sensor and the outlet end, or measurement is performed when the switch valve component is in an open state.

8. The device according to any one of claims 5 to 7, characterized in that: The flow measurement module calculates the flow in the pipeline according to the following formula: Where: P represents the currently measured pipeline pressure value; h0, represents the height difference between the pressure sensor and the outlet end; R0 represents the resistance from the pressure sensor installation point to the outlet end; Q represents the current flow rate of the pipeline.

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