Micro liquid flow dynamic weighing device and method

Abstract

The invention provides a micro liquid flow dynamic weighing device. The micro liquid flow dynamic weighing device comprises a flow source, a liquid inlet pipe, a weighing container and a weighing module, the flow source outputs a liquid medium to the weighing container through the liquid inlet pipe; the weighing container is arranged on the weighing module; the device is characterized in that the weighing container is of an inner-outer double-cylinder structure, the liquid inlet pipe end is arranged in an inner cylinder, and the inner cylinder is filled with liquid in advance and is in a full cylinder state; after weighing is started, the flow source outputs a liquid medium to the inner cylinder through the liquid inlet pipe, and preset liquid in the inner cylinder overflows to the outer cylinder; and the weighing module reads the weight of the entering liquid. In the measuring process, the height of the liquid level contacted with the liquid inlet pipe is not changed, so that the influence of buoyancy correction, pressure fluctuation, surface tension change and the like caused by the change of the height of the liquid level is reduced, and the dynamic weighing accuracy is improved.

Description

Technical Field

[0001] The invention relates to the technical field of liquid flow measurement, and in particular to a device and method for dynamically weighing tiny liquid flow. Background Art

[0002] like Figure 1 As shown, liquid flow standard devices can be divided into static mass method, static volume method, dynamic mass method and dynamic volume method liquid flow standard devices. The most common liquid flow standard devices are static mass method and dynamic mass method standard devices.

[0003] like Figure 2 As shown in the figure, the principle of the static mass method is to direct all the medium passing through the flow meter within a certain period of time into a container placed on the weighing instrument through a commutator, and then measure the mass of the medium in the container to obtain the mass of the medium flowing through the flow meter, and then obtain the mass flow rate by measuring the time. The static mass method test is measured at rest, eliminating the dynamic influence of the liquid flow, and has no mechanical connection with the pipeline, which greatly improves the accuracy of the system. In addition, its structure is simple and the range of force reproduction is wide.

[0004] The measurement principle of the dynamic mass method is to compare the change in the mass of the medium passing through the flow meter within a certain period of time with the time during the flow of the liquid, so as to calculate the mass flow rate. During the dynamic mass method test, the fluid passes through the flow meter into the weighing container at a stable flow rate. When the predetermined initial mass is reached, the timer starts timing, and when the collected medium reaches the predetermined mass, the timing stops. The dynamic mass method is fast and convenient to weigh, which can shorten the measurement time, and does not require a commutator, reducing the measurement uncertainty caused by the commutator system.

[0005] Under the condition of small flow, the static mass method needs to use a commutator. The commutation error introduced by the conventional commutator and the random error introduced by the dripping phenomenon become relatively large. The dynamic mass method standard device is easy to operate, avoiding the commutation action and dripping. At low flow rates, the dynamic weighing system can obtain high accuracy and reproducibility, which is more suitable for the measurement of small flow.

[0006] During the dynamic weighing process, since the pipeline is immersed in the liquid surface and the depth gradually increases, it will cause buoyancy changes and outlet pressure fluctuations. There is also a surface tension effect between the pipeline and the liquid surface. Under the condition of small liquid flow, these factors will have a non-negligible impact on the actual weighing value. Summary of the invention

[0007] In view of this, the present invention provides a method and device for dynamically weighing small liquid flow, which can achieve (0.0003~0.3)m 3It can dynamically weigh tiny liquid flows in the flow range of 1000 / h and effectively improve the dynamic weighing accuracy of tiny liquid flows.

[0008] In order to solve the above technical problems, the present invention is implemented as follows.

[0009] A device for dynamic weighing of tiny liquid flow rate comprises: a flow source, a liquid inlet pipe, a weighing container and a weighing module; the flow source outputs liquid medium to the weighing container through the liquid inlet pipe; the weighing container is arranged on the weighing module; the characteristic of this scheme is that the weighing container is an inner and outer double-cylinder structure, the end of the liquid inlet pipe is arranged in the inner cylinder, and the inner cylinder is pre-filled with liquid and is in a full cylinder state; after weighing starts, the flow source outputs liquid medium to the inner cylinder through the liquid inlet pipe, and the pre-filled liquid in the inner cylinder overflows into the outer cylinder; the weighing module reads the weight of the liquid entering the weighing container.

[0010] Preferably, the end of the liquid inlet pipe is a sealing structure, and a liquid outlet hole is provided on the side of the end, and the liquid medium flows out horizontally through the liquid outlet hole.

[0011] Preferably, the liquid outlet holes at the end of the liquid inlet pipe are evenly distributed on the side of the liquid inlet pipe.

[0012] Preferably, the device further comprises a windproof cover arranged around the weighing container.

[0013] Preferably, the device further comprises a humidity sensor disposed in the windproof outer cover, for detecting the humidity of the container environment and obtaining the relationship between the humidity of the container environment and the evaporation amount.

[0014] Preferably, the device further comprises a liquid recovery component for drawing the liquid in the outer cylinder of the weighing container back to the flow source.

[0015] Preferably, the liquid recovery assembly includes an XZ-axis slide, a slider, a return pipe and a pump; wherein the Z-axis is the direction in which the return pipe extends vertically into and out of the weighing container; the X-axis is perpendicular to the Z-axis and is the direction in which the return pipe moves from the periphery of the weighing container to the inner cylinder and is withdrawn;

[0016] The return water pipe is connected to the flow source, and a pump is arranged on the connecting pipe; the return water pipe is connected to the slide table through a slider, and can move along the X-axis and the Z-axis.

[0017] Preferably, the slide provides movement in the X-axis direction, the slide is vertically installed, and the slider provides movement in the Z-axis direction along the slide; the return pipe is an inverted U-shaped structure, one arm is fixed on the slider, and the other arm extends into the weighing container.

[0018] The present invention also provides a method for dynamically weighing a small liquid flow rate, using the above-mentioned dynamic weighing device for a small liquid flow rate, the method comprising:

[0019] Before weighing begins, the inner cylinder of the weighing container is pre-filled with liquid and is full;

[0020] After weighing begins, the flow source outputs liquid medium to the inner cylinder through the liquid inlet pipe; the preset liquid in the inner cylinder overflows into the outer cylinder; the mass indication and time scale are read continuously and dynamically during the entire metering time period; the least squares method is used for linear fitting to obtain the slope of the straight line, which is the standard flow value.

[0021] Preferably, the method further comprises: after weighing is completed, performing a water return operation, controlling the slide table to move to a specified position along the X direction, moving the slider along the Z direction to immerse the water return pipe under the liquid surface of the outer cylinder, and pumping the liquid in the outer cylinder to the flow source through a pump;

[0022] After the water return is completed, the pump is turned off, the control slider is moved in the Z direction to move the water return pipe outside the weighing container, and the control slide is returned to the initial position in the X direction.

[0023] The effects of this dynamic weighing device and method are mainly reflected in the following three aspects:

[0024] (1) The present invention provides a solution for dynamic weighing of tiny liquid flow. The weighing container is an inner and outer double-cylinder structure. Before measurement, the inner cylinder is pre-filled with liquid. The liquid in the inner cylinder is pushed by the flow source to overflow the inner cylinder into the outer cylinder. During the measurement, the liquid level of the liquid surface contacted by the liquid inlet pipe remains unchanged, thereby reducing the effects of buoyancy correction, pressure fluctuation, surface tension change, etc. caused by the change of liquid level, and improving the accuracy of dynamic weighing. Compared with the traditional method of using an open commutator to inject water into the weighing container or directly immersing the guide tube into the weighing container for weighing and collecting, it shows its advantages in weighing tiny liquid flow.

[0025] (2) In a preferred embodiment, the porous liquid inlet pipe structure on the side of the end cap can reduce the impact of the liquid flow on the weighing container, thereby eliminating the additional forces caused by buoyancy correction, pressure fluctuations and surface tension factors caused by liquid height changes and flow.

[0026] (3) In a preferred embodiment, a balance cover structure is added to eliminate the influence of ambient wind speed on the balance stability while also reducing the evaporation. In addition, the evaporation can be further suppressed by increasing the humidity of the container environment in the windproof cover and studying the relationship between humidity and evaporation through real-time monitoring of the internal humidity.

[0027] (4) In a preferred embodiment, the present invention adds a liquid recovery component to prevent the return pipe from dripping during weighing and affecting the weighing result, so that the device of the present invention can be reused while ensuring the accuracy of dynamic weighing. Secondly, an X-axis and Z-axis bidirectional slide is set to control the movement of the return pipe. First, the movement of the return pipe can be automatically controlled to improve the degree of automation of the liquid flow dynamic weighing system. Second, the return system forms a closed loop for easy control. In addition, the slide is set in a fixed position along the Z direction to ensure that the height of the outer cylinder behind the return pipe is appropriate, which is convenient for the rapid start of the next weighing.

[0028] (5) The present invention reduces the dynamic acquisition error of the electronic balance. In order to solve the problem of dynamic acquisition error of the electronic balance, interpolation or data fitting is used to reduce the influence. At the same time, according to the sampling theorem, a higher sampling rate is used to basically restore the change of the balance indication, and the time point of the mass jump and the corresponding mass value are extracted from it, which avoids the inconsistency between time and mass to a certain extent. In addition, a large amount of weighing data within the measurement time period is used to eliminate the influence of dynamic acquisition through relative error least squares fitting. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Classify liquid flow standard devices;

[0030] Figure 2 This is a schematic diagram of the measurement principle of the static mass method;

[0031] Figure 3 This is a schematic diagram of the measurement principle of the dynamic mass method;

[0032] Figure 4 It is a schematic diagram of the structure of an inner and outer double-cylinder weighing container;

[0033] Figure 5 It is a schematic diagram of the liquid inlet pipe structure;

[0034] Figure 6 This is a schematic diagram of the structure of the electronic balance housing;

[0035] Figure 7 This is a schematic diagram of the return pipe structure. DETAILED DESCRIPTION

[0036] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0037] Different from the standard device for tiny liquid flow in similar devices, this scheme uses inner and outer double-cylinder weighing containers. Before measurement, the inner cylinder is pre-filled with liquid. The liquid in the inner cylinder is pushed by the flow source to overflow into the outer cylinder. During the measurement, the liquid level height that the flow guide tube contacts remains unchanged, thereby reducing the effects of buoyancy correction, pressure fluctuation, surface tension change, etc. caused by changes in liquid level, and improving the accuracy of dynamic weighing.

[0038] The overall structural scheme of the micro liquid flow dynamic weighing device of the present invention is as follows:

[0039] like Figure 4 As shown, the micro liquid flow dynamic weighing device of the present invention includes a flow source, a liquid inlet pipe, a weighing container and a weighing module. The flow source is used to provide a liquid medium and a liquid drive component, push the liquid medium to the liquid inlet pipe, output it to the weighing container via the liquid inlet pipe, and the weighing module reads the weight of the liquid entering the weighing container. This solution has the following design points:

[0040] 1) Design a double-barrel weighing container, such as Figure 4 The water outlet pipeline is placed in the inner cylinder, and the inner cylinder is full. At the beginning of the experiment, the water in the inner cylinder will overflow into the outer cylinder, so that the liquid level at the outlet of the pipeline remains unchanged, solving the effects of buoyancy correction, pressure fluctuation, surface tension change, etc. caused by the change of liquid level.

[0041] 2) Design a porous liquid inlet pipe structure on the side of the end head to reduce the impact of the liquid flow on the weighing container. The structure is as follows: Figure 5 As shown. The length of the liquid inlet pipe is submerged below the liquid surface, the end of the liquid inlet pipe is a cap, and the liquid medium flows out horizontally from the liquid outlet holes opened on the side of the liquid inlet pipe. Preferably, the liquid outlet holes at the end of the liquid inlet pipe are evenly distributed on the side of the liquid inlet pipe, so as to achieve the purpose of dispersed outflow of the liquid medium. Since the medium flows out horizontally and is dispersed into many small holes, the impact on the weighing container has been weakened to a negligible level.

[0042] 3) Set up a windproof cover to reduce the impact of liquid evaporation, the structure is as follows Figure 4 In order to reduce the evaporation of the water medium in the weighing container, a wind shield is firstly set around each weighing container to eliminate the environmental wind speed and reduce the evaporation while affecting the weighing stability. Secondly, the humidity of the container environment is increased in the wind shield, and the relationship between humidity and evaporation is studied through real-time monitoring of the internal humidity to further inhibit evaporation.

[0043] 4) A liquid recovery component is provided to draw the liquid in the outer cylinder of the weighing container back to the flow source to facilitate repeated measurements. In the preferred embodiment of the present invention, a bidirectional movable slide is used in the X and Z axes to control the movement of the return pipe to avoid dripping from the return pipe affecting the weighing. Figure 5As shown. Among them, the Z axis is the direction in which the return pipe extends vertically into and out of the weighing container; the X axis is perpendicular to the Z axis and is the direction in which the return pipe moves from the periphery of the weighing container to the inner cylinder and is withdrawn. During water return, the slide moves in the X direction to the specified position, and the slider moves in the Z direction to immerse the return pipe under the liquid surface of the outer cylinder. The pump provides power for the return pipeline to pump the liquid in the outer cylinder to the water source. After the return water is completed, turn off the pump, move the slider in the Z direction to move the return pipe to the outside of the balance cover, and the slide returns to the initial position in the X direction. A two-way movable slide is set to ensure that the return pipe is away from the electronic balance in the non-working state to avoid dripping from the return pipe affecting the weighing result. In addition, the slide is set in a fixed position along the Z direction to ensure that the height of the outer cylinder is at an appropriate height after the return water, which is convenient for the next weighing to start quickly.

[0044] exist Figure 5 In the example shown, the return pipe is an inverted U-shaped structure, one arm of which is fixed on the slider and the other arm extends into the weighing container. This structural form facilitates the movement of the return pipe and its extension into the specified position of the weighing container.

[0045] 5) Select a weighing module with high-speed sampling, fast stabilization time and high-precision weighing performance. The electromagnetic weighing module has a weighing stabilization time of up to 150ms, a sampling speed of up to 92Hz, and a maximum readability of 0.1ms. The Monobloc technology is used as the core of the weighing platform to ensure the highest accuracy and flexibility. It has an integrated overweight protection function and a reliable mechanical interface to ensure good stability during long-term use. The scale body can have a maximum graduation value of 750,000d, and can be calibrated regularly with internal weights to ensure the accuracy of the weighing. According to different flow ranges, select electronic balances of models WMS404C, PBK-3kg, and PBK-15kg for dynamic weighing.

[0046] 6) The mass indication and time scale are read dynamically and continuously during the entire metering time period. By analyzing and linearly fitting a large amount of data, a slope representing the flow value is obtained. According to the sampling theorem, a higher sampling rate can basically restore the change in the balance indication, and the time point of the mass jump and the corresponding mass value are extracted from it, which avoids the inconsistency between time and mass to a certain extent. In view of the problem of dynamic acquisition error of the electronic balance, interpolation or data fitting is used to reduce the impact. In addition, a large amount of weighing data in the metering time period can be fitted by the relative error least squares method to a certain extent to eliminate the impact of dynamic acquisition. The common least squares method is the absolute error least squares method. The absolute error least squares method often makes the relative error distribution of each point uneven, that is, the relative error of the large observation value is small, and the relative error of the small observation value is large. The relative error least squares method pursues the minimum sum of squares of relative errors, which can improve the uneven distribution of relative errors to a certain extent and is more suitable for the fitting of small flow in this project. In theory, under the premise of high enough flow stability, the slope of the fitted straight line represents the standard value of flow.

[0047] The method for dynamic weighing of small liquid flow using the above device is specifically as follows:

[0048] Before weighing begins, the inner cylinder of the weighing container is filled with liquid and is full;

[0049] After weighing begins, the flow source outputs liquid medium to the inner cylinder through the liquid inlet pipe; the preset liquid in the inner cylinder overflows into the outer cylinder; the mass indication and time scale are continuously and dynamically read during the entire measuring time period; the least square method is used for linear fitting to obtain the slope of the straight line, which is the standard value of the flow rate;

[0050] After weighing is completed, the water return operation is performed, the slide is controlled to move to the specified position along the X direction, the slider moves along the Z direction to immerse the water return pipe under the liquid surface of the outer cylinder, and the liquid in the outer cylinder is pumped to the flow source through the pump; after the water return is completed, the pump is turned off, the slider is controlled to move along the Z direction to move the water return pipe outside the weighing container, and the slide is controlled to return to the initial position along the X direction.

[0051] The above specific embodiments only describe the design principle of the present invention. The shapes and names of the components in the description may be different and are not limited. Therefore, those skilled in the art in the field of the present invention may modify or replace the technical solutions recorded in the above embodiments; and these modifications and replacements do not deviate from the creative purpose and technical solutions of the present invention and should all fall within the protection scope of the present invention.

Claims

1. A dynamic weighing device for small liquid flow, comprising: Flow source, liquid inlet pipe, weighing container and weighing module; The flow source outputs the liquid medium to the weighing container through the liquid inlet pipe; the weighing container is arranged on the weighing module; and the feature is that: The weighing container is an inner and outer double-cylinder structure, the liquid inlet pipe end is arranged in the inner cylinder, and the inner cylinder is pre-filled with liquid and is in a full cylinder state; after the weighing starts, the flow source outputs the liquid medium to the inner cylinder through the liquid inlet pipe, and the pre-filled liquid in the inner cylinder overflows into the outer cylinder; the weighing module reads the weight of the liquid entering the weighing container.

2. The device according to claim 1, characterized in that The end of the liquid inlet pipe is a sealing head structure, and a liquid outlet hole is arranged on the side of the end, and the liquid medium flows out horizontally through the liquid outlet hole.

3. The device according to claim 2, characterized in that The liquid outlet holes at the end of the liquid inlet pipe are evenly distributed on the side of the liquid inlet pipe.

4. The device according to claim 1, characterized in that The device further comprises a windproof cover arranged around the weighing container.

5. The device according to claim 1, characterized in that The device further comprises a humidity sensor arranged in the windproof outer cover, which is used for detecting the humidity of the container environment and obtaining the relationship between the humidity of the container environment and the evaporation amount.

6. The device according to claim 1, characterized in that The device further comprises a liquid recovery component, which is used for drawing the liquid in the outer cylinder of the weighing container back to the flow source.

7. The device according to claim 6, characterized in that The liquid recovery assembly includes an XZ-axis slide, a slider, a return pipe and a pump; wherein the Z-axis is the direction in which the return pipe extends vertically into and out of the weighing container; the X-axis is perpendicular to the Z-axis and is the direction in which the return pipe moves from the periphery of the weighing container to the inner cylinder and is withdrawn; The return water pipe is connected to the flow source, and a pump is arranged on the connecting pipe; the return water pipe is connected to the slide table through a slider, and can move along the X-axis and the Z-axis.

8. The device according to claim 7, characterized in that The slide provides movement in the X-axis direction, the slide is vertically installed, and the slider provides movement in the Z-axis direction along the slide; the return pipe is an inverted U-shaped structure, one arm is fixed on the slider, and the other arm extends into the weighing container.

9. A method for dynamic weighing of small liquid flow, characterized in that: Using the micro liquid flow dynamic weighing device according to any one of claims 1 to 8, the method comprises: Before weighing begins, the inner cylinder of the weighing container is pre-filled with liquid and is full; After weighing begins, the flow source outputs liquid medium to the inner cylinder through the liquid inlet pipe; the preset liquid in the inner cylinder overflows into the outer cylinder; the mass indication and time scale are read continuously and dynamically during the entire metering time period; the least squares method is used for linear fitting to obtain the slope of the straight line, which is the standard flow value.

10. The method according to claim 9, characterized in that The method further comprises: after the weighing is completed, a water return operation is performed, the slide table is controlled to move to a specified position along the X direction, the slide block moves along the Z direction to immerse the water return pipe under the liquid surface of the outer cylinder, and the liquid in the outer cylinder is pumped to the flow source by a pump; After the water return is completed, the pump is turned off, the control slider is moved in the Z direction to move the water return pipe outside the weighing container, and the control slide is returned to the initial position in the X direction.

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