Calibration Method of Liquid Flowmeter

Abstract

A calibration method for a liquid flowmeter, the calibration method comprising: providing a first tank (12) for receiving a liquid to be measured and a liquid storage tank (14) connected to the first tank (12); providing a liquid delivery pipeline (9) for delivering the liquid from the liquid storage tank (14) to an external device; providing a weighing sensor (22) for weighing the liquid contained in the first tank (12) or the liquid storage tank (14), wherein during calibration of the flowmeter (20): disconnecting the liquid delivery pipeline (9) from the external device downstream of the liquid flowmeter (20) in the delivery direction; connecting the liquid delivery pipeline (9) to a calibration pipeline (7) downstream of the liquid flowmeter (20) in the delivery direction, the calibration pipeline being connected to the first tank (12); and determining the flow rate of the delivered liquid within a predetermined time interval based on the change in the liquid weight measured by the weighing sensor (22) within the predetermined time interval, wherein the liquid is delivered from the liquid storage tank (14) back to the first tank (12) through the liquid delivery pipeline (9), and the flow rate is controlled so that the flow rate of the liquid from the liquid storage tank (14) to the first tank (12) is substantially constant during calibration.

Description

Technical Field

[0001] The present invention relates to the field of engineering, and particularly to a calibration method for a liquid flow measurement system. Background Art

[0002] In an animal feed manufacturing system, solid and liquid raw materials such as cassava, corn, rice, and rice bran, which are components of animal feed, are mixed with liquid raw materials such as water, molasses, fungicides, feed quality preservatives, and flavors, which are animal feed additives used in animal feed manufacturing, so as to obtain animal feed having a complete nutrient content and a suitable moisture content according to its formula. Typically, the animal feed components and various chemical agents must be weighed or measured to obtain their appropriate amounts and introduced into a mixing tank before undergoing any further processing such as stirring, grinding, heating, granulating, and packaging, so as to obtain a finished animal feed product and prepare it for market.

[0003] For a continuous manufacturing process, raw materials and various components are continuously conveyed to the mixing tank. The solid raw materials and components are weighed by a weighing scale or a pressure measuring element while they are conveyed to the mixing tank through a conveyor belt or a screw conveyor. At the same time, the liquid components are weighed, and / or the liquid flow rate of the liquid components is measured by a flow meter so as to obtain an appropriate amount according to a given formula. Therefore, the accuracy of the liquid flow meter is extremely important, and the flow meters must be calibrated so that they can always obtain accuracy.

[0004] Currently, for flow meter calibration, the entire manufacturing process usually has to be stopped to perform the flow meter calibration, and then liquids used in the process, such as water and fungicides whose weights are of course known, are pumped through the flow meter to be calibrated at certain time intervals. Then, readings of the instrument are obtained so as to be compared with the average flow rate of the liquid calculated based on the known weight and the time interval used, thereby knowing the error of the flow meter, and then adjustments are made to obtain a correction value.

[0005] An actual flowmeter calibration system includes converting the count pulse signal obtained from the flowmeter into weight. This flowmeter calibration system generally must have a signal receiver, a processor, and a human-machine interface. By weighing the actual weight, obtaining the pulse signal value output from the flowmeter, and then using this data to calculate the parameters for comparing with the actual weight of the liquid flowing through the flowmeter. Among them, since the liquid flow rate and pressure in the pipe are different compared with the points near the flowmeter, the liquid flowing through the flowmeter must be output at the actual use point (end point) for weighing. If the actual weight is weighed at the flowmeter installation point and the actual use point, even if the display at the control system is equal to the same count and the same use parameters, there will be a deviation when comparing the actual weights obtained from the two points. Generally, if it is necessary to perform flowmeter calibration at another point that is not the use point, the valve for adjusting the liquid pressure in the pipe must be adjusted, or the flow rate in the pipe must be adjusted so that the pressure is equal to the pressure at the use point in order to obtain a corrected and accurate calibration.

[0006] However, the calibration method has drawbacks. That is, since the production line may have to be stopped for a long time, it takes a relatively long time to prepare for calibration, and the liquid undergoing calibration cannot be utilized immediately. Therefore, this may lead to difficulties and waste. In addition, the existing calibration methods are also prone to errors because the calibration environmental factors are different from the environmental factors in actual operation, such as the wear and breakage of machines, i.e., pressure pumps, and the pressure loss of the delivery pipes at various heights of the measurement points, etc., resulting in errors in the traditional calibration methods and lack of efficiency.

[0007] The Thai Patent Application No. 0801005493, published as Patent Application Publication No. 115985 on August 31, 2012, discloses a calibration system for a fuel delivery system in a fuel manufacturing process, i.e., an injection system for fuel catalysts or fuel additives, etc. The fuel contained in the tank is weighed by at least one pressure measuring element. Calibration is performed by delivering fuel of directly or indirectly known weight to the pressure measuring element and measuring the weight of the delivered fuel. Then, a comparison is made between the measured weight obtained from the pressure measuring element and the known weight in order to calculate the deviation between the two weights, and thus the measurement is adjusted accordingly.

[0008] U.S. Patent No. US 8,307,692 B2, entitled "Calibration of a Dust-Loaded Flow Measurement System," issued by Siemens Aktiengesellschaft of Germany on November 13, 2012, shows a method for calibrating a dust-loaded flow measurement system, in which pulverized fuel dust is pneumatically driven. In the method, the pressure between a receiving container and a metering container is controlled to a constant value of the actual operating pressure throughout the calibration process by opening / closing control of a pressure control valve. However, the method cannot be applied to the calibration of a liquid flowmeter, in which the liquid is driven by a pressure pump or gravity supply.

[0009] U.S. Patent Application Publication No. US 2017 / 0052056 A1, entitled "Method and Apparatus for Testing a Liquid Flowmeter," by Azbil Corporation of Japan, discloses a calibration of a liquid flowmeter, in which the liquid is pumped through the flowmeter into a weighing tank weighed by a pressure measuring element, while the temperature and pressure of the liquid flowing through the flowmeter are measured throughout the calibration process, and then the instrument error of the flowmeter is calculated based on the measured values. However, the method according to the application does not take into account the actual operating environment, such as the height of the weighing point for calibration, the height and length of the pipe, and the wear and breakage of the liquid delivery pump, which may result in the liquid flow rate not being equal to the flow rate during actual operation, even if the pump operates at the same rotational speed. In addition, it is not clear whether the liquid that has undergone calibration can be reused. Summary of the Invention

[0010] To solve the above problems, an object of the present invention is to provide a calibration method for a liquid flowmeter, in which the method is accurate, can be quickly performed in a semi-automatic or automatic manner, the method can also achieve cost savings in calibration without waste by reusing the liquid that has undergone calibration, and the method can also reduce the time of production line stoppage, so that the method can reduce the time and raw material losses in production, and thus, the production cost can be reduced.

[0011] A calibration method for a liquid flowmeter according to the present invention includes: providing a first tank for receiving the liquid to be measured and a liquid storage tank connected to the first tank; providing a liquid delivery pipeline for delivering the liquid from the liquid storage tank to an external device; providing a weighing sensor for weighing the liquid contained in the first tank or the liquid storage tank, wherein during calibration of the flowmeter: disconnecting the liquid delivery pipeline from the external device downstream of the liquid flowmeter in the delivery direction; connecting the liquid delivery pipeline to a calibration pipeline downstream of the liquid flowmeter in the delivery direction, the calibration pipeline being connected to the first tank; and determining the flow rate of the delivered liquid within the time interval by using the change in the liquid weight measured by the weighing sensor within a specific time interval, wherein the liquid is delivered from the liquid storage tank back to the first tank through the liquid delivery pipeline, and the flow rate of the liquid from the liquid storage tank to the first tank is controlled to be a substantially constant value.

[0012] In view of the method for delivering the liquid from the liquid storage tank back to the first tank through the liquid delivery pipeline, when the calibration is completed, the calibrated liquid can be reused immediately without any waste, so that the method can reduce the downtime of the production line, and the method can also reduce the time and raw material losses in production. Therefore, the production cost can be reduced.

[0013] In an embodiment of the present invention, the calibration method for a liquid flowmeter may include controlling the flow rate of the liquid from the liquid storage tank to the first tank to be constant during the calibration by a feedback control method using the signal from the flowmeter. In view of this method, the environment can be controlled to be similar to the actual operating environment during the calibration. Therefore, the calibration is accurate and the error can be reduced.

[0014] In addition, during the execution of the flowmeter calibration, the disconnection of the liquid delivery pipeline from the external device and the connection of the liquid delivery pipeline to the calibration pipeline are performed by two 2-way valves or 3-way valves controlled manually, electrically, or pneumatically. Therefore, the calibration can be performed automatically or semi-automatically.

[0015] In addition, the calibration method can be single-point calibration or multi-point calibration.

[0016] The method according to the present invention can be applied to animal feed manufacturing equipment, so as to obtain animal feed with appropriate liquid raw materials according to the formula and given physical properties.

[0017] In another embodiment of the present invention, the liquid used during calibration can flow from the first tank to the liquid storage tank by gravity supply or by the driving force of a pump inserted and installed in the flow line between the first tank and the liquid storage tank. This additional pump installation can result in an increase in the flow rate of the liquid flowing between the first tank and the liquid storage tank. Therefore, the time interval during which the production process needs to be stopped can be reduced.

[0018] In addition, the flow rate of the liquid flowing through the flow meter during calibration is adjusted to the actual operating flow rate.

[0019] In another embodiment of the calibration method according to the present invention, before performing the calibration, a set point for adjusting the flow rate of the liquid to be constant is calculated based on the average value of the actual operating flow rate. Therefore, the calibration error caused by wear and breakage of the machines used in the process can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The first embodiment of the device for the calibration process of the liquid flow meter according to the method of the present invention is shown.

[0021] Figure 2 The second embodiment of the device for the calibration process of the liquid flow meter according to the method of the present invention is shown.

[0022] Figure 3 It is a block diagram of a control system for controlling the liquid flow rate to be constant by a feedback control method.

[0023] Figure 4 An example of the data obtained from multi-point calibration is shown.

[0024] Figure 5 The workflow of the method according to the present invention is shown. DETAILED DESCRIPTION OF THE INVENTION

[0025] This specification provides an explanation of the present invention by way of examples and with reference to the accompanying drawings for the purpose of illustration and to help describe them more clearly, where like reference numerals in these drawings refer to like elements. However, this specification is not intended to limit the present invention, and the scope of the present invention is defined by the appended claims.

[0026] Figure 1 The first embodiment of the device for the calibration method of the liquid flow meter for performing the method according to the present invention is shown.

[0027] The device includes: a first tank 12 for receiving a liquid to be calibrated, such as a fungicide, water, and a feed quality preservative; a liquid storage tank 14 fluidly connected to the first tank 12 via a valve 36, which can be a manually controlled valve or a pneumatically or electrically operated open / close control valve. The liquid output from the liquid storage tank 14 flows through a liquid delivery line 9 to deliver the liquid from the liquid storage tank 14 to an external device, such as a conveying device and an animal feed mixing tank.

[0028] In normal operation, the liquid is driven by an electric motor and a pump 24 to obtain pressurized liquid. Preferably, the rotational speed of the electric motor is controlled by an inverter or the like. The liquid flowing through the pump 24 flows through a liquid flowmeter 20 for measuring the flow rate of the liquid flowing through the liquid delivery line 9, and then the liquid flowing through the pump flows through a valve 34, but the liquid is blocked so that the liquid cannot flow through a valve 32. The valves 32 and 34 can be two 2-way valves or only one 3-way valve, and these valves are manually controlled, or electrically controlled, or pneumatically controlled.

[0029] According to Figure 1 , a pipeline branched from the liquid delivery line 9 is provided at a position downstream of the liquid flowmeter 20. The branched pipeline serves as a calibration pipeline 7, and the other end of the calibration pipeline 7 is fluidly connected to the first tank 12.

[0030] In normal operation, the calibration pipeline 7 is blocked by a valve 32 to prevent the liquid from flowing into the calibration pipeline 7.

[0031] The flowmeter 20 can be a positive displacement flowmeter or the like. The flowmeter 20 outputs an electrical signal as a pulse, and such a pulse signal is sent to a signal converter 44 to convert the pulse signal into a standard electrical signal. The electrical signal output from the signal converter 44 is proportional to the measured liquid flow rate. Then, the signal output from the signal converter 44 is sent to a control device 10 to be used in operation control and to display the flow rate to notify the operator.

[0032] The flowmeter 20 must be calibrated to always output accurate measurement values; otherwise, it will cause errors during the manufacturing process and may not achieve the desired product quality.

[0033] The control device 10 can be, for example, a PID microcontroller or the like (e.g., a P controller with a gain (k constant) = 1). The control device has an internal memory unit for storing data and programs required for operations. The control device can receive electrical signals from external sensors and can output electrical signals to control devices connected to the control device 10 via input / output ports, so as to operate according to a desired writing program. The control device 10 performs operation control of all devices and can also include a display and a keyboard or keypad (not shown) or a device for receiving inputs typed by a user.

[0034] In addition, the device further includes at least one weighing sensor or device (pressure measuring element) 22, and the weighing sensor or device can be installed in many different forms. In Figure 1 the first embodiment shown, the pressure measuring element 22 of the weighing scale type is installed in a suspended manner from the ceiling so as to weigh the first tank 12, while in Figure 2 the second embodiment shown, the pressure measuring element 22 is installed so as to weigh the liquid storage tank 14, as described in further detail below.

[0035] In the first form, the first tank 12 is installed at a level higher than that of the liquid storage tank, so that the liquid can flow back into the liquid storage tank 14 by gravity supply. In this embodiment, the pressure measuring element is installed above the first tank 12 so as to be used as a weight reader for the liquid contained in the first tank 12.

[0036] The signal output from the pressure measuring element 22 is sent to the signal converter 42, where the signal is converted into an electrical analog signal (e.g., a signal of 0 - 10 Vdc or 4 - 20 mA) corresponding to the measured weight obtained from the pressure measuring element 22. The electrical signal output from the signal converter 42 is proportional to the weight of the liquid contained in the measured tank. Then, the signal output from the signal converter 42 is sent to the control device 10 for further processing.

[0037] During the calibration of the flowmeter 20, the control device is configured such that the liquid delivery line 9 is disconnected from the external device downstream of the liquid flowmeter 20 in the conveying direction, and at the same time, the liquid delivery line 9 is connected to the calibration line 7 (which is connected to the first tank 12) downstream of the liquid flowmeter 20 in the conveying direction, so that the liquid from the liquid storage tank 14 is pumped by the pump 24 through the flowmeter 20 via the valve 32 to the first tank 12.

[0038] According to a first embodiment of the present invention, the valve 36 is closed to block the flow of liquid from the first tank 12 to the liquid storage tank 14. Then, the control device 10 starts to store the weight and time data of the first tank 12 and the liquid contained therein, as well as the pulse signal data regarding time from the flow meter 20, which continuously increases as the liquid is pumped back through the calibration pipeline 7, and stops storing the weight and time data when the calibration is completed.

[0039] Then, the flow rate of the liquid delivered within the time interval is determined by using the change in the liquid weight measured by the load cell 22 at a certain time interval, wherein the liquid from the liquid storage tank 14 is delivered back to the first tank 12 through the liquid delivery pipeline, and the flow rate of the liquid flowing from the liquid storage tank 14 to the first tank 12 is controlled, for example, by an inverter (not shown) to be a substantially constant value, such that its conditions are as close as possible to the actual operating conditions.

[0040] Figure 2 A second embodiment of the device for calibrating a liquid flow meter according to the method of the present invention is shown.

[0041] According to Figure 2 , in addition to installing the pressure measuring element 22 to weigh the liquid storage tank 14 serving as a storage bin, the structure is similar to that of the Figure 1 shown embodiment, wherein the weight includes the weight of the liquid contained in the liquid storage tank 14. The second embodiment is adapted to calibrate the flow meter 20 by measuring the decrease in the weight of the liquid contained in the liquid storage tank 14. In this embodiment, the pump 39 can be used to pump the liquid from the first tank 12 back to the liquid storage tank 14, or the liquid can flow back by gravity through the valve 36. In this embodiment, the pressure measuring element 22 is installed below the liquid storage tank 14 to read the lost weight during the calibration.

[0042] During the calibration according to the second embodiment, the control device 10 starts to store the weight data of the liquid storage tank 14 and the liquid contained therein, which continuously decreases as the liquid contained in the liquid storage tank 14 is pumped out, as well as the pulse signal data regarding time from the flow meter 20, and stops storing the weight data obtained from the pressure measuring element when the calibration is completed, such that the control device is used to determine the change in weight during the calibration.

[0043] Furthermore, in the second embodiment, it also includes a pump 39 inserted and installed in the flow pipeline between the first tank 12 and the liquid storage tank 14, and the pump is used to quickly fill the liquid storage tank 14 with liquid to a predetermined weight before starting the calibration. Given that the liquid flows from the first tank 12 to the liquid storage tank 14 by pump 39 instead of gravity supply, the calibration time interval can be reduced.

[0044] According to the second embodiment, other elements are similar to those of Figure 1 the first embodiment shown, and use similar reference numerals, and thus, explanations thereof will not be repeated here.

[0045] After calibration is completed, when the liquid flowmeter 20 is properly calibrated so that its accuracy can be obtained therefrom, the control device will open the valve 34 and close the valve 32 so that further execution can be carried out according to the manufacturing process.

[0046] Figure 3 is a block diagram of a control system for controlling the liquid flow rate to be constant by a feedback control method.

[0047] According to Figure 3 , the inverter 11 is a device for driving the motor / pump 24 so as to control the flow rate of the pump 24 by continuously changing the motor input frequency of the motor and the pump 24 to a predetermined set point (pulses / minute or pulses / second) during the process, such that the flow rate of the liquid at the calibration point is equal to the flow rate at the end point connected to the external device. If the end point is located away from and below the calibration point, the inverter will reduce the flow rate of the pump 24 so that the liquid flowing out of the calibration point decreases. However, if the end point is located away from and above the calibration point, the inverter will increase the flow rate of the pump 24 so that the liquid flowing out of the calibration point increases. The pulse signal obtained from the flow measurement sensor (flowmeter) 20 during this process is converted into a flow rate in units of pulses / minute (or pulses / second, depending on the flowmeter specification), where one pulse is proportional to the instantaneous velocity and volume of the liquid flowing through the flow measurement sensor. The pulses / minute (or pulses / second) signal is sent as a feedback signal to the controller 10 to instruct the inverter to increase or decrease the output value of the inverter, which is the rotational speed control command of the electric motor / pump 24, so that the liquid flowing from the liquid storage tank 14 through the pump 24 to the first tank 12 during calibration is controlled to be a substantially constant flow rate. As described above, the result is that the measurement error is significantly reduced.

[0048] Next, with reference to Figure 4 and Figure 5 the calibration steps of the calibration method according to the present invention will be described.

[0049] Next, with reference to Figure 5 the calibration method according to the present invention will be described.

[0050] According to Figure 5, when calibration starts, respectively according to steps S502 and S504, after the liquid delivery pipeline 9 is disconnected from the external device downstream of the liquid flowmeter 20 in the conveying direction and the liquid delivery pipeline 9 is connected to the calibration pipeline 7 connected to the first tank 12 downstream of the liquid flowmeter 20 in the conveying direction, the controller then determines the actual flow rate of the conveyed liquid within a certain time interval, that is, from the calibration start point to a given point (target set point), so as to stop performing calibration, where data is intermittently stored in the memory of the controller 10 as given (step S506), and in step S508, the controller calculates the actual flow rate of the conveyed liquid within this certain time interval according to the change rate of the measured weight obtained from the pressure measuring element 22, and adjusts the reading from the flowmeter 20 so that the reading conforms to the calculated actual flow rate, as will be further described in detail later.

[0051] The controller preferably uses machine learning data obtained from actual operation to automatically control the inverter during calibration and adjust the flow rate of the motor / pump 24 to increase in order to compensate for the reduced flow rate in the case of pump efficiency degradation according to the examples to be further explained in detail later.

[0052] In actual operation, the controller 10 controls the flow rate via the operation of the inverter 11, and the inverter is used to operate the pump 24 so that the operation efficiency of the pump 24 is in the range of 50 - 90%, and the flow rate data is stored in the memory, where the flow rate is stored in units of pulses per second or Hertz.

[0053] For calibration, the controller 10 controls the valve 32 to open to fill the liquid back for use during calibration. The speed of the liquid flowing in the pipe may not be equal to the speed at the end points. The inverter 11 uses feedback control with a signal from the flowmeter to control the flow rate of the liquid flowing through the pump to be equal to the flow rate at the end points, where the signal can be an analog signal (4 - 20 mA, 0 - 10 VAC), or a signal obtained from a pulse train output, or a signal obtained from a serial bus communication system such as RS232, RS485, and CAN bus, or a similar signal, so that the flow rate of the liquid flowing through the pump during actual operation is equal to the flow rate at the end points.

[0054] Table 1 shows an example of the results of the weighing test.

[0055]

[0056]

[0057] where

[0058] (1) The count rate is obtained from the flowmeter 20 (pulses per second or Hertz).

[0059] (2) The duty cycle output of the inverter 11 is calculated in %,

[0060] (3) The weight is displayed on the controller (kg),

[0061] (4) The actual measured weight is obtained by weighing the liquid using an external scale, and

[0062] (5) The machine learns from the average value (calculating the average value) of the last 1 - 10 actual operations, so as to be set as a set point for regulating the flow rate of the liquid flowing through the pump to be constant.

[0063] Next, single - point calibration and multi - point calibration performed at a point near the flow meter installation point using the inverter 11 for controlling the flow rate will be described.

[0064] Single - point calibration is calibration using only a single pulse value as a given set point. As an example shown below, the pulse target is set to 400 pulses, then the actual weight is weighed as 50 kg, and calibration is stopped when the measured pulse obtained from the flow meter is equal to the pulse target. During the entire calibration process, the flow rate is controlled to be constant, and the flow rate of the liquid flowing through the flow meter 20 is adjusted to be equal to the flow rate during actual operation.

[0065] Y = Measured weight obtained from the pressure - measuring element, X = Numerical value of the counted pulses obtained from the flow meter, m = Parameter value

[0066]

[0067] Formula Y = mX; ----(1)

[0068] m = 0.125

[0069] Then, the measured data is used to calculate m used in the set value in the controller for use in further processes. The advantage of single - point calibration is that it can be completed in a short time.

[0070] Next, multi - point calibration will be described. Multi - point calibration is calibration using multiple pulse values as target set points. As Figure 4 shown, for example, the pulse targets are set to 400, 800, and 1,000 pulses, and then the actual weights are weighed as 50, 90, and 110 kg respectively. Then, these data are used to calculate parameters to find a linear relationship according to Equation (2):

[0071] Y = a + bX, -----(2)

[0072] Where Y is the measured weight obtained from the pressure measuring element, X is the value of the counting pulses obtained from the flow meter, a is the y value of the point where it intersects the Y-axis, and b is the slope, approximated from the data.

[0073] a and b can be calculated by the following equations:

[0074] and ----(3)

[0075]

[0076] where, Yi is the measured weight obtained from the pressure measuring element 22 at the i th th value, and Xi is the value of the counting pulses obtained from the flow meter at the i th th value, where i is a count value equal to or greater than 1.

[0077] Table 2 is an example of data obtained from a three-point calibration of the flow meter.

[0078]

[0079] Σx = 2200, Σy = 250, Σxy = 202000, Σx 2 = 1800000, Σy 2 = 22700, n = number of values in the data set = 3

[0080] a = 10

[0081] b = 0.1

[0082] The calculated values of a and b are used to adjust parameters in the controller for use in control during further processes.

[0083] As described above, the present invention relates to a calibration method for various flow meters such as positive displacement flow meters. In the prior art, the calibration method must be performed through testing, where liquid flows through an actual flow meter, and then the weight of the liquid flowing out of the flow meter is weighed in order to calculate the value of the parameters used in the control system, which can be divided into two main parts, namely, (1) a signal receiving and processing unit including off-the-shelf instruments and an embedded chip programmable logic control unit, and (2) a human-machine interface. The off-the-shelf instruments can have buttons or accessory displays for the user, such as an off-the-shelf screen controlled via control buttons, an off-the-shelf screen controlled via a touch screen, or a computer with an auxiliary program.

[0084] For the method according to the present invention, the liquid weighing process can be easily carried out, and at the same time, the novel calibration method can quickly calculate the parameter values, without wasting the calibrated liquid and without time loss related to the time for refilling the test liquid back into the tank.

[0085] For the method proposed according to the present invention, calibration can be carried out in the area near the flowmeter installation position using an inverter for appropriately controlling the liquid flow rate, and at the same time, the weighing system can be installed on the upper side of the device itself (first form), or the principle of weight loss with a valve control system can be used (second form), the valve control system being used to control the flow rate of the liquid flowing back to be weighed at the upper part. The object of the present invention is that single-point calibration and multi-point calibration can be easily carried out, wherein even if the actual use point is much farther from the flowmeter, single-point calibration and multi-point calibration can be carried out in the area within 5 m from the flowmeter.

[0086] For the method according to the present invention, the device can perform both manual flowmeter calibration and automatic flowmeter calibration. In manual flowmeter calibration, the flow rate is adjusted by the operator of the inverter. In automatic flowmeter calibration, machine learning obtained from actual operation is used so as to automatically control the inverter using the inverse statistics obtained from the actual operation of the motor and the pump as the set point of the inverter.

[0087] In addition, for the method according to the present invention, the calibrated liquid can be immediately reused without discarding the waste liquid, or can be refilled into the tank by pumping or forced dropping, while in the prior art, the weighed liquid must be discarded or must be subsequently refilled into the tank. Therefore, the contact with the liquid that may be a harmful substance can be reduced, which can promote the safety of the workers.

[0088] Although the present invention has been described in detail in connection with the accompanying drawings as embodiments of the present invention, it must be understood that various modifications or substitutions can be made by those of ordinary skill in the art without departing from the scope and concept of the present invention. The scope of the present invention is consistent with the features of the present invention defined by the appended claims. It also includes other characteristic structures or elements of the present invention, even if not specifically specified in the claims, but they are considered useful and provide the same results as the features of the present invention specified in the claims.

Claims

1. A calibration method for a liquid flowmeter, the calibration method comprises the following steps: providing a first tank (12) for receiving the liquid to be measured and a liquid storage tank (14) connected to the first tank (12); providing a liquid delivery pipeline (9) for delivering the liquid from the liquid storage tank (14) to an external device; providing a weighing sensor (22) for weighing the liquid contained in the first tank (12) or the liquid storage tank (14), during calibrating the liquid flowmeter (20): disconnecting the liquid delivery pipeline (9) downstream of the liquid flowmeter (20) in the conveying direction from the external device; connecting the liquid delivery pipeline (9) downstream of the liquid flowmeter (20) in the conveying direction to a calibration pipeline (7), the calibration pipeline being connected to the first tank (12); and determining the flow rate of the conveyed liquid within the predetermined time interval based on the change in the liquid weight measured by the weighing sensor (22) within the predetermined time interval, the calibration method is characterized in that the liquid is delivered from the liquid storage tank (14) back to the first tank (12) through the liquid delivery pipeline, and the flow rate is controlled so that the flow rate of the liquid from the liquid storage tank (14) to the first tank (12) is substantially constant during calibration, wherein the control of the flow rate so that the flow rate of the liquid from the liquid storage tank (14) to the first tank (12) is substantially constant during the calibration is a feedback control using a signal from the liquid flowmeter (20).

2. The calibration method according to claim 1, wherein, during calibrating the liquid flowmeter, the disconnection of the liquid delivery pipeline (9) from the external device and the connection of the liquid delivery pipeline (9) to the calibration pipeline (7) are performed by two 2-way valves (32, 34) or 3-way valves controlled manually, or electrically, or pneumatically.

3. The calibration method according to claim 1 or 2, wherein, the calibration method is single-point calibration or multi-point calibration.

4. The calibration method according to claim 1 or 2, wherein, the calibration method is applicable to animal feed manufacturing equipment.

5. The calibration method according to claim 1 or 2, wherein, the liquid flows from the first tank (12) to the liquid storage tank (14) by gravity supply or the driving force of a pump (39) inserted and installed in a flow pipeline between the first tank (12) and the liquid storage tank (14).

6. The calibration method according to claim 1 or 2, wherein, during calibration, the flow rate of the liquid flowing through the liquid flowmeter (20) is adjusted to be substantially equal to the actual operating flow rate.

7. The calibration method according to claim 1 or 2, wherein, a set point for adjusting the flow rate of the liquid so that the flow rate of the liquid is substantially constant is calculated based on the average value of the actual operating flow rate within a specific time period before performing the calibration.

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