Automatic testing device and method for precision of float-type glass tube gas flowmeter

Abstract

The embodiment of the invention discloses an automatic testing device and method for the precision of a float-type glass tube gas flowmeter, and the device comprises a gas path module which is formed by the sequential series connection of a gas source, a proportional valve, a tested glass tube gas flowmeter and an electronic gas flowmeter through a gas pipe; the control and acquisition module comprises a programmable logic controller, the analog quantity output channel of the programmable logic controller is connected with the control end of the proportional valve, and the analog quantity output end of the electronic gas flowmeter is connected with the analog quantity input channel of the programmable logic controller; the machine vision module comprises image acquisition equipment, and the image acquisition equipment directly faces a scale area of the measured glass tube gas flowmeter; and the upper computer module is used for running a control program, and the control program communicates with the programmable logic controller and the image acquisition equipment through the communication interface. According to the invention, the problems of low efficiency and poor precision of a manual reverse correction method are solved, full-automatic high-precision testing is realized through machine vision and a PLC, and the efficiency and objectivity are improved.

Description

Technical Field

[0001] This application relates to the technical field of fluid measurement and instrument calibration, and in particular to an automatic testing device and method for the accuracy of a float-type glass tube gas flow meter. Background Technology

[0002] Float-type glass tube gas flow meters (also known as rotor flow meters) are widely used flow measurement instruments in industrial fields. Their accuracy requires periodic calibration. The traditional "forward calibration method" involves reading the scale of the meter under test based on a given standard flow rate, which is subject to human reading errors. While the more intuitive "reverse calibration method" (setting a scale and reading a standard flow rate) can directly reflect the accuracy of the scale point, it has long relied on manual valve adjustment, which is inefficient and makes it difficult to accurately and stably control the float on the fine scale lines.

[0003] Existing automation solutions are mostly improvements within the framework of the "positive calibration method," or although they mention the "negative calibration method," the system integration is not high. For example, the control, vision, and data acquisition subsystems are independent of each other, and the communication is complex. In particular, there is a lack of mature solutions that use PLC to uniformly acquire standard device signals and form an efficient closed loop with visual feedback.

[0004] Therefore, a solution is urgently needed to address the above problems. Summary of the Invention

[0005] This application proposes an automatic testing device and method for the accuracy of a float-type glass tube gas flow meter, which addresses the shortcomings of the prior art.

[0006] According to a first aspect of the embodiments of this application, an automatic testing device for the accuracy of a float-type glass tube gas flow meter is provided, comprising: The gas circuit module consists of a gas source, a proportional valve, a glass tube gas flow meter to be measured, and an electronic gas flow meter connected in series via gas pipes. The control and acquisition module includes a programmable logic controller (PLC), wherein the analog output channel of the PLC is connected to the control terminal of the proportional valve, and the analog output terminal of the electronic gas flow meter is connected to the analog input channel of the PLC. The machine vision module includes an image acquisition device, which is positioned facing the scale area of ​​the gas flow meter in the glass tube being measured. The host computer module is used to run the control program, which communicates bidirectionally with the programmable logic controller and the image acquisition device through the communication interface.

[0007] In some implementations, the host computer module is configured to perform the following operations: Set a target scale value, and implement closed-loop control of the proportional valve through the programmable logic controller based on the set target scale value; The image acquisition device is controlled to acquire images, and an image processing algorithm is used to identify the current position of the float and generate visual feedback. When the float stabilizes at the target scale, the standard flow value of the electronic gas flow meter is read from the programmable logic controller through the communication interface. Calculate the accuracy difference between the standard flow rate value and the target scale nominal value.

[0008] In some embodiments, the proportional valve is an electro-proportional valve, and the control signal of the proportional valve has a linear or predefined functional relationship with the output flow rate or the outlet output pressure of the proportional valve. The electronic gas flow meter is used to output an analog signal representing the instantaneous flow rate to the programmable logic controller. The analog signal is a 4-20mA current signal or a 0-10V voltage signal.

[0009] In some implementations, the control program in the host computer module employs a PID control algorithm, taking the deviation between the target scale value and the visually recognized real-time position of the float as the process input, and outputting the control quantity to the analog output channel of the programmable logic controller to drive the proportional valve.

[0010] In some embodiments, the image acquisition device of the machine vision module is an industrial camera; the machine vision module also includes a light source for illuminating the scale area and a bracket for fixing the industrial camera.

[0011] In some embodiments, the image processing algorithm includes an edge detection algorithm for accurately identifying the position of the float's edge.

[0012] In some implementations, the communication interface between the control program and the programmable logic controller is the communication interface of an OPC server based on the OPC protocol; the control program sends control commands for driving the proportional valve to the programmable logic controller through the OPC server, and reads the standard flow value collected by the electronic gas flow meter from the programmable logic controller.

[0013] In some embodiments, the control program is further configured to calibrate the machine vision module to establish a mapping relationship between image pixel coordinates and the actual flow rate scale value of the measured glass tube gas flow meter; the control program is used to acquire images in real time through the image acquisition device, and based on the mapping relationship and image processing algorithm, identify the real-time position of the float set in the measured glass tube gas flow meter and generate position feedback for the closed-loop control.

[0014] In some embodiments, the gas path module, the control and acquisition module, and the machine vision module are all configured as a multi-channel structure capable of simultaneously connecting to and controlling multiple measured float-type glass tube gas flow meters.

[0015] According to a second aspect of this application, an automatic testing method for the accuracy of a float-type glass tube gas flow meter is provided, implemented based on the automatic testing device for the accuracy of a float-type glass tube gas flow meter as described above, comprising: Set the scale value of the target to be measured in the control program; Initiate closed-loop control, and adjust the proportional valve to move the float toward the target scale line and keep it stable. Once the machine vision module confirms that the float has stabilized at the target scale line, the standard flow value of the electronic gas flow meter is read from the programmable logic controller via the communication interface. The difference between the standard flow rate value and the inherent nominal value of the target scale is calculated and used as a basis for accuracy determination.

[0016] The beneficial effects of the automatic testing device and method for the accuracy of the float-type glass tube gas flow meter according to the embodiments of this application include at least the following: This application's embodiments organically combine the gas path system, control and acquisition system, machine vision system, and host computer system to construct a complete automated testing closed loop. Its core lies in utilizing the host computer software as a unified scheduling center, integrating the issuance of commands to the proportional valve of the actuator controlled by the PLC and the data acquisition of the high-precision electronic gas flow meter via OPC communication. This completely automates the traditional back-calibration process that relied on manual adjustment and reading, significantly improving verification efficiency and ensuring the objectivity of the results. The machine vision module provides high-precision, non-contact, real-time feedback of the float position, replacing the error-prone manual visual inspection. The host computer compares this feedback with the target value and calculates using algorithms such as PID, precisely adjusting the proportional valve via the PLC. This allows for rapid and stable stabilization of the float on the target scale line, with control precision far exceeding manual adjustment. This ensures that data acquisition is automatically and accurately determined by the system, avoiding the delays and subjectivity of manual judgment. The entire process, from float positioning and stability assessment to data reading and difference calculation, is completed automatically, eliminating reading errors and uncertainties introduced by manual operation and ensuring the accuracy and reliability of the calibration data. This embodiment can also be adjusted for different types or ranges of glass tube gas flow meters and provides convenience for functional expansion or upgrades to multi-channel simultaneous testing, demonstrating good adaptability. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of an automatic testing method and apparatus for the accuracy of a float-type glass tube gas flow meter according to an embodiment of this application. Figure 2 This is a flowchart illustrating an automatic testing method and apparatus for the accuracy of a float-type glass tube gas flow meter according to an embodiment of this application. Figure 3 This is a flowchart illustrating a specific implementation process of an automatic testing method device for the accuracy of a float-type glass tube gas flow meter, according to an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the automatic testing device and method for the accuracy of a float-type glass tube gas flow meter will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of this application. Obviously, the described embodiments are only some embodiments of the embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed embodiments of the present application, but merely to illustrate selected embodiments of the present application. Other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort are all within the scope of protection of the embodiments of the present application.

[0020] This application discloses an automatic testing device and method for the accuracy of a float-type glass tube gas flow meter. The automatic testing method for the accuracy of a float-type glass tube gas flow meter is implemented based on the automatic testing device for the accuracy of a float-type glass tube gas flow meter. The purpose is to overcome the shortcomings of the prior art and provide a highly integrated, fully automatic testing device and method for the reverse calibration method of float-type glass tube gas flow meters based on visual feedback and unified acquisition of programmable logic controller (PLC) signals.

[0021] See attached document Figure 1 As shown, the automatic testing device for the accuracy of a float-type glass tube gas flow meter includes: a gas path module, a control and acquisition module, a machine vision module, and a host computer module.

[0022] The gas path module consists of a gas source, a proportional valve, a gas flow meter for the glass tube under test, and an electronic gas flow meter connected in series via gas tubing. The gas source can be a laboratory clean air source or a supply unit consisting of an air compressor and a precision filter to ensure stable and clean airflow. All components are connected via this gas tubing, and quick-connect fittings or compression fittings can be used at the interfaces. The sealing of all connection points must be ensured to prevent gas leakage from affecting test accuracy.

[0023] The control and acquisition module includes a programmable logic controller (PLC). The analog output channel of the PLC is connected to the control terminal of the proportional valve, preferably via a cable. The analog output terminal of the electronic gas flow meter is connected to the analog input channel of the PLC, preferably via a cable.

[0024] For example, the proportional valve is a high-precision electro-proportional valve. The control signal of the proportional valve has a linear or predefined functional relationship with the output flow rate or outlet output pressure of the proportional valve. The electronic gas flow meter is preferably a high-precision electronic gas flow meter, used to output an analog signal representing the instantaneous flow rate value to the programmable logic controller (PLC) to ensure that the PLC can accurately convert the received current signal into the corresponding digital flow rate. The analog signal is a 4-20mA current signal or a 0-10V voltage signal. This embodiment of the application achieves precise and linear regulation of the gas pressure in the pipeline based on the proportional relationship between the valve opening and the magnitude of the input current signal (or voltage signal).

[0025] The machine vision module includes an image acquisition device that is setting the scale area of ​​the gas flow meter being measured in the glass tube.

[0026] For example, the image acquisition device of the machine vision module is an industrial camera.

[0027] For example, the machine vision module also includes a light source for illuminating the scale area and a bracket for fixing the industrial camera.

[0028] The industrial camera in this embodiment is securely mounted with a bracket, and its optical axis should be perpendicular to the scale plane of the gas flow meter in the glass tube being measured to reduce perspective distortion. The light source can be a ring-shaped LED light source, arranged around the camera to provide uniform, shadow-free illumination, ensuring image quality and facilitating subsequent image processing.

[0029] The host computer module is used to run the control program (such as LabVIEW software), which communicates bidirectionally with the programmable logic controller and the image acquisition device through the communication interface.

[0030] For example, the host computer module is configured to perform the following operations: set a target scale value, and implement closed-loop control of the proportional valve through the programmable logic controller based on the set target scale value; control the image acquisition device to acquire images, and use image processing algorithms to identify the current position of the float and generate visual feedback; when the float stabilizes at the target scale, read the standard flow value of the electronic gas flow meter from the programmable logic controller through the communication interface; and calculate the accuracy difference between the standard flow value and the nominal value of the target scale.

[0031] For example, the image processing algorithm includes an edge detection algorithm for accurately identifying the location of the float's edge.

[0032] For example, the communication interface between the control program and the programmable logic controller is the communication interface of an OPC server based on the OPC protocol.

[0033] For example, the control program (e.g., LabVIEW software) sends control commands to the programmable logic controller (PLC) via the OPC server to drive the proportional valve and reads the standard flow value collected by the electronic gas flow meter from the PLC.

[0034] For example, the control program is also configured to calibrate the machine vision module to establish a mapping relationship between image pixel coordinates and the actual flow rate scale value of the gas flow meter in the glass tube being measured.

[0035] For example, during measurement, the control program acquires images in real time through the image acquisition device, and based on the mapping relationship and image processing algorithm, identifies the real-time position of the float set in the gas flow meter in the glass tube being measured and generates position feedback for the closed-loop control.

[0036] For example, the control program in the host computer module uses a PID control algorithm, takes the deviation between the target scale value and the real-time position of the float identified by vision as the process input, and outputs the control quantity to the analog output channel of the programmable logic controller to drive the proportional valve.

[0037] For example, the gas path module, the control and acquisition module, and the machine vision module are all configured as a multi-channel structure that can simultaneously connect to and control multiple measured float-type glass tube gas flow meters.

[0038] The operation control program of this application embodiment is implemented in LabVIEW software for automatic control and data processing flow, including: determining the visual feedback position, judging the stability of closed-loop control, and reading and recording standard flow values.

[0039] For example, determining the visual feedback position includes: in this image processing algorithm, using an edge detection function (such as IMAQ Find Edge) to identify the top edge of the float. To improve repeatability accuracy, a clamping function can be used to define a region of interest near the float's trajectory, performing edge search only within this region, thereby improving processing speed and anti-interference capability. Finally, the float's current position (Current_Pos) is calculated through the mapping relationship between pixel coordinates and the flow rate scale.

[0040] For example, the stability assessment of closed-loop control includes: when the float approaches the target scale, it enters the fine-tuning stage. The LabVIEW software continuously monitors the position deviation e. The stability criterion can be set as follows: if the absolute value of deviation e is less than a preset allowable error threshold (e.g., half the width of the corresponding scale line) within N consecutive control cycles (e.g., N=5), the float is determined to have reached a stable state.

[0041] For example, reading and recording the standard flow rate value includes: once the stability criterion is met, LabVIEW immediately reads the converted standard flow rate digital value Q_standard from the PLC via OPC communication. This value is the direct basis for comparing the accuracy with the target scale nominal value Q_target. Data such as timestamps, target value, standard value, accuracy difference ΔQ, and corresponding image snapshots can be automatically recorded to data files or databases.

[0042] This application's embodiments organically combine the gas path system, control and acquisition system, machine vision system, and host computer system to construct a complete automated testing closed loop. Its core lies in utilizing the host computer software as a unified scheduling center, integrating the issuance of commands to the proportional valve of the actuator controlled by the PLC and the data acquisition of the high-precision electronic gas flow meter via OPC communication. This completely automates the traditional back-calibration process that relied on manual adjustment and reading, significantly improving verification efficiency and ensuring the objectivity of the results. The machine vision module provides high-precision, non-contact, real-time feedback of the float position, replacing the error-prone manual visual inspection. The host computer compares this feedback with the target value and calculates using algorithms such as PID, precisely adjusting the proportional valve via the PLC. This allows for rapid and stable stabilization of the float on the target scale line, with control precision far exceeding manual adjustment. This ensures that the timing of data acquisition is automatically and accurately determined by the system, avoiding the delays and subjectivity of manual judgment. The entire process, from float positioning and stability assessment to data reading and difference calculation, is completed automatically, eliminating reading errors and uncertainties introduced by manual operation and ensuring the accuracy and reliability of the calibration data. This embodiment can also be adjusted for different types or ranges of glass tube gas flow meters and provides convenience for functional expansion or upgrades to multi-channel simultaneous testing, demonstrating good adaptability.

[0043] See attached document Figure 2 As shown in the embodiment of this application, an automatic testing method for the accuracy of a float-type glass tube gas flow meter is also disclosed. This method is based on the automatic testing device for the accuracy of the float-type glass tube gas flow meter described above and includes the following steps 210-240.

[0044] Step 210: Set the scale value of the target to be measured in the control program; Step 220: Start closed-loop control, and adjust the proportional valve to make the float move toward the target scale line and keep it stable; Step 230: When the machine vision module confirms that the float has stabilized at the target scale line, the standard flow value Q_standard of the electronic gas flow meter is read from the programmable logic controller through the communication interface. Step 240: Calculate the difference ΔQ between the standard flow rate value Q_standard and the inherent nominal value Q_target of the target scale, which will be used as the basis for accuracy determination.

[0045] See attached document Figure 3 The illustration shows a specific implementation process of an automatic testing method for the accuracy of a float-type glass tube gas flow meter, based on an automatic testing device for the accuracy of such a flow meter. This process includes: a system initialization and preparation phase, an automated testing loop phase, and a result output and report generation phase.

[0046] For example, the system initialization and preparation phase includes: starting the equipment and running the control program in the host computer (such as LabVIEW). The program first completes initialization operations, including initializing the industrial camera in the machine vision module and establishing a communication connection with the OPC server. The operator then sets or imports all target scale values ​​(Q_target) that need to be verified in this test through the human-machine interface of the host computer.

[0047] For example, the automated test loop phase includes: the program automatically enters the test loop and sequentially executes the following closed-loop control and data acquisition process (a)-f) for each preset target scale value: a) Target Acquisition and Visual Feedback: The program acquires the next target scale value, Q_target. Subsequently, it triggers an industrial camera to capture images of the scale area of ​​the gas flow meter in the glass tube being measured. The control program calls an image processing algorithm (e.g., an edge detection process built based on functions such as IMAQ Find Edge) to process the acquired image, accurately identifying the position of the float's top edge in the image, and calculating the float's current physical position, Current_Pos, using a pre-defined pixel-flow rate relationship.

[0048] b) Closed-loop control adjustment: The control program calculates the deviation between the target position and the actual position, e = Q_target - Current_Pos. Then, the program's built-in PID control algorithm calculates the control quantity Output used to regulate the airflow based on the deviation e. This control quantity Output is written to the analog output channel register specified by the programmable logic controller (PLC) via the OPC communication interface.

[0049] c) Actuator Action: After receiving the instruction from the host computer, the PLC drives its analog output channel to convert the control quantity Output into a corresponding electrical signal (such as 4-20mA current), which is then applied to the electro-proportional valve. The proportional valve changes its opening degree according to this signal, thereby precisely regulating the gas flow rate in the test pipeline and pushing the float towards the target scale line.

[0050] d) Stability assessment: Repeat steps a) to c) to form a closed-loop control. A new position deviation e is calculated in each cycle. When the absolute value of deviation e is less than the preset allowable error value, and this stable state persists for a preset period of time, the float is determined to have stabilized at the target scale Q_target.

[0051] e) Standard Value Acquisition and Accuracy Calculation: Once stability is determined, the control program immediately reads the standard flow rate value Q_standard output by the electronic gas flow meter from the analog input channel register of the PLC via the OPC communication interface. Subsequently, the program automatically calculates the accuracy difference (indication error) ΔQ = Q_standard - Q_target at that point.

[0052] f) Data storage and looping: The program stores the data for this test point (including the target scale Q_target, the standard value Q_standard, and the precision difference ΔQ). After completion, it automatically returns to step a) to start testing the next target scale value, until all preset scale points have been tested.

[0053] The results output and report generation phase includes: throughout the entire test process, the host computer human-machine interface can display in real time the images captured by the industrial camera, the float position curve, the control quantity change curve, the real-time flow value, and the accuracy difference.

[0054] After all test cycles are completed, the control program can automatically compile and generate a complete calibration report. The report includes the raw data for each test point, the calculated accuracy difference, average error, maximum error, and other statistical information, and can also plot error curves.

[0055] This embodiment of the application clearly demonstrates how to combine machine vision feedback, PID closed-loop control, OPC industrial communication, and high-precision standard instruments to achieve fully automated and efficient reverse calibration testing. Through Figure 3 The logic flow shown allows the equipment to automatically, continuously, and accurately complete all tasks from float positioning and stability judgment to data acquisition and processing, completely replacing the traditional methods of manual visual inspection, manual adjustment, and manual recording, significantly improving testing efficiency, consistency, and reliability.

[0056] This application's embodiments unify the paths for control command issuance and standard data acquisition through OPC, simplifying the system architecture and improving communication efficiency and reliability. Utilizing high-precision, non-contact position feedback provided by machine vision, combined with a PID algorithm, the float can be quickly and smoothly stabilized at the target scale, far exceeding the accuracy of manual adjustment. This completely avoids subjective errors and uncertainties introduced by manual adjustment and reading, achieving full automation and digitization of the calibration process. The LabVIEW and PLC-based platform is easy to modify and maintain, allowing for easy parameter adjustment according to different flowmeter specifications and expansion to multi-channel simultaneous testing.

[0057] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of this application, and this application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this application, and these modifications and improvements are also considered to represent the scope of protection of this application.

Claims

1. An automatic testing device for the accuracy of a float-type glass tube gas flow meter, characterized in that, The device comprises: a gas circuit module, which is formed by connecting a gas source, a proportional valve, a measured glass tube gas flowmeter and an electronic gas flowmeter in series through gas pipes; a control and collection module, which comprises a programmable logic controller, an analog output channel of the programmable logic controller is connected with a control end of the proportional valve, and an analog output end of the electronic gas flowmeter is connected with an analog input channel of the programmable logic controller; a machine vision module, which comprises an image collection device, the image collection device is arranged opposite to a scale area of the measured glass tube gas flowmeter; a host computer module, which is used for running a control program, the control program is in bidirectional communication with the programmable logic controller and the image collection device through a communication interface.

2. The automatic precision testing device for float glass tube gas flowmeter according to claim 1, characterized in that, The host computer module is configured to perform the following operations: setting a target scale value, and performing closed-loop control on the proportional valve by the programmable logic controller based on the set target scale value; controlling the image collection device to collect images, and using an image processing algorithm to identify a current position of a float, and generating visual feedback; when the float is stabilized at the target scale, reading a standard flow value of the electronic gas flowmeter from the programmable logic controller through the communication interface; calculating a precision difference between the standard flow value and a nominal value of the target scale.

3. The device according to claim 1, wherein the proportional valve is an electrical proportional valve, a control signal of the proportional valve is in linear function relationship or predefined function relationship with an output flow of the proportional valve or an outlet output pressure of the proportional valve; the electronic gas flowmeter is used for outputting an analog signal representing an instantaneous flow value to the programmable logic controller, the analog signal is a 4-20 mA current signal or a 0-10 V voltage signal.

4. The automatic precision testing device for float glass tube gas flowmeter according to claim 2, characterized in that, the control program in the host computer module adopts a PID control algorithm, takes a deviation between the target scale value and a real-time position of the float identified by vision as a process input, and outputs a control quantity to an analog output channel of the programmable logic controller, which is used for driving the proportional valve.

5. The automatic precision testing device for float glass tube gas flowmeter according to claim 1, characterized in that, the image collection device of the machine vision module is an industrial camera; the machine vision module further comprises a light source for illuminating the scale area, and a bracket for fixing the industrial camera.

6. The automatic precision testing device for float glass tube gas flowmeter according to claim 2, characterized in that, the image processing algorithm comprises an edge detection algorithm for accurately identifying a position of an edge of the float.

7. The device according to claim 1, wherein the communication interface of the control program and the programmable logic controller is an OPC server communication interface based on an OPC protocol; the control program sends a control instruction for driving the proportional valve to the programmable logic controller through the OPC server, and reads a standard flow value collected by the electronic gas flowmeter from the programmable logic controller.

8. The automatic testing device for the precision of a float glass tube gas flowmeter according to claim 1, characterized in that, The control program is also configured to calibrate the machine vision module to establish a mapping relationship between image pixel coordinates and actual flow scale values of the measured glass tube gas flowmeter; the control program is configured to acquire images in real time through the image acquisition device, and identify the real-time position of the float arranged in the measured glass tube gas flowmeter and generate position feedback for the closed-loop control based on the mapping relationship and image processing algorithms.

9. The automatic testing device for the precision of a float glass tube gas flowmeter according to claim 1, characterized in that, The gas path module, the control and acquisition module, and the machine vision module are configured in a multi-channel structure that can simultaneously connect and control multiple measured float-type glass tube gas flowmeters.

10. A method for automatically testing the accuracy of a float glass tube gas flow meter, implemented based on an automatic testing device for the accuracy of a float glass tube gas flow meter according to any one of claims 1 to 9, characterized in that, The method comprises: Setting a target scale value to be measured in the control program; Starting closed-loop control to move the float to the target scale line and keep it stable by adjusting the proportional valve; When the machine vision module confirms that the float has stabilized at the target scale line, reading the standard flow value of the electronic gas flowmeter from the programmable logic controller through the communication interface; Calculating the difference between the standard flow value and the target scale inherent nominal value as the basis for precision determination.

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