Design of gas flow standard facility for continuous detection with two stations

The traditional gas flow standard facility can only carry out single station detection, so it is urgent to solve the problem of improving work efficiency. In this paper, the existing gas flow standard facilities and related technologies are studied in depth, especially for the same specifications, batch detection table, the design of double station continuous detection type gas flow standard facilities. Its main features are: according to the need to flexibly choose two stations alternating detection, two stations at the same time detection or single station detection mode, under the premise of ensuring the safety and reliability of the facility, greatly improve the work efficiency. In this paper, the operation process and flow diagram of the three detection methods are given in detail, and the applicability and improvement direction of the facility are analyzed and prospected. This facility design work efficiency enhancement advantage is significant, has a good promotion value.


Introduction
Flow metrology [1][2] is an important part of metrology science and technology, and gas flow metrology is an important branch of it, which is widely used in various fields such as industrial production, energy metrology and environmental discharge, including the use of gas flowmeters to measure gas consumption and carry out calibration work.Gas flow standard facility [3] are used to calibrate various types of gas flowmeters, usually using air or actual gas as the medium.Traditional gas flow standard facilities (as shown in Figure 1) are usually divided by the principle of master meter, including bell jar, piston, critical flow Venturi nozzle method, master meter method and other forms.The corresponding master meters are bell jar, piston, sonic nozzle (group), master meter (group), etc.
When carrying out calibration work, firstly install the gas flow meter under test (hereinafter referred to as the meter) on the fixed clamp table position of the detection pipeline, select the appropriate standard or combination of standard, and calculate the value error of the meter by recording the accumulative amount of gas flowing through the meter and the standard and the related temperature and pressure value within the specified time.This design can be used to calibrate the meter with different diameters.However, it also has obvious disadvantages: although multiple detection pipelines can be set, only one of them can be used for detection at a time, As shown in the structural diagram of Figure 2, only one of the detection pipelines can be selected for single station detection each time, that is, when C is connected to A, C and B are disconnected; On the contrary, when C and B are connected, C and A are disconnected, which is low working efficiency.For example, after completing the inspection of a meter, the typical operation steps include but are not limited to the following: stop all power sources of the facility, disconnect signal power and remove signal wires, remove the meter clamp and remove the meter; Place the other meter to be checked in the clip meter position, align the meter with the back, install the signal cable, turn on the signal power supply, start the power source of the facility, and start a new round of detection.Obviously, this kind of operation process is complicated and the detection efficiency is difficult to improve.

Design method
In response to the low efficiency of traditional gas flow standard devices, can a continuous and efficient standard facility be designed based on the existing technology [4][5][6][7] for the same specifications and batch tested lists?The answer is yes.The design method mainly includes: first, considering whether the power source can not be turned off after the completion of a meter detection, so as to achieve continuous detection.Second, consider adding another detection pipeline with the same specification on the basis of the existing detection pipeline to realize alternating or simultaneous detection of two inspected tables.Third, consider the realization of the working mode and working process of two-station continuous detection, to ensure that the detection process in the premise of safety and reliability, greatly improve the work efficiency.

Basic structure
Figure 3 shows the two-station continuous detection type gas flow standard facility.The facility is the principle of standard meter method, which is mainly composed of power source, detection pipeline, standard meter, clip meter and meter to be inspected, gas diverter, gas buffer, valve, transmitter, etc. Where:

Component application
The inspection pipeline (hereinafter referred to as the pipeline) is used to install the inspected  The gas buffer QH is designed as a sphere, which is mainly used to buffer the airflow medium after pipeline 1 and pipeline 2 are gathered, so as to facilitate stable flow.The blowdown valve J5 is installed below the gas buffer QH for clean blowdown.
The gas diverter HX is used to change the direction of air flow when the power source does not stop, so as to facilitate the operation of the detection pipeline.The A end is connected with the globe valve J3, the B end is connected with the flow regulator F3, and the C end is connected with the bypass valve J4.The bypass valve J4 is communicated with the atmosphere and is used for the communication between the power source DL and the atmosphere.
The power source DL is used to generate airflow power and consists of one or more power pumps.

Operation process
Taking the negative pressure standard table method and air medium as an example, the operation process of this device is described in 4.1, 4.2 and 4.3.The flow chart is shown in Figure 4.

Mode 1: Alternate detection of two stations
Double-station alternating detection, that is, only one pipeline of the device is used in each detection, and the other pipeline can be dismantled and installed in the detection process; After the detection of this pipeline is completed, the power source can be switched to the bypass first and then to another pipeline for further detection, so as to realize continuous and alternate detection of the device pipeline.
Operation process: (1) Open the stop valve of one pipeline and close the stop valve of the other pipeline; Stop valve J3 closed; Bypass valve J4 open; Blowdown valve J5 closed; Flow trimmer valve F1 or F2 of the pipeline is the maximum opening, flow regulator valve F3 is the typical opening of the first test flow point.The gas diverter HX is placed at the B end and communicated with the flow regulating valve F3.
(2) Reliably install the meter to the corresponding clamp position of the current pipeline and connect the signal line.
(3) Open the power source DL, slowly open the stop valve J3, and the current pipeline is connected to the power.After the air flows through all components of the current pipeline, gas buffer QH, flow regulator F3, gas diverter HX and stop valve J3, it is discharged through the power source DL.
(4) Control flow regulating valve F3 opening, so that the current pipeline basically reaches the detection flow point; Further adjust the flow trimmer valve F1 or F2 until the set flow point is reached.After the flow stabilized, the detection process of the flow point began.The accumulated flow, temperature, pressure and other data during the detection time of the standard table and the monitored table were recorded respectively.
(5) Repeat the operation (4), adjust the power source DL if necessary, and complete the detection of other flow points of the table being inspected.
Note: In the process of detection, the other pipeline can be dismantled and installed to prepare for the next round of detection.(7) Switch the gas diverter HX back to end B, at which time another pipeline is connected to power, and repeat operations ( 4) -( 5) to complete the detection process of the other table to be inspected.
(8) Repeat operations ( 6) -( 7) until all calibration tasks are completed and power source DL is turned off.

Method 2: Simultaneous detection on two stations
Simultaneous detection of two stations, that is, two pipelines of the device are used at the same time in each detection.After the detection is completed, the power source is switched to the bypass.At this time, the disassembly and installation of the inspected meters of the two pipelines should be completed quickly.Then, the power source is switched back to the two pipelines for further detection.In this way, not only the continuous detection of the device can be realized, but also the single detection of two tables to be inspected, which doubles the working efficiency.Operation process: (1) Open the stop valves of the two pipelines of the device; Stop valve J3 closed; Bypass valve J4 open; Blowdown valve J5 closed; Flow trimmer valve F1 and F2 are the maximum opening, flow regulator valve F3 is the typical opening of the first test flow point.The gas diverter HX is placed at the B end and communicated with the flow regulating valve F3.
(2) The two inspected meters shall be reliably installed to the corresponding clamped meter positions of the two pipelines and connected to the signal wires.
(3) Open the power source DL, slowly open the stop valve J3, and the two pipelines are connected to the power at the same time.The air flows through two pipeline components, gas buffer QH, flow regulating valve F3, gas diverter HX, and stop valve J3 at the same time, and is discharged through the power source DL.
(4) Control flow regulating valve F3 opening, so that the two pipelines basically reach the detection flow point; Further adjust the flow trimmer valves F1 and F2 until both test lines reach the set flow point.After the flow stabilized, the detection process of the flow point began.The accumulated flow, temperature, pressure and other data during the detection time of the two standard tables and the two monitored tables were recorded respectively.
(5) Repeat the operation (4), adjust the power source DL if necessary, and complete the detection of other detected flow points of the two monitored tables.
(6) Switch the gas diverter to end C, and when the flow rate of the two pipelines becomes "0", quickly complete the disassembly of the two inspected meters and the installation of the other two inspected meters.
(7) Switch the gas diverter HX back to end B. At this time, the two detection pipelines are connected to power again.Repeat operations (4) -(5) to complete the detection process of the other two monitored tables.
(8) Repeat operations ( 6) -( 7) until all calibration tasks are completed and power source DL is turned off.

Method 3: Single-platform detection
Single-station detection means that only one pipeline is used for detection during the detection process.It is generally used when a pipeline fails and another pipeline is used to carry out work.

Operation process:
(1) Open the normally used pipeline stop valve, and close the faulty pipeline stop valve; Stop valve J3 closed; Bypass valve J4 open; Blowdown valve J5 closed; Flow trimmer valve F1 or F2 of the pipeline is the maximum opening, flow regulator valve F3 is the typical opening of the first test flow point.The gas diverter HX is placed at the B end and communicated with the flow regulating valve F3.
(5) Repeat (4), adjust the power source DL if necessary, and complete the detection of other flow points of the table being inspected.
(6) Switch the gas diverter to end C, and when the pipeline flow becomes "0", quickly complete the disassembly of the monitored meter and the installation of another monitored meter.(7) The disassembly of the meter to be inspected and the installation of gas diverter HX of another meter to be inspected will be quickly completed and then switched back to end B. At this time, the pipeline will be re-connected with power, and operations (4) -( 5) will be repeated to complete the detection process of the other meter to be inspected.(8) Repeat operations ( 6) -( 7) until all calibration tasks are completed and power source DL is turned off.

Uncertainty analysis
The measurement uncertainty of traditional gas flow standard devices for work is generally U=0.2%~0.5%,k=2, and its main sources include the accuracy and stability of standard meters, the accuracy of other measuring instruments, and the impact of environmental conditions.This device changes the operation mode through the design of pipeline structure, thereby improving the efficiency of detection work, without fundamentally affecting the measurement uncertainty of the device.According to the evaluation, the measurement uncertainty of this device can still maintain a capacity level of U=0.2%~0.5% and k=2.

Work efficiency verification
Now let the same skilled operator use the traditional standard meter gas flow standard device and this device respectively to test several DN50 gas turbine flowmeters in roughly the same time, each meter to detect 4 flow points.
The comparison of work efficiency is shown in Figure 5.It can be seen that, when only one skilled operator is used, the work efficiency of alternating detection of two stations of this device is higher (D in the figure).When more than one auxiliary person is assigned to disassemble and assemble the table, the working efficiency of the device is the highest when two stations are used for simultaneous detection.

Applicability analysis
The device can detect two tables alternately or simultaneously.Especially for the tables with the same specifications and batch detection, the efficiency improvement advantage is more obvious.The power source on the device can be negative pressure (such as water ring vacuum pump, vacuum roots pump, etc.), or positive pressure (such as air compressor unit); The detection medium can be air, natural gas or steam; The standard table can choose Roots, ultrasonic, turbine and other principles of flowmeter; The principle and specification of the checked list can be the same or different, as long as the detection flow points are basically the same; The two bits on the device can even be expanded to many more, allowing for a wider range of applications.

Improvement direction
In the process of using this device to carry out testing, there may be risks of equipment damage.For example, improper operations during traffic regulation may cause the detected traffic to exceed the maximum traffic in the standard table or the checked table (also known as excessive traffic).Another example is that the overflow of two pipelines or one of them may occur at the same time due to pipeline blockage or equipment failure during detection.Excessive flow may cause damage to the standard table or the inspected table body, the consequences are very serious.Therefore, more detailed operation procedures can be prescribed to reduce the occurrence of such problems.In addition, the software and hardware design can be used to realize the automatic identification and processing of operational risks through the intelligent improvement of the device, so as to make the operation of the device more reliable.

Summary
Through the design of alternating or simultaneous detection of two stations, it saves the time of disassembly and installation of the meter being checked.Even once can complete the detection of two tables to be checked, the work efficiency is nearly doubled.Based on the design concept of this device, relevant industry personnel can combine the existing research experience in the field of flow in the future to conduct further research on the reliability, adaptability and intelligence of the device [8][9][10], so as to meet the needs of the society.

Figure 1 .
Figure 1.Realistic view of traditional gas flow standard facility.

Figure 2 .
Figure 2. Structure diagram of traditional gas flow standard device.

Figure 3 .
Figure 3. Structure diagram of gas flow standard device with two stations for continuous detection.
J12 are used in pairs to open or close pipeline 1, so they are also called stop valves of pipeline 1; Similarly, stop valves J21 and J22 are used in pairs to open or shut off pipeline 2; The stop valve J3 is used to open or close the connection between the pipeline and the power source; Flow trimmer valves F1 and F2 are used to fine-tune the detection flow of pipeline 1 and pipeline 2; Flow control valve F3 is used to adjust the detection flow of pipeline 1 and pipeline 2 at the same time (rough regulation).

( 6 )
Switch the gas diverter HX to end C, close the stop valve of this pipeline, and open the stop valve of the other pipeline.

Figure 4 .
Figure 4. Flow charts of three detection methods.