Analysis of the effectiveness monitoring system for main equipment of air compressor
This paper introduces a LabV iEW-based air compressor host performance test system, which uses high-precision sensors and NI high-performance data acquisition cards PX I4351, PXI6251, and virtual instruments designed by LabV IEW, so that this test not only tests The time is short, and the quality of the test data is high, which effectively saves the test cost.
2 Introduction to LabVIEW
LabV IEW is a graphical programming language for creating applications with icons instead of text. It is primarily used to develop test, measurement and control systems. The core concept of LabV IEW is that software is the concept of instrument, the virtual instrument. It integrates software with various measuring instrument hardware and computer, establishes virtual instrument system, adopts powerful graphical language programming, intuitive programming interface, convenient programming, friendly human-computer interface, and powerful data visualization analysis. And control capabilities provide a good environment for users to quickly construct their own control systems to form user-defined solutions. All programs in this test are implemented using LabV IEW.
3 host performance test bench
There are 2 key parameter quantities in this test quantity, one is the shaft power and the other is the exhaust volume. The formula for calculating the specific power is: q= N e Q( 1) where N e axis power Q actual displacement axis power N e is calculated as: N e= 2 Mw 10 - 3 =M n /9549( 2) Medium M transmission torque, N mn speed, rad /s actual displacement Q Calculation formula: Q 0 = 18. 82Cd 2 T x1 px 1 pp b T 1 1/2 (3) where Q 0 does not account for condensate Compressor volumetric flow, m 3 /s C Nozzle coefficient d Nozzle diameter, m T x 1 1 inspiratory temperature, K p nozzle differential pressure, Pa T 1 nozzle upstream gas temperature, K pb test atmospheric pressure, Pa P x1 Class 1 exhaust pressure, Pa test bench structure indicates that the parameters to be measured during the test are: M, n, T x1, p, pb, T 1, discharge pressure p, intake temperature and exhaust temperature.
For the collection of physical quantities, the temperature is measured by the NI-specific temperature acquisition board PX I4351, and the pressure and other physical quantities are used with the PX I6251 board. In the test, a single frequency converter is used to achieve different displacement changes. The virtual instrument was used in the test to monitor all variables and display them after the relevant processing. The signal processing flow is shown.
3. 1 axis power measurement
As can be seen from equation (2), the shaft power can be obtained as long as the input torque and the rotational speed are measured. The speed is relatively easy to obtain, and the torque is relatively difficult to obtain. In this test, a contact torque sensor was used, and only the phase difference was measured during the test to obtain the torque. There are many ways to obtain the phase difference. The spectrum analysis requires high data acquisition frequency. This test is responsible for collecting the torque meter signal DAQ board PX I6251, with the highest multi-channel acquisition speed of 1.0M S / s. In terms of spectrum analysis, it is completely satisfactory.
The torque signal acquisition procedure is shown.
The single-frequency measurement module is used in the test program to perform spectrum analysis, and the analyzed data is classified and solved, and finally the torsion angle and frequency are obtained, and then the shaft power is obtained. At the same time, in order to improve the compatibility of the program, an analog input interface of the secondary instrument of the torque meter is reserved in the program. Through this program module, the measured value of the secondary instrument of the traditional torque meter can be transmitted to the computer for analysis.
3. 2 calculation of gas volume
The gas volume is a calculated amount. It can be seen from equation (3) that except for d and C, the remaining parameters T x1, p, T 1 and pb can be directly measured by the sensor. For d, it is generally fixed, only C is a variation. The literature <7> has a numerical calculation equation for the nozzle coefficient, but it has great limitations. To obtain the C value, use the literature provided by <3>. Chart, designed a chart finder program, the core idea of ​​the program is to turn the lines in the graph into a mathematical equation: y = ax + f ( t) for each curve f ( t) corresponds to a constant, for the actual measurement The obtained T 1 and p are transformed by x = f 1(T 1) y= f 2( p ), and the specific point (x 0, y 0) in which the actual point (x 0, y 0) is obtained is obtained, and finally the corresponding C value is obtained, thereby It is possible to calculate the amount of gas.
4 main program composition and functional characteristics
The main program consists of three functional modules: acquisition, data analysis, data display and storage. In this program, the temperature is collected by the PX I4351, and the other quantities are collected by the PX I6251. In order to coordinate the different acquisition rates of the two boards, the temperature measurement program is in parallel with other measurement programs, and the measurement of the PX I6251 is performed. Its internal structure adopts a serial structure.
The interface of the main program is divided into main interface, auxiliary interface, initial setting and extended display. These three interfaces display measurement information from different aspects.
The main interface is mainly to complete the health monitoring, specific power display and record selected data points. The auxiliary interface is mainly to complete the detailed display of some key quantities, including the display of supply and exhaust pressure changes, virtual nozzle monitor, torque meter and atmospheric pressure gauge panel. Figure 4 shows the operation of the auxiliary interface. The content of the torque meter signal displayed on the torque meter panel is determined by the signal source of the torque meter. At this time, the DC voltage signal transmitted by the secondary meter is displayed.
The main function of the initial setting and extended display interface is to complete the temperature measurement, torque display, and initial setting of the nozzle diameter, which determine the display content of the main and auxiliary interfaces. This interface can also display a part of the long-term, high-precision change process for the needs.
The recorded data is processed, and the specific power curves of two different compressors at different pressures and different speeds are obtained. The curve in the figure is divided into three large sections from top to bottom. Each section represents one supply pressure. Each section contains two adjacent curves. Each curve represents a compressor with the same exhaust pressure. Next, change the performance curve of the exhaust volume.
5 test analysis
In order to measure the performance curve of a compressor under three different pressures, at least 60 stable operating points are required, and one operating point includes ambient temperature, suction temperature, gas temperature upstream of the nozzle, and local atmospheric pressure. 10 physical quantities such as nozzle pressure difference, exhaust pressure, oil pressure, and supply pressure. In the conventional mode, when reading an amount in 30s, the reading time required to measure 60 stable operating points is 5h, and the stabilization time between the two operating points is 5m in, which is consumed in stable conditions. The time is 4. 9h, plus the data is spent 4h, a total of 13. 9 h. The cost of the traditional method is about 3577. 64 yuan.
In this test system, the same 60 operating conditions are measured, because the data reading time is less than one second, and there is no data sorting time, so the time is 4. 9h, in the stable waiting time, consumables, If the depreciation fee is the same, the total amount is 1772.14 yuan, which is less than half of the traditional method, and only 35.3% of the time.
A comparison of the two methods is shown.
6 Conclusion
The test analysis software has been practiced and found that the test data fully meets the requirements of the literature <8>, suitable for industrial applications, and compared with the traditional method, the modern mode represented by the test analysis software is interface design, data processing, curve generation. Other aspects have obvious advantages.
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