This article describes a newly developed automated testing system for the performance of diffusion vacuum pumps. The system can automatically detect the ultimate pressure and pumping speed of the diffusion vacuum pump according to the national standard. System uses self-developed photoelectric level detection methods and components to achieve automatic dropper level reading and timing; the use of stepper motor-driven needle valve to achieve gas flow and the pressure test cover automatically adjust the use of PC and the next host Single-chip dual-stage control system to achieve the entire test system and test the process of automatic control.
As the most widely used high vacuum pumping equipment, oil diffusion pump in the country's production, research has reached a considerable technical level and a certain scale of production has been widely used in machinery, electronics, metallurgy, atomic energy, space simulation and other industrial areas And science and technology research, made significant contributions to the development of science and technology in our country. In recent years, domestic diffusion pump products have made great progress from appearance, function to performance.
Relative to the number of diffusion pump manufacturers and total production, the domestic diffusion pump in product performance testing is still relatively backward. At present, many companies do not yet have their own performance testing system, the pump product in the factory before the actual lack of performance indicators. Existing domestic related testing systems are all manual operation, the operator has a higher professional knowledge and experimental skills required to be specially trained to be competent for this work, and the accuracy of the test data is affected by many human factors, these It is more difficult for the manufacturer to conduct the diffusion pump performance test independently.
In response to this situation, this paper developed a set of automatic testing system of diffusion vacuum pump performance. The following will be the system test principle, the system hardware and software components, the development process encountered technical difficulties and solutions to be introduced.
1, automatic test system test principle
The set of test system for diffusion pump limit pressure and different inlet pressure pumping speed curve of the test principle and method, complete reference to the relevant national standards. One diffusion pump pumping speed curve of automatic detection, using "constant pressure method" principle test. Corresponding to each pressure measuring point of the test steps are: the working valve is open under the conditions of the needle valve used to adjust the gas flow into the test cover Q, so that the balance within the test cover pressure p stabilized at the expected pressure value close; The valve sequentially records the times t1 and t2 at which the liquid column in the pipette reaches the liquid level h1 and h2; and calculates the liquid column height h = h2-h1 and the time required for the rise t = (t2-t1) by using the following formula Corresponding to the volume flow rate under pressure, that pumping speed.
S = Q / P = Kh / Pt
Where S --- measured vacuum pump suction rate, L / s
Q --- gas flow through the pump port, Pa · L / s
p --- test cover the specified pressure balance position, Pa
h --- dropper within the liquid column rise net height, mm
t --- dropper within the liquid column rise time, s
K --- dropper function, Pa · L / mm.
According to the above formula we can see that in order to calculate the pumping speed S, K, h, p and t corresponding to the pressure measuring point need to be known. Among them, the dropper function K can be based on the different pipette and connecting pipe size, combined with the actual test conditions calculated in advance; therefore, the actual need to read only the specified position of the test cover balance pressure p, dropper within the column clear height h and liquid column height h required time t three volumes. The test system has the automatic test function, mainly refers to the working valve automatically open and close the solenoid valve; needle valve to complete the flow adjustment process using stepper motor-driven, and according to the actual measured pressure within the hood and the default pressure feedback Control; the use of optical liquid level switch to determine the level within the dropper reaches the set position h1 and h2 height t1 and t2. The entire testing process, as well as the subsequent pumping speed calculation, the results of the output work, are completed by the computer automatically control, but in the process of replacing the dropper and connecting the pipeline requires the operator manual operation.
2, automatic test system hardware
2.1, mechanical parts
The main part of the mechanical system design of the test system based on the detailed provisions of national standards. Mainly by the test cover, lifting mechanism, the former stage valve, pre-pumping valve, working valve, deflation valve, trim valve, dropper, photoelectric level switch, reservoir, trolley and vacuum piping and other components, K-200-type oil diffusion pump, pre-stage 2X-4-type rotary vane pump.
Taking into account the main purpose of the experimental platform is to serve the vacuum experimental teaching of Northeastern University process equipment and control engineering undergraduate students, so the structure and function of some changes, expansion. Corresponding to the K-200 type oil diffusion pump, this should be used with a diameter of 200mm test cover, but consider other teaching experiment purposes, the system uses a 400mm diameter test hood, the middle of the installation of tapered transitional interface and flapper valve Measured diffusion pump connected. These can lead to an increase in the conductance of the pipe, thus reducing the pumping speed of the pump without affecting the working principle and method of use of the test system. There are also two vacuum gauge ports on the test hood, a forelevel valve port, a trim valve inlet port, a bleeder port on the top, and two spare ports for connection to other vacuum testers. Lift the test hood can be lifted to facilitate the replacement of the main pump and other teaching experiments completed. Taking into account to achieve automatic control, all the valves are selected electromagnetic drive. In addition, according to the experimental needs, but also specially customized a diameter of 1.5,3,5,10,20,30,50 mm series of dropper.
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