Gas Vac

Tester gas permeation method of pressure difference can greatly improve efficiency. differential pressure method is the fundamental means of gas permeation test while the vacuum method is the most widely used method of differential pressure. In the past, the precision and test efficiency of test of this instrument is limited by the previous technology and key components. As instruments of pressure difference method were considered "low accuracy and bad performance." With improved testing techniques, test precision instruments of the pressure difference method has greatly improved and can be 0.01 ml/m2 · · 0.1 MPa 24 today. Comparing with equal pressure method, test its efficiency has also improved. However, the popularity of test instruments and barrier property to the growing demand for testing to establish higher standards for testing the effectiveness of current test instruments. Based on the characteristics of the test pressure differential, this article analyzes the efficiency of tests and introduces the corresponding current achievements.

1. Factors affecting the efficiency test

a reduction in yield is a reviews on common instruments previous differential pressure method, which reveals two main shortcomings of the tools of pressure differential method: the longest time and limited number of test specimens. These two factors directly limit the efficiency of the test. Therefore, to improve test efficiency of testing time should be shortened or specimen number should be increased.

1.1 Time Test

Time to test the method under vacuum, the representative method of the method of pressure difference, including the evacuation time and equilibrium time of transmission. Empirical tests have shown that the very short evacuation time affects test results. There are two aspects of accounting for influence. First, depleted gas pipeline under vacuum during the test process is calculated as a gas transmission test specimen (pressure sensor can not distinguish the type of gas). Therefore, the test data seems to be larger and the test data is not stable. On the other hand, although the material was pretreated, there are still impurities existing on the surface and transmission of certain gases in the dirt. The duration of the evacuation time has influences on the impurities and the difficulty of eliminating the gas inside. More evacuation time is, the better the effect of eliminating stale data and will test. It has been proven that maintaining the pressure seems to be more difficult if the evacuation time is not sufficient. Therefore, the evacuation time is specified to be more standards. In Great Britain 1038, the evacuation should continue for more than three hours after the sewage system has reached equilibrium necessary standards.

Test time sensor method, the method equally representative of pressure, is divided into the purge system and time period of equilibrium. There is a clear requirement on the purge time on testing standards and has been emphasized in many materials after the purge that can never be very short. In addition, in ASTM D 3985-05, the purge time is divided into time dehumidification and zero time bleed, which is about the same as the method under vacuum. In developing instruments for testing the method of oxygen sensor, Labthink has conducted studies on the reasonable period of purging the system. According to his study at the initial stage of testing, pre-purge two hours, and then guide carrier gas into the sensor to continue to bleed for 24 hours. Now, the oxygen content inside the system can be considered low enough to begin the test.

It can be seen that the evacuation time of preparation time (the method of vacuum and purging time sensor method) before the balance of transmission in these two methods are similar. Regarding the time to restore the balance of transmission, gas permeation specification.