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"blank test"
The “blank test†is a reflection of the comprehensive error of the equipment. The test error is due to the fact that there are indeed factors in the gas permeability test that cannot be effectively improved, such as system leaks and other unpredictable factors. Although there has been no clear "blank test" in the air permeability test standard, the test work on the "blank test" has been widely recognized by the society.
VAC-V1 “Blank Test†Data In order to obtain the combined effect of all factors, the VAC-V1 uses a sample that is considered to be completely airtight to be tested in accordance with normal operating procedures, and then to observe system leakage and other factors for the integration of the entire equipment. influences. The "blank test" value obtained by this method determines the pros and cons of the device to be more credible.
LabthinkVAC-V1's "blank test" uses 55μm copper foil (also can use thicker aluminum foil sample) as a sample to test, strictly sealed, the system is vacuumed for 48h (before entering the test state, the vacuum of the upper and lower chambers should be 10Pa) The following) was tested using the conventional volume of the VAC-V1 (the device has an optional extended volume function). In order to analyze the influence of environmental temperature and humidity changes on the test, there is no self-temperature control function of the starting device. The pressure time curve is obtained as shown in Fig. 1. (In addition, there are temperature time and humidity time curves, which will not be described here)
The test lasted for 12 days (including vacuuming time), the temperature was between 18 and 23 °C, and the ambient humidity was 50±8% RH (if the self-temperature control function of the equipment was used, the test effect was better). After entering the test state, the lower chamber pressure increased by 6.0Pa, and the test result was 0.023ml/m2·24h·0.1MPa. (If the extended volume or fuzzy test mode is selected, the comprehensive effects of the above various factors can be effectively reduced. The test results will be more accurate). It is not difficult to find out that the influence of temperature and humidity changes on the test is small when the whole test curve is analyzed with the data list.
In the first 60 hours of zui, the pressure change was relatively large, rising from 0Pa to 3.84Pa. In the subsequent 180h, the pressure increase was decreased, and the equivalent gas permeability was 0.012ml/m2·24h·0.1MPa. The reason for this phenomenon is related to the degassing state. The test proves that prolonging the vacuuming time can effectively improve the impact on the test results.
Data repeatability 1. Elements of data repeatability Because each manufacturer implements a test method, the component selection is large, so the data repeatability of the device is also an important indicator for evaluating the device. By analyzing the data repeatability of the device, it is possible to better understand the error and fluctuation of the detection data of the device and improve the detection efficiency. Data repeatability includes: S (standard deviation standard deviation), CV (percentcoefficient of variation data fluctuation percentage), and LZ (least significant difference of two independent test results of 95% confidence level of the 95% confidence level based on confidence level).
2. The measured data was selected from five samples of A, B, C, D, and E for oxygen permeability detection using a Labthink VAC-V1 gas permeation meter. The test temperature, O2GTR value and test results of the five samples are shown in Table 1:
The A and D samples were provided by the Thai Packaging Testing Center. The B sample was provided by the Mecadi laboratory in Germany. The O2GTR values ​​of the five samples increased in sequence, the standard deviation increased, and the data fluctuation gradually decreased. Mainly due to the detection of high barrier samples, the degassing state of the sample and the influence of the comprehensive factors on the test chamber are more obvious than when detecting the medium and low barrier samples. For example, an oxygen transmission of samples B and E The results of the test are different from the average O2GTR values ​​of 0.4. For sample B, the data fluctuations account for 2.06%, while for sample E, it is only 0.0332%. Therefore, the value of the fluctuations discussed separately is somewhat one-sided. Pay attention to the barrier properties of the sample.
The “blank test†data and the repeatability of the test results are important indicators for measuring the gas permeability testing equipment. The test error is not purely determined by the equipment, but also related to the test principle. It can be generally considered that the quality of the equipment blank test has a great influence on the detection of high barrier samples, but the reproducibility of the equipment data is a comprehensive reflection of the data error detected by the equipment in any range of gas permeability.
Accurately package mechanical permeability test data with important indicators
The gas permeability test has many influencing factors, such as sensor accuracy, effective range, system leakage, sample processing, material properties, test environment, hardware design, software processing, and so on. Many of the influencing factors are determined by the innate nature of the design. The “blank test†data and the repeatability of the test results are important indicators for measuring the gas permeability testing equipment. From the application point of view, the user is concerned not by how the manufacturer improves these conditions, but what requirements are met, and what conditions are met before objective and accurate test data can be obtained. This article introduces two main measures - "blank Test" and repeatability of test results.