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Why test the GTR (gas transmission rate) of the package?(2nd part)

Jun 05,2022

Source:Link Testing Instruments Co.,Ltd.

4. Features

  1.   Technique of integrate block of three test chambers
  2. Three test chambers are tightly designed together, which facilitates temperature and humidity control. The comparison of test results of the three test chambers will be more rational and precise as the humidity and the temperature are evenly distributed due to the patented technique, especially when the test materials are temperature and humidity sensitive. External humidity generator is optional for humidity controlling.
  • Three specimens can be tested at the same time, making it m re efficient;
  • Pipe connections are reduced, which minimizing the chance of gas leakage and the fault rate;
  • It takes less space.
  • Gas transmission rate, solubility, and coefficient of diffusion and permeability can be measured. Solubility and coefficient of diffusion a d permeability are essential to the modification study and analysis of materials. Link Testing instruments can measure all these indexes, beside of transmission rate.
  •  Data fit function of parameters under different temperatures: For those packages usually stored in extreme temperatures, for example the seafood packages that are stored under tens of degree below zero, users need to know the real transmission rate under such conditions. However, it is difficult or cost high to measure the transmission rate of materials in this case. Data fit function can meet this demand. With several groups of test data under normal temperatures, the system can work out the permeability data of materials under extreme conditions.
  •   Proportional and non-proportional test modes can meet different demands of users.
  •  Proportional test mode: when increments of pressure in lower chamber caused by gas passing through the specimens in several equal test periods t are almost the same (user can set the value, and the default value is that the difference is no more than 10%), instrument will determine that the transmission reaches equilibrium, and test stops. Test result will be calculated automatically.
  • Non-proportional test mode: If permeability of test materials is extremely low and test time will be very short, this test mode can be selected. User can set the initial pressure and end pressure. When pressure in lower chamber is equal to the initial pressure, the instrument starts timing. And test stops when pressure in lower chamber reaches the end pressure. The instrument will calculate the test result based on the time consumed for the pressure increasing to end pressure from the initial pressure.
  • Test capacity extension: One instrument can have two test capacities, meeting test demands of users. In this case, the instrument can test materials with whatever permeability. Based on ideal gas law, PV equals to nTR, i.e. PV=nTR, in which P is the pressure, V is the volume of lower chamber, n is the molar mass of gas, T is the temperature,and R is the constant. Under constant temperature, P is determined by the test capacity of vacuum sensor in the lower chamber. When test capacity of sensor is known, volume of lower chamber (v) has to be enlarged for larger permeation.
  • Large scope of humidity control and automatic temperature control can meet the requirements of test under various conditions. During test, humidity generator can be applied to control the humidity at high pressure side based on the actual needs of users.
  • Instruments can be calibrated with reference films. It is known that all test instruments have to be calibrated regularly, or test data may be affected by various environmental factors. Link Testing test instruments that conform to pressure differential test method can be calibrated with reference films, which is easy, convenient and efficient.

The Common GTR terms

  1. Test range: The unit used is cm3/m2·24h·0.1MPa. It is the volume of gas (cm3) passing through the specimen per square meters per day under 0.1 MPa pressure difference.
  2. Vacuum degree: vacuum degree in the lower chamber will be tested before testing, i.e., verifying the evacuation. Based on various reference standards, vacuum degree is usually required to be 26 Pa. With Link Testing instruments, the vacuum degree can be as low as 10 Pa. Vacuum degree in lower chamber is not only the result of evacuating ability, but also shows the sealing performance of the instrument, and proves whether the instrument can maintain the vacuum environment very well. In other words, should the instrument have low sealing performance, satisfactory vacuum degree is hardly to be reached, no matter of the grade of vacuum pump. Poor sealing performance of instrument may affect the test accuracy, further making it difficult to discern the pressure drop is caused by gas permeation or by system leakage.
  3. Vacuum accuracy: 0.1 pa. it is the precision of vacuum sensor in lower chamber, and it is better than that specified in reference standards. For example, for materials with permeation being 0.1034 cc/m2•d•0.1 MPa, the pressure fluctuation will be within 10 Pa.
  4. Test temperature: it is the temperature range controlled by the instrument. Normally, the temperature during testing is controlled to be 23℃. Link Testing instruments have different controlled temperature range, and we recommend customers the proper model based on their specific demands.
  5. Test humidity: Humidity generator can be employed if users want to control the humidity of test gas. Test gas flows through the humidity generator before entering test chamber, which will produce certain humidity in the test gas. It shall be noted that humidity can only controlled at the high pressure side. As lower chamber is evacuated, it shall not be humidified.
  6. Test area: the area that is used in calculating the final test result.
  7. Specimen size: diameter of specimen shall not be less than 97 mm. If customers want test their samples in Link Testing laboratory, or they want to know the appropriate test range of the instrument suitable for them before purchasing, they had better sent us samples with the same size of A4 paper, and samples shall not be folded.
  8. Test gas: for example, O2, N2, CO2, etc. Instruments conforming to pressure differential method measure the gas permeation by calculating the pressure increment in lower chamber. Sensors have low requirements to test gases. Theoretically, gas that will not change its form under pressure can meet the requirements, such as helium, argon, etc.
  9. Test pressure: the maximum pressure can be maintained in upper chamber, ranging from -0.1MPa~+0.1MPa. The pressure here is relative pressure that is calculated with 1 standard atmosphere pressure as zero point. The pressure is -0.1 MPa when upper chamber is in vacuum status, and the relative pressure will be 0.1 MPa when inflating 0.2 MPa (absolute pressure) into upper chamber.
  10. Specimen:including thickness and test area. Input the actual value of the thickness. The default test area is 38.48 cm2. If specimen is small, the test area shall be the actual permeation area of specimen.
  11. Purging of high pressure chamber:After specimen is clamped, there may be some air remaining in the upper chamber. Before test starts, the upper chamber shall be purged with test gas to ensure a reliable test environment. When test poisonous gas, for safety consideration, the test chamber shall be purged both before and after the testing.
  12. Evacuation of lower chamber: According to reference standards, lower chamber shall be evacuated, which would make the specimen tightly contacted with the lower chamber and ensure the seal performance. Generally, evacuation time of lower chamber is set to be 60 s.

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