1、 Sample preparation and installation precautions

1. Sample size and integrity

• Size matching：
  • The sample diameter should be ≥ the inner diameter of the test chamber sealing ring (usually ≥ 50mm), ensuring that the effective testing area (such as 50 cm ²) is unobstructed;
  • Avoid burrs and curls on the edges of the sample, as this may result in poor sealing or scratches on the testing chamber.
• Defect inspection：
  • Inspect the surface of the sample for defects such as pinholes, cracks, wrinkles, etc. using an optical microscope (≥ 100x) or a transparency meter;
  • For high barrier materials such as aluminum foil composite films, special attention should be paid to the uniformity of heat sealing edges or coatings.
• thickness consistency：
  • Use a micrometer to measure the thickness of the sample, ensuring that the thickness deviation of the same batch of samples is ≤ 5%, to avoid calculation errors in transmittance due to uneven thickness.

2. Sample pretreatment

• cleaning treatment：
  • Remove oil stains, fingerprints, dust and other pollutants from the surface of the sample (can be wiped with a dust-free cloth dipped in isopropanol);
  • Avoid using chlorine containing cleaning agents to prevent corrosion of metal testing chambers.
• State adjustment：
  • Equilibrate the sample under testing temperature and humidity conditions (such as 23 ℃/50% RH) for at least 4 hours to eliminate the influence of stress on the barrier performance;
  • For water containing materials (such as hydrogel coating film), it is necessary to soak them in advance to water absorption saturation state.

3. Installation and sealing

• Sealing ring selection：
  • Select the appropriate sealing ring based on the sample material (such as silicone rubber suitable for -60 ℃~200 ℃, and fluororubber suitable for chemical corrosion resistance scenarios);
  • Regularly replace the aging sealing ring (recommended every 500 tests or 3 months) to avoid leakage and low data.
• Installation strength：
  • Use a torque wrench to evenly tighten the test chamber bolts (refer to the equipment manual for torque values, such as 1.5-2.0 N · m);
  • Avoid excessive tightening that may cause deformation of the sample or damage to the sealing ring.
• leak check：

  • After installation, conduct an air tightness test (such as filling with 0.1 MPa nitrogen gas, holding pressure for 5 minutes, and a pressure drop of ≤ 0.001 MPa to be qualified);

  • Leakage can cause oxygen to seep through gaps, leading to inflated test results.

2、 Equipment operation precautions

1. Test parameter settings

• Standard selection：
  • Select corresponding standards based on product type (such as ASTM D3985, ISO 15105-2, GB/T 19789) to avoid parameter confusion and result incomparability;
  • For example, food packaging commonly uses ASTM D3985, while drug packaging must comply with USP<671>.
• Temperature and Humidity Control：
  • The testing temperature should be consistent with the actual usage environment of the sample (such as selecting 4 ℃ for cold chain drugs and 38 ℃ for baked goods);
  • Humidity has a significant impact on hydrophilic materials such as nylon and EVOH, and requires precise control (such as 50% RH ± 2%);
  • Avoid temperature fluctuations greater than 1 ℃/h, otherwise it may cause thermal expansion and contraction of the sample, leading to seal failure.
• gas flow rate：
  • It is recommended to set the flow rate of the upper chamber carrier gas (N ₂) to 20-50 mL/min to ensure that oxygen is fully carried to the sensor;
  • The flow rate of the lower chamber mixture (O ₂/N ₂) needs to be stable (such as 100 mL/min) to avoid concentration fluctuations affecting the current signal.

2. Calibration and Verification

• Standard membrane calibration：
  • Use Mocon certified standard film (such as OTR=0.5 cm ³/(m ² · 24h · 0.1MPa)) for calibration, and it is recommended to calibrate every 3 months;
  • Before calibration, the standard membrane needs to be equilibrated under test conditions for 2 hours to eliminate the influence of temperature on transmittance.
• blank test：
  • Regularly conduct no sample testing (only installing sealing rings) to verify the background noise of the equipment (current fluctuations should be less than 0.01 pA);
  • If the background noise exceeds the standard, it is necessary to check the sensor connection or clean the testing chamber.

3. Testing process monitoring

• Real time data recording：
  • Monitor parameters such as current, temperature, humidity, etc., and draw real-time curves (such as current time curves);
  • During normal testing, the current should gradually stabilize. If there is a continuous increase or fluctuation greater than 5%, the machine should be stopped immediately to inspect the sample or equipment.
• Termination condition judgment：

  • Set termination conditions according to standards (such as stable current for 10 minutes or reaching the preset test time);

  • Avoid premature termination that leads to inaccurate data or excessive testing that wastes resources.

3、 Environmental and safety precautions

1. Laboratory environment requirements

• Temperature and Humidity Control：
  • It is recommended to maintain a laboratory temperature of 20 ℃~25 ℃ and a humidity of ≤ 60% to avoid moisture or condensation on electronic components of the equipment;
  • If the environmental humidity is too high, a dehumidifier or air conditioner should be equipped.
• Ventilation and explosion prevention：
  • When testing high concentrations of oxygen (such as>25% O ₂), it is necessary to operate in a fume hood to prevent the risk of explosion caused by oxygen accumulation;
  • The equipment must comply with ATEX explosion-proof standards (such as Ex d IIB T4), and the electrical control box should be kept away from the testing chamber.
• Electromagnetic interference isolation：
  • Avoid placing equipment near strong electromagnetic sources such as large motors and frequency converters to prevent interference with current signals;
  • Suggest using shielded cables to connect the sensor to the host.

2. Gas management safety

• Gas cylinder fixation and labeling：
  • Oxygen cylinders need to be fixed with dedicated brackets to prevent tipping over;
  • Paste warning signs such as "high-purity oxygen" and "flammable and explosive" on the surface of the gas cylinder to avoid accidental operation.
• Pressure reducing valve and pipeline inspection：
  • Regularly check the outlet pressure of the pressure reducing valve (recommended 0.2~0.5 MPa) to avoid damaging the sensor due to excessive pressure;
  • Use stainless steel or PTFE tubing to avoid rubber tube aging and leakage;
  • Check the pipeline joints for air leaks every month with soapy water.
• Gas Switching Specification：

  • When replacing gas, the inlet valve of the equipment should be closed first, and the residual gas in the pipeline should be emptied before replacing the gas cylinder;

  • Avoid mixing air (containing 21% O ₂) to prevent impure concentration of the test gas.

4、 Notes on Data Management and Maintenance

1. Data recording and traceability

• Raw data preservation：
  • Save the original test data (including current, temperature, humidity, timestamp) to avoid only recording the final results;
  • It is recommended to use the device's built-in software to automatically generate PDF reports and backup them to the cloud or external hard drive.
• Audit tracking function：
  • If the device supports FDA 21 CFR Part 11, the audit trail function must be enabled to record information such as the operator and parameter modification time;
  • Regularly check audit logs to ensure that data cannot be tampered with.

2. Equipment maintenance and upkeep

• Daily cleaning：
  • Wipe the inner wall of the testing chamber with a soft cloth every week to avoid dust accumulation that may affect the sensitivity of the sensor;
  • Clean the sealing ring with alcohol swab every month to prevent leakage caused by aging and cracking.
• Consumables replacement cycle：
  • sealing ring: Replace every 500 tests or 3 months;
  • desiccantReplace every 3 months (or based on color indicator discoloration);
  • Electrochemical sensorReplace according to the service life (usually 2-3 years) or output attenuation (such as current drop>20%).
• Fault handling：

  • If the device alarms' sensor failure ', it is necessary to immediately shut down and contact the manufacturer for repair to avoid damaging the equipment during forced testing;

  • Common fault codes (such as E-01 indicating air path blockage and E-02 indicating temperature exceeding limit) need to be recorded and analyzed for their causes.