The water vapor permeability tester is a key instrument used for accurately detecting the water vapor permeability performance of materials, widely used in industries such as packaging, textiles, and construction. The following provides a detailed description of its usage from the aspects of pre testing preparation, testing process operation, post testing processing, and daily maintenance to ensure the accuracy and reliability of the test results.

1、 Preparation before testing

（1） Environmental regulation

1. Temperature and humidity control: Place the tester in a stable experimental environment, with an ideal room temperature of 23 ± 2 ℃ and a relative humidity of 50% ± 5%. Excessive or insufficient temperature and humidity may affect material properties and water vapor transmission status, interfering with test results. If the environmental conditions are unstable, a constant temperature and humidity chamber can be equipped to place the instrument and sample together to maintain constant environmental parameters.

2. Avoid light and shock: Protect the instrument from direct sunlight and vibration. Strong light exposure may cause aging of instrument components, temperature rise, and affect sensor accuracy; Vibration can damage the internal precision structure and cause measurement errors. Choose a stable and light shielded experimental platform to place the instrument and ensure its smooth operation.

（2） Sample preparation

1. Sampling standard: According to the testing standards, uniformly sample from the material to be tested. For flat materials such as films and coatings, the sample shape is usually circular, with a diameter of 70-90mm depending on the requirements of the instrument testing chamber. For three-dimensional products such as containers and packaging bags, it is necessary to ensure that the sampling site is representative, avoid special areas such as sealing and splicing, and cut them into appropriate sizes to fit the testing device.

2. Pre treatment: Clean the sample to remove surface dust, oil stains, and other impurities to avoid blocking the ventilation channel and affecting the passage of water vapor. It can be lightly swept with a soft bristled brush, wiped with a dust-free cloth, or cleaned with a mild solvent. After cleaning, it should be dried in a dryer to a constant weight to prevent residual moisture from interfering with the test.

（3） Instrument calibration

1. Sensor calibration: After turning on the instrument, follow the operation manual to enter the calibration program. Use standard calibration gases or standard membranes with known water vapor permeability to calibrate the sensors of the instrument. During the calibration process, ensure that the sensor is in good contact with the calibration source, and wait for the instrument to display that the calibration is complete and the error is within the allowable range before proceeding with subsequent testing.

2. Parameter setting: Set test parameters on the instrument operation interface based on the characteristics of the sample and testing requirements. It mainly includes testing modes (such as weight gain method, weight loss method, infrared method, etc., different methods are applicable to different materials and scenarios), testing temperature (usually similar to the ambient temperature or simulating actual usage conditions), testing time (determined based on the material's moisture permeability, generally ranging from several hours to tens of hours), etc. Accurately setting parameters is a prerequisite for obtaining reliable test results.

2、 Testing process operation

（1） Sample installation

1. Sample installation: Carefully place the pre treated sample in the designated position of the instrument testing chamber, ensuring that the sample is flat, wrinkle free, and well sealed with the chamber. For samples fixed with fixtures, adjust the fixture pressure appropriately. If it is too tight, it may damage the sample, and if it is too loose, it may cause air leakage, affecting the accuracy of the test.

2. Connecting pipelines: If the instrument involves gas circulation pipelines, check whether the pipeline connections are firm and undamaged. Connect the air inlet and outlet to the corresponding air source and detection device to ensure smooth air flow, avoid bends and blockages, and prevent abnormal fluctuations in air pressure.

（2） Start testing

1. Observe the initial state: After starting the testing program, closely monitor the data changes during the initial stage of the instrument. At the beginning of the test, observe whether the sensor reading stabilizes and returns to zero. If there is any abnormal fluctuation, pause the test in a timely manner, check the sample installation, pipeline connection, and instrument status. After troubleshooting, restart.

2. Real time monitoring: During the testing process, continuously monitor the operating status and data curve of the instrument. Pay attention to whether environmental parameters such as temperature, humidity, and air pressure are stable, and whether data point collection is normal. If data mutation, excessive drift or instrument alarm is found, immediately stop testing, analyze the cause, such as sample damage, pipeline leakage, sensor failure, etc., and take corresponding measures to solve it.

（3） Data recording

1. Automatic collection: Using the instrument's built-in data collection system, real-time recording of water vapor transmission rate data, time, environmental parameters, and other information during the testing process. Setting a reasonable data collection frequency can capture key data changes while avoiding storage and analysis burdens caused by excessive data volume. Generally, data is collected once per second or every minute, which can be adjusted according to the testing duration and accuracy requirements.

2. Manual recording: In addition to automatic instrument collection, experimental personnel also need to manually record some key operation nodes, sample status changes, and other information, such as sample loading time, gas source replacement time, and the time and phenomenon of sample abnormalities. These supplementary information will help with comprehensive analysis and traceability of the data in the future.

3、 Post test processing

（1） Data organization

1. Outlier elimination: After the test is completed, the collected data is preliminarily screened to eliminate outliers that deviate significantly from the normal range. Outliers may be caused by instrument malfunctions, sudden sample damage, external interference, and other factors, and can be identified through comparing data curve trends, repeated testing verification, and other methods.

2. Data analysis: Use statistical methods to analyze valid data, calculate parameters such as the average, standard deviation, and coefficient of variation of water vapor permeability, and evaluate the stability and consistency of the material's moisture permeability performance. Draw the curve of transmittance over time, observe its linear or nonlinear characteristics, and provide a basis for material performance research and quality control.

（2） Sample processing

1. Proper storage: After the completion of testing, if samples need to be retained for review or other analysis, they should be properly stored. Remove the sample from the testing chamber, place it in a dry and sealed container, label the sample information, testing date, etc., and store it in the designated sample cabinet. For damaged or contaminated samples, dispose of them according to laboratory waste disposal regulations.

2. Cleaning and maintenance: Timely clean the residual sample debris, water vapor condensation, etc. on the testing chamber, fixtures, pipelines, and other components. Use specialized cleaning tools and reagents to avoid scratching the surface of the instrument or corroding metal parts. Regularly conduct comprehensive cleaning and maintenance of the instrument to ensure its performance is always in the best condition.

4、 Key points of daily maintenance

（1） Hardware maintenance

1. Regular inspection: Check the appearance of the instrument every week for scratches, looseness, rust, and other conditions; Every month, check whether the internal wiring and connectors are secure, and whether key components such as sensors and displays are working properly. Discover problems and promptly repair or replace them to ensure the safety and stability of the instrument.

2. Lubrication and maintenance: Regularly lubricate the mechanical transmission components of the instrument, such as the shaft and screw, to prevent wear and jamming. Select appropriate lubricating grease and apply it according to the prescribed cycle and amount to avoid excessive adsorption of dust or affecting component performance.

（2） Software maintenance

1. System update: Pay attention to software update information released by instrument manufacturers, and download and install the latest versions of operating systems and applications in a timely manner. Software updates can fix vulnerabilities, optimize functionality, enhance compatibility, and ensure stable communication and efficient operation between instruments and computer systems.

2. Data backup: Regularly backup the test data stored in the instrument, which can be exported to external storage devices such as portable hard drives, USB drives, etc., or uploaded to the laboratory data management platform. At the same time, clean up expired or useless data in the instrument memory, free up storage space, and prevent data loss or confusion.

（3） Calibration and verification

1. Periodic calibration: Calibrate and calibrate measuring instruments such as sensors, pressure gauges, and flow meters according to the prescribed cycles in the instrument manual. Use high-precision standard instruments to ensure that the measurement accuracy of the instrument always meets the requirements. Calibration records should be kept in detail for traceability and verification.

2. Periodic verification: Periodic verification is conducted between two formal calibrations. Select some standard samples or samples with known performance for testing, compare the difference between the test results and the calibration values, and determine whether the instrument is in normal working condition. If the difference exceeds the allowable range, promptly identify the cause and recalibrate.