Water Vapor Transmission Rate Tester – Electrolytic Method

Both are sensor methods with high precision. The electrolytic method is absolute coulometric with a lower detection limit and better stability for long, low-transmission runs; the infrared method is faster with no sensor equilibration wait, suiting high sample volumes. Send us representative samples and we will run a comparison and advise.

Because the sensor electrolyses all the vapour that permeates the specimen, and the charge produced stands in a strict stoichiometric relationship to the amount of water — it measures an absolute quantity rather than a reading against a calibration curve. The result is a stable relative error: film range 0.001–20 g/m²·24h (a 0.001–25 variant also exists), resolution 0.001 g/m²·24h, upgradeable to 0.0001. For low-transmission materials that must be compared over the long term, or whose numbers go into a regulatory file, this independence from a calibration curve is worth a great deal.

They share a lot: both are sensor methods, both use 99.999% high-purity nitrogen as carrier gas, both operate at 15–45 °C and cover 0% RH as well as 35%–90% RH. The difference is in range structure and where each is stronger. The electrolytic method covers 0.001–20 g/m²·24h for films with 0.001 resolution (upgradeable to 0.0001) — a finer scale in the very-low-transmission region. The infrared method covers 0.005–100 g/m²·24h for films and, in container mode, 0.00005–0.5 g/pkg·24h at 0.00001 resolution — a wider span, and notably strong on finished containers. Rule of thumb: for fine comparisons confined to very low transmission, take the electrolytic method or the high-resolution option; to cover both films and finished containers, or to span high to medium barrier, take the infrared method. If you have both, cross-checking the same specimen will strengthen comparability further.

Choose by range and purpose. The gravimetric cup method is closest to the pharmacopoeia and ASTM E96 classic: a wide range, finished containers can be measured directly, but each run is long — best for compliance comparison and referee testing. The electrolytic method is an absolute coulometric method suited to low-transmission films and containers. The infrared (TDLAS) method responds fast and suits trace water vapour in high-barrier materials and high-throughput work. Pick the cup method when compliance leads, electrolytic or infrared when line efficiency leads.

The differential-pressure method creates a pressure difference across the specimen and tracks the pressure rise on the low-pressure side; one instrument measures oxygen, carbon dioxide, nitrogen and other non-toxic gases, making it the general-purpose choice. The equal-pressure method keeps both sides at the same pressure and uses a coulometric sensor for oxygen only, giving higher sensitivity for the extremely low OTR of high-barrier materials. Two rules: choose differential pressure when you need several gases, coulometric when you measure oxygen only and need the lowest detection limit.

Because the transmitted amount is extremely small, you must wait until permeation reaches steady state and the accumulated signal exceeds the instrument resolution; temperature and humidity equilibration and the system background (residual oxygen or water vapour) also take time. Practical ways to shorten it: raise the test temperature and note it in the report, reduce background and leaks, use a more sensitive sensor, and add parallel test chambers. No speed-up should compromise the steady-state criterion.

The effect is significant: conditions must match the method standard and be stated in the report. Higher temperature raises transmission; for hydrophilic materials, a change in relative humidity markedly changes both water vapour and oxygen transmission. This instrument controls 15–45 °C to ±0.3 °C and covers 35%–90% RH (some models also offer 0% RH). Before comparing data between laboratories, check that both used the same temperature and humidity.

Yes. Standard models ship as-is, while chamber count, specimen size, fixtures, temperature range and software modules (including the GMP Computerized System module) can be tailored to your SOP and URS. IQ/OQ/PQ validation documentation packages are available.

Standard models usually ship in 4–8 weeks; customised builds depend on the agreed scope. Instruments are packed in export wooden cases and can move by sea, air or rail. We supply proforma invoice, packing list and certificate of origin (CO / Form E), and work under EXW, FOB, CIF or DAP terms.

We provide remote installation guidance, bilingual (Chinese/English) manuals and video training; on-site commissioning by our engineers is available. Users can self-calibrate with standard weights, reference films or calibrated leak standards, and third-party calibration certificates can be supplied.

The instrument carries a 12-month warranty from acceptance plus lifetime maintenance support. Consumables (molecular sieve, desiccant, sealing grease, printer paper) are kept in long-term stock, and key components are international brands available worldwide. We respond to technical enquiries within 24 hours.

Yes. Every instrument lists its applicable standards on the specification page (ASTM, ISO, GB, YBB, Chinese Pharmacopoeia, USP, EP, JIS, DIN, TAPPI and more). The software outputs raw records and reports suitable for audit trails, with an optional GMP / FDA 21 CFR Part 11 compliance module.

The software ships with Chinese and English interfaces; other languages can be added on request. Data export is available over RS232, USB, Ethernet or Wi-Fi, and reports can be exported to Excel, PDF or structured files for LIMS integration.