New facility for gas cylinder weighing

All standards in the VSL Primary Reference Gas Standards Programme are prepared in accordance with ISO Standard 6142. This Standard  prescribes the preparation of gas mixtures by gravimetry. Vital instrumentation in this process is the balance to perform the weighings of the gas cylinder after each addition of pure gas. Recently VSL completed the development of a new fully automated facility for cylinder weighing based on a commercial comparator balance.

With a servo controlled positioner both the sample cylinder and a reference cylinder are positioned under the balance and stabilized. An accurate reading can then be taken. A series of weighings consists of 5 sample cylinder weighings and 4 reference cylinder weighings. The difference in weight is calculated before and after each addition of gas. By using a reference cylinder buoyancy effects can be eliminated. Once the sample cylinder is placed on the resting position of the set-up, the weighing cycle is automatically performed and no staff involvement is required. The new set-up is very robust and easy to operate. The final uncertainty is very close to the balance specifications.

The new facility is in full operation for some months, allowing VSL to produce even better gas standards.