Bubble generator and soap bubble flow meter calibration

Bubble generator calibration involves verifying the accuracy of the burette volume and, for electronic instruments, the timing system, against traceable reference standards. Although the soap bubble method is a primary measurement technique, the glass burette volume can deviate from its nominal value, and electronic timing components require verification. UKAS calibration provides a traceable certificate confirming the instrument’s actual performance and measurement uncertainty.

A sampling pump is connected to the inlet of the bubble generator. Soap solution is introduced at the base of the glass burette to form a bubble, and the time taken for the bubble to travel between graduation marks is used to calculate the flow rate. This measured flow rate is then compared to the pump’s set flow. For the calibration to be traceable, the bubble generator itself must hold a current UKAS calibration certificate establishing the accuracy of the burette volume and timing.

Although the soap bubble method is inherently primary — deriving volume from the glass burette geometry — the actual burette volume can differ from the nominal value, and electronic timing systems require verification. More importantly, regulatory and accreditation frameworks require that all measurement equipment used in sampling programmes holds current, traceable calibration certificates. A UKAS certificate for the bubble generator maintains the traceability chain for all instruments calibrated using it.

For most occupational hygiene and environmental monitoring applications, annual calibration is standard. Protocols such as MDHS14 (Health and Safety Executive) for asbestos air sampling specify that calibration equipment must be maintained and calibrated at appropriate intervals. Where bubble generators are used to support regulatory compliance sampling, annual UKAS calibration is the accepted standard.

A manual bubble generator requires the user to time the bubble passage with a stopwatch or similar, introducing human timing error. An electronic bubble generator, such as the Gilian Gilibrator, uses a photoelectric sensor system to detect the bubble and calculate flow automatically, removing timing variability. Both types require UKAS calibration, but electronic instruments typically offer better repeatability for routine calibration work.