Technical Information Sheet
Gravimetric & Volumetric Calibration Methods for Gas Flow Meters
For gravimetric systems the vessel is weighed before and after filling. Generally, the vessel must be disconnected to prevent the connection pipes interfering with the weighing and gas vented during disconnection which must be accounted for. For small systems, dynamic weighing has been employed both as a collection system and by a delivery system, where the vessel is pressurised and then discharged through the device under test and the effect of filling hoses accounted for in the weighing.
For volumetric systems the vessel must be very stable and of known volume. The pressure and temperature in the vessel is measured before and after the fill which allows the mass of gas to be calculated. Filing and emptying the vessel will create significant temperature changes due to the changes in pressure. In the most accurate systems the vessel is submerged in a water bath to maintain the wall temperature as stable as possible hence minimising temperature corrections in the vessel.