Constant pressure primary flow standard for gas flows from 0.01 cm3/min to 100 cm3/min (0.007–74 μmol/s)

• Primary standard for gas flows in the range from 0.01 to 100 cm3/min.
• It can act as a flow source or a flow meter at pressures from 10 kPa to 300 kPa.
• Its standard uncertainty at 1 cm3/min is 0.03%.
• Innovations improve convenience and lower cost without sacrificing accuracy.

We describe a flow standard for gas flows in the range from 0.01 sccm to 100 sccm with a relative standard uncertainty (68% confidence) of 0.03% at 1 sccm (1 sccm≡1 cm3/min of an ideal gas at 101325 Pa and 0 °C ≈ 0.74358 μmol/s). The flow standard calibrates a secondary meter by withdrawing a piston from a cylinder held at constant pressure P while gas flows from the secondary meter into the cylinder. The flow standard can operate anywhere in the range 10 kPa