Two Primary Standards for Low Flows of Gases

Area of Science:

• Metrology
• Fluid Dynamics
• Physical Chemistry

Background:

• Accurate gas flow measurement is crucial for scientific research and industrial processes.
• Existing primary standards for low gas flow rates have limitations in precision and range.

Purpose of the Study:

• To establish two new primary standards for gas flow measurement.
• To cover the flow range from 0.1 to 1000 μmol/s with high accuracy.
• To validate the new standards against each other and an existing primary standard.

Main Methods:

• Volumetric primary standard: Utilizes measurements of pressure, volume, temperature, and time with a constant pressure bellows system.
• Gravimetric primary standard: Compares the integrated throughput of a laminar flow meter to the weight decrease of a gas cylinder.
• Comparison with NIST primary standard: Cross-validation using a pressure-based constant volume method.

Main Results:

• Both developed primary standards achieve a standard uncertainty of 0.019%.
• The two new standards demonstrate agreement within their combined uncertainties.
• The results align with the established primary standard at NIST.

Conclusions:

• The developed volumetric and gravimetric techniques provide reliable primary standards for gas flow.
• These standards enhance the accuracy and traceability of gas flow measurements in the specified range.
• The agreement between independent primary standards reinforces confidence in gas flow metrology.