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TOOLS & INSTRUMENTS

# Gas Flow Standards

NIST uses pressure, volume, temperature, and time (*PVTt*) standards to calibrate gas flow meters. *PVTt*flow standards generate selected, steady gas flows through a meter under test and measure the time *t* it takes to fill a collection volume *V* starting from an initial, evacuated state and ending at a final state with a pressure on the order of 1 bar. The initial and final densities of the collected gas are calculated from the gas’ measured pressure *P* and temperature *T*.  These densities, together with the known collection volumes, determine the mass of the gas collected during the timed interval.  NIST has three collection tanks: 34 L, 677 L, and 26 m3. The 34 L and 677 L tanks are submerged in a water bath that has 1 mK stability and uniformity.  The uncertainty of the temperature of the collected gas is low enough to achieve a flow uncertainty of less than 0.025 % (with a 95 % confidence level) for flows up to 2000 L/min. NIST calibrates meters for larger flows with low uncertainties by calibrating several meters, one at a time, and then using the calibrated meters in parallel.  For example, NIST’s natural gas calibration service calibrates gas flow meters up to 4 x 107 L/min.  (This step-up of flow by a factor of 20,000 in flow is conducted at CEESI’s site that handles large flows of natural gas in Garner, Iowa.)  The *PVTt* standards are also used to make dynamic (or rate of rise) measurements of gas flows as low as 0.1 cm3/min.  The volumes of the 34 L and 677 L tanks are known within 0.01 %; they have been used to measure the volume of other pressure vessels *via* the gas-expansion method. The *PVTt* standards are research tools used to study, for example, gas species effects on laminar flow meters and thermal boundary layers in critical flow venturis.

Flow metrology and rheology

## Organizations

                          - NIST Headquarters
                            - Laboratory Programs
                              - Physical Measurement Laboratory
                                - Sensor Science Division
                                  - Fluid Metrology Group

## Details

## Related Publications

Lower Uncertainty (0.015 % TO 0.025 %) OF NIST S Standard For Gas Flows From 0.01 TO 2000 Standard Liters/Minute

Gas Flowmeter Calibrations with the 34 L and 677 L PVTt Standards

Gas Flowmeter Calibrations With the 26 m3 PVTt Standard

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