Mechanical Measurements

Flow Measurements

Gina Kline (Gas Flow and Hydrocarbon Flow)
Tel: 301/975-4813
E-mail: gina.kline@nist.gov

John D. Wright (Gas Flow and Water Flow)
Tel: 301/975-5937
E-mail: john.wright@nist.gov

Aaron Johnson (Gas Flow)
Tel: 301/975-5954
E-mail: aaron.johnson@nist.gov

Sherry Sheckels (Hydrocarbon Flow)
Tel: 301/975-5940
E-mail: sherry.sheckels@nist.gov

Do not ship instruments or standards to the mailing address listed below. Contact the technical staff for the shipping address. 

Mailing Address:
National Institute of Standards and Technology
100 Bureau Drive, Stop 8361
Gaithersburg, MD 20899-8361
Fax: 301/258-9201

Water Flow Calibration Facility

See 30063S Special Tests for Low-Gas-Flow Instrumentation

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Gas Flow Meters (18010C)

NIST provides calibration services for gas flow meters using three pressure, volume, temperature, and time (PVTt) systems with collection tanks of 34 L, 677 L, and 26 m³; and a Working Gas Flow Standard (WGFS). The three PVTt standards cover flow ranges of (1) 1 L/min to 100 L/min, (2) 10 L/min to 2000 L/min, and (3) 900 L/min to 78 000 L/min respectively. The 34 L PVTt can calibrate flow meters in any non-corrosive and non-hazardous gas that is available in pressurized cylinders, including nitrogen, argon, helium, etc. The uncertainty of the 34 L and 677 L PVTt standards is between 0.02% and 0.05%., depending on the gas and flow that is tested. The 26 m³ standard uses dry air and has a flow uncertainty of 0.13%.

The PVTt systems are best suited for calibrating critical flow venturis (CFV) or critical nozzles since pressure at the inlet of the standard varies between vacuum and 100 kPa as the collection tanks fill. The Working Gas Flow Standard (WGFS) is normally used for other flow meter types, e.g. laminar flow elements, turbine meters, and positive displacement meters.

The WGFS uses critical venturis and critical nozzles that have been calibrated in the PVTt standards as working standards or reference flow meters to calibrate customer flow meters. The uncertainty of the WGFS is 0.1% at flows less than 2000 L/min and 0.16% at flows larger than 2000 L/min. Pressure regulators provide CFV pressures up to 700 kPa. The gas source for the WGFS can be dried air from our compressor, nitrogen from a dewar (-150 L/min), or other gases from compressed gas cylinders (-100 L/min).

Fittings available include national pipe thread (NPT), Swagelok-, VCR, VCO, AN 37 degree flare, ASA 150 lb, ASA 300 lb, and ASA 600 lb and pipe diameters range from 3 mm to 203 mm (1/8" to 8").

We deliver a calibration report that includes an uncertainty analysis for the flow meter calibration factor. The uncertainty includes the uncertainty of the flow standards given above as well as uncertainties related to instrumentation associated with the meter under test and its reproducibility. A normal flow calibration includes five flow set points (e.g., 200 kPa, 300 kPa, 400 kPa, 500 kPa, and 600 kPa for a CFV, or at 10%, 25%, 50%, 75%, and 100% of the meter full scale for a laminar flow element). At each of the five flows three (or more) measurements are gathered on two different occasions to assess the flow meter reproducibility. As a result, the tabulated data for the calibration are averages of six or more individual measurements. It is helpful if the customer specifies the flow set points and the instrumentation requirements of the meter (pressure, temperature, full scales required).

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Natural Gas Flow Calibration (18015C)

NIST provides calibration services for flowmeters used in high pressure natural gas. The calibration flow range extends from 0.125  m³/s (7.5 x 10³  L/min or 1.6 x 10⁴ acfh) to 9 m³/s (2.7 x 10⁵ L/min or 5.7 x 10⁵ acfh) at a nominal pipeline pressure of 7 500 kPa (1 088 psi) and at ambient temperatures.  Corresponding mass flow calibrations extend from 6 kg/s (13 lbm/s) to 585 kg/s (1290 lbm/s). The uncertainty for flow calibrations at the ninety-five percent confidence level is 0.25% at the highest flow with increased uncertainties at lowest flow.

Flow calibrations are performed offsite at the Colorado Engineering Experimental Station Incorporated in Garner, Iowa. All calibrations are performed using turbine meter working standards that are traceable to NIST primary flow standards. The calibration process is under NIST's metrological control. The turbine meters as well as all other auxiliary measurments (e.g., temperature, pressure, frequency, gas compostiion, etc.) are routinely calibrated by NIST using suitable transfer standards. Additional details on traceability and uncertainty of the calibration service can be obtained on NIST website www.cstl.nist.gov/div836/Group_02/publications.html.

Ultrasonic flowmeters are the most common meter type that is calibrated, however, many other flowmeter types can also be calibrated (e.g., turbinemeters, critical venturi flowmeters, coriolis flowmeters, etc.). Flow calibrations are performed in pipe sizes ranging from 30.48 cm (12 inches) to 76.2 cm (30 inches). In cases where the flowmeter installed in upstream and downstream piping lengths supplied by the customer, the associated flanges should be rated to withstand a minimum pressure of 10 MPa at ambient temperatures (i.e., flange ratings must be 600 lb or higher). Additionally, for safety reasons, customers must have all flange welds x-rayed and hydrostatically tested before shipping their flowmeters for calibration.

We deliver a calibration report that includes an uncertainty analysis for the flow meter calibration factor. This uncertainty includes the uncertainty of the flow standards given above as well as uncertainties related to instrumentation associated with the meter under test and its reproducibility. A normal flow calibration includes six flow set points. For example, for an ultrasonic flowmeter these six setpoints include five flows at 10%, 25%, 40%, 70%, and 100% of the meter full scale as well as a single point at the minimum flow (i.e., typically 0.76 m/s or 2.5 ft/s depending on meter type). At each of the six flows three (or more) measurements are gathered on two different occasions to assess the flow meter reproducibility. As a result, the tabulated data for the calibration are averages of six or more individual measurements. It is helpful if the customer specifies the flow set points and the instrumentation requirements of the meter (pressure, temperature, and full scales required). After completing the six setpoints a single verification point is taken, typically at 40% to 70% of the full scale. (Note, if the flow setpoints shown above are inadequate, the customer can select to distribute the six setpoints and verification point as desired).

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Water Flow Meters (18020C)

NIST provides calibration services for water flow meters using a water flow facility. The NIST water flow facility consists of a reservoir, pumps, meter runs, and weigh tanks. The system operates as a constant flow facility and uses timed collections of water to compute the average flow through the meter being calibrated. The relative expanded uncertainty for these facilities is 0.12 %. Flows up to 38 000 L/min (10 000 gal/min) can be provided in pipes up to 40.6 cm (16 in) in diameter. Pipe connections should be ASA 150 lb steel flanges, Victaulic- couplings, or adapters thereto.

Meters can be tested if the flow range and piping connections are suitable, and if the system to be tested has precision appropriate for calibration with the NIST flow measurement uncertainty. We deliver a calibration report which includes an uncertainty for the flow meter calibration factor. The uncertainty of these flow meter calibration coefficients will also depend on the reproducibility of the meter under test and the uncertainty of any instrumentation associated with measuring the flow meter output.

A normal flow calibration includes five different flows, with five averages of the meter readings and the standard flow made at each set point, with this entire test sequence repeated on a second day to assess reproducibility. It is helpful if the customer specifies the flow set points and the instrumentation requirements of the meter (pressure, temperature, full scales required, etc.).

Hydrocarbon Liquid Flow Meters (18030C)

Two flow standards are used for the calibration services. In the low flow range, from 0.1 L/min to 5.7 L/min (0.03 gal/min to 1.5 gal/min), the facility uses a passive piston prover technique where fluid is driven by pumps while the measuring piston is pushed by the fluid over a measured length during a measured time. The facility has uncertainty of 0.01 % at 95 % confidence level. In the high flow range, from 5 L/min to 1000 L/min (1.3 gal/min to 265 gal/min), a dynamic gravimetric flow standard is used. In the dynamic gravimetric flow standard, the start and stop events, are produced when the mass of the liquid in a collection tank reaches selected tare and gross values. The gravimetric flow standard has an expanded uncertainty of 0.12 % at 95 % confidence level.

Calibrations of hydrocarbon flow meters can be performed using a surrogate liquid for JP-4 and JP-5 jet fuels. Preferred piping connections are A/N fittings, ASA 150 lb flanges, and National Pipe Threads up to 5.5 cm (2 in) in diameter.

Meters can be tested if the flow range and piping connections are suitable, and if the system to be tested has precision appropriate for calibration with the NIST flow measurement uncertainty. A normal flow calibration includes five different flows, with five averages of the meter readings and the standard flow made at each set point, with this entire test sequence repeated on a second day to assess reproducibility. It is helpful if the customer specifies the flow set points and the instrumentation requirements of the meter (pressure, temperature, full scales required, etc.). We deliver a calibration report that includes an uncertainty analysis for the flow meter calibration factor. The uncertainty of these flow meter calibration coefficients will also depend on the reproducibility of the meter under test and the uncertainty of any instrumentation associated with measuring the flow meter output.

Transfer Standards (18040C)

Transfer standards are available for in situ calibrations of flow meters or flow standards at the customer site. Details about this calibration service can be obtained from the technical contacts listed at the beginning of this section.

Special Tests Using Gas, Water, or Liquid Hydrocarbon Flows (18050S-18070S)

Special tests for liquid and gas flows are available. Examples include interlaboratory comparisons, round robin tests, and proving other fluid measurement systems. Tests to establish or maintain realistic flow measurement traceability for flow facilities can be designed and performed for specific situations. Details about this calibration service can be obtained from the technical contacts listed at the beginning of this section.

References-Flow Measurements

Hydrocarbon Liquid Flow Calibration Service , T. T. Yeh, Jesus Aguilera, and J. D. Wright, NIST SP 250-1039 (Aug. 1998).

Uncertainty in Primary Gas Flow Standards Due to Flow Work Phenomena , J. D. Wright and A. N. Johnson, FLOMEKO 2000 (Salvador, Brazil: IPT 2000).

NIST Calibration Services for Gas Flow Meters: Piston Prover and Bell Prover Gas Flow Facilities , J. D. Wright and G. E. Mattingly, NIST SP 250-49 (Aug. 1998).

The Effect of Vibration Relaxation on the Discharge Coefficient of Critical Flow Venturis , A. N. Johnson, J. D. Wright, S. Nako, C. L. Merkle, and M. R. Moldover, Flow Measurement and Instrumentation, 11 (2000), pp. 315-327.

The Long Term Calibration Stability of Critical Flow Nozzles and Laminar Flowmeter , J. D. Wright, Proc. 1998 NCSL Workshop and Symp. (Albuquerque, NM: NCSL 1998).

Validating Uncertainty Analyses for Gas Flow Standards via Intra-and Inter-laboratory Comparisons , J. D. Wright, D. B. Ward, and G. E. Mattingly, Proc. 1999 NCSL Workshop and Symp. (Charlotte, NC: NCSL 1999).

The Performance of Transit Time Flowmeters in Heated Gas Mixtures , J. D. Wright, Proc. 1998 ASME Fluids Engineering Division Summer Meeting (Washington, DC: ASME 1998). FEDSM98-5290.

Flowmeter Calibration Facility for Heated Gas Mixtures , J. D. Wright and P. I. Espina, NCSL Proc., Atlanta (1997).