Flow Measurements

Mechanical Measurements

Flow Measurements

Rate our Services

Technical Contacts:

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

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

Iosif Shinder (Air Speed)
Tel: 301-975-5943
E-mail: iosif.shinder@nist.gov

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

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

Please contact the technical staff before shipping instruments or standards to the address listed below.

Mailing Address:
National Institute of Standards and Technology
100 Bureau Drive, Stop 8361

Gaithersburg , MD 20899-8361
Fax: 301-258-9201

Service ID Number	Description of Services	Fee ($)
18010C	Gas Flow Meters	4889
18015C	Natural Gas Flow Calibration	At Cost
18020C	Liquid Flow Meters	4697
18050S	Gas Flow Special Tests	At Cost
18060S	Liquid Flow Special Tests	At Cost

Fees are subject to change without notice.

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

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).

Natural Gas Flow Calibration (18015C)

NIST provides calibration services for flow meters 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 volumetric flow calibrations at the ninety-five percent confidence level is 0.22 % at the highest flow with increased uncertainties at lowest flow.

Flow calibrations are performed offsite at the Colorado Engineering Experimental Station Incorporated in Garner (CEESI), 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, meaning the turbine meters as well as all other auxiliary measurements (e.g., temperature, pressure, frequency, gas composition) are routinely calibrated by NIST using suitable transfer standards. To read more about the Natural Gas Flow Calibration Service, see NIST Special Publication 1081.

Ultrasonic flow meters are the most common meter type that is calibrated; however, many other flow meter types can also be calibrated (e.g., turbine meters, critical flow venturis, coriolis flow meters). Flow calibrations are performed in pipe sizes ranging from 30.48 cm (12 inches) to 76.2 cm (30 inches). In cases where the flow meter is 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 flow meters 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 five flow set points. For example, for an ultrasonic flow meter these five set points 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 five flows five (or more) measurements are gathered to assess the flow meter repeatability. As a result, the tabulated data for the calibration are averages of five 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 five set points three verification points are taken, typically between 20 % and 80 % of the full scale. Verification points compare the meter reported values after calibration coefficients have been installed to the flow measured by the turbine meter working standards. (Note, if the flow set points shown above are inadequate, the customer can select to distribute the five set points and verification point as desired).

Calibration fees for this and other services can be found in the Calibration Fee Schedule.

Turnaround time for a single flow meter is approximately 4 weeks:

Allow 2 weeks for shipping;
1 week for set-up and data collection; and
1 week for report writing and review

This calibration service must be scheduled in advance due to testing schedules at CEESI's Iowa Facility.

To have your flow meters calibrated:

Contact Gina Kline to schedule your calibration date;
Details on ordering instructions, purchase orders, shipping, and Service ID Numbers, can be found at NIST's Calibration Services.

Liquid Flow Meters (18020C)

NIST provides calibration services for liquid flow meters. There are three primary calibration standards for liquid flow, two are volumetric based and one is gravimetric based. The volumetric based primary standards use a 5% propylene glycol and water mixture as the working fluid to match the properties of jet fuel and are: 1) The 0.1 L/s Liquid Flow Standard (formally called the 2 L Hydrocarbon Liquid Flow Standard) and 2) The 2.5 L/s Liquid Flow Standard (formally called 20 L Hydrocarbon Liquid Flow Standard). The gravimetric based primary standard uses water as its working fluid and is called the 65 L/s Liquid Flow Standard (formally known as the Water Works).

The 65 L/s Liquid Flow Standard consists of a reservoir, pumps, meter runs, and a 3700 L weigh tank. 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 expanded uncertainty for this facility is 0.05 %, or less (k = 2 or approximately 95 % confidence level) for flows from 0.67 L/s to 65 L/s.
Pipe connections should be ASA 150 lb steel flanges, VictaulicTM couplings, or adapters thereto.

The 0.1 L/s and the 2.5 L/s Liquid Flow Standards are piston provers. Flow determination is based on the piston displacing a known volume of liquid in a measured amount of time. The expanded uncertainty for the 0.1 L/s standard is 0.03 % for flows from 0.003 L/s to 0.1 L/s and 0.06 % for the 2.5 L/s standard for flows from 0.02 L/s to 2.5 L/s (k = 2 or approximately 95 % confidence level).
Pipe connections should be A/N fittings and National Pipe Threads up to 2.54 cm (1 in) in diameter. Because meters calibrated on these standards are typically used to meter hydrocarbon liquids and may contain parts that are not compatible with water, meters are cleaned and dried following calibration on these provers. Meters are rinsed with ethanol and then dried by capping off one end of the meter and applying vacuum to the other for approximately one hour. Meters may be treated with a lubricant following drying at the customer's request.

Meters can be calibrated 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 occasion 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 (Note that the uncertainties in meter factor may be larger than the uncertainties of the primary standard due to extra reproducibility of the meter under test and the uncertainty of instrumentation associated with the meter under test). NIST reported uncertainties include the uncertainty of the primary flow standard as well as uncertainty attributed to reproducibility of the meter under test and the uncertainty of any customer provided instrumentation associated with measuring the flow meter output.

Calibration fees for this and other services can be found in the Calibration Fee Schedule. To read more about our facilities, see the NIST Special Publication 250-1039 and NIST Special Publication 250-73.

Turnaround time for a single flow meter is approximately 4 weeks:

1. Allow 2 weeks for shipping;
2. 1 week for set-up and data collection; and
3. 1 week for report writing and review.

To have your flow meter calibrated on one of the 0.1 L/s standard or the 2.5 L/s standard contact Sherry Sheckels to schedule your calibration dates. To have your flow meter calibrated on the 65 L/s primary standard contact Joey Boyd to schedule your calibration dates. Details on ordering instructions, purchase orders, shipping, and Service ID Numbers, can be found at NIST's Calibration Services.

Special Tests for Gas, Natural Gas, and Liquid Flows (18050S-18060S)

Special tests for gas, natural gas, and liquid flows are available. Example applications include interlaboratory comparisons, round-robin tests, and the validation of 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).

Program questions: Calibrations

Phone: 301-975-2200, Fax: 301-975-2950

NIST, 100 Bureau Drive , Stop 8363, Gaithersburg , MD 20899-8363

Mechanical Measurements