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Gas Flow Calibrations
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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
tank fills. 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).
To read more about
the principles
of
operation and uncertainties of our gas flow standards and see sample
calibration reports see our Technical
Notes and Publications.
A typical calibration costs $4,673. 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 (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).
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.
However, please contact Gina Kline to schedule the calibration of your instrument(s).
To have your flow meters calibrated:
- Contact Gina Kline to schedule your calibration dates;
- Fax or mail a purchase order to Gina Kline following purchase order guidelines and choosing a Service ID Number ,
- Ship your flow meters to Gina Kline following shipping procedures outlined in the NIST Calibrations User's Guide SP 250.
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Gina Kline |
John
D. Wright |
Aaron
Johnson |
