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Flow/Leak Standards & Calibrations

Summary:

Leak artifacts are calibrated in the range 1 x 10-6 to 1 x 10-13 mol/s (2 x 10-2 to 2 x 10-9 std. cm3/s at 0 °C). The calibration can be performed directly against the NIST primary leak standard or can be calibrated on a comparison system with respect to NIST-calibrated reference leaks.

High precision low-gas-flow instruments are calibrated in the range of 10-8 to 10-3 mol/s with inert gases and other gases by special arrangement. The calibration is performed by direct comparison to a NIST primary flow standard and can be accomplished with down stream pressures ranging from 10 Pa (vacuum) to 300 kPa. 

Note: Flow rates are quoted at standard conditions for leak measurements of 101 325 Pa and 0 °C. When referenced to the specific temperature, std. cm3/s can be converted to mol/s by multiplying by 4.45 x 10-5.

 

Description:

Vacuum Leak Primary Standard
This primary standard measures helium flow rates from permeation leak artifacts in the range from 10-13 to 10-6 mol/s. The standard has three major components: a vacuum chamber with a flow orifice and a large turbomolecular pump, the constant pressure vacuum flow meter, and a thermally controlled manifold on which the uncalibrated leak artifact is mounted. The measurement procedure has two steps. First, helium from the uncalibrated leak artifact flows into the vacuum chamber, and the resulting partial pressure of helium is measured by a quadrupole mass spectrometer. Next, the flow from the leak artifact is stopped and replaced by a flow from the vacuum flow meter. The second flow is adjusted to produce a partial pressure helium signal that is close to the signal that was produced by the unknown leak artifact. The known flow rate from the vacuum flow meter and the helium signal ratio determine the flow rate of helium from the leak artifact.

Vacuum Leak Comparator
Helium leak artifacts in the range from 10-13 to 10-9 mol/s may be calibrated with respect to NIST-calibrated reference leaks. In this system a mass spectrometer is used to compare the unknown helium leak artifact with a NIST reference leak artifact. This unique calibration service routinely measures leak rate versus temperature over the range of 0-50 °C. This is important because the leak rate of a helium permeation leak artifact may vary by as much as 4% per °C.

Low Gas Flow Standard
This primary standard uses measurements of pressure, volume, temperature, and time to source or sink a known molar flow rate. It operates at constant pressure to eliminate problems due to adiabatic heating or cooling that can appear in a constant-volume (pressure-rate-of-rise) technique. It is similar to the bellows flow meter used in the Group's vacuum lab in that it inserts a piston into an oil-filled chamber which in turns squeezes gas held in a stainless steel bellows. However, the piston diameter is larger (10 cm), and its drive train can handle pressures up to 900 kPa. The flow meter's standard uncertainty of 0.019% has been verified by comparisons with two independent flow meters that have comparable uncertainty but operate on different principles.

Lead Organizational Unit:

pml

Staff:

Low gas Flow - Robert Berg
Leaks - Dana Defibaugh

Contact
Leak Calibrations (Service ID: 30060S-30062C)
Dana R. Defibaugh
Tel: 301-975-2471
E-mail: dana.defibaugh@nist.gov
Low Gas Flow Calibrations (Service ID: 30063S)
Robert F. Berg
Tel: 301-975-2466

E-mail: robert.berg@nist.gov  

Additional Links:

Leak Calibration Information

Low Gas Flow Calibration Information

Calibration Costs