NIST Develops New Gas Flow Standard

NIST Publications

Published March 17th, 2026

Detected February 27th, 2026

Summary

The National Institute of Standards and Technology (NIST) has developed a new Semiconductor Low Flow Standard (SLowFlowS) capable of measuring gas flows as low as 0.01 standard cm³/min. This development aims to improve accuracy in determining small volumes for ultra-low flowrate measurements.

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What changed

NIST has announced the development of the Semiconductor Low Flow Standard (SLowFlowS), a new gas flow standard designed to measure flows as low as 0.01 standard cm³/min. This standard utilizes two independent rate-of-rise (RoR) systems with collection tanks of 2.5 liters and 0.3 liters, respectively. The development addresses the challenge of accurately determining small volumes essential for ultra-low flowrate measurements and includes methods for independently determining tank volumes and calibrating flow elements.

This publication is primarily informational, detailing a new measurement standard developed by NIST. While it does not impose new regulatory requirements or compliance deadlines on regulated entities, manufacturers in sectors requiring precise gas flow measurement, such as semiconductor manufacturing, may find this standard useful for improving their own metrology and calibration processes. The document is a notice of a published paper detailing the standard's development and performance.

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PUBLICATIONS

Accurate Volume Determination for Low Gas Flow Standards

Published

March 17, 2026

Author(s)

Jodie Pope, Christopher Crowley, Max Low, John Wright, Aaron Johnson

Abstract

The National Institute of Standards and Technology (NIST) has developed the Semiconductor Low Flow Standard (SLowFlowS), a new rate-of-rise (RoR) gas flow standard capable of measuring flows as low as 0.01 standard cm³/min. SLowFlowS incorporates two independent RoR standards, based on collection tanks of nominal volumes 2.5 liters and 0.3 liters, respectively. These standards have associated relative expanded uncertainties of 0.06 % and 0.12 % in flow, with the higher uncertainty attributed to the smaller volume. Accurately determining small volumes is challenging but essential for efficiently measuring gas flows at ultra-low flowrates. To independently determine the tank volumes, we employed a gas expansion technique using a reference volume determined gravimetrically with low uncertainty. Recognizing the limitations in characterizing very small volumes, we also compared the performance of both RoR standards by calibrating the same laminar flow elements (LFEs) across a wide range of flow rates and gas species. These comparisons revealed a consistent and repeatable calibration offset between the two standards. This persistent offset, confirmed across many LFEs, provides a basis for relating the smaller standard to the larger, more accurate one, allowing the lower uncertainty of the larger volume to be effectively transferred to the smaller standard through statistical correlation. By doing this, the relative expanded uncertainty in flow using the smaller collection tank is lowered from 0.12 % to 0.07 %. Proceedings Title Proceedings of FLOMEKO 2026 20th International Flow Measurement Conference Conference Dates May 17-20, 2026 Conference Location Nara, JP Conference Title FLOMEKO 2026, The 20th International Flow Measurement Conference Pub Type Conferences

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Keywords

gas flow, standard, volume determination Standards and Metrology

Citation

Pope, J.
, Crowley, C.
, Low, M.
, Wright, J.
and Johnson, A.

(2026),
Accurate Volume Determination for Low Gas Flow Standards, Proceedings of FLOMEKO 2026 20th International Flow Measurement Conference, Nara, JP, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=961628       
  (Accessed February 27, 2026)