SIST EN ISO 6145-7:2019 PDF

Overview

EN ISO 6145-7:2018 - "Gas analysis - Preparation of calibration gas mixtures using dynamic methods - Part 7: Thermal mass-flow controllers" (CEN adoption of ISO 6145-7:2018) defines a continuous, dynamic method for preparing calibration gas mixtures using thermal mass‑flow controllers (TMCs). The standard covers system principles, set‑up, operating conditions, calculations and uncertainty assessment for preparing mixtures from nominally pure gases or pre‑mixed gases. It applies to non‑reacting species (gases that do not react with materials in the flow path).

Key topics and requirements

• Principle and set‑up: each component gas is routed through a calibrated TMC at controlled mass flow; TMCs typically use heaters and temperature sensors (Wheatstone bridge) - documented variants include constant‑current and constant‑temperature control.
• Flow measurement and calibration: mass flow measurement is not absolute - TMCs require independent calibration and accurate flow meters or references to achieve stated uncertainties.
• Uncertainty targets: optimum performance is specified as a relative expanded uncertainty U ≤ 2% (coverage factor k = 2) for prepared calibration mixtures.
• Dilution capability: using pre‑mixed gases enables very low mole fractions (below 10−6) in the final mixture.
• Validity limitations: only applicable for non‑reacting species; selection of materials and flow path compatibility is essential.
• Documentation and computations: the standard describes procedures for volume‑fraction calculations, sources of uncertainty, and includes informative annexes on pre‑mixed gases, practical hints and uncertainty calculation.

Applications and users

EN ISO 6145-7:2018 is intended for laboratories and industries that prepare and use calibration gas mixtures, including:

• National metrology institutes and calibration laboratories
• Environmental and emissions monitoring labs
• Process and industrial gas calibration providers
• Manufacturers of gas analyzers and gas blending systems
• Suppliers of TMC‑based gas blending equipment (commercial systems often include computerization and automated control)

Typical uses:

• Continuous on‑site generation of calibration gases for instrument calibration and quality control
• Producing large volumes of multi‑component or binary calibration mixtures with fast, continuous composition adjustment
• Generating high‑dilution standards by blending pre‑mixed gases

Related standards

• ISO 6145 series (dynamic volumetric methods)
• ISO 6145‑1 (Methods of calibration)
• ISO 6143, ISO 7504, ISO 12963, ISO 19229 - referenced for comparison methods, terminology and purity analysis

Keywords: EN ISO 6145-7:2018, thermal mass‑flow controllers, calibration gas mixtures, gas blending, dynamic methods, mass flow calibration, uncertainty, pre‑mixed gases, continuous gas preparation.