EN ISO 6145-6:2017 PDF

Overview - EN ISO 6145-6:2017 (Critical flow orifices)

EN ISO 6145-6:2017 specifies a dynamic method for preparing calibration gas mixtures using critical flow orifices. The standard covers preparation of multi‑component and binary mixtures from pure gases or pre‑mixtures for gas analysis, principally for non‑reactive gases that do not react with materials in the gas circuit. The method supports high dilution control (a dilution ratio up to 1 × 10^4), is most applicable at atmospheric pressure (but can be used above atmospheric pressure when upstream pressure is at least twice downstream pressure), and covers flow rates from 1 ml/min to 10 l/min.

Key topics and technical requirements

• Principle of operation: dynamic volumetric preparation using critical flow orifices to generate reproducible mass and volume flow rates.
• Flow calculations: mass flow rate, molar flow, and volume flow computations under ideal and real conditions (including isentropic coefficient, viscosity, throat Reynolds number).
• Uncertainty evaluation: identification and estimation of uncertainty sources for flow rates and resulting amount‑of‑substance/volume fractions.
• Calibration and verification: procedures for flow calibration (including examples using pure nitrogen) and system verification with gas mixtures.
• Design & operation: recommendations on orifice selection (multiple orifices for multi‑component mixtures), system materials (for non‑reactive gas compatibility), and operating conditions (stagnation pressure/temperature considerations).
• Annexes and examples: informative annexes provide worked examples for calculations, toroidal orifices, and real‑condition corrections.

Applications and practical value

• Preparation of precise calibration gas mixtures for:
  • Analytical instrument calibration (GC, IR, electrochemical sensors)
  • Environmental and emissions monitoring QA/QC
  • Industrial process control and safety sensor checks
  • Metrology laboratories and proficiency testing
• Enables reliable, repeatable dilution from trace to percent levels across a wide flow range, simplifying production of both binary and multi‑component standards.

Who should use this standard

• Calibration and metrology laboratories
• Gas cylinder and calibration gas suppliers
• Environmental monitoring and emission testing labs
• Instrument manufacturers (gas analyzers, detectors)
• Process industries requiring on‑site calibration gases

Related standards

• ISO 9300 (critical flow Venturi/flow measurement)
• ISO 6143, ISO 12963 (comparison/calibration methods)
• ISO 16664 (handling of calibration gases)
• ISO 7504 (vocabulary)

Using EN ISO 6145-6:2017 helps organizations produce traceable, reproducible calibration gases with quantified uncertainty using critical flow orifice systems - an essential capability for accurate gas analysis and instrument calibration.