ISO 6145-5:2009

Overview

ISO 6145-5:2009 - "Gas analysis - Preparation of calibration gas mixtures using dynamic volumetric methods - Part 5: Capillary calibration devices" specifies methods for continuous production of calibration gas mixtures using capillary calibration devices (single capillaries and multi‑capillary gas dividers). The standard is part of the ISO 6145 series covering dynamic volumetric gas‑mixing techniques and defines performance, calibration and verification practices, uncertainty assessment and example calculations (Annex A) plus a derivation of combined uncertainty (Annex B).

Key topics and technical requirements

• Purpose: Continuous preparation of calibration gas mixtures from pure gases or mixtures using capillaries and gas dividers.
• Concentration ranges:
  • Single capillary: minor component volume fractions from about 10^‑8 to 0.5.
  • Gas dividers: dilutions from 0.0005 to 0.9 of the primary concentration.
• Performance:
  • Relative expanded uncertainty: < ±2% (k = 2) (technique dependent).
  • Repeatability of gas dividers: better than 0.5%.
• Apparatus and controls:
  • Two‑stage pressure regulators, fine adjustment valves, differential manometer, gas filters, mixing manifold; optional thermostatic control of capillaries.
  • Thermostatic control (e.g., water jacket ±1 °C) recommended to limit viscosity/temperature effects on mixture accuracy.
• Flow determination and calibration:
  • Flow through a capillary is governed by capillary geometry, pressure drop and gas viscosity; an individual calibration factor K is used to relate pressure differential to volumetric flow.
  • Each capillary (or set of capillaries in a gas divider) must be calibrated and verified; for identical capillaries, overall flow divided by number of capillaries is used.
• Uncertainty and traceability:
  • Sources of uncertainty (temperature, viscosity, pressure, capillary geometry) are addressed and procedures for verification against national/international gas standards are specified.

Applications and users

• Practical uses:
  • Production of trace and span calibration gases for gas analysers, industrial gas mixing panels, environmental monitoring, process control and research.
  • Generating defined atmospheres for instrument calibration or performance testing.
• Typical users:
  • Metrology and calibration laboratories, instrument manufacturers, industrial gas suppliers, environmental and emissions testing labs, and quality/technical teams responsible for gas calibration systems.

Related standards

• ISO 6145 series (other parts cover pumps, syringes, critical orifices, mass‑flow controllers, diffusion, saturation, permeation, electrochemical generation).
• Normative references: ISO 6143 (comparison methods) and ISO 6145‑1 (methods of calibration).

Keywords: ISO 6145-5, capillary calibration devices, gas dividers, calibration gas mixtures, gas analysis, dynamic volumetric methods, uncertainty, traceability, gas mixing panels.