ISO 6145-2:2014

Overview

ISO 6145-2:2014 - Gas analysis: Preparation of calibration gas mixtures using dynamic methods - Part 2: Piston pumps specifies a dynamic, volumetric method for preparing calibration gas mixtures using piston (gas‑mixing) pumps. The standard defines how to obtain defined mixture compositions (expressed in volume fractions) from controlled piston displacements, how to calibrate piston pumps by dimensional measurements, and how to evaluate associated uncertainties. It applies to gaseous or totally vaporized components (including some corrosive gases) provided no chemical reactions occur between components or with wetted surfaces.

Key topics and technical requirements

• Principle: mixtures are formed by continuously forwarding discrete gas portions from two or more piston pumps, merging and homogenizing them. Volume contribution is determined by stroke volume and stroke count.
• Stroke volume calculation: Vgeo = π d^2 h / 4 (diameter d, piston stroke h).
• Pump configuration: gas‑mixing pumps contain at least two piston pumps driven by a common motor with defined reduction gear ratios and switch gears; stroke number N and gear ratio L determine delivered volumes.
• Composition calculation: Clause 7 provides two calculation methods (Method A and Method B) for volume fractions; Annex A gives equations to express compositions in amount‑of‑substance fractions.
• Uncertainty: with appropriate QA/QC, relative expanded uncertainty of 0.5 % (k = 2) in volume fraction is achievable; Annexes B–D give uncertainty evaluation and numerical examples.
• Dilution performance: discrete dilution ratios up to 1:10 000; lower fractions down to 1 × 10−8 achievable via multi‑stage dilution or use of parent gas mixtures.
• Flow rates: final mixture flow rates typically 5 L/h to 500 L/h, depending on equipment.
• Operational controls and QA: input pressure control, temperature control, homogenization, stability, and verification procedures are covered.
• Safety: precautions to avoid hazardous reactions, toxic or flammable discharge, and transient concentration peaks are required.

Applications and users

ISO 6145-2:2014 is intended for:

• Calibration gas producers and gas‑mixture manufacturers
• Metrology institutes and calibration laboratories
• Environmental monitoring and emissions testing laboratories
• Instrument manufacturers (gas analyzers, detectors)
• Industrial users needing traceable calibration gases (process control, safety monitoring)

Practical benefits include traceable preparation of multi‑component calibration gases, controlled dilution to very low fractions, and documented uncertainty budgets suitable for laboratory accreditation and instrument calibration.

Related standards

• Other parts of ISO 6145 series (e.g., Part 1 Methods of calibration; Parts 4–11 cover alternative dynamic methods: syringe injection, capillaries, critical orifices, mass‑flow controllers, diffusion, saturation, permeation, electrochemical generation).
• Normative references cited: ISO 7504, ISO 14912, ISO/IEC Guide 98‑3 (GUM), and ISO/IEC Guide 99 (VIM).

Keywords: ISO 6145-2:2014, piston pumps, calibration gas mixtures, gas‑mixing pumps, dynamic methods, volume fraction, uncertainty, dilution ratio, gas analysis.