ISO 6145-4:2004

Overview

ISO 6145-4:2004 - "Gas analysis - Preparation of calibration gas mixtures using dynamic volumetric methods - Part 4: Continuous syringe injection method" specifies a reproducible technique for continuously producing calibration gas mixtures by injecting one or more calibration components from a syringe into a complementary gas stream. The method applies to binary and multi-component mixtures prepared from pure gases or pre-mixed gases (Annex A) and supports preparing substantial quantities of gas on a continuous basis for gas analyser testing and calibration.

Key topics and technical requirements

• Principle: Continuous displacement of the calibration component (gas or liquid) from a driven syringe through a capillary/needle into a flowing complementary gas stream.
• Expression of composition: Volume fraction ϕ is determined from the flow rates of the injected component and the complementary gas (ϕ = qA / (qA + qB)). When liquid is injected, an additional density correction is applied to convert injected liquid flow to gaseous volume flow.
• Syringe and driver calibration: Traceable volume calibration of syringe barrel at multiple graduations and temperature, and calibration of the syringe drive (linear speed) against length/time standards (see Annex C).
• Operating conditions: Use non-adsorbing, low-porosity materials; avoid backpressure; maintain uniform temperature; ensure adequate mixing to achieve homogeneity. Use appropriate safety measures for hazardous or potentially explosive gases.
• Uncertainty and validity: Main uncertainty sources are complementary-gas flow measurement, syringe volume calibration, and plunger travel rate. For binary mixtures, the relative expanded uncertainty (k = 2) is reported as ±5%, with an applicability range of 10^-5 to 10^-2 in volume fraction. Validation of mixing effectiveness is required; do not rely solely on flow ratios unless validated.

Applications and users

• Who uses it: Calibration laboratories, gas analyser manufacturers, environmental monitoring labs, process control and safety instrumentation teams, and research facilities requiring accurate gas calibration standards.
• Practical uses:
  • Continuous production of calibration gas for analyzer calibration and performance testing.
  • Creation of multi-component mixtures using multiple syringes or pre-mixed syringes.
  • Generating small incremental concentration steps for evaluating minimum detection limit, dead zone, linearity and accuracy of gas analysers.
  • Producing high-dilution mixtures when combined with pre-mixed gases (Annex A).

Related standards

• ISO 6145-1 - Methods of calibration (dynamic volumetric methods)
• ISO 6143 - Comparison methods for determining/checking composition of calibration gas mixtures
• Other parts of ISO 6145 (Parts 2, 5–11) cover alternative dynamic methods (pumps, capillary devices, orifices, mass-flow controllers, diffusion, saturation, permeation, electrochemical generation).

Keywords: ISO 6145-4:2004, continuous syringe injection method, calibration gas mixtures, dynamic volumetric methods, syringe driver, volume fraction, uncertainty, gas analysers.