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ISO 6145-2 2nd Edition, August 15, 2014 Gas analysis - Preparation of calibration gas mixtures using dynamic methods - Part 2: Piston pumps
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Availability date: 07/13/2021
Description / Abstract:
ISO 6145 comprises a series of International Standards dealing
with various dynamic methods used for the preparation of
calibration gas mixtures. This part of ISO 6145 describes a method
and preparation system using piston pumps. The mixture composition
and its associated uncertainty are based on calibration of the
piston pumps by dimensional measurements.
The calibration gas mixtures prepared using this method consist
of two or more components, prepared from pure gases or other gas
mixtures using gas-mixing pumps. Such gas-mixing pumps contain at
least two piston pumps, each driven with a defined ratio of
strokes, and appropriate accessories for gas feeding and mixture
homogenization.
This part of ISO 6145 is applicable only to mixtures of gaseous
or totally vaporized components including corrosive gases, as long
as these components neither react with each other nor with the
wetted surfaces of the mixing pump. The use of gas mixtures as
parent gases is covered as well. Multi-component gas mixtures and
multi-step dilution procedures are included in this International
Standard as they are considered to be special cases of the
preparation of two-component mixtures.
This part of ISO 6145 describes a method of preparing
calibration gas mixtures whose composition is expressed in volume
fractions. The necessary equations and associated uncertainty
evaluation to express the gas composition in amount–of–substance
fractions are given in Annex A.
With this method, provided that sufficient quality assurance and
control measures are taken, calibration gas mixtures can be
prepared with a relative expanded uncertainty of 0,5 % (coverage
factor k = 2) in the volume fraction. Numerical examples showing
that under specified conditions smaller uncertainties are
attainable are given in Annexes B through D.
Using this method, dilution ratios of 1:10 000 can be achieved
in discrete increments. Lower fractions (down to 1 × 10−8) can be
achieved by multi-stage dilution or by the use of gas mixtures as
input gases. Final mixture flow rates of 5 l/h to 500 l/h can be
realized depending on the equipment used.