Gas analysis - Preparation of calibration gas mixtures using dynamic volumentric methods - Part 4: Continuous syringe injection method (ISO 6145-4:2004)
This part of ISO6145 specifies a method for continuous production of calibration gas mixtures, containing twoor more components, from pure gases or other gas mixtures by continuous injection of the calibrationcomponent(s) into a complementary gas stream by means of a syringe.
If pre-mixed gases are used instead of pure gases (see AnnexA), much lower volume fractions can beobtained. The volume flow rates, from which the volume fractions are determined, can be calculated from theindividual flow rates and can be independently measured by a suitable method given in ISO 6145-1.
The merits of the method are that a substantial quantity of the gas mixture can be prepared on a continuousbasis and that multi-component mixtures can be prepared almost as readily as binary mixtures if theappropriate number of syringes is utilized, or if the syringe already contains a multi-component mixture ofknown composition. This method also provides a convenient means for increasing the volume fraction of thecalibration component in the mixture in small steps. It is therefore a useful method for evaluation of othercharacteristics of gas analysers, such as minimum detection limit and dead zone, as well as accuracy. Therelative expanded uncertainty in the volume fraction obtainable for a binary mixture (at a coverage factor of 2) ......