ISO 16664:2017 pdf – Gas analysis — Handling of calibration gases and gas mixtures — Guidelines

ISO 16664:2017 pdf – Gas analysis — Handling of calibration gases and gas mixtures — Guidelines.
1 Scope This document describes factors that may influence the composition of pure gases and homogeneous gas mixtures used for calibration purposes. This document only applies to gases or gas mixtures that are within the “utilization period”. It provides the following guidelines for the handling and use of calibration gas mixtures: — storage of calibration gas cylinders; — calibration gas withdrawal from cylinders; — transfer of calibration gas from cylinders to the point of calibration. It also outlines a method of assessing the stability of a gas mixture, taking into account the gas composition uncertainty given on the certificate and the user’s measurement uncertainty. 2 Normative references There are no normative references in this document. 3? Terms? and? definitions For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — IEC Electropedia: available at http:// www .electropedia. org/ — ISO Online browsing platform: available at http:// www. iso. org/ obp 3.1 calibration gas pure gas or gas mixture used for calibration 3.2 calibration gas mixture gas mixture of known stability (3.9) and homogeneity (3.4) whose composition is well established for use in the calibration or verification of a measuring instrument or for the validation of a measurement Note 1 to entry: Calibration gas mixtures are measurement standards (Annex A) as defined in ISO/IEC Guide 99:2007. [SOURCE: ISO 7504:2015, 5.1] 3.3 component chemical entity at a defined physical state present in a material or in a mixture [SOURCE: ISO 7504:2015, 3.3]
3.5 impurity undesired minor component present in a parent gas (and thus detectable in a gas mixture made of this parent gas [SOURCE: ISO 7504:2015, 5.5] 3.6 leak rate volume of fluid leaking from the system per unit of time due to incomplete sealing of materials 3.7 leak tightness conformity to a specified leak rate 3.8 step response time duration between the instant when an input quantity value of a measuring instrument or measuring system is subjected to an abrupt change between two specified constant quantity values and the instant when a corresponding indication settles within specified limits around its final steady value [SOURCE: ISO/IEC Guide 99:2007] 3.9 stability attribute of a gas mixture, under specified conditions, to maintain its composition within specified uncertainty limits for a specified period of time (maximum storage life) [SOURCE: ISO 7504:2015, 3.2] 3.10 maximum storage life period after which the properties stated for a gas mixture cannot be warranted to lie within their limits Note 1 to entry: This period is usually identified as that for which the producer ensures that the gas mixture maintains its composition within the specified limits when it is stored in accordance with the requirements based upon the concepts defined in ISO 7504:2015, 7.1 to 7.4. Note 2 to entry: The end of this period may be indicated by an “expiry date” (see also ISO 6142-1). [SOURCE: ISO 7504:2015, 7.5] 3.11 transfer system gas-conducting system which begins at the cylinder valve and ends at the gas sample inlet to the measuring instrument and includes all structural elements
3.12 measurement uncertainty non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the information used Note 1 to entry: Measurement uncertainty includes components arising from systematic effects, such as components associated with corrections and the assigned quantity values of measurement standards, as well as the definitional uncertainty. Sometimes estimated systematic effects are not corrected for but, instead, associated measurement uncertainty components are incorporated. Note 2 to entry: The parameter may be, for example, a standard deviation called standard measurement uncertainty (or a specified multiple of it), or the half-width of an interval, having a stated coverage probability. Note 3 to entry: Measurement uncertainty comprises, in general, many components. Some of these may be evaluated by Type A evaluation of measurement uncertainty from the statistical distribution of the quantity values from series of measurements and can be characterized by standard deviations. The other components, which may be evaluated by Type B evaluation of measurement uncertainty, can also be characterized by standard deviations, evaluated from probability density functions based on experience or other information. Note 4 to entry: In general, for a given set of information, it is understood that the measurement uncertainty is associated with a stated quantity value attributed to the measurand. A modification of this value results in a modification of the associated uncertainty.