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首页> 外文期刊>Science, Measurement & Technology, IET >Molar fraction stability in dynamic preparation of reference trace gas mixtures
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Molar fraction stability in dynamic preparation of reference trace gas mixtures

机译：动态制备参考微量混合气的摩尔分数稳定性

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摘要

Volatile Organic Compounds (VOC) at trace level are common indicators for climate change and ambient air quality. The calibration of detection systems at trace level needs VOC mixtures at nmol/mol level with 5% uncertainty, the dynamic preparation can fulfil it. A source of uncertainty for dynamic generation is the stability of the VOC molar fraction averaged on the sampling time. A general method for the calculation of the relevance of the stability contribution to the total uncertainty is here proposed. VOC molar fraction is here considered as a composed quantity. Threshold values for stability contribution were set to consider it either as negligible and relevant. The stability of the operative quantities of a device, for the dynamic preparation of accurate VOC reference mixtures, was measured at the working conditions by the Allan deviation algorithm. Stabilities of operative quantities were composed to calculate the VOC molar fraction stability and their contribution to total uncertainty of VOC molar fraction. The stability of the air inlet pressure gave the main stability contribution. The stability contribution to the total uncertainty resulted to be negligible for observation times below 60 min for VOC molar fraction uncertainty of 2% at 30 nmol/mol level.
机译：痕量水平的挥发性有机化合物（VOC）是气候变化和环境空气质量的常见指标。痕量水平检测系统的校准需要nmol / mol水平的VOC混合物，不确定性为5％，动态制备可以满足要求。动态生成不确定性的来源是在采样时间上平均的VOC摩尔分数的稳定性。本文提出了一种计算稳定性贡献与总不确定性相关性的通用方法。这里VOC摩尔分数被认为是组成量。稳定性贡献的阈值被设置为可以忽略不计且相关。通过Allan偏差算法在工作条件下测量了用于动态制备准确的VOC参考混合物的设备操作量的稳定性。组成操作量的稳定性以计算VOC摩尔分数的稳定性及其对VOC摩尔分数的总不确定度的贡献。进气压力的稳定性是主要的稳定性贡献。对于30 nmol / mol水平下2％的VOC摩尔分数不确定度，对于60分钟以下的观察时间，对总不确定度的稳定性影响可忽略不计。

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