对天然气分析中测量不确定度评定的认识

2011年国家质量监督检验检疫总局发布了经修订的国家计量技术规范JJF 1059，并同时发布了新版的JJF 1001-2011“计量学通用术语及定义”，用以替代1998版的“通用计量术语及定义”。为了更好地贯彻执行该标准，结合天然气气质控制与能量计量实验室建设的需要，从不确定度评定与实验室认可的关系、实验室的校准和测量能力、标准物质生产者能力准则以及用蒙特卡洛（MCM）法评定测量不确定度等4个方面分析了天然气分析中测量不确定度评定存在的问题：①水露点的测定必须与相对湿度测量比对才能建立溯源链，目前对其不确定度的测量还未开展全面研究，从溯源性的角度分析，GB/T 17283规定的水露点测定方法不具备作为基准方法或仲裁方法的条件；②在天然气质量控制及能量测定领域，我国目前尚无经国家实验室认可委员会（CNAS）认可的实验室；③JJF 1059“测量不确定度评定与表示”（GUM）法在实际操作中无法应用于天然气能量计量时在线气相色谱分析系统的整体不确定度评定。同时，明确了确定标准物质特性值及生产标准物质的注意事项，建议GUM法在实际操作中无法应用时使用JJF 1059.2规定的另一种不确定度评定方法--MCM法来进行评定。

A discussion on the evaluation of measurement uncertainty in natural gas analysis

In 2011, the Chinese General Administration of Quality, Supervision, Inspection and Quarantine issued the revised National Measurement Technical Code JJF1059, meanwhile issued the new edition JJF1001 2011 General Glossary and Definition of Metrology in place of the 1998 edition. In view of this, in combination with the need of the laboratory establishment for natural gas quality control and energy measurement, this paper analyzes the existing problems in the uncertainty measurement in natural gas analysis in the following aspects: the relationship between uncertainty evaluation and laboratory accreditation, the calibration and measurement capacity of laboratories, the criterion of certified reference material producers, and the Monte Carlo evaluation method of measurement uncertainty. The results are obtained as follows. (1) Measurement traceability can be built only by the matching measurement between water dew point and relative humidity; an overall study of uncertainty measurement has not been conducted till now, so from the perspective of traceability, the water dew point method described in the GB/T 17283 can not be regarded as the reference or arbitration in the uncertainty measurement. (2) There is no one laboratory recognized by the China National Accreditation Service for Conformity Assessment (CNAS) in the sector of natural gas quality control and energy measurement. (3) The Guide to the Expression of Uncertainty in Measurement (GUM) JJF1059 1999 can not be applied in the evaluation of uncertainty in measurement of the on line chromatograph analyzer in the energy measurement of natural gas. In this case, the Monte Carlo method, another evaluation method of uncertainty in measurement (see JJF1059.2) is suggested to be adopted instead. Moreover, this paper also clarifies the characteristic values of reference materials and the precautions for the reference material production.