水分活度仪的校准

Calibration of water activity meter

根据水分活度仪的工作原理和计量特性,利用溴化锂、氯化锂、乙酸钾、氯化镁、碳酸钾、溴化钠、碘化钾、氯化钠、氯化钾、硫酸钾饱和溶液作为标准物质,研究制订一种简单、准确、可靠的水分活度仪校准方法。对于不具备温度控制功能的水分活度仪,环境温度每变化10 ℃,乙酸钾、溴化锂、溴化钠饱和溶液的水分活度值变化分别可达6.67%、6.25%、5.38%。故环境温度控制对校准结果有重要影响。而环境相对湿度在20%~90%、大气压在80~106 kPa对冷镜露点法或电容法水分活度仪的校准结果几乎没有影响。该方法利用可溯源至国家湿度标准的精密露点仪测量值代替饱和盐溶液文献值,测量不确定度为0.002~0.006(k=2),解决了饱和盐溶液文献值无法溯源或不确定度较大等问题。

Based on the working principle and measurement characteristics of water activity meter,a simple,accurate and reliable calibration method of water activity meter was proposed by using saturated salt solutions such as LiBr,LiCl,KAC,MgCl2,K2CO3,NaBr,KI,NaCl,KCl and K2SO4 as reference materials.As for water activity meters without temperature control,when ambient temperature changed by 10℃,the water activation of KAC solution changed by 6.67%,which of LiBr solution changed by 6.25%,and which of NaBr solution changed 5.38%,so the environmental temperature control had an important influence on the calibration results.However,when the relative humidity was 20%–90%and the atmospheric pressure was 86–106 kPa,the calibration results of water activity meter by cold mirror dew point method or capacitance method were scarcely influenced.By this method,the reference value of saturated salt solution was replaced by the measured value of precision dew point meter which could be traced to national humidity standard.After that,the uncertainty of measurement is 0.002–0.006(k=2),and the problem of the literature value of saturated salt solution not be traced or with large uncertainty is solved.