Accurate, Adjustable Calibration Source for Measurements of Trace Water Vapour

Abstract

A number of manufacturing processes are adversely affected by the presence of trace amounts of water vapour in purge and process gases. It is important for the operators of such processes to monitor the levels of water vapour in these gases continuously. There are many analytical methods for determination of trace water vapour which all require regular, traceable calibration. In this paper, a new standard facility for generating an adjustable level of trace water vapour is described. It uses continuous accurate measurements of the mass loss from a permeation device coupled with a dilution system based on an array of critical flow orifices. Details of the verification of the facility are presented along with results of comparisons with the National Physical Laboratory thermally-based dew/frost point humidity standards facility.