Non-intrusive methods of on-line analysis are of particular value in those industries such as food manufacture and biotechnology, where sterility, plant integrity and ease of cleaning are of major importance. Radio frequency and microwave techniques, such as capacitance, NMR and ESR, being by their nature deeply penetrating, are attractive candidates to meet this requirement. Their current uses are described - mainly for moisture measurement- and their future potential examined. It appears that not only is this significant but that there exists a real need for further development and engineering of suitable industrial systems.
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