On-line process control monitoring system

Apparatus for monitoring at a plurality of locations within a system the concentrations of at least one chemical substance involved in a chemical process, said apparatus comprising:

• a source of light;
• plurality of process cells for directing said light through a sample of said at least one chemical substance so that said chemical substance can absorb a portion of said light, each of said process cells having an interior through which light from said source of light is directed;
• first means for carrying said light, said first carrying means carrying said light from said source of light to each of said plurality of process cells;
• second means for carrying said light, said second carrying means carrying said light after said portion of light has been absorbed by said at least one chemical substance from each of said plurality of process cells;
• means for producing a spectrum from said light received by said second carrying means, said producing means in optical communication with said second carrying means;
• multiplexing means for selecting one process cell of said plurality of process cells at a time so that said producing means can produce a process spectrum from said one cell of said process cells;
• a reference cell for producing a reference spectrum for comparison to said process spectrum, said reference cell having an interior containing none of said chemical substance and directing said light from said source of light through said interior;
• a standard cell for producing a standard spectrum for comparison to said process spectrum, said standard cell having an interior containing a known concentration of said chemical substance and directing said light from said source of light through said interior;
• and
• means for comparing said reference spectrum, said standard spectrum and said process spectrum and determining said concentration of said chemical substance in said process cell.