Optical digitizer for measuring spirometer output

摘要

A spirometer includes an expansible chamber of the piston type fitted with an indicia strip. The indicia comprise two columns of alternating light and dark bars. The columns are offset from one another by one-half the thickness of a bar and are respectively viewed by two photodetectors which generate signals which are shifted 90 DEG from one another as the columns pass through their respective fields of view. The signals are continuously sampled as digital words and consecutive words are compared to determine whether a counter should be incremented or decremented by one or two counts.