Abstract: A circuit is disclosed for monitoring the output voltage of a magnetic pickup and for producing output signals representing the valid detection of bars of magnetized ink moved past the pickup. The circuit is capable of detecting and providing correct output data from input signals ranging from relatively weak signals of low amplitude to relatively strong signals which are of high amplitude and include overshoot pulses of substantial amplitude. The circuit is disclosed in association with a system for sorting envelopes containing inserts coded with bars of magnetic ink, the output of the signal detecting circuit being used as the input to a sorter logic controlling a sorter mechanism.

Abstract: A device for checking supposedly emptied envelopes for documents, as the envelopes are fed in spaced end-to-end relationship past an inspection station, consists of three sensors at the inspection station arranged along a line perpendicular to the envelope path to sense the opacity of each envelope along three zones located respectively near the top, near the bottom and near the center of the envelope. The output of the center sensor serves as a reference for the top and bottom sensors and a signal processing circuit connected with the sensors produces a suspect signal, indicating the suspected presence of a document in an envelope, when the output of either the top or bottom sensor compares unfavorably with that of the center sensor for an amount of time sufficient to make the device insensitive to short duration opacity differences caused by overlapping envelope seams.