Oki C7200 Service Manual page 61

Duplex in sensor Detects the beginning of paper that enters into the
duplex unit, to determine the time taken until the
reversed rollers turn in forward direction.
Duplex Rear sensor Detects the beginning of reverses paper in the
duplex unit.
Duplex Front sensor Detects the end of reversed paper in the duplex unit
to determine the paper ejection timing.
Stacker Full sensor Detects the face-down stacker full of paper.
Copyright 1999, Okidata, Division of OKI America, Inc. All rights reserved.
ON: paper is present.
OFF: Paper is absent.
ON: paper is present.
OFF: Paper is absent.
ON: paper is present.
OFF: Paper is absent.
ON: Stacker is full.
OFF: Stacker is empty.