| 摘要 |
A reflection sensing apparatus detects the prior exposure history of an annotatable archival microfiche film card frame. A light source used to expose the microfiche to the record image is positioned to convert a reserved sensing area, which is outside the record image but within the frame, from an opaque and reflecting area to an irreversibly clear and transparent area upon exposure. The reserved area of the microfiche film card frame is interrogated by automatic photoreflection sensing immediately prior to exposure of a given frame to disclose its prior exposure history. Suitable warning systems indicate the imminence of multiple exposure, and an automatic disabling feature prevents accidental re-exposure. A manual override means controlled by the operator must be actuated to allow re-exposure of a previously exposed frame. An alternative pre-exposure sensing of the reserved area by optical transmission methods is described. The apparatus also serves to detect failure of the light source on initial exposure of a chosen frame by a second photoreflection sensing after exposure, or alternatively by transmission sensing during exposure.
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