| 摘要 |
A device for sensing a moving sheet for imperfections. The device comprises a plurality of light sources and corresponding photocells for receiving the radiation thereof after reflection from or transmission by the sheet. Each photocell has its own pre-amplifier which is provided with automatic gain control means which controls the pre-amplifier in such a way that the average output signal thereof remains equal to a pre-determined value. The device is insensitive to incorrect mounting of the photocells relative to the light sources and insensitive to spreadings in the characteristics of the electric components, and a change from a more specular material being sensed to a more diffuse material does not require a re-adjustment of the device. |
