| 摘要 |
In order to determine when a roll of web material, such as paper, wound on a core has reached its end, a photoelectric detecting circuit is provided. The photoelectric apparatus is shown in combination with an electrostatic copying machine and includes a pair of photocells in a bridge circuit. One photocell receives light directly from a source while the other receives light reflected from the surface of a roll of web material. When the web material has been unwound to expose a core of a different color, the intensity of the reflected light changes causing the bridge circuit to become unbalanced, which unbalance is amplified and utilized to operate control means.
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