Strip marking detection equipment - has two photoelectric detectors which deliver signals to differential amplifier with filter to suppress negative voltages

摘要

The equipment detects markings, preferably punched holes in a strip of material passed over a photoelectric cell. In the travel direction (3) of the strip (1) there are two detectors for the marks (4), preferably photoelectric cells (9a, 9b) close one behind the other. A differential amplifier compares the voltages across the detectors, and initiates a control operation if these are unequal. The amplifier may be followed by a filter for suppressing negative voltages, and the light-sensitive portions of the cells may be oblong in shape, extending at right angles to the travel direction. Each can extend beyond the likely position of the strip edge for the same distance, and over all possible positions of the marks.