US Patent 7381939 Optical cargo detection

A detector for detecting cargo in a container has a controller block, a transmitter for transmitting light into the field of view, a receiver for receiving reflected light, and a threshold comparator for determining whether the received light meets a threshold for cargo detection. The receiver includes a DC block for removing effects of ambient light. The detector performs detection multiple times and averages the results, which can be compared with a previously stored condition of cargo presence or absence to increase the detection accuracy further.