Material flow sensing system in a combine harvester

A combine harvester comprising:

• a threshing apparatus;
• a separating apparatus;
• a grain cleaning system located downstream of the separating apparatus;
• a material conveyance system arranged to convey crop material from the separating apparatus to the grain cleaning system;
• and
• an electronic control unit (ECU),
• wherein the grain cleaning system comprises:
• a screening apparatus having at least one adjustable sieve, and
• a fan arranged to generate a cleaning airstream through the screening apparatus,
• wherein the material conveyance system comprises a return pan positioned below the separating apparatus and serving to catch crop material that falls from the separating apparatus and convey said material as a mat in a forward direction to a front edge of the return pan from where said mat falls under gravity,
• wherein a photoelectric sensing device is in communication with the ECU and is arranged forward of, and below, said front edge to generate a light beam across a path of the mat as the mat falls under gravity, and wherein the ECU is configured to generate one of a fan speed setting and a sieve opening setting in dependence upon detection signals generated by the photoelectric sensing device.