In combination, the chaffer sieve and cleaning fan of a combine make up a cleaning or fanning mill for separating chaff from grain. The steady flow of cleaning air supplied by the fan is intended to blow through the chaffer sieve and carry the lighter chaff off of the sieve and out the back of the combine, allowing the heavier grain to fall through onto the cleaning sieve. When this fanning mill does not perform as intended, chaff and grain will be carried along with the chaff over the tail end of the chaffer. Since the chaffer sieve and fan combination do not represent a screening operation, but rather a fanning mill, usually the solution to its malfunction has been to increase fan speed. Thus, sensing devices have been located in the immediate adjacency of the tail end of the chaffer sieve. When too much grain strikes the sensor, fan speed is increased.
While it is important to detect grain which is carried over the rear of the sieve due to slow fan speed, the other side of the coin is the effect of too much fan speed. When too much air is applied to the chaffer sieve, grain and chaff are blown back and over a sensor which is located adjacent to the tail end of the chaffer sieve.
The inventor is aware of sensing devices of various types being located at innumerable positions throughout the combine harvester. See for example U.S. Pat. No. 3,939,846 to Drozhzhin et al which locates a sensor under the sieve of the cleaner, U.S. Pat. No. 4,036,065 to Strelioff et al which locates sensors across the rear of the sieve and at the rear portion of the straw walker, U.S. Pat. No. 4,259,829 to Strubbe in which sensors are located on the louvres of the chaffer sieve, and U.S. Pat. No. 4,360,998 to Somes which provides a matrix of sensors disclosed about the cleaning sieve (which is below the chaffer sieve). While these and other sensor locations serve to provide information useful in improving many aspects of combine operation, the inventor is unaware of any prior art sensors which are located to detect grain loss above the tail end of the chaffer sieve caused by too much air from the fan.