Development and evaluation of a real-time cotton flow rate sensor

Cotton producers are interested in quantifying yields site-specifically within large fields. In order to measure yield site-specifically during harvest, cotton flow rate into the harvester must be sensed. A system has been developed to measure cotton flow rates on a spindle-type cotton picker. It uses a non-intrusive optical technique to estimate flow rate as the cotton passes through harvester conveyer pipes. Discrete beams of light are projected across the conveyer pipes, and beam intensities are measured by individual photo-detectors mounted opposite the light emitters. As cotton passes between emitters and detectors, light beams ai'e deflected, thus reducing the amount of light energy reaching detectors. The photo-detectors give an integrated measure of light energy attenuation over time. This measurement is related to the amount of cotton that travels between emitters and detectors during the time interval. Since the time interval is typically short (measured in ms), measurement of the amount of cotton that passes through the system during one time interval approximates an instantaneous flow rate measurement.

The system was prototyped and tested in both the laboratory and field. Test results show that the system is capable of measuring cotton flow rate with some degree of accuracy. Accuracy measurements were based on predicted load weight totals with load weights ranging between 275 and 1361 lb. Seventy-five out of 79 loads harvested were measured with errors less than +/-10 percent with an average absolute error for the 79 loads of 4.7 percent. Accuracy was independent of flow rate over the range tested.

Refinements are needed in the data transmission circuitry to eliminate signal noise that may have reduced measurement accuracy in the data set. Future test efforts should concentrate on high cotton flow rates to determine the maximum range of system operation.