OPTICAL SENSOR FOR GRANULAR FERTILIZER FLOW RATE MEASUREMENT

Abstract

An optical sensor to measure granular fertilizer flow in an airstream was designed, built, and laboratory tested. The sensor components included a laser line generator that transmitted light across a trapezoidal chamber to a 32-element photodiode array. The air-suspended granules would break the light, causing a count to be recorded. The counts were translated into a mass flow rate. Static tests of five materials and six mass flow rates were performed in a replicated block design. Dynamic tests of one material with six step changes in mass flow rate were performed. Results of the static tests showed a strong linear, repeatable relationship between sensor output and mass flow rate. For maximum accuracy, individual calibrations were required for different fertilizer products. Dynamic test results showed that the sensor followed step changes in mass flow rate well, but indicated some limitations in the data analysis algorithm. The optical sensor system showed potential as a first step to a real-time granular fertilizer flow rate sensor.