Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2000
Publication Date: 5/1/2000
Citation: Thomson, S.J., Smith, L.A. 2000. Evaluation of a control system for isokinetic hi-volume sampling of airborne spray. Applied Engineering in Agriculture. 16(3):309-314. Interpretive Summary: Accurate sampling of airborne spray droplets is essential for improving efficiency of spray application and reducing drift to non-target areas. Determination of droplet concentrations at various points in the field can yield useful data for better targeting of pests from ground-based or aerial-based spraying equipment. Motor-driven air samplers are one method of sampling airborne spray. To obtain an accurate, representative spray sample, wind speed must be the same as the speed of air traveling through the sampler. Air samplers in use today are not being operated in this manner; they are set at one speed, regardless of wind speed. A controller was designed around a newly developed air sampler to adjust motor speed so air speed through the sampler equals wind speed. The controller was designed to operate at all wind conditions that might be encountered in the field and to work at very low wind speeds; something that cannot be done reliably with present motor control designs. Tests indicate the controller tracked changing air speeds very well and the system responded quickly to changing air speeds. The unit is being used in drift and deposition studies.
Technical Abstract: An isokinetic air sampling system was developed to sample spray drift from ground and aerial application equipment. Two identical airflow sensors were used in the system. One sensor detects airflow due to wind speed and the other detects airflow through the sensor due to sampler motor speed. An isokinetic control system was designed to compare sensor outputs and adjust the sampler motor so air speed through the sampler could track wind speed. The design uses the STAMP II microcontroller and newly developed motor control circuitry for reliable and sustained low speed operation necessary to track low wind speeds. Algorithms were designed to accommodate delays in system response. The controller tracked changing ambient air speeds well and showed good stability at wind speeds normally encountered during field application of agrichemicals.