Using Pulse Width Modulation to Control Spray Droplet Size Robert E. Wolf Extension Specialist Application Technology Biological and Agricultural Engineering

Efficacy and Drift Potential is Influenced by: Size of the Spray Droplets - Volume Median Diameter (VMD) Droplet Spectrum (Range - big to small) % Volume in droplets less than 200 microns in size

One micron (  m ) =1/25,000 inch Drop Size:

1/2 of spray volume = larger droplets VMD 1/2 of spray volume = smaller droplets

Important Droplet Statistics Operational Area

Example Reference Graph Cumulative Volume Fraction Drop Size (microns) very fine/ fine fine/medium medium/ coarse coarse/ very coarse very coarse/ extremely coarse VF F M C VC XC Guidance to Chemical Manufacturers Match the crop protection product to the target Adhere to label guidelines based on an industry standard ASAE S-572 Buffer Zones or No Spray Zones Maximize Efficacy Minimize Drift EPA Requested Changes Coming !?!?

Pulsed Emissions from Nozzles Pulse Width Modulation - PWM

SYNCHRO® - Nozzle System Capstan Ag Systems Topeka, KS Developed by the Precision Spray Laboratory U of CA - Davis

Synchro Nozzles Blended Pulse Technology Independent Flow Control (1-8X) Independent Drop Size Control Independent Band Width Control (Fan Nozzles) Separate boom section controls GPS - program management control

Synchro Controller Components:

How it Works Uses high speed solenoid valves to regulate flow Varies application rate with duty cycle: independently of pressure

Pulse compared to conventional:

What is Pulse Width? Type of control system Modulates a DC square wave signal

Synchro® Blended Pulse Each Synchro® nozzle emits 10 pulses per second, with adjacent nozzles having alternating timing. The alternating pulses, combined with overlapping spray patterns and the natural dispersion of droplets traveling in air, blend together to provide consistent coverage.

Spray pattern quality not sacrificed:

Electronics/Rate Controllers How does your system work when speed changes? Is it pressure based? What is the effect of going slower? What is the effect of going faster?

Procedures: Treatment 1 Conventional, 20 psi, 5 mph, tt11002, 8 GPA Treatment 2 Conventional, 75 psi, 10 mph, tt11002, 8 GPA Treatment 3 PWM, 40 psi, 5 mph, tt11004, 8 GPA Treatment 4 PWM, 40 psi, 10 mph, tt11004, 8 GPA

Drift

Sharp Shooter/Synchro Controller: Pulse generator On/Off Select volume % Valve Driver Power from battery Nozzle valve Creates spray pulse

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