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
Drop Size:
One micron (m) =1/25,000 inch
1/2 of spray volume = smaller droplets
VMD
1/2 of spray volume = larger droplets
Important Droplet Statistics
Operational
Area
EPA Requested Changes Coming!?!?
 Buffer Zones or No
Spray Zones
 Maximize Efficacy
 Minimize Drift
8
0
0
800
7
0
0
700
v
e
r
y
f
i
n
e
/
f
i
n
e
f
i
n
e
/
m
e
d
i
u
m
very fine/ fine
m
e
d
i
u
m
/
c
o
a
r
s
e
fine/medium
c
o
a
r
s
e
/
v
e
r
y
c
o
a
r
s
e
medium/
coarse
v
e
r
y
c
o
a
r
s
e
/
e
x
t
r
e
m
e
l
y
c
o
a
r
s
e
coarse/
very
coarse
very coarse/ extremely coarse
6
0
0
600
5
0
0
500
4
0
0
400
Drop Size (microns)
• ASAE S-572
9
0
0
900
E
x
a
m
p
l
e
R
e
f
e
r
e
n
c
e
G
r
a
p
h
Example Reference Graph
X
C
XC
M
3
0
0
300
M
2
0
0
200
F
1
0
0
100
C
V
CC
VC
DropSize(microns)
 Guidance to Chemical
Manufacturers
 Match the crop
protection product to
the target
 Adhere to label
guidelines based on
an industry standard
F
V
F
VF
0
0
0
.
1
0.1
0
.
5
0
.
9
0.5
0.9
C
u
m
u
l
a
t
i
v
e
V
o
l
u
m
e
F
r
a
c
t
i
o
n
Cumulative Volume Fraction
Pulse Width Modulation - PWM
Pulsed Emissions from Nozzles
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:
11008 Flat Fan Tip, 5gpa, 15mph, 50psi
EVEN
ODD
EVEN
ODD
EVEN
ODD
EVEN
21"
110°
20"
Good Pulse Blending
ODD
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
Horizontal Drift Deposition
1.60
1.40
% Coverage
1.20
Treatment 1
1.00
Treatment 2
0.80
Treatment 3
0.60
Treatment 4
0.40
0.20
0.00
20
25
30
35
40
Card Position - Horizontal
45
50
Sharp Shooter/Synchro Controller:
Pulse generator
• On/Off
• Select volume %
Valve Driver
• Power from battery
Nozzle valve
• Creates spray pulse
For more information contact:
rewolf@ksu.edu
www.capstanag.com/
www.caseih.com/
www.bae.ksu.edu/faculty/wolf