Variable Rate
Application
BAE 4213
April 6, 2007
Randy Taylor, Bio & Ag Engineering
VRN - The Holy Grail?
Introduction
Variable-Rate Application (VRA)
Variable-Rate Technology (VRT)
Site-Specific Crop Management
(SSCM)
VRA is one aspect of SSCM
Variable Rate Application
Production inputs are applied on an
optimum basis for the local
conditions.
VRA requires
Knowledge of optimum rates
Ability to apply desired rate
Implementing VRA
Map-Based VRA
Sensor-Based VRA
The primary element of either
approach is a rate controller
Map-Based VRA
Uses a georeferenced map as a
guideline for adjusting application
rate
Need a means for determining
machine location
Need to “Look Ahead”
Rate is based on a user-defined and
monitored algorithm
Sensor-Based VRA
Application rate is determined from
sensors
Rate is based on an algorithm that
ties the sensor reading to a
prescription
Machine location is not that important
(unless collecting data)
Feedback Loop Rate Controllers
Adjust rate to a desired value
Measure actual rate
Readjust rate
When desired rate changes, they
must be able to quickly adjust to the
new rate
Select Rate Measure Flow
Set Flow
Basic Feedback Control
Adjust outlet flow
to maintain fluid
level.
Rate Controllers
Rate controllers were developed to account
for variation in application speed
Nebraska looked at application rate errors
of 61 NH3 applicators
Traditional Regulator Systems
17% of had acceptable error
32% over applied
41% under applied
Electronic or Ground Drive Controllers
59% of had acceptable error
41% over applied
Back To Basics
Application Rate is a
function of speed, width,
and flow rate
Does width change?
To keep application rate
constant, flow rate must
change when speed
changes Liquid Application
GPM 5940
GPA
MPH width
So How do we Control Flow?
It depends on the metering method
Orifice metering – pressure increase
Valve metering – ground driven,
pressure based
Before we get too deep into how, let’s
consider what we need.
Controller Components
Speed Sensor
Radar, Sonar, Proximity, GPS
Flow Sensor
Turbines (small impeller)
Pressure Sensor
Used to predict flow based on orifice size
Control Valve
Ball or butterfly flow control
Microprocessor
Brains of the outfit
Electronic Monitor System for NH3
What is the Goal?
Apply the desired amount of product
Account for changes in speed
Wheel slip
Turns
Account for desired rate changes
Raven 440 – NH3 Controller
1.5 s of response time.
About 9 ft at 4 mph
5 mph 3 mph
Response Times
PAMI Evaluation Report 723 – NH3
Controllers
About 2 seconds to adjust to speed or
rate changes
At 5 mph, 2 s => 15 ft
At 15 mph, 2 s => 44 ft
So we can typically change rates with
more resolution than applicator width
Raven 440 – NH3 Flow Limitations
35 ft width
5 mph
Ground Driven Pumps
Variable stroke piston pump (PD)
Pump speed is tied to ground speed
Change rates by adjusting stroke or
speed
Must have liquid to meter (for NH3)
Drive wheel should not be allowed to
slip
Flow Control
Mixture Tank Flow Control
Valve
Flowmeter
Pump
Console Spray Boom
Radar
Flow Control
Used with tank mix
Automatic adjustment for speed
Rate changes from console
Flow Control
Advantages
Consistent application rate regardless of
speed
Wider speed range of operation
Easier calibration
Chemical savings greater than controller
cost
Flow Controller
Disadvantages
Cost $1500-2000
Require radar for most accurate
operation
With fixed nozzles, majority of flow
range required for speed changes.
Flow Control
Application rate of active ingredient is
controlled by measuring the flow of a
tank mix. Pressure at nozzle varies.
Status: suitable but not optimum
for Prec. Agric.
Orifice Metering
50 100
40 80
Pressure, psi
Flow, gpm
30 60
20 40
2
10
Q20
0 p 0
20 pr
5 10
Speed, mph
15
Qr
Flow Pressure
Potential Road Blocks
Flow Limitations
Orifice metering is pressure limited
Quadruple the pressure to double the
flow
Potential Solutions
VariTargetTM Nozzles
Variable Rate TurboDrop®
Synchro PWM
VariTargetTM Nozzle
Variable
Orifice
VariTargetTM Nozzle - Operation
VeriTargetTM Flow Data
1.6
1.4
They claim a
1.2 10x flow rate
change with a
Nozzle Flow, GPM
1.0
6.7x pressure
0.8 change.
0.6
Data collected
0.4 by OSU BAE
Mfg. Data students seem
0.2
Student Data similar to mfg.
0.0 data.
0 20 40 60 80 100 120
Pressure, psi
VeriTargetTM Nozzle Flow
1.2
1.0 Flow data from
three individual
Nozzle Flow, GPM
0.8
VeriTargetTM
0.6
nozzles collected
by OSU BAE
0.4 students.
0.2
0.0
20 30 40 50 60 70 80
Pressure, psi
Should be
released soon.
Double the
pressure, double
the flow rate.
Synchro Controller Components
What PWM Does
Allows control of both nozzle
pressure and flow
independently
Increases the effective
operating range by a factor
of 4 (8:1 versus 2:1)
Increased control of spray
particle droplet size
Even coverage using blended
pulse technology
What is the Duty Cycle?
Pulse Width Modulation
Nozzles on time and off time per second
The Aim Command System changes the
amount of “on time” each second to control
nozzle flow (application rate)
Duty Cycle and Flow Control
LONG ON TIME = HIGH FLOW RATE
SHORT ON TIME = LOW FLOW RATE
Blended Pulse Coverage
Nozzles pulse 10 times per second
Even and odd nozzles are alternately
fired for blended coverage
Direct Injection System
Direct Injection Controller
Active ingredient (AI) and carrier fluid
in separate tanks
Flow rate of AI and carrier
independently controlled
Direct Injection Controller
Advantages
Same as flow control
No mixing of chemicals
Minimize disposal and rinsing problems
Quickly change chemical or rate
Direct Injection Controller
Disadvantages
Greater cost ($6-8k - 1st AI tank, $1-2k
- additional tanks)
More complex operation
Lag time too great for real time sensing
and control
Direct Injection Controller
Application rate of the active
ingredient is determined by pumping
the unmixed chemical into the carrier
fluid. Pressure at nozzles varies.
Status: suitable for Prec. Agric.
Variable Rate Application
Production inputs are applied on an
optimum basis for the local
conditions.
VRA requires
Knowledge of economic optimum rates
at chosen management scale
Ability to apply desired rate at desired
scale