1. Variable Rate Application
BAE 4213
April 6, 2007
Randy Taylor, Bio & Ag Engineering

2. VRN - The Holy Grail?

3. Introduction Variable-Rate Application (VRA)
Variable-Rate Technology (VRT)
Site-Specific Crop Management (SSCM)
VRA is one aspect of SSCM

4. 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

5. Implementing VRA Map-Based VRA Sensor-Based VRA
The primary element of either approach is a rate controller

6. 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

7. 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)

8. 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

9. Basic Feedback Control
Adjust outlet flow to maintain fluid level.

10. 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

11. 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

12. 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.

13. 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

14. Electronic Monitor System for NH3

15. What is the Goal? Apply the desired amount of product
Account for changes in speed
Wheel slip
Turns
Account for desired rate changes

16. Raven 440 – NH3 Controller 1.5 s of response time. About 9 ft at 4 mph

17. 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

18. Raven 440 – NH3 Flow Limitations
35 ft width
5 mph

19. 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

20. Flow Control Radar Flow Control Valve Mixture Tank Flowmeter Pump
Spray Boom
Console
Radar

21. Flow Control Used with tank mix Automatic adjustment for speed
Rate changes from console 9

22. Flow Control Advantages
Consistent application rate regardless of speed
Wider speed range of operation
Easier calibration
Chemical savings greater than controller cost 10

23. Flow Controller Disadvantages Cost $1500-2000
Require radar for most accurate operation
With fixed nozzles, majority of flow range required for speed changes. 11

24. Flow Control Status: suitable but not optimum for Prec. Agric.
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.

25. Orifice Metering

27. Potential Road Blocks Flow Limitations Potential Solutions
Orifice metering is pressure limited
Quadruple the pressure to double the flow
Potential Solutions
VariTargetTM Nozzles
Variable Rate TurboDrop®
Synchro PWM

28. VariTargetTM Nozzle
Variable Orifice

29. VariTargetTM Nozzle - Operation

30. VeriTargetTM Flow Data
They claim a 10x flow rate change with a 6.7x pressure change.
Data collected by OSU BAE students seem similar to mfg. data.

31. VeriTargetTM Nozzle Flow
Flow data from three individual VeriTargetTM nozzles collected by OSU BAE students.

32. Should be released soon.
Double the pressure, double the flow rate.

33. Synchro Controller Components

34. 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

35. 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)

36. Duty Cycle and Flow Control
LONG ON TIME = HIGH FLOW RATE
SHORT ON TIME = LOW FLOW RATE

37. Blended Pulse Coverage
Nozzles pulse 10 times per second
Even and odd nozzles are alternately fired for blended coverage

39. Direct Injection System

40. Direct Injection Controller
Active ingredient (AI) and carrier fluid in separate tanks
Flow rate of AI and carrier independently controlled 5

41. Direct Injection Controller
Advantages
Same as flow control
No mixing of chemicals
Minimize disposal and rinsing problems
Quickly change chemical or rate 6

42. 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 7

43. 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.

44. 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