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

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

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

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

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

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

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.

Orifice Metering

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

VariTargetTM Nozzle Variable Orifice

VariTargetTM Nozzle - Operation

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.

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

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 5

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

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

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