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Variable Rate Application

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.

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Variable Rate Application

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  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. Liquid Application 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

  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 3 mph 5 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 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

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

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

  24. 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.

  25. Orifice Metering

  26. 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

  27. VariTargetTM Nozzle Variable Orifice

  28. VariTargetTM Nozzle - Operation

  29. 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.

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

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

  32. Synchro Controller Components

  33. 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

  34. 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)

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

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

  37. Direct Injection System

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

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

  40. 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

  41. 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.

  42. 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

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