Interfacing Sensors with (VR)Application Equipment Scott Drummond Ken Sudduth IT Specialist Agricultural Engineer

Objectives Understand the “big picture” of developing a sensor based system for VRA of N. Recognize design details that often get ignored or at least “underappreciated”. See how these details affect the design and development of one such research system.

Sense Decide Control

Crop Sensing Remote sensing –Satellite based –Aerial based Real time sensing –Passive Sensors –Active Sensors

Active Sensors By using an internal light source, these sensors eliminate problems with sun angle and cloud variations –GreenSeeker by NTech –Crop Circle by Holland Scientific –CropSpec by Topcon

Effect of soil on active sensors? V7 corn with 0 N

Is soil an important part of the signal? Do we need to consider a way to remove the effect of soil? What happens when the soil “color” varies across time or across the landscape?

Stability of sensor readings? Courtesy: Dr. Peter Scharf

Is variable crop height an issue?

If more H 2 O affects readings – how about less?

Variable Rate Controllers Things you must consider when selecting the controller for your VRA system… –VRA control type –Range of rates –Response time –Precision and accuracy –Communication method(s)

Variable Rate Controllers Many systems claim VRA control but… –Real time control Message based Controller includes decision module –Map based control Useful for image based methods – much less attractive for active sensor applications

Variable Rate Controllers Range of rates for: –Dry fertilizers Range generally not an issue –Liquid fertilizers Standard pressure regulated Capstan spray system (PWM) SprayTarget variable flow nozzles

Variable Rate Controllers What COULD happen IF our response time was too slow?

Variable Rate Controllers Communication issues –Serial (RS-232/RS-422/RS-485) –CAN Bus –As applied maps – stored where/how? –Message formats can be open or proprietary

Sense Decide Control

Decision Module Things to consider when selecting the decision module for your VRA system… –Communication –Algorithm(s) –Flexibility

Decision Module Questions to ask yourself… –How many algorithms are available? –Is my algorithm “stable”? –Can I adjust (timing/layout/parameters)? –What happens when a new piece of information (sensor/map) appears?

Designing a VRA System Now that we have an idea of some of the questions to ask… let’s look into the design of a system based upon a set of requirements. This system was designed for research applications, and may have more stringent requirements than some.

Requirements Use existing Spra-Coupe Plot sizes down to 5x10 m in size Range = lb/a N Precision = 30 lb/a Accuracy < 5% of full scale. Map based and sensor based VRA needed GS & CC sensor data collected and/or used Algorithm – complete flexibility needed

Application System Used existing AGCO Fieldstar controller in the SpraCoupe to change system operating pressure to compensate for changes in ground speed. To get fast response, we chose a “bypass” or 3-way valve system. –When a particular valve (1x, 2x, or 4x) was not sending N to the ground, that same volume of flow was returned to the sprayer tank through a matched orifice. –The pump was always putting out the same volume at the same pressure, and the pressure control system did not have to respond (at least theoretically).

Application System We chose a 6-row system for reasonable plot widths –Near maximum capacity of the SpraCoupe pump at normal operating speeds Drop nozzles with 1x, 2x, and 4x orifice plates were installed in row middles Nominal application rates: –1x = 30 lb N/acre –2x = 603x = 90 –4x = 1205x = 150 –6x = 1807x = 210

Data Flow Collect Reference Strip Data Interpolate/ extrapolate whole-field reference map Get Current GPS data Prior to Application Get Reference Value at Current Point N Recommendation Algorithm Smoothing, Deadband, Hysteresis Solenoid Valve Control 0, 1x, 2x, 3x, 4x, 5x, 6x, or 7x Green GreenSeeker 1 Green GreenSeeker 2 Crop Circle 3 Crop Circle 4 Select and/or Combine Sensor Outputs Spatial or time-base filtering Decision Module

Finding the target sensor data… Drop Nozzles N Sensors a b Given that: Sensor data buffered at 10 Hz v = GPS velocity (m/s) a+b = dist from sensors to drops (m) L = system latency (s) The target sensor data was taken this many readings ago… t = 10*(((a+b)/v)+L) In practice, we have averaged 1s of data (10 values per sensor) centered around this target point.

Positioning details… Drop Nozzles N Sensors GPS Antenna Gives Easting(x), Northing(y), h(eading) and v(elocity) a b Application Boom Center e boom = cos(90-h)*b+e gps n boom = sin(90-h)*b+n gps Individual Sensor Locations e right = cos(90-(h+atn(c/a))*sqrt(c 2 +a 2 )+e gps n right = sin(90-(h+atn(c/a))*sqrt(c 2 +a 2 )+n gps e left = cos(90-(h-atn(d/a))*sqrt(d 2 +a 2 )+e gps n left = sin(90-(h-atn(d/a))*sqrt(d 2 +a 2 )+n gps c d Sensor Boom Location e sens = cos(90-h)*a+e gps n sens = sin(90-h)*a+n gps

Software Control Loop… Collect store and buffer data: sensors, GPS, psi, status, etc. Find Target Data Find N-Ref Data Calc Raw N-Rate Time >1s? N-Rate < MIN? N-Rate > MAX? Map to 0X-7X Beyond Deadband? N-Rate = MIN N-Rate = MAX Send New Rate To Controller No Yes

How Well Did it Work ? Accuracy and consistency of response