Transcript Interfacing Sensors with (VR)Application Equipment Scott Drummond IT Specialist Ken Sudduth Agricultural Engineer Objectives • Understand the “big picture” of developing a sensor based system for VRA.

Interfacing Sensors with
(VR)Application Equipment
Scott Drummond
IT Specialist
Ken Sudduth
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
N applied at Planting (kg ha-1)
Days after
planting /
Growth stage
Is soil an important
part of the signal?
0
45
246
23 DAP
V4
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?
NDVI:
ISR:
SPAD:
0.36
0.47
39.8
NDVI:
ISR:
SPAD:
0.36
0.47
41.1
NDVI:
ISR:
SPAD:
0.36
0.47
43.7
NDVI:
ISR:
SPAD:
0.53
0.31
48.6
NDVI:
ISR:
SPAD:
0.53
0.31
52.8
NDVI:
ISR:
SPAD:
0.57
0.28
58.8
NDVI:
ISR:
SPAD:
0.64
0.22
49.9
NDVI:
ISR:
SPAD:
0.66
0.21
52.8
NDVI:
ISR:
SPAD:
0.70
0.18
57.6
NDVI:
ISR:
SPAD:
0.66
0.21
45.1
NDVI:
ISR:
SPAD:
0.68
0.19
52.4
NDVI:
ISR:
SPAD:
0.73
0.16
59.8
41 DAP
V7
47 DAP
V10
56 DAP
V13
20:41
19:59
19:31
19:03
18:35
18:07
17:39
17:11
16:43
0.8
16:15
15:47
15:19
14:51
14:23
13:55
13:27
12:59
12:31
12:03
Dew
11:35
11:07
10:39
10:11
9:43
9:15
0.7
8:47
8:19
7:51
7:23
0.9
6:55
6:27
NDVI
Stability of sensor readings?
Rain
0.85
40 inch
0.75
20 inch
0.65
10 inch
0.6
Time on 10 July 2006
Courtesy: Dr. Peter Scharf
Is variable crop height an issue?
If more H2O 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
Delay Time = 9 s
Delay Time = 14 s
Corn Yield
(bu/ac)
124 to 180
110 to 124
101 to 110
95 to 101
89 to 95
83 to 89
76 to 83
68 to 76
52 to 68
30 to 52
What COULD happen IF our response time was too slow?
Variable Rate Controllers
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 = 0-210 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 = 60
3x = 90
4x = 120
5x = 150
6x = 180
7x = 210
Data Flow
Prior to Application
Collect
Reference
Strip Data
Interpolate/
extrapolate
whole-field
reference map
Get Current
GPS data
Green
GreenSeeker 1
Green
GreenSeeker 2
Crop
Circle 3
Crop
Circle 4
Select and/or Combine Sensor Outputs
Get Reference
Value at
Current Point
Spatial or
time-base
filtering
N
Recommendation
Algorithm
Smoothing,
Deadband,
Hysteresis
Solenoid
Valve
Control
Decision Module
0, 1x, 2x, 3x, 4x, 5x, 6x, or 7x
Finding the target sensor data…
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.
a
b
Drop Nozzles
N Sensors
Positioning details…
a
b
Drop Nozzles
N Sensors
Sensor Boom Location
esens = cos(90-h)*a+egps
nsens = sin(90-h)*a+ngps
c
Application Boom Center
eboom = cos(90-h)*b+egps
nboom = sin(90-h)*b+ngps
d
Individual Sensor Locations
eright = cos(90-(h+atn(c/a))*sqrt(c2+a2)+egps
nright = sin(90-(h+atn(c/a))*sqrt(c2+a2)+ngps
eleft = cos(90-(h-atn(d/a))*sqrt(d2+a2)+egps
nleft = sin(90-(h-atn(d/a))*sqrt(d2+a2)+ngps
GPS Antenna
Gives Easting(x), Northing(y),
h(eading) and v(elocity)
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?
Yes
No
N-Rate
< MIN?
N-Rate = MIN
No
N-Rate
> MAX?
No
Map to 0X-7X
Send New Rate
To Controller
Yes
Yes
Beyond
Deadband?
No
Yes
N-Rate = MAX
How Well Did it Work ?
• Accuracy and consistency of response