april 2007 new soil moisture sensors enable high performance swat controllers mike van bavel,...
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![Page 1: April 2007 New soil moisture sensors Enable high performance SWAT Controllers Mike van Bavel, President Dynamax Inc. - Our Mission Combine science and](https://reader030.vdocuments.net/reader030/viewer/2022032600/56649d965503460f94a7f131/html5/thumbnails/1.jpg)
April 2007
New soil moisture sensors New soil moisture sensors Enable high performance SWAT Enable high performance SWAT
ControllersControllersMike van Bavel, President Mike van Bavel, President
Dynamax Inc. - Our MissionDynamax Inc. - Our Mission • Combine science and technology to produce
advanced & affordable soil moisture irrigation control solutions for efficient water management and water conservation.
• Delta-T Devices (UK)} sensor design and production
• Dynamax Inc (Houston) } system design, controls manufacturing, USA sales / support
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April 2007
Background - Portable Moisture Probes
• Multiple soil moisture readings
• Battery operated hand held
recorder & display – HH2
• ThetaProbe soil moisture sensors
• Portable Sensors
- Surface readings
-or inserted in access tubes
-Profile Probes
• Irrigation system audits, test application, and soil surveys for salinity (EC) – electrical conductivity
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April 2007
New Conservation Controllersvs Plain Old Timer
• There are 2 basic conservation controller types:– Soil Moisture Sensor:
• Uses actual soil conditions for irrigation start / stop points.
• Uses real-time information on soil moisture conditions for irrigation. Regulates a Timer according to water needs.
– ET (Evapotranspiration):
• Uses historical / pre-programmed water usage, or actual ET from a local station or the controller, updated manually or automatically.
• Regulates a timer according to estimated water use.
• The plain old timer has no feedback on the actual soil or the weather conditions.
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April 2007
Why Soil Moisture ?• Properly applied soil moisture irrigation
scheduling is the most accurate and efficient conservation method!
• Both technologies work for water conservation but soil moisture is the most most accurate, when you use accurate and accurate, when you use accurate and proven sensors.proven sensors.
• The answer is: soil moisture is what the plants use and people intuitively understand how it works.
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April 2007
SM200 Introduction• Low cost• Good accuracy• Excellent temp stability• Excellent salinity response• Durable• Buriable• Compact for limited space
applications• Patented design• Proven Delta-T technology
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April 2007
SM200 specifications
Water tight connector
½” ThreadFor conduits
2.5mm pins 50mm longStainless steel –
indefinite lifespan
Durable plastic body
Shaped pin termination
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April 2007
SM200 SpecificationsPower 5 to14 V @15mA typically, low power
Output 0 to 1.2V full scale, easy to read
Range 0 to 40% accuracy 3%
Range 0 to 60% accuracy 5%
Add. Temp errors
0.01%/ C over 0 to 40%, 0 to 60 C
Add. Salinity errors
3.5% over 0 to 40%, to 500mSm-1
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April 2007
Why are Delta-T SM200 Soil Moisture Sensors Accurate and Reliable?
• Developed by Scientists and produced for scientists (since 1996). Wide range of applications needed for research.
• The first FDR probe with a single voltage output - ThetaProbe patented technology.
• FDR - (Frequency Domain Reflectometer) Measures soil dielectric with a microwave signal. Wide moisture range 0-60%.
• Operates with a wide range of soils, and includes a calibration built into each and every sensor.
• Salinity and temperature instability are designed out, and have limited effects.
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April 2007
Soil Moisture Control –Soil Moisture Control –Set Point RequirementsSet Point Requirements
Yellow Zone - Deficit Irrigation Green Zone - Optimum Growth Range
45%
40%
28%29%
32%
36%
30%
27%
10%
21%
16%
7.0%
11.5%
15.0%
19.5%
22.5%
28.0%
25.0%23.5%
21.5%
30.0%
33.0%
22%
20%
15%
18%18%20%
15%
12%
4%
9%
7%
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
1) Sand 2) LoamySand
3)SandyLoam
4)Loam 5)Silt Loam 6)SandyClay Loam
7)SandyClay
8)ClayLoam
9)SiltyClay Loam
10)SiltyClay
11)Clay
Soil Type
% W
ate
r b
y V
olu
me
Field Capacity(Ratcliff 1983)
Irrigation StartPoint
Wilting Point
Field CapacityWater Above this Line is
Wasted - Run-off
Wilting PointPlants Unable to Take Up Water
M.A.D - IrrigationStart Point
Set Point
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April 2007
Moisture Control theory and requirements
•A closed-loop controller (C) uses feedback (-) from sensors to control states or outputs of a dynamical system (y).
• The reference values ( r +) are set by the user to a desired beneficial level.
•A operational controller must also have: Stability, Controllability, and Observability.
• Sensor feedback that has error in excess of the desired control function feedback (e), causes uncontrollability and problems with observability.
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April 2007
Closed Loop Controllers- The good news:
Advantages over open loop, ex. timers:• disturbance rejection • guaranteed performance even with model uncertainties, when the model structure does not match perfectly the real process and the model parameters are not exact • unstable processes can be stabilized • reduced sensitivity to parameter variations • improved reference tracking performance
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April 2007
What Sensor Accuracy do We need ? What Sensor Accuracy do We need ?
Stress Level < 7%
Irrigation Start (7%)
Stress Level < 33%
Deficit Irrigated
Clay Sand
0%
10%
30%
40%
50%
Field Capacity (10%)
WIlting Point 4%
Over Irrigated
Optimum GrowthMoisture Range
Optimum Moisture Range
Wilting Point 22%
Dead Plants - No Production
Wasted Water & Fertilizer
Irrigation Start Point (33%)
Field Capacity (45%)
Over Irrigated
20%
60%
Maximum Error Allowable +/ – 3 %
Wasted Water
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April 2007
Real Time Example - Seattle
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April 2007
CIT SWAT Testing protocol - Results
• What does the test result show us?• A correlation between a soil simulator drying
out and a soil moisture sensor reading in the top 4 inches. (not a calibration for the sensor)
• The soil drying trend will show a correlation to the soil sensor in a single installation to be accurate enough for control purposes.
• If there are poor correlations due to salinity effects or temperature operating range changing the sensor characteristics.
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April 2007
Correlation of all data with weight loss vs all Delta -T SM200 Sensor readings
y = 1.0253x
R2 = 0.9104
0%
10%
20%
30%
40%
50%
60%
0% 10%
20%
30%
40%
50%
60%
Calculated water content %
Sen
sor
Mo
istu
re c
on
ten
t %
"Overall Soil Texture"
Linear fit for Sensor Measurements vs. Calculated Water Content
Zero Intercept
Linear ("Overall Soil Texture")
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April 2007
CIT SWAT Test ResultsAll Salinity Levels Compared On Medium Texture Soil
y = 0.8368x + 0.0417
R2 = 0.9776
y = 0.8077x + 0.0572
R2 = 0.9959
y = 0.9157x + 0.0427
R2 = 0.9815
y = 0.9181x + 0.0199
R2 = 0.95360%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50%
Gravimetric Readings
Se
ns
or
Re
ad
ing
s
6.4.1 - 1.0 dS/m
6.4.2 - 1.5 dS/m
6.4.3 - 3 dS/m
6.2.2
Linear (6.4.1 - 1.0 dS/m)
Linear (6.4.2 - 1.5 dS/m )
Linear (6.4.3 - 3 dS/m)
Linear (6.2.2)
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April 2007
6.2.3 Delta-T SM200 Rep1Sensor Measurement vs Calculated Volumetric Water
Coarse Textured Soil
y = 0.9x + 0.0289
R2 = 0.9922
0%
10%
20%
30%
40%
50%
60%
0%
10
%
20
%
30
%
40
%
50
%
60
%
Calculated water content %
Sen
so
r M
ois
ture
co
nte
nt
%
6.2.3 Calibration in a CoarseTextured Soil
Upper Limit
Lower Limit
Linear fit for SensorMeasurements vs.Calculated Water Content
The range of 95% confidence, (2*SD) = +/-1.4%.Well within the minimum accuracy needed to control moisture in sandy soils.
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April 2007
Advanced Moisture Level Advanced Moisture Level Control IL200-MCControl IL200-MC
• How does it work? – Set desired initial
Irrigation Start Point (% Vol) by soil type chart.
– The output relay triggers when below the set point.
• Or use a learning curve– Determine site specific
field capacity one day after irrigation.
– Adjust the moisture to the ISP, about 0.9 * field capacity.
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April 2007
IL200-MC Irrigation System ApplicationsIL200-MC Irrigation System Applications • Satellite and Standard Timer Upgrade Scheduling:• IL200-MC controls the water for 5-8 zones grouped together. • The moisture sensor, SM200, is buried in most critical zone. • Valve power is enabled when moisture is below the irrigation set
point.
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April 2007
Moisture ClikTM Setup
• The setup is fairly simple.
• There are only three connections to be made after the box is mounted.
• The basic steps are:– Connect the power lead.
– Connect the sensor leads.
– Connect the output / control wires from the relay to the sensor input.
– Other applications• Direct Valve Control
• Common Interrupt line
• Alarms to central control
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April 2007
Set the Dial for the Irrigation Start
• Set by Soil Type Directly, or
• Irrigate and adjust by Soil Field Capacity
• Timer Program - - Short cycles, with multiple start times:
Repeat water & soak so all zones are the same soil moisture.
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April 2007
New - Advanced Irrigation Control with SM200, GP1
Precision Moisture control and monitor with recordings:
Soil moisture, water used, rainfall, temperature
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April 2007
Conclusions • Accurate water conservation control
solutions with soil sensors are available.
• Smart water solutions may be successful with tested sensors.
• Next: Develop the protocol to measure savings and water efficiency certification.
• Thank you for attending, Dynamax appreciates your time and interest!