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Installation and Calibration of
Moisture Probes
Minnesota Department of Transportation (MnROAD)
More details contact Len for the full presentation & written documentation
MnROAD Moisture Probes(Experience With)
Model Description Dates InstalledGauges
Installed
EC Decagon-TE and 5TE 2006, 2007, 2008 227
HDHeat Dissipation Sensor - Campbell
Scientific CS229 2006 18MH Concrete Moisture 2004 30MH Concrete Moisture - Sensirion SHT75 2010, 2011 116MP Wescor PST-55-15-SF Psychrometer 1997, 2000 30MR ELE EI23-7724 Moisture Resistance Gauge 1997, 2000 39RE Water Content Relectometer CS616 1999, 2006, 2008 58
TD Fabricated or CS605 or CS610 or CS6451993, 1999, 2000, 2004, 2007, 2008 784
WM Irrometer Watermark 200-X1993, 1999, 2005,
2008, 2011 851
Installation of Moisture Probes at MnROAD
1. Bore Hole2. Separate Materials3. Install Sensors
• Flat installation• 1” Sieve #4 Material - Lite Compaction• 3” Material – Heavy Compaction
May add water as neededCheck void ratio – cup sampler
Installation of Moisture Probes at MnROAD
Campbell CR1000 data logger and multiplexer
Sensor Protectionto Cabinet
Cabinet Setup
Calibration Experience with Moisture Probes
• Calibration efforts prior to 2012– 2006 calibrations for TE (manufacturer’s process)– 2009 generic calibration equations are found not useable – 2010 and 2011 experimented with small scale calibrations
• 2012 Calibration approach– Procedures developed by Starr and Paltineanu (2002) and
refined by Decagon Devices (2010)– MnROAD Experience
(Need calibration for each sensor and materials type)
– Soil drying containers– Scale or mass balance– Drying oven– Volumetric soil sampler– Calibration containers– Sensors (MnROAD started with Decagon TE and 5TE)– Data collection and storage system
Moisture Probe Calibration Lab Equipment
Moisture Probe Calibration Procedure• Sample Preparation
– Air dry material - Sieve material with #4 (2-5mm) sieve• Preliminary Calibration Procedure
– Recording mass and volumes of calibration containers, volumetric samplers, and sensors with wire
– Programming the data logger - Create spreadsheet templates• Calibration Procedure
1. Start with air-dry material2. Fill calibration containers with sensors
(Compact in 5 lifts – 20% of Max Density)
3. Weigh containers to determine density4. Record sensor output
(1 hour of 1 minute intervals)
5. Sample volumetric moisture content6. Record moisture content7. Repeat procedure for next moisture content
(6 Data Points Required)
300 400 500 600 700 800 9000
0.05
0.1
0.15
0.2
0.25
0.3
f(x) = 0.000318416008237754 x − 0.00214153552983726R² = 0.738356391489068
Cal. Eq. for 5TE in Clay Subgrade
VWC MeasuredLinear (VWC Measured)
250 300 350 400 450 500 550 6000
0.020.040.060.08
0.10.120.140.160.18
f(x) = 0.000330034333482609 x − 0.0239136637309051R² = 0.978879250392444
Cal. Fcn. for 5TE in Class 5 Base
Meas. VwLinear (Meas. Vw)
Raw Data
VWC
250 300 350 400 450 5000
0.02
0.04
0.06
0.08
0.1
0.12
0.14
f(x) = 0.000460052139242447 x − 0.0908326943720288R² = 0.964217216122499
Cal. Fcn. for 5TE in Select Granular Sub-base
Meas VWCLinear (Meas VWC)
300 350 400 450 500 5500
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
f(x) = 0.000367331180682297 x − 0.0481024615096635R² = 0.898151625822559
Cal. Fcn. for 5TE in Class 3 Sub-base
Meas VWCLinear (Meas VWC)
Moisture Probe Calibration Functions
Moisture Probe Calibration Functions
SensorMnROADMaterial
Calibration Equation
TE Generic (2006) VWC= 0.00109 RAW - 0.629Sand VWC= 0.0009 RAW - 0.4929Clay VWC = 0.0009 RAW - 0.4693
Select Granular VWC = 0.0011 RAW - 0.6615Class-3 VWC = 0.0009 RAW - 0.5149Class-4 VWC = 0.0008 RAW - 0.4120Class-5 VWC = 0.0007 RAW - 0.3524Class-6 VWC = 0.0011 RAW - 0.6787
Class-7 (Reclaimed) 5TE Generic (2008) VWC = 0.00109 RAW - 0.629
Sand VWC = 0.0004 RAW - 0.0780Clay VWC = 0.0003 RAW - 0.0021
Select Granular VWC = 0.0005 RAW - 0.0908Class-3 VWC = 0.0004 RAW - 0.0481Class-4 VWC = 0.0004 RAW - 0.0520Class-5 VWC = 0.0003 RAW - 0.0239Class-6 VWC = 0.0006 RAW - 0.1438
Class-7 (Reclaimed HMA) VWC = TBD
Next sensor types - Moisture Block (851) and CS616 (58) calibrations
With (top base) - ~.50 VMCWith (bottom base) - ~.35 VMC
Without (top base) - ~1.30 VMCWithout (bottom base) - ~.80 VMC
With Calibration
With Generic Calibration
Moisture Probe Generic and Calibration FunctionsApplied to MnROAD Data
Moisture Gauge - Installation Discussion
• Vertical (with forks) or Horizontal (without fork)• Collect Raw data only (no factors) – apply later• Use sieved material around sensor• Sensor Lead Length effect (50’ vs 500’)• Frequency of measurements (MnROAD 15 minutes)• Excitation Voltage (MnROAD 12 volts)• Data Collection Temperature Ranges (Cabinet Temps)
• Role of material density and moisture measurements?– Differences – maybe soil sampler field?
• Does a generic calibration function work for other types of non-capacitance sensors used in pavement research?
• Does every sensor installed need a calibration? • Discussion on the process (manufacture vs modified)
– Manufacture use same volume of soil compacted in a calibration container– Modified working to get maximum density (minimize voids)
Moisture Gauge – Calibration Discussion
Moisture Probe – Data Use Discussion
• Can moisture sensors detect bound and unbound water in fine-grained clay materials?
• Observe variation in the data• (6 hour running average used) – why?
• Observed manufacture calibration factored data above 100% and negative data (why we did a calibration)
• Flat vs vertical (eliminate potential of condensation)• Installation of sensor at a material interface• Do the readings vary with temperature extreams• Sensor Recommendations
• Capacitance sensors seem the best• Moisture blocks have been improved (not fully tested)
