Sensor accuracy in environmental sensor networks

Alex Dionisio Calado

Joan Suris Miret

EPFL, 10.06.2011

Outline

Introduction Coding part Temperature range experiment Tests Performance Conclusion

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusion

The temperature sensor of the Mica-z mote is fairly inaccurate More accurate devices are expensive Calibration methods exist

to improve the accuracy Goal: Take measures from a

reference mote and an

uncalibrated mote and perform

a calibration on the latter

to improve the data

Goals and motivation

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusion

The java code activates the temperature sensor and exports the data to a text file.

Two columns, one with the node ID ant the other with the corresponding values

The Matlab code : Filters the raw data in order to only treat ours Removes the data that doesn’t alternate Separates the data in two vectors Converts data into degrees Kelvin

Java and Matlab code

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusionMatlab code

Step 1: filter other data

Step 2: filter data holes

Step 3: create 2 vectors

Step 4: convert to Kelvin

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusion

Two hour experiment Temperature range:

10-50°C Gradual increase

of temperature

Main experiment

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusionCalibration curve

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusion

6-7 minutes experiment Temperature range:

33-35°C Steady heating Local temperature

variations due to

point source Improvement idea:

box with homogeneous

temperature

Hairdryer experiment

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusion

One hour experiment Temperature range:

21-23°C Ambient temperature

(in computer lab)

Ambient air experiment

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusion

One hour experiment Temperature range: 2-16°C Good homogeneity From 2-10°C,

the calibration curve

has been extrapolated,

but yields good results

Camping cooler experiment

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusion

For experiments performed under optimal conditions (homogeneous temperature, low data holes), the accuracy improvement is on average ~75%

Performance assessment

||

|_|1[%]

TobsTref

improvedTobsTreftimprovemen i

n

timprovementimprovemen

n

ii

tot

1[%]

Improvement = 57.3 % Improvement = 93.5%Improvement = 75.4 %

IntroductionCoding part

Temperature range experimentTests

PerformanceConclusion

Calibration returns good results (~75% improvement) With more time, more temperature range experiments can be

performed, as well as more tests, to improve the accuracy and the reliability

Using an actual thermometer or another sensor as reference would probably yield more realistic results

The environment where the experiments are taken is non-homogeneous

Conclusion

[1] Crossbow, MTS/MDA Sensor Board Users Manual, pp. 7-8, Revision A, June 2007

[2] A. Martinoli, “Signals, instruments and systems”, presented at EPFL during spring 2011, Switzerland

[3] http://www.java-tips.org/java-se-tips/java.lang/how-to-use-for-each-loop.html

[4] http://zamov.online.fr/EXHTML/JAVA/JAVA_785340.html

References

Thank you for your attention