Sensor accuracy in environmental sensor networks Alex Dionisio Calado Joan Suris Miret EPFL,

Outline Introduction Coding part Temperature range experiment Tests Performance Conclusion

Introduction Coding part Temperature range experiment Tests Performance Conclusion 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

Introduction Coding part Temperature range experiment Tests Performance Conclusion 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

Introduction Coding part Temperature range experiment Tests Performance Conclusion Matlab code Step 1: filter other data Step 2: filter data holes Step 3: create 2 vectors Step 4: convert to Kelvin

Introduction Coding part Temperature range experiment Tests Performance Conclusion Two hour experiment Temperature range: 10-50°C Gradual increase of temperature Main experiment

Introduction Coding part Temperature range experiment Tests Performance Conclusion Calibration curve

Introduction Coding part Temperature range experiment Tests Performance Conclusion 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

Introduction Coding part Temperature range experiment Tests Performance Conclusion One hour experiment Temperature range: 21-23°C Ambient temperature (in computer lab) Ambient air experiment

Introduction Coding part Temperature range experiment Tests Performance Conclusion 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

Introduction Coding part Temperature range experiment Tests Performance Conclusion For experiments performed under optimal conditions (homogeneous temperature, low data holes), the accuracy improvement is on average ~75% Performance assessment Improvement = 57.3 %Improvement = 93.5%Improvement = 75.4 %

Introduction Coding part Temperature range experiment Tests Performance Conclusion 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] each-loop.html [4] References

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