Surface sensor consolidation and new in-situ tests

Over the past few months, various tests have been conducted by the project team. While the pIOT pilot project mission conducted in April 2019 on the island of Europa confirmed and validated several technological developments, a few malfunctions did occur, especially the surface sensor which triggers the data transmission when turtles come up at the surface.

The project team conducted various tests on new prototypes. The surface sensor of the tags that seemed to be at the origin of a mechanical failure affecting the transmission of LoRa signals was tested for 3 weeks in the laboratory and in a tank. The results of all these tests made it possible to improve on the electronic board, the mechanical design of the tag, and the software algorithms.

Electronic card developed for the project © IFREMER

Version 2 of the tag © IFREMER

All technological advances and therefore prototypes undergo a battery of tests and improvements are constantly being made.

Focus on the operation of the surface sensor version 1 :
The principle of the sensor consists in reading the measurement of a current going through two electrodes placed on the tag. When the tag reaches the surface, the two electrodes are in the contact of the air (a very good insulator) and the current no longer flows between the electrodes. The current measured value is thus supposed to be zero. However, sea water has an impact on the operation of the sensor: corrosion of the electrodes which degrades the reading of the current values, sediment deposition layer and degradation of the coating of the tag which retains a fine layer of water even when the tag is removed from the water. As a result, a current still flows between the electrodes and the surface is no longer detected.
Detecting the surface is essential because it is only out of the water that you can activate GPS and send LoRa messages.

Testing of the electronic board and surface sensor in the laboratory
© IFREMER, Anne-Laure CLEMENT

Testing of surface sensors in a seawater corridor at the Kélonia experimental platform and daily measurement of the parameters © IFREMER, Andréa GOHARZADEH