We are located in Brazil, ...

We are located in Brazil, and install instrumentation since 1997. I can see the spikes in some data when reading papers or looking databases, and I believe that skypes can have several origins.  To long time monitorings, can happen that when the user take out the sensor the system take a reading. In others situations can be a mistake from the logger system about power up the sensor (low power in the batteries), low water temperature where the sensor take more time to send back the values.  Several others are the possible reasons.  Could be important know a little more about the system like: battery and logger submersed in coll water or in surface, long cables, battery type, etc.

Mauro Banderali