The Basic Idea

Making a probe like this is not exactly revolutionary. Our goal is to build a robust unit, both physical and software wise. Experience has shown that developing a reliable datalogger from scratch is a process that can take months, if not years ('Good software takes 10 years. Get used to it') So we soon decided to cut short and use a Campbell datalogger as the core of the system. Campbell already gone through the ten year cycle and datalogging is their core business so these units are extremely reliable. Interfacing to sensors is very well documented and programming is relatively simple.

The only disadvantage is their size. The brick shaped wall mount housing is not very well suited for mounting in a tube. So we take it apart...
And then it's not too bad. The metal box is the actual logger and the PCB just contains the connectors, fuses and overvoltage protectors. These parts will fit in a 10 cm inner diameter tube which is a very acceptable size.
Obviously we benefit most from choosing a Campbell datalogger if we also use their sensors. Unfortunately not all of these are really suitable for use in extreme sea-conditions but they will do fine in fresh to brackish water of rivers harbours and estuaries. This settles our choice for the Conductivity, Temperature, pH and OBS sensors. Choosing a Dissolved Oxygen sensor is easy. We will use the InsiteIG optical DO sensor which has already proven itself in the Nortek Oxybox. Finally we will need a pressure sensor. The easiest solution is to use the same sensor as used in the all other Nortek current meters.This will require some additional electronics for the signal conditioning but we will need an additional PCB anyway for connections, power supply and some interfacing.