Ocean CTD

The New D-2 Closed Field Conductivity Cell Technology

Inductive versus Closed Field Cells

What makes the D2 CTD unique revolutionary technology? Not only can our CTD deliver closed field precision but also offer a flow through cell. Our Ocean CTD combines the performance advantage of the traditional 3 electrode sensor where the end electrodes are electrically tied together ensuring there is no external electric field.  That electrode system couple with a novel inductive drive, eliminates the need for additional center electrode, or other electrodes in the measurement field.  The two-electrode sensor with inductive drive is hence called a Hybrid as it incorporates the best aspects of both the electrode type & inductive type conductivity sensors that have a strong history of performance oceanographic conductivity measurements.

Closing the Field to Measure Accurately

As the two outside electrodes are sorted together electrically so by theory the outside potential of the sensor is “zero” hence there is no current flow outside the path sorted by the end electrodes.  The inductive drive creates a current that flows through the center measurement region, the current flows in direct proportion the conductivity of sea water.  This current is collected by the end electrodes and passed through a simple current to voltage transformer.  As current is in direct proportion to the conductivity of sea water and the magnitude to the drive signal. 

Free Flowing Precision

The drive signal level can be precisely controlled, and the collection electrodes and shorting path can be constructed to have very low impendence as compared to the external sea water path, hence the ‘all’ of the current flows through the short, and, hence the current measurement transformer.  The result is a two-electrode cell that is ½ the length of a traditional a 3-electode cell and has a large center diameter. A sensor that can free pass water through the cell without the need for a pump in almost all applications.  In applications where a pump is needed, say for biological control, this can be easily added as the sensor measurement volume is 100% enclosed in the sensor and the addition of tubing a pump will not affect the calibration.  The sensor is fully described in US Patent #9,410,910.