Hach-Lange 3705 sc - Manual (Page 10)

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General Information
2.2 General Sensor Information
Optional equipment, such as mounting hardware for the probe, is supplied with
instructions for all user installation tasks.
Figure 1 Sanitary-style Sensor
Figure 2 Convertible-style Sensor
2.3 The Digital Gateway
The Digital Gateway was developed to provide a means to use existing analog sensors
with the new digital controllers. The gateway contains all the necessary software and
hardware to interface with the controller and output a digital signal.
2.4 Theory of Operation
Inductive conductivity measurements are made by passing an AC current through a
toroidal drive coil which induces a current in the electrolyte solution. This induced solution
current produces a current in a second toroidal coil. The amount of current induced in the
second coil is proportional to the solution conductivity.
The major advantage of toroidal conductivity is that the coils are not in contact with the
solution. Because the coils are isolated from the solution, oils and other contaminants in
moderate amounts do not interfere with the measurement. In addition, the coil housing can
be chosen to withstand corrosive environments which would quickly corrode traditional
sensors with metal electrodes.