Contact-less toroidal fluid conductivity sensor based on RF detection

A contact-less toroidal coil based fluid conductivity sensor has been designed, prototyped and tested on sea water samples of different salinities. The novelty of the design lies in the coil construction and RF phase detection used for the conductivity sensing. The sensor is made of two insulated toroidal coils having an area of 15/spl times/15 mm/sup 2/, 1.5 mm thick and embedded in a printed circuit board (PCB). The conductivity detection technique involves detecting a phase change that occurs between an alternating signal that couples between two such closely held coils inside the fluid. The sensing circuitry, which provides the input and converts the phase change into an output voltage was also assembled and integrated with the sensor.