An inductive conductivity sensor is based on electromagnetic induction and it has some advantages such as robust structure and low manufacturing cost over conductive sensors. These sensors have no bare metal electrodes directly contacted with solutions, so they are free from damage by chemical corrosive solutions such as sulphuric acid and sodium hydroxide.
A transformer type sensor has robust structure and good linearity. It is easy to install and convenient to use in the industrial field. Using these characteristics, Kang Hwi Song, a section head at the Faculty of Electronics, has designed a new type transformer inductive conductivity sensor (TICS).
TICS has one or more magnetic cores. Its permeability values change with temperature and pressure. It is very important to compensate or eliminate the effects of magnetic core permeability change for improving the sensing performance.
TICS consists of a drive coil, a sense coil and a temperature sensor. Applying alternating voltage to the drive coil induces an ionic electric current in the solution around the sensor. This ionic electric current also induces an electric current in the sense coil which is proportional to the conductivity of the solution. Here, the two coils are encapsulated by chemical-resistant plastic material that protects them from corrosive electrolytes.
The equivalent loss resistances of the drive coil and the sense coil depend on both their turn number and frequency. From the investigation into the new model, he set the rational turn numbers as 10 each. The signal voltage was hardly affected when the drive frequency over 10kHz was used. As frequencies higher than 10kHz may cause magnetic loss, 10kHz was selected as a drive frequency.
In a word, it is important to use magnetic cores which have high permeability and small magnetic loss. He selected HS10 as the most suitable magnetic core for his purpose.
The drive coil and the sense coil are fixed on the PCB and welded to the lead wire. The main body encapsulates the two coils and PCB. The seal ring, fixing cap and gland are assembled each other. The seal ring and gland are for waterproof structure and the fixing cap is for the tank. Each part is fabricated of ABS plastic by a 3D printer. ABS plastic material has high chemical resistance and high water resistance and it is cheap. The thickness of the main body is 2 mm.
This sensing device is cheap and consumes less power. It also has simple circuitry, good linearity, high sensitivity and wide measuring range.
You can find more information in his paper “A new design of inductive conductivity sensor for measuring electrolyte concentration in industrial field” presented to the SCI Journal “Sensors and Actuators A: Physical”.
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