The Hansatech Instruments oxygen electrode disc is a specialised form of electrochemical cell known as a Clark type polarographic sensor which comprises a resin bonded central platinum cathode and a concentric silver anode. During measurements, the anode and cathode are linked by a 50% saturated potassium chloride (KCl) electrolyte solution. The electrolyte forms a bridge between the 2 electrode elements via the aid of a fine paper wick which is applied to the electrode disc during the preparation process along with a fine layer of PTFE membrane which is selectively permeable to oxygen molecules. Both are held in place with an O-ring.

Once preparation of the electrode is complete, the disc assembly is mounted into the base of an electrode chamber with the membrane covered dome section of the disc forming the floor of the reaction vessel. The electrode disc is connected to a control unit which supplies a polarising voltage of 700mV. In the presence of oxygen, a polarised disc generates a small current which is directly proportional to the concentration of oxygen in the reaction vessel above the cathode. This current is converted to a voltage, conditioned and digitised with high resolution before display by the electrode control unit.