Electrode potential is measured with reference electrodes. Electrochemical cells have two conductive electrodes (the anode and the cathode). In supercapacitors electrolytes are the electrically conductive connection between the two electrodes. Bilayer cells contain two layers in between the conductive electrodes (Fig. 4). Electrolytic aluminium smelting also uses graphitic carbon electrodes. These consist of both internal implanted electrodes and magnets and external components. The ceramic forms the dielectric and serves as a carrier for the metallic electrodes. There is also the contact resistance between the welding electrodes and the workpiece. The detector circuit maintains a constant current between the two detector electrodes during titration. Graphite is an electrical conductor, hence useful in such applications as arc lamp electrodes. The electrolysis starts with the application of an external voltage between the electrodes. There is also electrical interference inherent in these electrodes and amplifiers. Hafnium is used in filaments and electrodes. Available ozone generators vary in the arrangement and design of the high-voltage electrodes. Electrodeless induction lamps are fluorescent lamps without internal electrodes.