ACD MEASUREMENT AND THEORY

People generally assume that ACD is spatially constant in prebake pots. The argument is that anode consumption will soon bring any deviations in ACD to zero because the current will increase where ACD is lower and vice versa. Measurements, however, show that there are great variations in ACD between the different anodes in the same pot. Differences of 2 cm are not uncommon, and there are also more regular variations along the pot side depending on the position in the anode set cycle. This is because anodes are being replaced, and the ACD is therefore never in equilibrium, but always in a transient state. The current distribution and the magnetic field are constantly changing and affecting the ACD distance. Findings agree with model results. A method was developed to measure the ACD.