Cathode Voltage Drop Control

The measurement of cathode lining voltage drop is a well-established method of monitoring cathode-lining condition in many smelters. Despite being a relatively infrequent measurement at many smelters the cathode lining voltage drop, if measured accurately, provides important information on how a cathode is performing with age. Accurate measurement of cathode lining voltage drop also enables the optimisation of cell target voltage. Furthermore, with accurate CVD measurements, regular monitoring can also highlight cathode-lining abnormalities such as sludge and ridge build up. A further application of CVD measurements is the ability to compare the performance of different cathode types, or different cathode suppliers.

The successful implementation of the above applications depends upon a reliable and accurate method of measuring cathode lining voltage drop. With the above limitations in mind the C-V-Therm disposable sensor has been developed to provide a combined measurement of cryolite bath temperature and cathode lining voltage drop. The combined sensor for bath temperature and CVD measurement* consists of a Pt-PtRh disposable thermocouple and a thin steel strip running along the outside of the cardboard protection tube designed to make contact with the metal pad. The circuit is completed when an electrical contact is made to the busbar and cathode lining voltage drop is measured on the dedicated instrument.

The measurement is carried out in 2 stages. In the first stage the cryolite bath temperature is measured as described earlier when using disposable Pt-PtRh thermocouples. When bath temperature has been obtained the sensor is then immersed to the bottom of the pot to measure the cathode lining voltage drop. The total measurement cycle takes less than 20 seconds. A dedicated hand held, portable data logging instrument is available for use with the sensor.

Sensor: C-V-Therm