Clark-cell, polarographic technology supplies constant electrical voltage across the anode and cathode. As oxygen is reduced, the current supplied to the cathode is increased. The amount of electricity required to reduce the oxygen at the cathode is equivalent to the dissolved oxygen present.
This technology was developed in 1956 and is familiar to most operators. The challenges of polarographic technology include necessary warm-up time, membrane replacement, and the potential of electrolyte solutions degrading.
Galvanic technology, developed in 1964, consists of an anode and cathode in electrolyte solution covered with an oxygen-permeable membrane. As oxygen permeates the membrane, the cathode reduces the oxygen, creating a potential that is equal to the amount of oxygen in the system.
This method offers the advantages of eliminating warm-up times, as the self-polarized probe is ready to read. However, galvanic technology still struggles with membranes and electrolyte solutions. Interference occurs with the presence of any chemical that produces an electrical charge.