The free chlorine sensor works
according to the principle of depolarization of a galvanic
The sensor contains a platinum and a copper electrode.
With the sample water acting as the
electrolyte, galvanic potential develops between the
two electrodes, depending on the electrode material.
With non-flowing water the electrodes would polarize
and interrupt the current flow (hydrogen gas at the
platinum electrode, oxide layer at the copper electrode).
The constant flow causes small glass balls inside the
sensor to circulate and remove any passivation layer
from the electrodes. With these stable conditions, the
sensor current increases proportionally to the free