This device efficiently measures the saturation level of a bed of activated carbon.

The indicator is built with a transparent tube containing a special granulate inside. When new, this granulate is of a shiny purple colour, however, it turns brown when it detects contaminants (SH2).

When all the granules have become brown it can be assumed that the properties of the activated carbon below the location of the indicator have become exhausted. Various indicators can be installed throughout the bed in order to know the level of saturation of the carbon at different locations to accurately predict the moment when substitution is required.