[45] Circuit diagram: Contamination indicator

It is important that the effectiveness of a filter can be checked by a contamination indicator. The contamination of a filter is measured by the pressure drop; as the contamination increases, the pressure upstream of the filter increases. The pressure acts on a spring- loaded piston. As the pressure increases, the piston is pushed against a spring.

There are a number of different display methods. Either the piston movement is directly visible or it is converted into an electrical or visual indication by electrical contacts.