[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.