ISO 21018-4:2019

This document specifies a method for the determination of the particulate contamination level using the light extinction technique (also known as light blockage or light obscuration) either online or offline in containers. It also defines procedures for calibrating the instruments and verifying their correct operation both in the laboratory and in service.
In general, the techniques described in this document are suitable for monitoring:
-  the general cleanliness level in hydraulic systems,
-  the progress in flushing operations, and
-  support equipment and test rigs.
The use of this method is applicable to single-phase liquid systems only.