1 Scope
This standard describes the sampling procedures and methods for the determination
of particle concentration and size distribution.
Three methods are specified. One uses an automatic particle size analyser, working
on the light interruption principle. The other two use an optical microscope, in either
the transmitted light or incident light mode, to count particles collected on the
surface of a membrane filter. The optical microscope methods are described in ISO 4407.
All three methods are applicable to both used and unused insulating liquids.
Annex A contains an alternative sampling procedure using a syringe and Annex B reports a reference for the calibration of automatic particle counters.
NOTE 1 The methods are not intended to measure particulate matter in liquids containing sludge.
While analysing solid content on oils containing sludge refers to method for sediment
and sludge determination in IEC 60422, Annex C.
NOTE 2 The methods specified are only applicable to measurements related to a limited range
of size and number.