The surface of the insulator salt density and ash density is to determine the insulator contamination degree basis, its value also represents the local external insulation equipment contamination degree.
According to the soluble impurity (called salt) and insoluble matter (called grey) ratio,  filthy species class can be divided into two categories, A, B.
Class A: solid containing insolubles unclean attached to the surface of insulation, conductive when be affected with damp be affected with damp unclean. The impurity content can be measured by the equivalent salt and grey guhya to characterize its features.
Class B: liquid electrolyte attached to the surface of the insulation, multi containing a small amount of insoluble matter. This kind of filth by measuring equivalent salt density and ash density to characterize its properties.
Class A filthy generally exists in the inland, desert or industrial pollution region. The coastal area is formed on the surface of insulator salt pollution layer in the dew, fog or rain down, also can be regarded as class A filthy.
Class B contamination exists mainly in the coastal area, the sea breeze carrying salt spray deposition directly on the surface of the insulator. Usually chemical enterprises discharge chemical mist and atmospheric pollution caused by high salt fog and drizzle can also be classified as such.
The polluted degree measurement:After 3 years to 5 years in a row in the insulator product equivalent salt density and ash fouling measurement after the surface.The contamination degree can reference disc suspension insulators in operation on the measurement of charged, can also be hung on the operating insulator string near the uncharged reference disc insulator measurement.