Many test dust users have expressed an interest in correlation between AC Spark Plug Fine and Coarse test dusts formerly manufactured by AC Spark Plug and ISO Fine and Coarse test dusts manufactured by PTI. Recent particle size analysis of AC Coarse, AC Fine, ISO Coarse, and ISO Fine Test Dust samples indicate differences, which could translate to variations in testing performance.

The above two studies involve particle size data generated using a Leeds & Northrup Microtrac Model X-100 laser diffraction type analyzer. The Microtrac X-100 analyzer is capable of measuring particulates between 0.12 and 704 micron size. The principle of operation involves projection of a laser beam through a transparent sample cell containing a stream of moving particles suspended in water. Light rays, which strike particles, are scattered through angles inversely proportional to particle size. A photo detector array measures quantity of light (flux) at predetermined angles. Electrical signals proportional to measured light flux values are processed by a computer system to form a multi-channel histogram of particle size distribution. A secondary high angle lens system and photo detector gathers high angle scattered signal data from small particles. This data is merged with large particle signal data and correlated into a composite distribution. The Microtrac Analyzer was selected for this particle size comparison because it provides a rapid, repeatable means of comparing broadband distributions.


Seven samples of ISO Fine Test Dust manufactured by Powder Technology Inc. and six samples of AC Fine Test Dust manufactured by AC Spark Plug division of General Motors were analyzed for comparison.

The ISO Fine samples (formerly SAE Fine) selected are those previously used to determine particle size limits shown in ISO 12103-1 Test Dust Standard. ISO Fine batch ID numbers are 4377B, 4382A, 4400B, 4402B, 4422B, 4443A, and 4492B. Graph A indicates the cumulative volume spread of ISO Fine samples analyzed.

Graphical Comparison of ISO 12103-1 Test Dust Grades
Based on ISO 12103-1 Specified Limits Median
(Cumulative Volume)

AC Spark Plug Fine Test Dust samples analyzed were selected randomly and included batch ID numbers 054, 258, 520, 958, 1125, and 1472. Graph B indicates the cumulative volume spread of AC Spark Plug Fine samples analyzed.

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