Appendix G
New ISO Medium Test Dust and its effect on ISO . . .
53
New ISO Medium Test Dust and its effect on
ISO Contamination Control Standards
When General Motors gave advance warning to the International Standards
Organization (ISO) that it was intending to stop the production of AC Fine
Test Dust (ACFTD), work commenced immediately on finding an improved
replacement dust. ACFTD was used extensively within the fluid power and
automotive industries for calibrating Automatic Particle Counters (APCs)
and for the testing of components.
APCs are used for testing oil filters, and also for contaminant sensitivity test-
ing of hydraulic components. For 25 years, APCs have been the main stay in
the measurement of solid particles in hydraulic fluids. The growth in demand
for measuring fluid cleanliness in a variety of industrial processes, including
fluid power, has resulted in APCs moving from the laboratory environment
out into the factory. In fact, they are now a critical part of many production
processes. It is therefore essential that the data they provide is both accurate
and consistent.
Calibration
ACFTD has been used as an artificial contaminant since the 1960s and its
original particle size distribution was determined using an optical micro-
scope. This particle size distribution subsequently formed the basis of ISO
4402, the method for calibrating APCs. Due to the limitations of that method
of measurement, the particle size distribution was questioned below about
5µm. It was also not traceable to any national standard of measurement - a
critical requirement for today’s quality management systems.
There was also an absence of formal controls over the distribution of the
test dust, and batch-to-batch variability was much greater than is acceptable
nowadays.
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