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As a policy of continual improvement, RMF reserves the right to alter the specification without prior notice.
201.028 REV 1
Date of Issue: 18 June 2018
11.9 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 testing 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 microscope. 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 ab
out 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.
ISO therefore defined the requirements for the replacement for ACFTD and asked the National Institute of
Standards and Technology (NIST) in the USA to produce a standard, traceable reference material. The new
dust’s
particle size distribution has been accurately determined with the aid of modern scanning electron microscope
and image analysis techniques.
ISO Medium Test Dust Benefits
The new ISO Medium Test Dust (ISO MTD) consists of similar materials to the old ACFTD, but to minimize particle
counting errors, it is of a slightly coarser grade because ACFTD included too many particles smaller than 5μm
which gave problems during testing.
ISO MTD is produced to a standard distribution and stringent quality control procedures, thereby ensuring
excellent batch-to-batch repeatability. These procedures, combined with a revised ISO APC calibration method
give:
• A traceable and controlled reference test dust with greatl
y reduced variation in particle size distribution. This
gives the trace-ability required by ISO 9000, QS9000 and similar quality management systems.
• A procedure for determining the performance of APCs so that minimum acceptable
levels can be set by the
user.
• Improved calibration techniques and proce
dures.
• More accurate calibration.
• Improved levels of particle count reproducibility with different equipment.
• More accurate and consistent filter test results.
Effect on Industry
The introduction of ISO MTD has necessitated changes to certain ISO standards.
The standards affected include:
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