SIST-TP ISO/TR 16386:2016

TECHNICAL ISO/TR
REPORT 16386
Second edition
2014-11-15
Impact of changes in ISO fluid power
particle counting — Contamination
control and filter test standards
Conséquences des changements survenus dans les normes ISO
relatives au comptage des particules — Contrôle de la contamination
et essais de filtres
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Historical background . 1
2.1 What is ACFTD? . 1
2.2 Calibrating particle counters using ACFTD . 1
2.3 The original multi-pass filter test . 2
3 New test dusts . 2
4 New APC calibration procedure . 2
5 Why changes were necessary . 5
6 Impact on particle sizes and contamination measurements . 5
6.1 Redefinition of particle sizes . 5
6.2 Apparent particle concentrations . 6
6.3 Contamination code reporting . 8
7 Impact on filter test results . 8
7.1 Filter retained contaminant capacity . 8
7.2 Filtration ratio and filter efficiency . 9
8 Conclusion .11
Bibliography .12
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
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The committee responsible for this document is ISO/TC 131, Fluid power systems, Subcommittee SC 6,
Contamination control.
This second edition cancels and replaces the first edition (ISO/TR 16386:1999) which has been
technically revised.
iv © ISO 2014 – All rights reserved

Introduction
This Technical Report has been prepared as an information document to give users an understanding
into the background and implications of a number of new and revised contamination control standards,
namely ISO 11171, ISO 11943, ISO 16889 and ISO 4406.
The adoption of four revised and updated contamination control standards, ISO 11171, ISO 11943,
ISO 16889, and ISO 4406:1999, has produced significant changes in terms of how solid contamination
levels and filter performance are reported.
With ISO 11171, the method of calibrating automatic particle counters (APCs) using AC Fine Test Dust
(ACFTD) used since the early 1970s has been replaced by a new method traceable to the USA’s National
Institute of Standards and Technology. As a result, contaminant particle sizes previously referred to as
2 μm, 5 μm, 10 μm, and 15 μm became 4 μm(c), 6 μm(c), 10 μm(c), and 14 μm(c), respectively, where (c)
refers to particle sizing and counting done with an APC calibrated in accordance with ISO 11171.
ISO 11943 is a new standard for calibrating online particle counting systems that are primarily used
to evaluate filter performance. With the ISO 16889 filter multi-pass test, which replaces the original
ISO 4572 method, ISO Medium Test Dust (ISO MTD) replaces ACFTD as the test dust and the new
ISO 11171 traceable particle counter calibration method is used. In ISO 4406:1999, the new calibration
method is used, and a new 4 μm(c) size class has been added to the solid contamination code for particle
counts made with an automatic particle counter.
These improvements in particle counting and filter testing have a significant impact on contamination
control activities. However, it is important to note that there has been no change in the actual
contamination levels or in the performance of filters, or their effectiveness in protecting the reliability
of components. This Technical Report discusses what the changes are, why they were made, how they
impact contamination levels and filter ratings, and how they benefit the industry.
TECHNICAL REPORT ISO/TR 16386:2014(E)
Impact of changes in ISO fluid power particle counting —
Contamination control and filter test standards
1 Scope
This Technical Report discusses the impact of changes in International Standards for particle counting,
contamination control, and filter testing.
Liquid automatic particle counters (APCs) are used in monitoring contamination levels in hydraulic
fluids, to establish component and assembly cleanliness level specifications, and in determining filter
efficiencies and particle size ratings. As a result of the replacement of ISO 4402 with ISO 11171 (APC
calibration), the replacement of ISO 4572 with ISO 16889 (multi-pass filter test), and the publication
of ISO 11943 (online particle counter calibration), the quality and reliability of particle count and filter
test data have improved, increasing their usefulness to industry. However, the resultant redefinition of
particle sizes and the use of a new test dust affect how contamination levels and filter performance are
reported and interpreted.
NOTE The first editions of ISO 11171, ISO 16889 and ISO 11943 were published in 1999; all three of these
International Standards either have been, or are in the process of being, revised.
2 Historical background
2.1 What is ACFTD?
ACFTD was a test dust that was originally produced in batches by the AC Spark Plug Division of General
Motors Corporation. ACFTD was manufactured by collecting dust from a certain location in Arizona
(USA), then ball milling and classifying it into a consistent particle size distribution, including particle
sizes from roughly 0 μm to 100 μm. The manufacturer supplied the average volumetric particle size
distribution of each batch of ACFTD, as determined by either the roller analyser of laser diffraction
technique. In 1992, the production of ACFTD ceased.
Because of its relatively consistent particle size distribution, ACFTD had been used to calibrate APCs in
ISO 4402 and to evaluate filter performance in ISO 4572 for hydraulic and other applications. With its
irregular shape and siliceous nature, ACFTD was believed to be representative of contaminants found in
typical hydraulic systems. In ISO 4402, a particle size distribution for ACFTD is given which is based on
optical microscopy work done in the late 1960s. At that time, there was no statistical analysis of batch-
to-batch variations in ACFTD. Later, it was discovered that differences exist between the published
particle size distribution and actual particle size distributions of subsequent batches of ACFTD. These
differences are a significant source of variability in particle count results.
2.2 Calibrating particle counters using ACFTD
Though often taken for granted, particle counting is the mainstay of contamination control programs.
APCs are used to monitor contamination levels in the hydraulic fluid of operating equipment, to establish
component and assembly cleanliness level specifications, and to provide a basis for determining filtration
ratios (beta ratios), efficiencies, and particle size ratings of hydraulic filters.
Calibration consists of establishing the relationship between APC’s threshold voltage setting and particle
size. This was done by comparing observed particle contamination levels at known threshold settings
to the published ACFTD particle size distribution. Because of this, calibration accuracy depends on the
accuracy of the published particle size distribution.
In the absence of a more controlled contaminant, ACFTD had been used for APC calibration for hydraulic
and other applications. The ACFTD particle size distribution used for calibration in ISO 4402 is based
on the longest chord dimension of particles as measured by optical microscopy in the late 1960s. At the
time, optical microscopy was the most common method used to size and count particles. The goal of the
APC calibration procedure was to ensure that particle counts obtained with an APC agreed as closely as
possible with counts obtained by optical microscopy.
The accuracy of the published ACFTD particle size distribution and the corresponding APC particle
counter calibration has been questioned since the late 1970s. Because the original microscopy work
was done on specific batches of ACFTD, the effects of batch-to-batch variability on the particle size
distribution and APC calibration were not considered. Despite this, ISO 4402:1991 required laboratories
to calibrate to the original published size distribution, even though the particular batch of ACFTD used
likely had a different distribution.
2.3 The original multi-pass filter test
While the ACFTD method of APC calibration was being developed, the hydraulic filter multi-pass test
method was developed to measure filter performance, primarily efficiency and contaminant capacity. In
1981, the multi-pass test was published as ISO 4572:1981 and is still widely used. The characteristics of
ACFTD that made it valuable for APC calibration also make it ideal for filter testing. In a multi-pass test,
hydraulic fluid is recirculated through the filter under test while a slurry of ACFTD in hydraulic fluid is
continually added to a reservoir located upstream of the filter under test. Particle counts are taken both
upstream and downstream of the filter under test throughout the test. These counts are used to calculate
particle removal efficiency as a function of
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