ISO/TR 16386:2014
(Main)Impact of changes in ISO fluid power particle counting — Contamination control and filter test standards
Impact of changes in ISO fluid power particle counting — Contamination control and filter test standards
ISO/TR 16386:2014 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.
Conséquences des changements survenus dans les normes ISO relatives au comptage des particules — Contrôle de la contamination et essais de filtres
Vpliv sprememb standardov ISO na štetje delcev - Standardi za kontrolo onesnaženosti in za preskušanje filtrov
To tehnično poročilo opisuje vpliv sprememb v mednarodnih standardih za štetje delcev, kontrolo onesnaženosti in preskušanje filtrov.
Tekoči samodejni števci delcev (APC) se uporabljajo pri nadziranju ravni onesnaženosti v hidravličnih tekočinah za določitev specifikacij ravni čistosti komponent in sklopov, učinkovitosti delovanja filtrov ter nazivnih vrednosti za velikosti delcev. Na podlagi nadomestitve standarda ISO 4402 s standardom ISO 11171 (umerjanje samodejnih števcev delcev), nadomestitve standarda ISO 4572 s standardom ISO 16889 (preskus večkratno prepustnega filtra) ter izdaje standarda ISO 11943 (umerjanje števca delcev prek spleta), sta se povečali kakovost in zanesljivost postopka štetja delcev in rezultatov preskusov filtrov, s čimer se je povečala njihova uporabnost za industrijske namene. Vendar posledična vnovična določitev velikosti delcev in uporaba novega preskusnega prahu vplivata na način sporočanja ter tolmačenja ravni onesnaženosti in zmogljivosti filtrov.
OPOMBA: Prve izdaje standardov ISO 11171, ISO 16889 in ISO 11943 so bile objavljene leta 1999; vse tri različice teh mednarodnih standardov so bile ali so v postopku revidiranja.
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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/TR 16386:2014(E)
©
ISO 2014
---------------------- Page: 1 ----------------------
ISO/TR 16386:2014(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2014
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2014 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TR 16386:2014(E)
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
© ISO 2014 – All rights reserved iii
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ISO/TR 16386:2014(E)
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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
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
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT), see the following URL: Foreword — Supplementary information.
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
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ISO/TR 16386:2014(E)
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.
© ISO 2014 – All rights reserved v
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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
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ISO/TR 16386:2014(E)
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 particle size. The results, expressed as a filtration ratio (beta
ratio) depend not only on the APC calibration but also the particle size distribution of the test dust. The
retained contaminant capacity of the filter under test is also reported as the amount of ACFTD needed to
cause the filter to reach its terminal differential pressure. The particle size distribution and morphology
of the test dust also have a significant impact on filter efficiency and retained contaminant capacity.
3 New test dusts
In 1992, efforts to revise particle counter calibration and filter test standards took on new urgency
when the AC Rochester (formerly AC Spark Plug) Division of General Motors Corporation discontinued
production of ACFTD. ISO Technical Committee 22 responded by developing ISO 12103-1, a filter test
dust standard that specifies the physical, chemical, and particle size distribution characteristics of four
silica test dusts. The new test dusts are manufactured by jet milling instead of the ball milling process
used for ACFTD. As a result, their particle size distribution and the shape of individual particles differ
from ACFTD. Further, ISO 12103-1 specifies electrozone techniques, instead of the roller analyser or
laser diffraction methods used in the production of ACFTD, to specify the particle size distribution of
the new test dusts. Because of ISO 12103-1, the new test dusts are better controlled, and batch-to-batch
variability is less than that of ACFTD.
One of the test dust specified in ISO 12103-1, ISO medium test dust (ISO MTD) (ISO 12103-1 grade A3)
was chosen by ISO/TC 131/SC 6 to replace ACFTD for particle counter calibration and multi-pass filter
testing. ISO MTD is chemically identical to ACFTD but contains fewer particles smaller than 5 μm and
is easier to disperse in hydraulic fluid. The high concentration of fine particles in ACFTD can result in
coincidence errors during particle counting. Thus, the use of ISO MTD reduces the potential for error
while retaining the desirable characteristics of ACFTD.
4 New APC calibration procedure
Due to concerns about the accuracy of the ACFTD particle size distribution, the National Fluid Power
Association (NFPA) in the USA began a project in 1980 to develop a traceable APC calibration method.
The first attempt at a traceable method resulted in the American National Standard ANSI/(NFPA)
T2.9.6 R1-1990, which used mono-sized latex particles suspended in MIL-H-5606 mineral oil with sizes
traceable to the USA’s National Institute for Standards and Technology (NIST). Usage of this method
was discouraged, however, because shortly after its publication, it was found that different types of
APCs calibrated with latex particles showed poor agreement with each other. APCs made by different
manufacturers and APCs using different light sources (such as laser diode or white light) or different
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ISO/TR 16386:2014(E)
measurement principles (light scattering or light extinction) and calibrated using latex particles yielded
different particle count results when analysing ACFTD or similar contaminants. This is due to differences
in the optical properties of latex and silica. It was concluded that the APC calibration contaminant should
be optically similar to the contaminants typically used in filter testing.
In order to develop a traceable particle counter calibration method, NIST was asked in 1993 to certify the
particle size distribution of suspensions of particulate contaminant in MIL-H-5606 hydraulic fluid. The
certified suspensions, NIST Standard Reference Material (SRM) 2806, consist of 2,8 mg/l suspensions
of particulate contaminant in MIL-H-5606 hydraulic fluid. Scanning electron microscopy (SEM) and
image analysis software were used to measure the projected area equivalent diameters of particles
and to determine the particle size distribution of the SRM. The projected area equivalent diameter is
used as the basis for determining particle size because it more closely approximates the dimension
actually measured by liquid APCs than the longest chord dimension used to define the ACFTD particle
size distribution. A particle sensor measures the change in light intensity caused by the presence of a
particle in its sensing zone; in a sense, a light extinction sensor measures the size of the shadow cast
by a particle. The difference between the longest chord dimension and the projected area equivalent is
illustrated in Figure 1.
Key
1 actual size
2 as seen by an APC calibrated in accordance with ISO 4402 (ACFTD particle size distribution) – longest chord
3 as seen by an APC calibrated using NIST SRM 2806 (NIST particle size distribution) – projected area
equivalent diameter
4 longest chord dimension d = 13 μm
2
5 area = 78,5 μm
2
6 area = 78,5 μm
7 area equivalent diameter d = 10 μm
Figure 1 — Particle size (d) as defined using longest chord dimension and projected area
equivalent diameter
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ISO/TR 16386:2014(E)
As shown in Figure 2, particle size distribution data obtained using APCs calibration with the NIST
SRM differ considerably from those obtained using an APC calibrated with the ISO 4402 method. The
results shown in Figure 2 represent the particle size distribution of 2,8 mg/l suspensions of SAE 5-80
micrometer test dust analysed by NIST and by APCs calibrated using ACFTD in accordance with ISO 4402.
The latter results were obtained during an international round robin conducted under the auspices of
ISO/TC 131/SC 8. Figure 2 illustrates two interesting features:
a) at particle sizes smaller than about 10 μm, significantly more particles were observed by APCs
calibrated using the NIST SRM than by APCs calibrated using ACFTD. These higher particle counts
are a result of the enhanced sensitivity of electron microscopy when compared to optical microscopy;
b) at particle sizes larger than 10 μm, fewer particles were observed by APCs calibrated using the NIST
SRM than by APCs calibrated using ACFTD. This is the case primarily because NIST reported the
projected area equivalent diameter of particles, which is smaller than the longest chord dimension
used to general the published ACFTD particle size distribution, as illustrated in Figure 1.
Key
X particle size in micrometres
Y number of particles per millilitre larger than the indicated size
1 calibration using NIST SRM 2806
2 calibration using ACFTD
3 suspension of 2,8 mg/l of SAE 5-80 MICROMETER TEST DUST in hydraulic fluid
Figure 2 — Comparison of the particle size distribution of a suspension of 2,8 mg/l of SAE 5-80
MICROMETER TEST DUST in hydraulic fluid, measured using the ISO 4402 (ACFTD) and
ISO 11171 (NIST SRM 2806) calibration methods
ISO 11171 (APC calibration), ISO 16889 (multi-pass filter test), and ISO 11943 (online particle counter
calibration) all provide traceability to NIST SRM 2806. The quality and reliability of both particle count
and filter test data are expected to improve as a result of the use of these International Standards. In
1995, this was established by means of a series of international round robin test programs conducted
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ISO/TR 16386:2014(E)
to evaluate these International Standards. The results of the round robin test programs were discussed
extensively in informative annexes in the first editions of these International Standards.
5 Why changes were necessary
ISO and other standards developing organizations are charged with developing technically sound
industrial standards that permit valid comparisons among data from different sources. Such standards
make it possible to compare data from various suppliers or laboratories that test in accordance with the
same standard. For this reason, ISO encourages the use of certified reference materials for calibration. In
the past, ACFTD, an uncertified reference material, had been used for both multi-pass filter testing and APC
calibration. Although the methods that used ACFTD had long been used to establish a common calibration
among laboratories, it had shortcomings that affected the accuracy of the test results and agreement
among laboratories. An even greater problem is that ACFTD is no longer commercially available.
From the standpoint of APC calibration, the ISO 4402 calibration method had several inherent
weaknesses, perhaps the greatest of which was that the ACFTD particle size distribution was not
certified and lacked traceability. Calibration accuracy depends on the accuracy of the reference particle
size distribution. For some time, it had been known that modern electron microscopy and electrozone
counting techniques yield particle size distributions that differ from the ACFTD particle size distribution
given in ISO 4402, which were obtained by optical microscopy, particularly for particles smaller than
about 10 μm. The ACFTD particle size distribution given in ISO 4402 was based on analyses done in the
late 1960s on specific batches of ACFTD and ignored batch-to-batch variability. Further, the ISO 4402
calibration method does not require validation of the APC or qualification of the analytical techniques
used. The ISO 11171 calibration method corrects many of these deficiencies through the use of certified
calibration suspensions. In addition, it establishes minimum APC performance requirements and uses
statistical methods to evaluate the data and analytical techniques. One consequence of the change in
calibration method is a redefinition of particle sizes, as discussed later in this Technical Report.
From the standpoint of filter testing, the changes to a new test dust and APC calibration method for multi-
pass filter testing were necessitated by the lack of commercial availability of ACFTD. As had been mentioned
previously, the replacement of ACFTD with ISO MTD offered several advantages for filter testing:
a) compared with ACFTD, ISO MTD is more reproducible in its properties and particle size distribution,
is more defined, and is easier to disperse in hydraulic fluid;
b) ISO MTD has significantly fewer particles smaller than 5 μm, which reduces the risk of coincidence
errors in particle counting; this is particularly important in the online particle counting systems
used in multi-pass testing.
In addition to the change in test dust, improvements in the multi-pass testing and reporting techniques
have been included in ISO 16889. Unfortunately, the differences in the particle size distributions and
particle morphology of ACFTD and ISO MTD, as well as the changes in testing and reporting techniques,
contribute to differences between results from tests conducted in accordance with ISO 4572 and
ISO 16889. However, ISO 16889 provides an overall improvement in the repeatability of multi-pass filter
test results; the impact of this is discussed later in this Technical Report.
6 Impact on particle sizes and contamination measurements
6.1 Redefinition of particle sizes
Both particle size and concentration are important in contamination control. The change in APC
calibration method results in an immediate change in reported particle sizes and concentrations. The
magnitude of the change depends on the particle size of interest. Because of this change, ISO 11171
specifies that particle sizes measured by an APC calibrated in accordance with that International
Standard should be expressed in the unit μm(c), where the (c) refers to calibration in accordance with
ISO 11171. Table 1 compares particle sizes measured by APCs calibrated in accordance with ISO 4402 and
ISO 11171. At the particle size 10 μm, there is only about a 2 % difference in the reported size. However,
the ISO 4402 particle size of 15 μm determined using an APC calibrated with ACFTD in accordance
© ISO 2014 – All rights reserved 5
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ISO/TR 16386:2014(E)
with ISO 4402 is equivalent to a particle size of 13,6 μm(c) using an APC calibrated with ISO MTD in
accordance with ISO 11171, while the ISO 4402 particle size 5 μm is equivalent to the ISO 11171 particle
size of 6,4 μm(c). The biggest difference appears at very small particle sizes; particles measured as 1 μm
under the old system are measured as 4,2 μm(c) in the new. This difference in reported size can lead to
confusion when reporting contamination levels or comparing filtration (beta) ratios and efficiencies.
Table 1 — Comparing particle sizes obtained by different calibration methods
To convert from size determined using ISO 11171 to To convert from size measured using ISO 4402 to
size determined using ISO 4402 size determined using ISO 11171
Particle size deter- Corresponding particle size Particle size deter- Corresponding par-
mined by an APC determined by an APC cal- mined by an APC cali- ticle size determined
calibrated in accord- ibrated in accordance with brated in accordance by an APC calibrated
ance with ISO 11171 ISO 4402:1991 (withdrawn) with ISO 4402:1991 in accordance with
(NIST suspension) (ACFTD) (withdrawn) (ACFTD) ISO 11171 (NIST suspen-
µm(c) µm µm sion)
µm(c)
4 Not defined 1 4,2
5 2,7 2 4,6
6 4,3 3 5,1
7 5,9 5 6,4
8 7,4 7 7,7
9 8,9 10 9,8
10 10,2 15 13,6
15 16,9 20 17,5
20 23,4 25 21,2
25 30,1 30 24,9
30 37,3 40 31,7
Table 1 should be used only as a guideline. The exact relationship between particle sizes obtained using
APCs calibrated in accordance with ISO 11171 and ISO 4402 can vary between laboratories, depending on
the characteristics of the APC and the accuracy of the original ACFTD calibration. During the transition
from ISO 4402 to ISO 11171 APC calibration, laboratories performing particle counting that requires a
high degree of accuracy should establish the precise correlation for their specific conditions.
As a result of the redefinition of particle sizes, many APCs in use today are unable to count particles that
are smaller than about 5 μm(c). In general, an APC calibrated in accordance with ISO 4402 which could
count 1 μm particles now sizes those same particles at 4 μm(c) when the APC is calibrated in accordance
with ISO 11171. Based on round robin test program results (see ISO 11171:2010, Annex G), only newer
light extinction sensors and light scattering sensors are able to count and size smaller particles. Some
APC manufacturers produce light extinction sensors that are able to count particles as small as 2 μm(c)
to 3 μm(c) in size when calibrated in accordance with ISO 11171. In order to count smaller particles, light
scattering sensors are most likely required.
6.2 Apparent particle concentrations
Particulate contamination levels are reported in terms of the number of particles of various sizes in a
given volume of hydraulic fluid. With the ISO 11171
...
SLOVENSKI STANDARD
SIST-TP ISO/TR 16386:2016
01-maj-2016
1DGRPHãþD
SIST ISO/TR 16386:2001
Vpliv sprememb standardov ISO na štetje delcev - Standardi za kontrolo
onesnaženosti in za preskušanje filtrov
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
Ta slovenski standard je istoveten z: ISO/TR 16386:2014
ICS:
23.100.60 )LOWULWHVQLODLQ Filters, seals and
RQHVQDåHYDQMHWHNRþLQ contamination of fluids
SIST-TP ISO/TR 16386:2016 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST-TP ISO/TR 16386:2016
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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/TR 16386:2014(E)
©
ISO 2014
---------------------- Page: 3 ----------------------
SIST-TP ISO/TR 16386:2016
ISO/TR 16386:2014(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2014
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2014 – All rights reserved
---------------------- Page: 4 ----------------------
SIST-TP ISO/TR 16386:2016
ISO/TR 16386:2014(E)
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
© ISO 2014 – All rights reserved iii
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SIST-TP ISO/TR 16386:2016
ISO/TR 16386:2014(E)
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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
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
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT), see the following URL: Foreword — Supplementary information.
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.
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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.
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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
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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 particle size. The results, expressed as a filtration ratio (beta
ratio) depend not only on the APC calibration but also the particle size distribution of the test dust. The
retained contaminant capacity of the filter under test is also reported as the amount of ACFTD needed to
cause the filter to reach its terminal differential pressure. The particle size distribution and morphology
of the test dust also have a significant impact on filter efficiency and retained contaminant capacity.
3 New test dusts
In 1992, efforts to revise particle counter calibration and filter test standards took on new urgency
when the AC Rochester (formerly AC Spark Plug) Division of General Motors Corporation discontinued
production of ACFTD. ISO Technical Committee 22 responded by developing ISO 12103-1, a filter test
dust standard that specifies the physical, chemical, and particle size distribution characteristics of four
silica test dusts. The new test dusts are manufactured by jet milling instead of the ball milling process
used for ACFTD. As a result, their particle size distribution and the shape of individual particles differ
from ACFTD. Further, ISO 12103-1 specifies electrozone techniques, instead of the roller analyser or
laser diffraction methods used in the production of ACFTD, to specify the particle size distribution of
the new test dusts. Because of ISO 12103-1, the new test dusts are better controlled, and batch-to-batch
variability is less than that of ACFTD.
One of the test dust specified in ISO 12103-1, ISO medium test dust (ISO MTD) (ISO 12103-1 grade A3)
was chosen by ISO/TC 131/SC 6 to replace ACFTD for particle counter calibration and multi-pass filter
testing. ISO MTD is chemically identical to ACFTD but contains fewer particles smaller than 5 μm and
is easier to disperse in hydraulic fluid. The high concentration of fine particles in ACFTD can result in
coincidence errors during particle counting. Thus, the use of ISO MTD reduces the potential for error
while retaining the desirable characteristics of ACFTD.
4 New APC calibration procedure
Due to concerns about the accuracy of the ACFTD particle size distribution, the National Fluid Power
Association (NFPA) in the USA began a project in 1980 to develop a traceable APC calibration method.
The first attempt at a traceable method resulted in the American National Standard ANSI/(NFPA)
T2.9.6 R1-1990, which used mono-sized latex particles suspended in MIL-H-5606 mineral oil with sizes
traceable to the USA’s National Institute for Standards and Technology (NIST). Usage of this method
was discouraged, however, because shortly after its publication, it was found that different types of
APCs calibrated with latex particles showed poor agreement with each other. APCs made by different
manufacturers and APCs using different light sources (such as laser diode or white light) or different
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measurement principles (light scattering or light extinction) and calibrated using latex particles yielded
different particle count results when analysing ACFTD or similar contaminants. This is due to differences
in the optical properties of latex and silica. It was concluded that the APC calibration contaminant should
be optically similar to the contaminants typically used in filter testing.
In order to develop a traceable particle counter calibration method, NIST was asked in 1993 to certify the
particle size distribution of suspensions of particulate contaminant in MIL-H-5606 hydraulic fluid. The
certified suspensions, NIST Standard Reference Material (SRM) 2806, consist of 2,8 mg/l suspensions
of particulate contaminant in MIL-H-5606 hydraulic fluid. Scanning electron microscopy (SEM) and
image analysis software were used to measure the projected area equivalent diameters of particles
and to determine the particle size distribution of the SRM. The projected area equivalent diameter is
used as the basis for determining particle size because it more closely approximates the dimension
actually measured by liquid APCs than the longest chord dimension used to define the ACFTD particle
size distribution. A particle sensor measures the change in light intensity caused by the presence of a
particle in its sensing zone; in a sense, a light extinction sensor measures the size of the shadow cast
by a particle. The difference between the longest chord dimension and the projected area equivalent is
illustrated in Figure 1.
Key
1 actual size
2 as seen by an APC calibrated in accordance with ISO 4402 (ACFTD particle size distribution) – longest chord
3 as seen by an APC calibrated using NIST SRM 2806 (NIST particle size distribution) – projected area
equivalent diameter
4 longest chord dimension d = 13 μm
2
5 area = 78,5 μm
2
6 area = 78,5 μm
7 area equivalent diameter d = 10 μm
Figure 1 — Particle size (d) as defined using longest chord dimension and projected area
equivalent diameter
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As shown in Figure 2, particle size distribution data obtained using APCs calibration with the NIST
SRM differ considerably from those obtained using an APC calibrated with the ISO 4402 method. The
results shown in Figure 2 represent the particle size distribution of 2,8 mg/l suspensions of SAE 5-80
micrometer test dust analysed by NIST and by APCs calibrated using ACFTD in accordance with ISO 4402.
The latter results were obtained during an international round robin conducted under the auspices of
ISO/TC 131/SC 8. Figure 2 illustrates two interesting features:
a) at particle sizes smaller than about 10 μm, significantly more particles were observed by APCs
calibrated using the NIST SRM than by APCs calibrated using ACFTD. These higher particle counts
are a result of the enhanced sensitivity of electron microscopy when compared to optical microscopy;
b) at particle sizes larger than 10 μm, fewer particles were observed by APCs calibrated using the NIST
SRM than by APCs calibrated using ACFTD. This is the case primarily because NIST reported the
projected area equivalent diameter of particles, which is smaller than the longest chord dimension
used to general the published ACFTD particle size distribution, as illustrated in Figure 1.
Key
X particle size in micrometres
Y number of particles per millilitre larger than the indicated size
1 calibration using NIST SRM 2806
2 calibration using ACFTD
3 suspension of 2,8 mg/l of SAE 5-80 MICROMETER TEST DUST in hydraulic fluid
Figure 2 — Comparison of the particle size distribution of a suspension of 2,8 mg/l of SAE 5-80
MICROMETER TEST DUST in hydraulic fluid, measured using the ISO 4402 (ACFTD) and
ISO 11171 (NIST SRM 2806) calibration methods
ISO 11171 (APC calibration), ISO 16889 (multi-pass filter test), and ISO 11943 (online particle counter
calibration) all provide traceability to NIST SRM 2806. The quality and reliability of both particle count
and filter test data are expected to improve as a result of the use of these International Standards. In
1995, this was established by means of a series of international round robin test programs conducted
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to evaluate these International Standards. The results of the round robin test programs were discussed
extensively in informative annexes in the first editions of these International Standards.
5 Why changes were necessary
ISO and other standards developing organizations are charged with developing technically sound
industrial standards that permit valid comparisons among data from different sources. Such standards
make it possible to compare data from various suppliers or laboratories that test in accordance with the
same standard. For this reason, ISO encourages the use of certified reference materials for calibration. In
the past, ACFTD, an uncertified reference material, had been used for both multi-pass filter testing and APC
calibration. Although the methods that used ACFTD had long been used to establish a common calibration
among laboratories, it had shortcomings that affected the accuracy of the test results and agreement
among laboratories. An even greater problem is that ACFTD is no longer commercially available.
From the standpoint of APC calibration, the ISO 4402 calibration method had several inherent
weaknesses, perhaps the greatest of which was that the ACFTD particle size distribution was not
certified and lacked traceability. Calibration accuracy depends on the accuracy of the reference particle
size distribution. For some time, it had been known that modern electron microscopy and electrozone
counting techniques yield particle size distributions that differ from the ACFTD particle size distribution
given in ISO 4402, which were obtained by optical microscopy, particularly for particles smaller than
about 10 μm. The ACFTD particle size distribution given in ISO 4402 was based on analyses done in the
late 1960s on specific batches of ACFTD and ignored batch-to-batch variability. Further, the ISO 4402
calibration method does not require validation of the APC or qualification of the analytical techniques
used. The ISO 11171 calibration method corrects many of these deficiencies through the use of certified
calibration suspensions. In addition, it establishes minimum APC performance requirements and uses
statistical methods to evaluate the data and analytical techniques. One consequence of the change in
calibration method is a redefinition of particle sizes, as discussed later in this Technical Report.
From the standpoint of filter testing, the changes to a new test dust and APC calibration method for multi-
pass filter testing were necessitated by the lack of commercial availability of ACFTD. As had been mentioned
previously, the replacement of ACFTD with ISO MTD offered several advantages for filter testing:
a) compared with ACFTD, ISO MTD is more reproducible in its properties and particle size distribution,
is more defined, and is easier to disperse in hydraulic fluid;
b) ISO MTD has significantly fewer particles smaller than 5 μm, which reduces the risk of coincidence
errors in particle counting; this is particularly important in the online particle counting systems
used in multi-pass testing.
In addition to the change in test dust, improvements in the multi-pass testing and reporting techniques
have been included in ISO 16889. Unfortunately, the differences in the particle size distributions and
particle morphology of ACFTD and ISO MTD, as well as the changes in testing and reporting techniques,
contribute to differences between results from tests conducted in accordance with ISO 4572 and
ISO 16889. However, ISO 16889 provides an overall improvement in the repeatability of multi-pass filter
test results; the impact of this is discussed later in this Technical Report.
6 Impact on particle sizes and contamination measurements
6.1 Redefinition of particle sizes
Both particle size and concentration are important in contamination control. The change in APC
calibration method results in an immediate change in reported particle sizes and concentrations. The
magnitude of the change depends on the particle size of interest. Because of this change, ISO 11171
specifies that particle sizes measured by an APC calibrated in accordance with that International
Standard should be expressed in the unit μm(c), where the (c) refers to calibration in accordance with
ISO 11171. Table 1 compares particle sizes measured by APCs calibrated in accordance with ISO 4402 and
ISO 11171. At the particle size 10 μm, there is only about a 2 % difference in the reported size. However,
the ISO 4402 particle size of 15 μm determined using an APC calibrated with ACFTD in accordance
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with ISO 4402 is equivalent to a particle size of 13,6 μm(c) using an APC calibrated with ISO MTD in
accordance with ISO 11171, while the ISO 4402 particle size 5 μm is equivalent to the ISO 11171 particle
size of 6,4 μm(c). The biggest difference appears at very small particle sizes; particles measured as 1 μm
under the old system are measured as 4,2 μm(c) in the new. This difference in reported size can lead to
confusion when reporting contamination levels or comparing filtration (beta) ratios and efficiencies.
Table 1 — Comparing particle sizes obtained by different calibration methods
To convert from size determined using ISO 11171 to To convert from size measured using ISO 4402 to
size determined using ISO 4402 size determined using ISO 11171
Particle size deter- Corresponding particle size Particle size deter- Corresponding par-
mined by an APC determined by an APC cal- mined by an APC cali- ticle size determined
calibrated in accord- ibrated in accordance with brated in accordance by an APC calibrated
ance with ISO 11171 ISO 4402:1991 (withdrawn) with ISO 4402:1991 in accordance with
(NIST suspension) (ACFTD) (withdrawn) (ACFTD) ISO 11171 (NIST suspen-
µm(c) µm µm sion)
µm(c)
4 Not defined 1 4,2
5 2,7 2 4,6
6 4,3 3 5,1
7 5,9 5 6,4
8 7,4 7 7,7
9 8,9 10 9,8
10 10,2 15 13,6
15 16,9 20 17,5
20 23,4 25 21,2
25 30,1 30 24,9
30 37,3 40 31,7
Table 1 should be used only as a guideline. The exact relationship between particle sizes obtained using
APCs calibrated in accordance with ISO 11171 and ISO 4402 can vary between laboratories, depend
...
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