Impact of changes in ISO fluid power particle counting - Contamination control and filter test standards

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.

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.

General Information

Status
Published
Publication Date
28-Mar-2016
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
21-Mar-2016
Due Date
26-May-2016
Completion Date
29-Mar-2016

RELATIONS

Buy Standard

Technical report
ISO/TR 16386:2014 - Impact of changes in ISO fluid power particle counting -- Contamination control and filter test standards
English language
13 pages
sale 15% off
Preview
sale 15% off
Preview
Technical report
SIST-TP ISO/TR 16386:2016
English language
17 pages
sale 10% off
Preview
sale 10% off
Preview

e-Library read for
1 day

Standards Content (sample)

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
---------------------- Page: 3 ----------------------
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
---------------------- Page: 4 ----------------------
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
---------------------- Page: 5 ----------------------
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

© ISO 2014 – All rights reserved 1
---------------------- Page: 6 ----------------------
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

2 © ISO 2014 – All rights reserved
---------------------- Page: 7 ----------------------
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
5 area = 78,5 μm
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
© ISO 2014 – All rights reserved 3
---------------------- Page: 8 ----------------------
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

4 © ISO 2014 – All rights reserved
---------------------- Page: 9 ----------------------
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
---------------------- Page: 10 ----------------------
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
---------------------- Page: 2 ----------------------
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
---------------------- Page: 5 ----------------------
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.
iv © ISO 2014 – All rights reserved
---------------------- Page: 6 ----------------------
SIST-TP ISO/TR 16386:2016
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
---------------------- Page: 7 ----------------------
SIST-TP ISO/TR 16386:2016
---------------------- Page: 8 ----------------------
SIST-TP ISO/TR 16386:2016
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

© ISO 2014 – All rights reserved 1
---------------------- Page: 9 ----------------------
SIST-TP ISO/TR 16386:2016
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

2 © ISO 2014 – All rights reserved
---------------------- Page: 10 ----------------------
SIST-TP ISO/TR 16386:2016
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
5 area = 78,5 μm
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
© ISO 2014 – All rights reserved 3
---------------------- Page: 11 ----------------------
SIST-TP ISO/TR 16386:2016
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

4 © ISO 2014 – All rights reserved
---------------------- Page: 12 ----------------------
SIST-TP ISO/TR 16386:2016
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
---------------------- Page: 13 ----------------------
SIST-TP ISO/TR 16386:2016
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, depend

...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.