ISO/TR 4813:2021
(Main)Hydraulic fluid power — Background, impact and use of ISO 11171:2020 on particle count and filter test data
Hydraulic fluid power — Background, impact and use of ISO 11171:2020 on particle count and filter test data
This document provides the background for ISO 11171:2020 and the use of µm(c) as the sole means of reporting particle size for APC particle count data. It also summarizes results of the international inter-laboratory study (ILS) of its reproducibility using SRM 2806d candidate material and suspensions of Reference Material (RM) 8632a. The ILS results provided the basis for certification of SRM 2806d used for primary calibration of APC. Their implications with respect to particle counting and filter testing are discussed in this document.
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TECHNICAL ISO/TR
REPORT 4813
First edition
2021-02
Hydraulic fluid power — Background,
impact and use of ISO 11171:2020 on
particle count and filter test data
Reference number
©
ISO 2021
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Undesirable consequences of ISO 11171:2016 . 1
5 Rationale for ISO 11171:2020 . 2
6 Inter-laboratory study experimental design . 3
7 Results of ILS . 6
8 Impact of ISO 11171:2020 on particle count data .11
9 Impact of ISO 11171:2020 on filter performance data .14
10 Use of ISO 11171:2020 .17
BIBLIOGRAPHY .19
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 of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee
SC 6, Contamination control.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
Introduction
The 2020 revision of ISO 11171 was initiated due to depletion of supplies of the National Institute of
Standards and Technology (NIST) Standard Reference Material® (SRM) 2806b, which is required for
primary calibration of liquid automatic particle counters (APC) using ISO 11171:2016. The 2016 edition
of ISO 11171 also provides an option for reporting particle size in units of either µm(c) or µm(b), which
has resulted in confusion among users of particle count data. µm(b) sizes are about 10 % larger than
the corresponding µm(c) sizes. Thus, µm(b) concentrations can be as much as 8 times (3 ISO Codes)
lower, and µm(b) filter Beta Ratios can be an order of magnitude lower than the same numerical value
reported in µm(c). This is problematic when attempting to conform with fluid cleanliness and filter
performance specifications.
ISO 11171:2020 addresses these issues by specifying the historically consistent, traceable µm(c) as
the sole acceptable means of reporting particle size. Unlike the 2016 edition, ISO 11171:2020 is not
dependent upon a specific batch of SRM 2806, as NIST henceforth certifies the material as a consensus
standard to minimize the potential for shifts in particle size with future batches. Additional refinements
to ISO 11171 facilitate calibration at smaller and larger particle sizes.
TECHNICAL REPORT ISO/TR 4813:2021(E)
Hydraulic fluid power — Background, impact and use of
ISO 11171:2020 on particle count and filter test data
1 Scope
This document provides the background for ISO 11171:2020 and the use of µm(c) as the sole means of
reporting particle size for APC particle count data. It also summarizes results of the international inter-
laboratory study (ILS) of its reproducibility using SRM 2806d candidate material and suspensions of
Reference Material (RM) 8632a. The ILS results provided the basis for certification of SRM 2806d used
for primary calibration of APC. Their implications with respect to particle counting and filter testing
are discussed in this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3534-1, Statistics — Vocabulary and symbols — Part 1: General statistical terms and terms used in
probability
ISO 3534-2, Statistics — Vocabulary and symbols — Part 2: Applied statistics
ISO 3534-3, Statistics — Vocabulary and symbols — Part 3: Design of experiments
ISO 4406, Hydraulic fluid power — Fluids — Method for coding the level of contamination by solid particles
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
ISO 11171, Hydraulic fluid power — Calibration of automatic particle counters for liquids
ISO 16889, Hydraulic fluid power — Filters — Multi-pass method for evaluating filtration performance of
a filter element
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3534-1, ISO 3534-2,
ISO 3534-3, ISO 4406, ISO 5725-1, ISO 11171 and ISO 16889 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Undesirable consequences of ISO 11171:2016
ISO 11171:2016 specified the use of NIST SRM 2806b for primary APC sizing calibration. Prior to this,
SRM 2806 and SRM 2806a, which have the same certified particle size distribution, were used for
primary calibration. Supplies of SRM 2806 and SRM 2806a were exhausted by 2010. The replacement
batch, SRM 2806b, was released to the market in 2014. SRM 2806 and SRM 2806b were certified
by scanning electron microscopy (SEM), but SRM 2806b was produced by a different supplier and
advanced methods of metrology were used. An important difference between the batches is that the
images of particles for SRM 2806 were manually processed, while SRM 2806b used automated image
analysis. Particle sizes obtained by APC calibrated with SRM 2806b were found to be about 10 % larger
than sizes obtained using SRM 2806 or SRM 2806a calibrations that yielded the same particle number
concentration. This 10 % difference in size is significant and prompted the revision of ISO 11171.
In response to the particle size shift, ISO 11171:2016 introduced an alternative method for reporting
particle size, µm(b). Prior to 2016, APC calibrated with ISO 11171 reported particle size in units of µm(c).
With ISO 11171:2016, users had the option to report size in units of µm(c) or µm(b), whereby µm(c) sizes
were obtained by multiplying µm(b) sizes by a factor of 0,898 and are numerically equivalent to the
previous µm(c). Users wanting to report sizes directly related to the NIST SRM 2806b SEM results could
report data as µm(b) sizes. Users attempting to meet existing cleanliness levels or filter performance
specifications or desiring historical consistency in the data could report as µm(c) sizes.
The alternative methods of reporting particle size resulted in confusion. There was an unfounded
belief that µm(b) sizes were more accurate, but this is not supported by statistical analysis. There is
no evidence that µm(b) sizes are closer to the true particle sizes than the µm(c) sizes obtained using
SRM 2806 or SRM 2806a. Regardless, some chose to report µm(b) sizes, while others used µm(c).
This is problematic when vendors and customers, or analytical laboratories and end-users report in
different units of size. For example, if fluid cleanliness is specified in terms of an ISO 4406 Code at
4, 6 µm(c) and 14 µm(c), but the APC reports data in 4 µm(b), 6 µm(b) and 14 µm(b), how can it be
decided if fluid is clean enough? According to ISO 11171:2016, 4 µm(b), 6 µm(b) and 14 µm(b) sizes
correspond to 3,6 µm(c), 5,4 µm(c), and 12,6 µm(c), but there is no mathematical relationship to directly
relate particle concentrations. The problem is compounded if the conversion between µm(b) and µm(c)
sizes was calculated incorrectly or if the measurement units for particle size were mis-labelled. While
ISO 11171:2016 provided a convenient alternative means for converting particle size, it resulted in
confusion that needed to be addressed.
5 Rationale for ISO 11171:2020
Like the previous editions, ISO 11171:2020 retains traceability to the internationally accepted definition
of a metre. Unlike the 2016 edition, ISO 11171:2020 allows only a single method of reporting particle
size in units of µm(c). Reporting size in units µm(b) is no longer an option. The ISO 11171:2020 µm(c)
is equivalent to the historical µm(c) obtained using SRM 2806. It no longer specifies a specific batch of
SRM 2806 for primary calibration and does not need to be revised with each new batch of SRM 2806x.
ISO 11171:2020 includes other changes, including a standardized method for creating APC calibration
curves, the use of dilution to facilitate calibration at small sizes, and a standardized method for
calibrating at sizes larger than 30 µm(c).
ISO 11171:2020 uses samples with an NIST certified particle size distribution, NIST SRM 2806x, for
primary calibration. Certification provides a measure of the true value of the particle concentration
at different sizes, but there is uncertainty associated with any measurement. For SRM 2806 and SRM
2806b, sources of uncertainty include the number of bottles analysed, bottle to bottle differences,
sub-sampling from a bottle, fractionation on the membrane used for SEM, particle orientation on the
membrane, digitization, pixilation, and measurement of length. The certified concentrations for each
batch of SRM are likely to be near the median particle concentration, but a different measure of the
median is likely to be obtained each time a new batch is certified. Thus, there is likely to be a particle
size shift with each new batch of SRM 2806 certified in this manner. The challenge is to reduce the size
shift to insignificance.
Beginning with SRM 2806d, NIST will certify SRM 2806x as a consensus standard to reduce the potential
for a shift in particle size. Previously, SRM 2806 and SRM 2806b were certified by SEM analysis of the
calibration fluid, but there are many sources of uncertainty resulting in the apparent particle size shift
between batches. In contrast, a consensus standard, like SRM 2806d, is develo
...
TECHNICAL ISO/TR
REPORT 4813
First edition
2021-02
Hydraulic fluid power — Background,
impact and use of ISO 11171:2020 on
particle count and filter test data
Reference number
©
ISO 2021
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Undesirable consequences of ISO 11171:2016 . 1
5 Rationale for ISO 11171:2020 . 2
6 Inter-laboratory study experimental design . 3
7 Results of ILS . 6
8 Impact of ISO 11171:2020 on particle count data .11
9 Impact of ISO 11171:2020 on filter performance data .14
10 Use of ISO 11171:2020 .17
BIBLIOGRAPHY .19
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 of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee
SC 6, Contamination control.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
Introduction
The 2020 revision of ISO 11171 was initiated due to depletion of supplies of the National Institute of
Standards and Technology (NIST) Standard Reference Material® (SRM) 2806b, which is required for
primary calibration of liquid automatic particle counters (APC) using ISO 11171:2016. The 2016 edition
of ISO 11171 also provides an option for reporting particle size in units of either µm(c) or µm(b), which
has resulted in confusion among users of particle count data. µm(b) sizes are about 10 % larger than
the corresponding µm(c) sizes. Thus, µm(b) concentrations can be as much as 8 times (3 ISO Codes)
lower, and µm(b) filter Beta Ratios can be an order of magnitude lower than the same numerical value
reported in µm(c). This is problematic when attempting to conform with fluid cleanliness and filter
performance specifications.
ISO 11171:2020 addresses these issues by specifying the historically consistent, traceable µm(c) as
the sole acceptable means of reporting particle size. Unlike the 2016 edition, ISO 11171:2020 is not
dependent upon a specific batch of SRM 2806, as NIST henceforth certifies the material as a consensus
standard to minimize the potential for shifts in particle size with future batches. Additional refinements
to ISO 11171 facilitate calibration at smaller and larger particle sizes.
TECHNICAL REPORT ISO/TR 4813:2021(E)
Hydraulic fluid power — Background, impact and use of
ISO 11171:2020 on particle count and filter test data
1 Scope
This document provides the background for ISO 11171:2020 and the use of µm(c) as the sole means of
reporting particle size for APC particle count data. It also summarizes results of the international inter-
laboratory study (ILS) of its reproducibility using SRM 2806d candidate material and suspensions of
Reference Material (RM) 8632a. The ILS results provided the basis for certification of SRM 2806d used
for primary calibration of APC. Their implications with respect to particle counting and filter testing
are discussed in this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3534-1, Statistics — Vocabulary and symbols — Part 1: General statistical terms and terms used in
probability
ISO 3534-2, Statistics — Vocabulary and symbols — Part 2: Applied statistics
ISO 3534-3, Statistics — Vocabulary and symbols — Part 3: Design of experiments
ISO 4406, Hydraulic fluid power — Fluids — Method for coding the level of contamination by solid particles
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
ISO 11171, Hydraulic fluid power — Calibration of automatic particle counters for liquids
ISO 16889, Hydraulic fluid power — Filters — Multi-pass method for evaluating filtration performance of
a filter element
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3534-1, ISO 3534-2,
ISO 3534-3, ISO 4406, ISO 5725-1, ISO 11171 and ISO 16889 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Undesirable consequences of ISO 11171:2016
ISO 11171:2016 specified the use of NIST SRM 2806b for primary APC sizing calibration. Prior to this,
SRM 2806 and SRM 2806a, which have the same certified particle size distribution, were used for
primary calibration. Supplies of SRM 2806 and SRM 2806a were exhausted by 2010. The replacement
batch, SRM 2806b, was released to the market in 2014. SRM 2806 and SRM 2806b were certified
by scanning electron microscopy (SEM), but SRM 2806b was produced by a different supplier and
advanced methods of metrology were used. An important difference between the batches is that the
images of particles for SRM 2806 were manually processed, while SRM 2806b used automated image
analysis. Particle sizes obtained by APC calibrated with SRM 2806b were found to be about 10 % larger
than sizes obtained using SRM 2806 or SRM 2806a calibrations that yielded the same particle number
concentration. This 10 % difference in size is significant and prompted the revision of ISO 11171.
In response to the particle size shift, ISO 11171:2016 introduced an alternative method for reporting
particle size, µm(b). Prior to 2016, APC calibrated with ISO 11171 reported particle size in units of µm(c).
With ISO 11171:2016, users had the option to report size in units of µm(c) or µm(b), whereby µm(c) sizes
were obtained by multiplying µm(b) sizes by a factor of 0,898 and are numerically equivalent to the
previous µm(c). Users wanting to report sizes directly related to the NIST SRM 2806b SEM results could
report data as µm(b) sizes. Users attempting to meet existing cleanliness levels or filter performance
specifications or desiring historical consistency in the data could report as µm(c) sizes.
The alternative methods of reporting particle size resulted in confusion. There was an unfounded
belief that µm(b) sizes were more accurate, but this is not supported by statistical analysis. There is
no evidence that µm(b) sizes are closer to the true particle sizes than the µm(c) sizes obtained using
SRM 2806 or SRM 2806a. Regardless, some chose to report µm(b) sizes, while others used µm(c).
This is problematic when vendors and customers, or analytical laboratories and end-users report in
different units of size. For example, if fluid cleanliness is specified in terms of an ISO 4406 Code at
4, 6 µm(c) and 14 µm(c), but the APC reports data in 4 µm(b), 6 µm(b) and 14 µm(b), how can it be
decided if fluid is clean enough? According to ISO 11171:2016, 4 µm(b), 6 µm(b) and 14 µm(b) sizes
correspond to 3,6 µm(c), 5,4 µm(c), and 12,6 µm(c), but there is no mathematical relationship to directly
relate particle concentrations. The problem is compounded if the conversion between µm(b) and µm(c)
sizes was calculated incorrectly or if the measurement units for particle size were mis-labelled. While
ISO 11171:2016 provided a convenient alternative means for converting particle size, it resulted in
confusion that needed to be addressed.
5 Rationale for ISO 11171:2020
Like the previous editions, ISO 11171:2020 retains traceability to the internationally accepted definition
of a metre. Unlike the 2016 edition, ISO 11171:2020 allows only a single method of reporting particle
size in units of µm(c). Reporting size in units µm(b) is no longer an option. The ISO 11171:2020 µm(c)
is equivalent to the historical µm(c) obtained using SRM 2806. It no longer specifies a specific batch of
SRM 2806 for primary calibration and does not need to be revised with each new batch of SRM 2806x.
ISO 11171:2020 includes other changes, including a standardized method for creating APC calibration
curves, the use of dilution to facilitate calibration at small sizes, and a standardized method for
calibrating at sizes larger than 30 µm(c).
ISO 11171:2020 uses samples with an NIST certified particle size distribution, NIST SRM 2806x, for
primary calibration. Certification provides a measure of the true value of the particle concentration
at different sizes, but there is uncertainty associated with any measurement. For SRM 2806 and SRM
2806b, sources of uncertainty include the number of bottles analysed, bottle to bottle differences,
sub-sampling from a bottle, fractionation on the membrane used for SEM, particle orientation on the
membrane, digitization, pixilation, and measurement of length. The certified concentrations for each
batch of SRM are likely to be near the median particle concentration, but a different measure of the
median is likely to be obtained each time a new batch is certified. Thus, there is likely to be a particle
size shift with each new batch of SRM 2806 certified in this manner. The challenge is to reduce the size
shift to insignificance.
Beginning with SRM 2806d, NIST will certify SRM 2806x as a consensus standard to reduce the potential
for a shift in particle size. Previously, SRM 2806 and SRM 2806b were certified by SEM analysis of the
calibration fluid, but there are many sources of uncertainty resulting in the apparent particle size shift
between batches. In contrast, a consensus standard, like SRM 2806d, is develo
...
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