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/TR 4813:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO/TR 4813:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© 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
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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
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ISO/TR 4813:2021(E)
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

© ISO 2021 – All rights reserved iii
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ISO/TR 4813:2021(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 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
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ISO/TR 4813:2021(E)
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.
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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

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ISO/TR 4813:2021(E)

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 developed in co-operation with

all parties with an interest in participating in the development or use of the standard. In this case, NIST

and ISO TC 131/SC 6 agreed to use the traceable SRM 2806 certification to define µm(c) and APC (rather

than SEM) data to obtain the number concentration of particles as a function of particle size. To avoid

commercially significant shifts in particle size between batches, the certified particle size distribution

for SRM 2806x batches are based upon particle count data from ILS conducted using APC calibrated

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ISO/TR 4813:2021(E)

according to ISO 11171:2020 in µm(c) using the most recent previous batch of SRM 2806x. In the case

of SRM 2806d, SRM 2806b was used to calibrate all 4 APCs used to certify the ILS secondaries as per

ISO 11171:2020 and to maintain traceability. Samples of SRM 2806b had been put aside by NIST at the

request of the Project Leaders specifically for this purpose. The traceable secondaries were used to

calibrate ILS APCs. In this manner, the ILS data represents the industry consensus definition of µm(c)

and ensures that particle size does not deviate significantly with each new batch of SRM 2806x.

In addition to changes in the manner of reporting particle size and certification of primary calibration

suspension, ISO 11171:2020 also specifies how calibration curves are determined. Previously, there

was discretion in the way calibration curves were determined, e.g. how channels were selected,

whether to use latex or test dust to calibrate for sizes greater than 30 µm(c), what mathematical

function is used to create a calibration curve. Collectively, these legitimate discretionary choices

increased uncertainty in particle count data and, in some cases, introduced artefacts into the data. This

is addressed in ISO 11171:2020, which requires that data from at least 12 different threshold settings

spaced logarithmically over the entire particle size range of interest be used to create a calibration

curve. The lowest of these threshold settings is 1,5 times the threshold noise level of the instrument,

corresponding to the smallest size that can be counted. The calibration curve itself is created using the

constrained cubic spline method. In this manner, the uncertainty between laboratories is reduced.

Counting particles smaller than 4 µm(c) has been problematic, as the concentrations of particles in

calibration suspensions are typically above coincidence error limits. In contrast to prior versions,

ISO 11171:2020 permits dilution of calibration samples using a defined method derived from ISO 11500.

To minimize contamination, verification of dilution fluid and glassware cleanliness is required. As a

result, some laboratories participating in the ILS were able to calibrate to particle sizes as small at

1,5 µm(c).

In some applications, such as gear and transmission fluids, interest is primarily in particles larger than

30 µm(c). Previous versions of ISO 11171 allowed either latex or test dust calibration suspensions to

be used at these sizes, but they can yield different results. Furthermore, test dust calibration samples

generally contain insufficient numbers of large particles for a valid calibration. Also, primary calibration

samples are not certified above 30 µm(c) and therefore not traceable. To address this, ISO 11171:2020

specifies that primary calibration for particle sizes larger than 30 µm(c) be done with monodispersed

latex particles and provides guidance for selection of their sizes. APC calibrated in this manner can

be used to produce secondary calibration suspensions certified at sizes larger than 30 µm(c). These

changes are intended to reduce uncertainty and to facilitate calibration at particle sizes larger than

30 µm(c).
6 Inter-laboratory study experimental design
An inter-laboratory study (ILS) of ISO 11171:2020 was conducted to:

— Measure the intra-company repeatability and inter-company reproducibility of particle count data

obtained using APC calibrated to the standard using SRM 2806d candidate material and suspensions

of RM 8632a;

— Generate particle count data to be used by NIST to certify consensus standard SRM 2806d in size

units of µm(c);

— Determine the extent, if any, of the shift in particle size resulting from the use of SRM 2806d; and

— Generate particle count data for NIST RM 8632a that will provide a basis to update ISO 11171:2020,

Table A.1.
The ILS experimental design consisted of:

1) Production of traceable secondary calibration samples for use by ILS participants.

2) Selection and qualification of participating laboratories and APC.
3) ISO 11171:2020 calibration of APC.
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ISO/TR 4813:2021(E)

4) Analysis of samples of SRM 2806d candidate suspensions and RM 8632a test dust, and

5) Analysis of data as per ISO 5725-2.

The ILS results were provided to NIST for use in certifying consensus standard SRM 2806d.

The traceable secondary calibration samples for use in the ILS were prepared by Aviation Industry

(Xinxiang) Metrology and Test Science Technology Company Limited, commonly known as CFPC. These

were used to calibrate the APC used by ILS participants. They were produced to the same specifications

as the SRM 2806d candidate material according to ISO 11171:2020, Annex F. Four laboratories were

selected to analyse the secondary calibration samples. Two of the laboratories, Pamas and CFPC,

utilized Pamas light scattering APC. All data for particle sizes of 1,5 µm(c) and 2 µm(c) were generated

by Pamas light scattering APC. The other two laboratories, NIST and Beckman, utilized Beckman

light extinction APC. Each laboratory performed a full primary ISO 11171:2020 calibration but using

SRM 2806b for particle sizes up to 30 µm(c) for light extinction sensors or to the largest size that the

instrument was capable of counting for light scattering sensors. Each was sent five bottles of secondary

calibration fluid for analysis. The data from all four laboratories was analysed by NIST and used to

generate the composite certified size distribution for the secondary calibration samples. Thus, the

certified size distribution is not biased with respect to a single laboratory, APC operating principle

or manufacturer. ILS participants were required to demonstrate that their APC met all ISO 11171

performance specifications and asked to provide their most recent ISO 11171:2016 calibration curve.

Eighteen APC participated in the ILS, including laboratories from five countries (USA, Germany, United

Kingdom, China, France), two different operating principles (light extinction, light scattering), and

three APC manufacturers (Pamas, Beckman, Stanhope-Seta).
The characteristics of these 18 individual APC are summarized in Table 1.
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ISO/TR 4813:2021(E)
© ISO 2021 – All rights reserved 5
Table 1 — APC operating and performance characteristics
Coincidence Sample Working
Noise
APC CV, vol Resolution Number of
APC identi-
level
Type error limit volume flow rate
fier
manufacturer % µm(c) thresholds
Particles/mL mL mL/min
1 X extinction 105 27 000 2,7 % 13,4 % 10 25 16
2 Y extinction 10 19 000 0,4 % 5,0 % 10 50 12
3 X extinction 150 59 129 0,4 % 8,5 % 10 10 16
4 X scattering 80 12 713 0,2 % 6,8 % 10 10 16
5 X extinction 200 27 171 1,9 % 9,5 % 10 25 16
6 X extinction 120 89 813 0,8 % 9,6 % 10 10 18
7 Z extinction 178 30 000 0,4 % 7,4 % 10 30 17
8 Y extinction 3 40 246 0,6 % 11,2 % 10 30 18
9 Y extinction 10 6 000 0,9 % 4,5 % 25 25 101
10 X extinction 77 34 251 0,1 % 6,7 % 10 25 13
11 X extinction 190 19 418 0,2 % 9,6 % 10 25 16
12 X extinction 190 20 743 0,3 % 6,0 % 25 25 24
13 X scattering 150 12 245 0,6 % 3,0 % 10 10 24
14 X extinction 170 25 780 1,0 % 10,1 % 10 25 16
15 X extinction 155 19 617 0,9 % 5,8 % 10 25 16
16 X scattering 40 14 003 0,8 % 10,0 % 10 10 16
17 Y extinction 8 15 789 0,6 % 7,0 % 10 20 18
18 Z extinction 181 30 000 0,4 % 7,4 % 10 30 17
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ISO/TR 4813:2021(E)

ILS participants calibrated their APC as per ISO 11171:2020 using the CFPC secondary calibration

samples previously described. Participants were asked to calibrate to the smallest size that their APC

was capable of counting and, if possible, to calibrate up to a particle size of 50 µm(c) or the largest

size that their APC was capable of counting. Each participant received 3 samples of SRM 2806d

candidate material and 1 bottle of RM 8632a to analyse. The candidate material samples were analysed

as described in ISO 11171:2020 at as many of the following particle sizes as possible using their

ISO 11171:2020 calibration: 1,5 µm(c), 2 µm(c), 3 µm(c), 4 µm(c), 6 µm(c), 10 µm(c), 14 µm(c), 21 µm(c),

30 µm(c), 38 µm(c) and 50 µm(c). Participants were also asked to prepare three 1,0 mg/L samples of

RM 8632a test dust and analyse these at as many of the integral particle sizes as possible between

2 µm(c) and 15 µm(c), inclusive. The results were provided to the Project Leaders and analysed as

per ISO 5725-2. The data and statistical analysis were also provided to NIST for use in certifying the

consensus standard SRM 2806d. Further details regarding the ILS and the certification of SRM 2806d

are described in Reference [6].
7 Results of ILS

Tables 2 and 3 summarize the ILS data for the SRM 2806d candidate material and RM 8632a samples,

respectively. Figures 1 and 2 show the mean particle concentration data from each ILS participant

for the samples in graphical form. As per ISO 5725-2, Mandel h and k, Grubbs test, and Cochran test

were used to detect outlier data. Outlier data are noted in Tables 2 and 3 and were excluded from the

statistical analysis.

The following are suspected outliers, but did not meet the criteria for exclusion from the data analysis:

— 6 µm(c), 10 µm(c) and 14 µm(c) data of participant 13 for the SRM 2806d candidate samples;

— 38 µm(c) and 50 µm(c) data of participant 7 for the SRM 2806d candidate samples;

— 3 µm(c), 7 µm(c) and 8 µm(c) data for the second RM 8632a sample analysed by participant 9;

— 6 µm(c) through 15 µm(c) data of participant 1 for their RM 8632a sample; and
— 3 µm(c) data of participants 16 and 17 for their RM 8632a sample.

Referring to Figure 1, the SRM 2806d candidate material data at particle sizes larger than 30 µm(c)

for participants 7 and 11 are suspected outliers. Statistical grounds exist to exclude participant

11, but not participant 7 at these sizes. In both cases, the particle concentration data appeared to

approach a horizontal asymptote at larger sizes and the corresponding APC calibration curve also

demonstrated asymptotic behaviour. In some cases, the latex calibration samples were reported to

be cloudy in appearance, suggesting that the water drops from the latex did not completely disperse

in the dilution fluid, thus causing the APC to count water droplets. This results in the asymptotic

behaviour at these sizes. The root cause appears to be incomplete dissolution of the Aerosol OT in the

dilution fluid. Dissolution requires heat and time and can be difficult to verify visually. Participant 6

initially encountered a similar issue, but resolved it by using a higher dilution ratio, i.e. a lower latex

concentration in the calibration samples. Another approach is to increase the heating and stirring time

used to dissolve Aerosol OT in the dilution fluid, thus ensuring complete dissolution. Guidance on how

to avoid this issue was added to ISO 11171:2020 based upon these results.

Referring to Figure 2, RM 8632a data for participants 1 and 5 were suspected to be outliers. While

participant 1 consistently exhibited the lowest RM 8632a data, it did not meet the outlier criteria and

was not excluded. Participant 5 data was excluded as an outlier. These data were approximately twice

the mean value of all other laboratories at each size, suggesting that a math or weighing error occurred,

but this could not be confirmed.
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Table 2 — Statistical summary of ILS data for SRM 2806d candidate material samples

Number Standard deviation, particles/mL CV, %
Particle
Mean,
size,
Between
of Outliers
Repeatability Reproducibility Repeatability Between labs Reproducibility
particles/mL
µm(c)
labs labs
1,5 2 67 419,93 614,10 0,00 614,10 0,91 % 0,00 % 0,91 %
2 3 40 430,44 505,51 2 402,69 2 455,30 1,25 % 5,94 % 6,07 %
3 12 5 18 014,44 276,26 1 098,51 1 132,71 1,53 % 6,10 % 6,29 %
4 16 5,13 10 862,58 164,49 401,09 433,50 1,51 % 3,69 % 3,99 %
6 17 5 4 642,08 86,18 222,73 238,82 1,86 % 4,80 % 5,14 %
10 18 1 071,04 37,40 74,13 83,03 3,49 % 6,92 % 7,75 %
14 18 346,64 20,62 32,02 38,08 5,95 % 9,24 % 10,99 %
21 17 88,20 8,61 13,53 16,04 9,77 % 15,34 % 18,19 %
30 13 10,11 14,05 3,30 2,17 3,95 23,50 % 15,43 % 28,12 %
38 12 11 4,59 1,46 1,61 2,17 31,83 % 35,04 % 47,34 %
50 11 11 1,45 0,68 1,36 1,52 47,02 % 93,26 % 104,45 %
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ISO/TR 4813:2021(E)
Key
Y particle/mL> indicated size
X particle size, µm(c)
1 sizes covered only by light scattering sensors
2 sizes covered by light scattering and extinction sensors
3 sizes cover only by light extinction sensors
4 participant 11
5 participant 7

Figure 1 — Mean particle concentration versus particle size results for SRM 2806d

candidate material samples
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ISO/TR 4813:2021(E)
© ISO 2021 – All rights reserved 9
Table 3 — Summary of RM 8632a ILS data
particle Number Standard deviation, particles/mL CV, %
Mean,
size,
Between
of Outliers
Between
Repeatability Reproducibility Repeatability Reproducibility
particles/mL
µm(c)
labs
labs labs
2 3 19 377,69 127,58 2 217,84 2 221,51 0,66 % 11,45 % 11,46 %
3 11 10 527,80 547,04 775,94 949,39 5,20 % 7,37 % 9,02 %
4 16 5,9b 6 561,31 68,52 763,56 766,62 1,04 % 11,64 % 11,68 %
5 16 5,9b 3 597,02 55,14 531,32 534,18 1,53 % 14,77 % 14,85 %
6 16 5,9b 1 761,37 44,51 356,31 359,08 2,53 % 20,23 % 20,39 %
7 16 5 844,71 51,68 182,14 189,33 6,12 % 21,56 % 22,41 %
8 16 5 425,40 37,85 105,11 111,71 8,90 % 24,71 % 26,26 %
9 14 5 218,68 28,14 63,83 69,76 12,87 % 29,19 % 31,90 %
10 17 5 113,21 18,62 41,06 45,09 16,45 % 36,27 % 39,83 %
11 13 5 62,74 14,29 31,33 34,43 22,78 % 49,94 % 54,89 %
12 15 5 34,01 10,39 22,11 24,43 30,53 % 65,01 % 71,82 %
13 13 5 23,27 8,91 19,02 21,00 38,28 % 81,74 % 90,26 %
14 16 5 15,53 6,62 14,48 15,92 42,62 % 93,26 % 102,54 %
15 15 5 11,22 5,21 13,09 14,09 46,47 % 116,68 % 125,60 %
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ISO/TR 4813:2021(E)
Key
Y particl
...

TECHNICAL ISO/TR
REPORT 4813
First edition
Hydraulic fluid power — Background,
impact and use of ISO 11171:2020 on
particle count and filter test data
PROOF/ÉPREUVE
Reference number
ISO/TR 4813:2020(E)
ISO 2020
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ISO/TR 4813:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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
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Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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ISO/TR 4813:2020(E)
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

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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.
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ISO/TR 4813:2020(E)
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 either of 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.
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TECHNICAL REPORT ISO/TR 4813:2020(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 11171:2020, 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

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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 claculated 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 developed in co-operation with

all parties with an interest in participating in the development or use of the standard. In this case, NIST

and ISO TC 131/SC 6 agreed to use the traceable SRM 2806 certification to define µm(c) and APC (rather

than SEM) data to obtain the number concentration of particles as a function of particle size. To avoid

commercially significant shifts in particle size between batches, the certified particle size distribution

for SRM 2806x batches are based upon particle count data from ILS conducted using APC calibrated

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according to ISO 11171:2020 in µm(c) using the most recent previous batch of SRM 2806x. In the case

of SRM 2806d, SRM 2806b was used to calibrate all 4 APCs used to certify the ILS secondaries as per

ISO 11171:2020 and to maintain traceability. Samples of SRM 2806b had been put aside by NIST at the

request of the Project Leaders specifically for this purpose. The traceable secondaries were used to

calibrate ILS APCs. In this manner, the ILS data represents the industry consensus definition of µm(c)

and ensures that particle size does not deviate significantly with each new batch of SRM 2806x.

In addition to changes in the manner of reporting particle size and certification of primary calibration

suspension, ISO 11171:2020 also specifies how calibration curves are determined. Previously, there

was discretion in the way calibration curves were determined, e.g. how channels were selected,

whether to use latex or test dust to calibrate for sizes greater than 30 µm(c), what mathematical

function is used to create a calibration curve. Collectively, these legitimate discretionary choices

increased uncertainty in particle count data and, in some cases, introduced artefacts into the data. This

is addressed in ISO 11171:2020, which requires that data from at least 12 different threshold settings

spaced logarithmically over the entire particle size range of interest be used to create a calibration

curve. The lowest of these threshold settings is 1,5 times the threshold noise level of the instrument,

corresponding to the smallest size that can be counted. The calibration curve itself is created using the

constrained cubic spline method. In this manner, the uncertainty between laboratories is reduced.

Counting particles smaller than 4 µm(c) has been problematic, as the concentrations of particles in

calibration suspensions are typically above coincidence error limits. In contrast to prior versions,

ISO 11171:2020 permits dilution of calibration samples using a defined method derived from ISO 11500.

To minimize contamination, verification of dilution fluid and glassware cleanliness is required. As a

result, some laboratories participating in the ILS were able to calibrate to particle sizes as small at

1,5 µm(c).

In some applications, such as gear and transmission fluids, interest is primarily in particles larger than

30 µm(c). Previous versions of ISO 11171 allowed either latex or test dust calibration suspensions to be

used at these sizes, but they can yield different results.

Furthermore, test dust calibration samples generally contain insufficient numbers of large particles for

a valid calibration. Also, primary calibration samples are not certified above 30 µm(c) and therefore not

traceable. To address this, ISO 11171:2020 specifies that primary calibration for particle sizes larger than

30 µm(c) be done with monodispersed latex particles and provides guidance for selection of their sizes.

APC calibrated in this manner can be used to produce secondary calibration suspensions certified

at sizes larger than 30 µm(c). These changes are intended to reduce uncertainty and to facilitate

calibration at particle sizes larger than 30 µm(c).
6 Inter-laboratory study experimental design
An inter-laboratory study (ILS) of ISO 11171:2020 was conducted to:

— Measure the intra-company repeatability and inter-company reproducibility of particle count data

obtained using APC calibrated to the standard using SRM 2806d candidate material and suspensions

of RM 8632a;

— Generate particle count data to be used by NIST to certify consensus standard SRM 2806d in size

units of µm(c);

— Determine the extent, if any, of the shift in particle size resulting from the use of SRM 2806d; and

— Generate particle count data for NIST RM 8632a that will provide a basis to update ISO 11171:2020,

Table A.1.
The ILS experimental design consisted of:

1. Production of traceable secondary calibration samples for use by ILS participants.

2. Selection and qualification of participating laboratories and APC.
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ISO/TR 4813:2020(E)
3. ISO 11171:2020 calibration of APC.

4. Analysis of samples of SRM 2806d candidate suspensions and RM 8632a test dust, and

5. Analysis of data as per ISO 5725-2.

The ILS results were provided to NIST for use in certifying consensus standard SRM 2806d.

The traceable secondary calibration samples for use in the ILS were prepared by Aviation Industry

(Xinxiang) Metrology and Test Science Technology Company Limited, commonly known as CFPC. These

were used to calibrate the APC used by ILS participants. They were produced to the same specifications

as the SRM 2806d candidate material according to ISO 11171:2020, Annex F. Four laboratories were

selected to analyse the secondary calibration samples. Two of the laboratories, Pamas and CFPC,

utilized Pamas light scattering APC. All data for particle sizes of 1,5 µm(c) and 2 µm(c) were generated

by Pamas light scattering APC. The other two laboratories, NIST and Beckman, utilized Beckman

light extinction APC. Each laboratory performed a full primary ISO 11171:2020 calibration but using

SRM 2806b for particle sizes up to 30 µm(c) for light extinction sensors or to the largest size that the

instrument was capable of counting for light scattering sensors. Each was sent five bottles of secondary

calibration fluid for analysis. The data from all four laboratories was analysed by NIST and used to

generate the composite certified size distribution for the secondary calibration samples. Thus, the

certified size distribution is not biased with respect to a single laboratory, APC operating principle

or manufacturer. ILS participants were required to demonstrate that their APC met all ISO 11171

performance specifications and asked to provide their most recent ISO 11171:2016 calibration curve.

Eighteen APC participated in the ILS, including laboratories from five countries (USA, Germany, United

Kingdom, China, France), two different operating principles (light extinction, light scattering), and

three APC manufacturers (Pamas, Beckman, Stanhope-Seta).
The characteristics of these 18 individual APC are summarized in Table 1.
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Table 1 — APC operating and performance characteristics
Coincidence Sample Working
Noise
APC C . Resolution Number of
APC identi- v vol
level
Type error limit volume flow rate
fier
manufacturer % µm(c) thresholds
Particles/mL mL mL/min
1 X extinction 105 27 000 2,7 % 13,4 % 10 25 16
2 Y extinction 10 19 000 0,4 % 5,0 % 10 50 12
3 X extinction 150 59 129 0,4 % 8,5 % 10 10 16
4 X scattering 80 12 713 0,2 % 6,8 % 10 10 16
5 X extinction 200 27 171 1,9 % 9,5 % 10 25 16
6 X extinction 120 89 813 0,8 % 9,6 % 10 10 18
7 Z extinction 178 30 000 0,4 % 7,4 % 10 30 17
8 Y extinction 3 40 246 0,6 % 11,2 % 10 30 18
9 Y extinction 10 6 000 0,9 % 4,5 % 25 25 101
10 X extinction 77 34 251 0,1 % 6,7 % 10 25 13
11 X extinction 190 19 418 0,2 % 9,6 % 10 25 16
12 X extinction 190 20 743 0,3 % 6,0 % 25 25 24
13 X scattering 150 12 245 0,6 % 3,0 % 10 10 24
14 X extinction 170 25 780 1,0 % 10,1 % 10 25 16
15 X extinction 155 19 617 0,9 % 5,8 % 10 25 16
16 X scattering 40 14 003 0,8 % 10,0 % 10 10 16
17 Y extinction 8 15 789 0,6 % 7,0 % 10 20 18
18 Z extinction 181 30 000 0,4 % 7,4 % 10 30 17
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ILS participants calibrated their APC as per ISO 11171:2020 using the CFPC secondary calibration

samples previously described. Participants were asked to calibrate to the smallest size that their APC

was capable of counting and, if possible, to calibrate up to a particle size of 50 µm(c) or the largest

size that their APC was capable of counting. Each participant received 3 samples of SRM 2806d

candidate material and 1 bottle of RM 8632a to analyse. The candidate material samples were analysed

as described in ISO 11171:2020 at as many of the following particle sizes as possible using their

ISO 11171:2020 calibration: 1,5 µm(c), 2 µm(c), 3 µm(c), 4 µm(c), 6 µm(c), 10 µm(c), 14 µm(c), 21 µm(c),

30 µm(c), 38 µm(c) and 50 µm(c). Participants were also asked to prepare three 1,0 mg/L samples of

RM 8632a test dust and analyse these at as many of the integral particle sizes as possible between

2 µm(c) and 15 µm(c), inclusive. The results were provided to the Project Leaders and analysed as

per ISO 5725-2. The data and statistical analysis were also provided to NIST for use in certifying the

consensus standard SRM 2806d. Further details regarding the ILS and the certification of SRM 2806d

are described in Reference [6].
7 Results of ILS

Tables 2 and 3 summarize the ILS data for the SRM 2806d candidate material and RM 8632a samples,

respectively. Figures 1 and 2 show the mean particle concentration data from each ILS participant

for the samples in graphical form. As per ISO 5725-2, Mandel h and k, Grubbs test, and Cochran test

were used to detect outlier data. Outlier data are noted in Tables 2 and 3 and were excluded from the

statistical analysis.

The following are suspected outliers, but did not meet the criteria for exclusion from the data analysis:

— 6 µm(c), 10 µm(c) and 14 µm(c) data of participant 13 for the SRM 2806d candidate samples;

— 38 µm(c) and 50 µm(c) data of participant 7 for the SRM 2806d candidate samples;

— 3 µm(c), 7 µm(c) and 8 µm(c) data for the second RM 8632a sample analysed by participant 9;

— 6 µm(c) through 15 µm(c) data of participant 1 for their RM 8632a sample; and
— 3 µm(c) data of participants 16 and 17 for their RM 8632a sample.

Referring to Figure 1, the SRM 2806d candidate material data at particle sizes larger than 30 µm(c)

for participants 7 and 11 are suspected outliers. Statistical grounds exist to exclude participant

11, but not participant 7 at these sizes. In both cases, the particle concentration data appeared to

approach a horizontal asymptote at larger sizes and the corresponding APC calibration curve also

demonstrated asymptotic behaviour. In some cases, the latex calibration samples were reported to

be cloudy in appearance, suggesting that the water drops from the latex did not completely disperse

in the dilution fluid, thus causing the APC to count water droplets. This results in the asymptotic

behaviour at these sizes. The root cause appears to be incomplete dissolution of the Aerosol OT in the

dilution fluid. Dissolution requires heat and time and can be difficult to verify visually. Participant 6

initially encountered a similar issue, but resolved it by using a higher dilution ratio, i.e. a lower latex

concentration in the calibration samples. Another approach is to increase the heating and stirring time

used to dissolve Aerosol OT in the dilution fluid, thus ensuring complete dissolution. Guidance on how

to avoid this issue was added to ISO 11171:2020 based upon these results.

Referring to Figure 2, RM 8632a data for participants 1 and 5 were suspected to be outliers. While

participant 1 consistently exhibited the lowest RM 8632a data, it did not meet the outlier criteria and

was not excluded. Participant 5 data was excluded as an outlier. These data were approximately twice

the mean value of all other laboratories at each size, suggesting that a math or weighing error occurred,

but this could not be confirmed.
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Table 2 — Statistical summary of ILS data for SRM 2806d candidate material samples

Number Standard deviation, particles/mL CV, %
Particle
Mean,
size,
Between
of Outliers
Repeatability Reproducibility Repeatability Between labs Reproducibility
particles/mL
µm(c)
labs labs
1,5 2 67 419,93 614,10 0,00 614,10 0,91 % 0,00 % 0,91 %
2 3 40 430,44 505,51 2 402,69 2 455,30 1,25 % 5,94 % 6,07 %
3 12 5 18 014,44 276,26 1 098,51 1 132,71 1,53 % 6,10 % 6,29 %
4 16 5,13 10 862,58 164,49 401,09 433,50 1,51 % 3,69 % 3,99 %
6 17 5 4 642,08 86,18 222,73 238,82 1,86 % 4,80 % 5,14 %
10 18 1 071,04 37,40 74,13 83,03 3,49 % 6,92 % 7,75 %
14 18 346,64 20,62 32,02 38,08 5,95 % 9,24 % 10,99 %
21 17 88,20 8,61 13,53 16,04 9,77 % 15,34 % 18,19 %
30 13 10,11 14,05 3,30 2,17 3,95 23,50 % 15,43 % 28,12 %
38 12 11 4,59 1,46 1,61 2,17 31,83 % 35,04 % 47,34 %
50 11 11 1,45 0,68 1,36 1,52 47,02 % 93,26 % 104,45 %
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ISO/TR 4813:2020(E)
Key
Y particle/mL> indicated size
X particle size, µm(c)
1 sizes covered only by light scattering sensors
2 sizes covered by light scattering and extinction sensors
3 sizes cover only by light extinction sensors
4 participant 11
5 participant 7

Figure 1 — Mean particle concentration versus particle size results for SRM 2806d

candidate material samples
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Table 3 — Summary of RM 8632a ILS data
particle Number Standard deviation, particles/mL CV, %
Mean,
size,
Between
of Outliners
Between
Repeatability Reproducibility Repeatability Reproducibility
particles/mL
µm(c)
labs
labs labs
2 3 19 377,69 127,58 2 217,84 2 221,51 0,66 % 11,45 % 11,46 %
3 11 10 527,80 547,04 775,94 949,39 5,20 % 7,37 % 9,02 %
4 16 5,9b 6 561,31 68,52 763,56 766,62 1,04 % 11,64 % 11,68 %
5 16 5,9b 3 597,02 55,14 531,32 534,18 1,53 % 14,77 % 14,85 %
6 16 5,9b 1 761,37 44,51 356,31 359,08 2,53 % 20,23 % 20,39 %
7 16 5 844,71 51,68 182,14 189,33 6,12 % 21,56 % 22,41 %
8 16 5 425,40 37,85 105,11 111,71 8,90 % 24,71 % 26,26 %
9 14 5 218,68 28,14 63,83 69,76 12,87 % 29,19 % 31,90 %
10 17 5 113,21 18,62 41,06 45,09 16,45 % 36,27 % 39,83 %
11 13 5 62,74 14,29 31,33 34,43 22,78 % 49,94 % 54,89 %
12 15 5 34,01 10,39 22,11 24,43 30,53 % 65,01 % 71,82 %
13 13 5 23,27 8,91 19,02 21,00 38,28 % 81,74 % 90,26 %
14 16 5 15,53 6,62 14,48 1
...

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