Hydraulic fluid power — Calibration of automatic particle counters for liquids

This document specifies procedures for the following: a) primary particle-sizing calibration for particle sizes 1 µm(c) and larger, sensor resolution and counting performance of liquid automatic particle counters that are capable of analysing bottle samples; b) secondary particle-sizing calibration using suspensions verified with a primary calibrated APC; c) establishing acceptable operation and performance limits; d) verifying particle sensor performance using a test dust; e) determining coincidence and flow rate limits. This document is applicable for use with hydraulic fluids, aviation and diesel fuels, engine oil and other petroleum-based fluids. This document is not applicable to particle-sizing calibration using NIST SRM 2806b primary calibration suspensions.

Transmissions hydrauliques — Étalonnage des compteurs automatiques de particules en suspension dans les liquides

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Published
Publication Date
17-Mar-2022
Current Stage
4099 - Full report circulated: DIS approved for registration as FDIS
Start Date
20-Nov-2021
Completion Date
20-Nov-2021
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INTERNATIONAL ISO
STANDARD 11171
Fifth edition
2022-03
Hydraulic fluid power — Calibration of
automatic particle counters for liquids
Transmissions hydrauliques — Étalonnage des compteurs
automatiques de particules en suspension dans les liquides
Reference number
ISO 11171:2022(E)
© ISO 2022
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ISO 11171:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
© ISO 2022 – All rights reserved
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ISO 11171:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .............................................................................................................................................................................................................................. vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Materials and equipment ............................................................................................................................................................................3

5 Sequence of APC calibration procedures ................................................................................................................................... 5

6 Sizing calibration procedure .................................................................................................................................................................. 9

7 Data presentation ............................................................................................................................................................................................19

8 Identification statement ...........................................................................................................................................................................20

Annex A (normative) Preliminary APC check .........................................................................................................................................21

Annex B (normative) Coincidence error procedure .........................................................................................................................25

Annex C (normative) Flow rate limit determination .......................................................................................................................29

Annex D (normative) Resolution determination .................................................................................................................................34

Annex E (normative) Verification of particle-counting accuracy ......................................................................................39

Annex F (normative) Preparation and verification of bottles of secondary calibration

suspensions ............................................................................................................................................................................................................42

Annex G (normative) Dilution of calibration suspension samples ...................................................................................46

Annex H (informative) Verification of particle size distribution of calibration samples ........................49

Bibliography .............................................................................................................................................................................................................................51

iii
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ISO 11171:2022(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, SC 6,

Contamination control.

This fifth edition cancels and replaces the fourth edition (ISO 11171:2020), which has been technically

revised.
The main changes are as follows:
— in term 3.8, particle size distribution, Note 1 to entry has been amended;
— in 6.12 c), 0,72 has been changed to 0,56;
— in 6.12 d) 1,32 has been changed to 1,56;
— in B.4, 3 line, “mass concentrate” has been changed to “mass concentration”;

— B.8 has been amended to read: ……”calculate the theoretical number concentration of particles for

each mass concentration, X .”;

— in Table B.1, the units for “X (particles/L)” have been corrected to “X (particles/mL)”;

t t
— in D.3 c), 0,72 has been changed to 0,56;
— in D.3 d), 1,32 has been changed to 1,56;
— in D.7 a), 0,72 has been changed to 0,56;
— in D.7 e), 1,32 has been changed to 1,56;

— in G.6, the subscript in the denominator of Formula G.3 has been corrected from “V ” to “V ”;

0 S

— in Reference [6] in the Bibliography, the RM 8631 batch identifier has been changed from “a” to “b”;

— in Reference [7] in the Bibliography, the RM 8632 batch identifier has been changed from “b” to “a”.

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ISO 11171:2022(E)

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.
© ISO 2022 – All rights reserved
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ISO 11171:2022(E)
Introduction

In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure

within an enclosed circuit. The fluid is both a lubricant and a power-transmitting medium. Reliable

system performance requires control of the contaminants in the fluid. Qualitative and quantitative

determination of the particulate contaminants in the fluid medium requires precision in obtaining

the sample and in determining the contaminant particle size distribution and concentration. Liquid

automatic particle counters (APC) are an accepted means of determining the concentration and size

distribution of the contaminant particles. Individual APC accuracy is established through calibration.

This document is a standard calibration procedure for APC that are used for determining particle sizes

and counts. The primary particle-sizing calibration is conducted using NIST SRM 2806x suspensions

with particle size distribution certified by the United States National Institute of Standards and

Technology (NIST) for particle sizes 30 µm(c) and smaller, and using polystyrene latex spheres at larger

sizes.

A secondary calibration method uses suspensions of NIST RM 8631x, ISO MTD, or other test dust

conforming to ISO 12103-1, which are independently analysed using an APC calibrated by the primary

method. Minimum performance specifications are established for the APC coefficient of variation (CV)

of sample volume, CV of flow rate, resolution and particle counting accuracy. The operating limits of an

APC, including its threshold noise level, coincidence error limit and flow rate limits are determined.

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INTERNATIONAL STANDARD ISO 11171:2022(E)
Hydraulic fluid power — Calibration of automatic particle
counters for liquids
1 Scope
This document specifies procedures for the following:

a) primary particle-sizing calibration for particle sizes 1 µm(c) and larger, sensor resolution and

counting performance of liquid automatic particle counters that are capable of analysing bottle

samples;

b) secondary particle-sizing calibration using suspensions verified with a primary calibrated APC;

c) establishing acceptable operation and performance limits;
d) verifying particle sensor performance using a test dust;
e) determining coincidence and flow rate limits.

This document is applicable for use with hydraulic fluids, aviation and diesel fuels, engine oil and

other petroleum-based fluids. This document is not applicable to particle-sizing calibration using

NIST SRM 2806b primary calibration suspensions.
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 3722, Hydraulic fluid power — Fluid sample containers — Qualifying and controlling cleaning methods

ISO 4787, Laboratory glass and plastic ware — Volumetric instruments — Methods for testing of capacity

and for use
ISO 5598, Fluid power systems and components — Vocabulary

ISO 12103-1, Road vehicles — Test contaminants for filter evaluation — Part 1: Arizona test dust

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 5598 and the following apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
automatic particle counter
APC
instrument that automatically:
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ISO 11171:2022(E)

a) senses individual particles suspended in a controlled volume of fluid using optical light extinction

or light scattering principles;
b) measures the size of particles;
c) sorts or compiles particles into size ranges;
d) counts particles in each size range;
e) reports the number of particles in each size range per unit volume; and
f) facilitates instrument calibration according to this document.

Note 1 to entry: APC used for particle size (3.7) determination with hydraulic fluids, aviation and diesel fuels,

engine oil and other petroleum-based fluids shall be calibrated in accordance with Clause 5 of this document.

3.2
threshold noise level

minimum voltage setting of an APC (3.1) at which the observed pulse-counting frequency does not

exceed 60 counts/min due to electrical noise in the absence of flow in the sensing volume (3.3)

Note 1 to entry: The Brownian motion of any detectable particles in the sensing zone during performance of

subclause A.2 can result in erratic results.
3.3
sensing volume

portion of the illuminated region of the sensor through which the fluid stream passes and from which

the light is collected by the optical system
3.4
resolution

measure of the ability of an APC (3.1) to distinguish between particles of similar, but different, sizes as

determined in accordance with Annex D of this document
3.5
coincidence error limit

highest concentration of NIST RM 8632x that can be counted with an automatic particle counter (3.1)

with an error of less than 5 % resulting from the presence of more than one particle in the sensing

volume (3.3) at one time
3.6
working flow rate
flow rate through the sensor used for sample analysis
3.7
particle size

projected area equivalent diameter of particles as determined by NIST using scanning electron

microscopy traceable to SI units through a NIST length standard or using a liquid optical single particle

APC (3.1) calibrated according to this document

Note 1 to entry: NIST uses scanning electron microscopy to determine the projected area equivalent diameter

of particles in NIST standard reference material 2806x, where x is the letter used by NIST to designate the batch

number of the certified primary calibration (3.9) suspension.
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ISO 11171:2022(E)
3.8
particle size distribution

cumulative number concentration of particles larger than a specified size, expressed as a function of

particle size (3.7)

Note 1 to entry: A certified particle size distribution is one provided by a producer of primary (3.9) or secondary

calibration (3.10) suspensions, and certifies that the particle size distribution reported for the suspensions was

determined by NIST or determined according to Annex F of this document. The particle size distribution of SRM

2806x used for primary calibrations (3.9) shall consist of the values for Diameter [µm(c)] and the corresponding

Cumulative Particle Concentration (part/mL) given in the Certificate of Analysis for Standard Reference

[5]
Material® 2806x .

Note 2 to entry: Verification of particle size distribution of calibration samples is detailed in Annex H of this

document.
3.9
primary calibration

sizing calibration conducted according to the sizing calibration procedure specified in Clause 6 of this

document using NIST standard reference material 2806x for particle sizes (3.7) 30 µm(c) and smaller,

and using polystyrene latex spheres at larger sizes
Note 1 to entry: For details of NIST standard reference material 2806x, see 4.4.
3.10
secondary calibration
sizing calibration conducted using secondary calibration suspensions

Note 1 to entry: The sizing calibration procedure is specified in Clause 6 and the preparation of secondary

calibration suspensions is set out in Annex F.
3.11
multi-channel analyser
MCA

electronic device capable of sorting incoming electric pulses according to their amplitude

4 Materials and equipment
4.1 Polystyrene latex spheres that:
a) are in aqueous suspension;
b) have a nominal diameter of:
1) 10 µm if used for resolution determination in accordance with Annex D;

2) larger than 30 µm for particle size calibration in accordance with Clause 6 for particle sizes of

larger than 30 µm;

c) have a coefficient of variation that is less than 5 % where the coefficient of variation is the ratio

of the standard deviation of the latex particle diameters in the suspension to their mean particle

diameter;

d) have a certificate of analysis that indicates that the latex spheres mean particle diameter and

coefficient of variation were determined using techniques with traceability to national standards.

Once opened, suspensions of polystyrene latex spheres shall be used within three months unless the

size distribution and cleanliness of the suspension have been verified.

NOTE 1 The size distribution of polystyrene latex spheres can be verified using the method described in D.14.

NOTE 2 Polystyrene latex spheres in aqueous suspension have a limited shelf life. Shelf life is a function of a

variety of factors including temperature and microbial contamination of the suspension.

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ISO 11171:2022(E)

4.2 Clean diluent, consisting of the test liquid used in ISO 16889 and containing:

a) an antistatic additive at such a concentration that resultant conductivity of the clean diluent is

(2 500 ± 1 000) pS/m at room temperature; and

b) less than 0,5 % of the number concentration of particles equal to or larger than the smallest particle

size of interest expected to be observed in the samples.

4.3 Clean aerosol OT diluent, for use in calibration for particle sizes greater than 30 µm(c) and to

determine sensor resolution in Annex D (the clean diluent specified in 4.2 is used for all other operations

in this document), which:

a) is prepared from a concentrate made by adding 120 g of aerosol OT to each litre of clean diluent

(4.2), which is:

1) heated to approximately 60 °C and stirred until no undissolved aerosol OT is visible to the eye;

and

2) diluted with clean diluent (4.2) to a final concentration of 12 g of aerosol OT per litre; and

b) meets the same cleanliness levels as the diluent specified in 4.2.

Aerosol OT (dioctyl sulfosuccinate, sodium salt) is a waxy, hygroscopic solid. If it appears damp, or has

absorbed water prior to use, dry it first for at least 18 h at approximately 150 °C.

NOTE In 4.3 a) 1), it is critical that all of the aerosol OT be dissolved prior to proceeding to 4.3 a) 2).

Depending upon the local conditions, complete dissolution can require in excess of 6 hours of heating and stirring

as described.

WARNING — Follow the precautions for safe handling and usage described in the safety data

sheet (available from the supplier of the aerosol OT).

4.4 NIST standard reference material 2806x (SRM 2806x) primary calibration suspension,

where x is the letter used by NIST to designate the batch number of the certified primary calibration

suspension available from NIST, for use in primary calibrations. SRM 2806b shall not be used for

calibrations according to this document.

4.5 NIST reference material 8631x (RM 8631x) dust, where x is the letter used by NIST to

designate the batch number of the reference material, available from NIST, prepared by drying the dust

for at least 18 h at a temperature between 110 °C and 150 °C, for use if secondary calibration is to be

performed (see 6.1).

4.6 ISO medium test dust (MTD) or other test dust conforming to ISO 12103-1, dried for at least

18 h at a temperature between 110 °C and 150 °C before use, for use if secondary calibration is to be

performed (see 6.1).

4.7 NIST reference material 8632x (RM 8632x) dust, where x is the letter used by NIST to

designate the batch number of the reference material, prepared by drying the dust for at least 18 h at

a temperature between 110 °C and 150 °C, before use, required for determination of coincidence error

limit and in Annexes A, B, C and E.

NOTE The reference materials specified in 4.4, 4.5, 4.6 and 4.7 can change as new batches are produced. Such

a change does not affect the particle sizing calibration (Clause 6), but the ability of an APC to meet the counting

accuracy requirements of E.9 can be affected if the batch of RM 8632x used to prepare the samples differs from

the batch used to create Table A.1.

4.8 Automatic particle counter for liquids, with bottle sampler with at least 8 channels that can be

set at various threshold settings.
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ISO 11171:2022(E)

4.9 Clean sample containers, with closures (appropriate bottle caps, for example), and volumetric

glassware of at least class B accuracy as defined in ISO 4787, with cleanliness levels lower than 0,5 % of

the number of concentration of particles (larger than the smallest particle size of interest) expected to

be observed in the samples, confirmed in accordance with ISO 3722.

4.10 Mechanical shaker, such as a paint or laboratory shaker, suitable for dispersing suspensions.

2 2

4.11 Ultrasonic bath, with a power density of 3 000 W/m to 10 000 W/m of bottom area.

4.12 Linear-linear graph paper or computer software, for generating graphics.
4.13 Log-log graph paper or computer software, for generating graphics.

4.14 Analytical or electronic balance, with the following minimum specifications:

a) readability: 0,01 mg;
b) accuracy (agreement with true mass): ±0,05 mg;
c) precision (repeatability): 0,05 mg;

d) front or side doors and a covered top to eliminate the effect of air currents.

4.15 Secondary calibration suspension, prepared according to Annex F for use in secondary

calibrations. Secondary calibration samples shall not be used for primary calibrations.

5 Sequence of APC calibration procedures

5.1 Conduct the procedures of this Clause when a new APC is received or following the repair or re-

adjustment of an APC or sensor as shown in Table 1. See Figure 1 for a recommended sequence of steps

to be followed when performing a full calibration on a new APC. Annexes A and B shall be performed

prior to proceeding to Clause 6. Proceed to Clause 6 if neither the APC nor the sensor has been repaired

or readjusted, if no detectable change in the operating characteristics has occurred since the last sizing

calibration was performed, and if the APC has been subjected to the procedures in Annexes A, B, C,

D, and E and the results have been documented. The specific order of annexes and clauses given in

Figure 1 and Table 1 are recommendations. The operator may follow a different order, as long as all

required parts are performed.

Annexes A, B, C, D and E may be performed by an individual laboratory or by the manufacturer of the

APC prior to delivery. If these are performed prior to delivery, it is not always required to repeat these

annexes upon receipt of the APC, depending upon the manufacturer's recommendations.

NOTE For the purposes of this subclause, repair or re-adjustment of an APC refers to service or repair

procedures that affect the ability of the APC to accurately size and count particles.

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ISO 11171:2022(E)
Figure 1 — Recommended sequence of APC calibration procedures

A change in the operating characteristics of the APC can be detected by several different methods,

including but not limited to the following:

a) using particle data from control samples collected over time and a statistical process control chart,

such as an individual moving range (IMR) chart, to detect significant changes in calibration;

b) comparing calibration curves reporting particle size in units of µm(c) over time to detect a

significant change in calibration;

c) returning the APC to its manufacturer for evaluation and assessment of the change in calibration;

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ISO 11171:2022(E)

d) analysing a primary or secondary calibration suspension in accordance with 6.5 through 6.7, then

comparing the resulting particle concentration data to the corresponding particle size distribution

for the sample:

1) if the results agree within the limits for the maximum allowable D (6.6) given in Table C.2, the

ability of the APC to size and count particles has not been significantly affected;

2) if the results do not agree, a significant change has occurred, so proceed as indicated in Table 1.

e) determining the threshold noise level of the APC in accordance with A.2, then comparing the

resulting noise level to previously obtained results. If the threshold noise level has increased by

more than 30 % since the last time it was determined, this can be an indication that the calibration

of the APC has changed and the APC is in need of repair. If the threshold noise level has not changed,

this is not proof that the APC's operating characteristics are unchanged.

If the light source or any part of the optics is adjusted, repaired or replaced, repeat the procedures of

Clause 6 and Annexes A, B, D, and E.

If the sensor or counting electronics is adjusted, repaired or replaced, repeat the procedures of Clause 6

and Annexes A, B, C, D, and E.

If the volume measurement system is repaired, replaced or re-adjusted, the procedures of A.3 to A.9

and of Annex C shall be performed.

It is not necessary to repeat these procedures following normal cleaning procedures, the attachment of

cables or peripheral equipment, the replacement of plumbing lines or connections, or following other

operations that do not involve disassembly of the APC, sensor or volume measurement system.

5.2 Perform the preliminary APC check, which includes volume accuracy, in accordance with Annex A.

5.3 Determine the coincidence error limits of the APC in accordance with Annex B.

5.4 Perform the sizing calibration procedure in accordance with Clause 6.
5.5 Determine the flow rate limits of the APC in accordance with Annex C.
5.6 Determine the APC resolution in accordance with Annex D.
5.7 Verify the particle-counting accuracy in accordance with Annex E.
5.8 In order to conform to the requirements of this document, the APC shall:
a) be calibrated in accordance with 5.4;

b) meet the volume accuracy, resolution and sensor performance specifications determined in 5.2, 5.6

and 5.7;

c) be operated using the calibration curve determined in accordance with 5.4 within the coincidence

error and flow rate limits determined in accordance with 5.3 and 5.5.
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ISO 11171:2022(E)
© ISO 2022 – All rights reserved
Table 1 — Schedule of APC calibration procedures
Relevant clause or annex of this document to be performed
Clause 6 Annex A Annex B Annex C Annex D Annex E
APC status
Sizing
Preliminary Coincidence Flow rate
calibration Resolution Accuracy
APC check error limits limits
procedure

New APC or existing APC not calibrated to this Perform Perform Perform Perform Perform Perform

document procedure procedure procedure procedure procedure procedure
Perform

Last calibration was more than 6 m to 12 m ago Not required Not required Not required Not required Not required

procedure
Perform

Suspicion that calibration has changed significantly Not required Not required Not required Not required Not required

procedure
Perform Perform Perform Perform Perform
Optics (including light source) repaired or readjusted Not required
procedure procedure procedure procedure procedure
Perform Perform Perform Perform Perform Perform
Sensor or counting electronics repaired or readjusted
procedure procedure procedure procedure procedure procedure
Volume measurement components (e.g. flow meter, Perform Perform
Not required Not required Not required Not required
burette, level detectors) repaired or readjusted procedure procedure
Sensor cleaned No action necessary
Cables or peripheral equipment attached No action necessary
Plumbing lines and connections replaced No action necessary
Operation performed that does not involve disassembly of
No action necessary
APC, sensor or volume measurement system

Repair or re-adjustment refers only to service or repair procedures that affect the ability of the APC to accurately size and count particles. In order to verify the ability of

an APC to accurately size and count particles, analyse a primary or secondary calibration suspension in accordance with 6.5 through 6.7, then compare the resulting particle

concentration data to the corresponding particle size distribution for the sample. If the results agree within the limits given for the maximum allowable D in Table C.2, the ability

of the APC to size and count particles has not been significantly affected. If the results do not agree, proceed as indicated in this Table.

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ISO 11171:2022(E)
6 Sizing calibration procedure

6.1 Conduct the sizing calibration set out in Figure 2 every three to six months, when a new APC is

received, or after the repair or re-adjustment of an APC or sensor. After a suitable calibration history

for an APC and sensor has been developed, the time interval between successive calibrations can be

increased, but shall
...

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