ISO 11171:2022
(Main)Hydraulic fluid power — Calibration of automatic particle counters for liquids
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
Fluidna tehnika - Hidravlika - Umerjanje naprav za avtomatsko štetje delcev v tekočinah
Ta dokument določa postopke za:
a) primarno kalibracijo velikosti delcev za velikosti delcev 1 µm(c) in večje, ločljivost senzorja in učinkovitost štetja tekočih samodejnih števcev delcev, ki lahko analizirajo vzorce iz steklenic;
b) sekundarno kalibracijo velikosti delcev z uporabo suspenzij, preverjenih s primarno kalibriranimi samodejnimi števci delcev;
c) določanje sprejemljivih meja delovanja in učinkovitosti;
d) preverjanje delovanja senzorja delcev z uporabo preskusnega prahu;
e) določanje meja stopenj koincidence in pretoka.
Ta dokument se uporablja za uporabo s hidravličnimi tekočinami, letalskimi in dizelskimi gorivi, motornim oljem in drugimi tekočinami naftnega izvora. Ta dokument se ne uporablja za kalibracijo velikosti delcev z uporabo primarnih kalibracijskih suspenzij NIST SRM 2806b.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-april-2023
Fluidna tehnika - Hidravlika - Umerjanje naprav za avtomatsko štetje delcev v
tekočinah
Hydraulic fluid power - Calibration of automatic particle counters for liquids
Transmissions hydrauliques - Étalonnage des compteurs automatiques de particules en
suspension dans les liquides
Ta slovenski standard je istoveten z: ISO 11171:2022
ICS:
17.120.01 Merjenje pretoka tekočin na Measurement of fluid flow in
splošno general
23.100.01 Hidravlični sistemi na splošno Fluid power systems in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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 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
ii
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
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;
rd
— 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 .”;
t
— 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”.
iv
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.
v
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.
vi
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:
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.
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.
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.
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.
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;
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
Q
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.
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
a
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
a
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
Q
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.
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 not exceed one year. For particle sizes 30 µm(c) and smaller, use NIST calibration
suspensions (see 4.4) for primary calibrations or secondary calibration suspensions (4.15) prepared
in accordance with Annex F for secondary calibrations. For particle sizes larger than 30 µm(c), use
polystyrene latex spheres (see 4.1) for primary calibrations or use secondary calibration suspensions
prepared in accordance with Annex F for secondary calibrations.
Conduct all phases of the calibration at the same working flow rate. Determine the flow rate limits of
the APC in accordance with Annex C. Discard any data obtained at flow rates outside these limits and
repeat the corresponding part of the procedure using the proper flow rate.
Conduct the sizing calibration using the same sample volume used in 5.2. If a different volume is used,
repeat the procedure in 5.2 using the new sample volume to avoid volume measurement errors.
Determine the threshold noise level of the APC using the method in A.2 before proceeding to 6.2.
Proceed to 6.2 to calibrate for particle sizes smaller than or equal to 30 μm(c) and for secondary
calibrations for particles larger than 30 μm(c) using samples prepared in full conformance with Annex F.
The procedure described in 6.2 through 6.10 shall not be used for primary calibration at particle sizes
larger than 30 μm(c). Proceed to 6.11 for primary calibration at particle sizes larger than 30 μm(c). The
procedure described in 6.11 through 6.14 shall not be used for particle sizes 30 μm(c) and smaller.
The procedure described in 6.2 to 6.15 assumes manual calibration of an APC with at least 8 channels
that can be set at various threshold settings. Alternatively, calibration can be performed using a multi-
channel analyser (MCA) or software that follows the same procedure. If an MCA is used, the relationship
between the measured voltage of the MCA and the APC threshold setting shall be established. In general,
software and MCA methods tend to be faster and more accurate than manual methods.
Figure 2 — Sizing calibration procedure
6.2 Choose at least 16 different particle sizes from those listed in the certified particle size distribution
of the calibration suspension samples. The smallest particle size chosen shall be the smallest particle
size of interest and the largest particle size shall not exceed 30 μm(c) for primary calibrations and
shall not exceed the largest reported particle size that is in conformance with Annex F for secondary
calibrations.
Record these particle sizes and their corresponding particle concentrations from the certified particle
size distribution in the corresponding columns of the Particle Size Calibration Summary of Table 4.
6.3 Determine a minimum of 12 different threshold settings to use in constructing a calibration
curve. The first (lowest) threshold setting, J, shall be 1,5 times the threshold noise level of the APC. The
highest threshold setting, H, shall correspond to a particle size of approximately 30 μm(c) or less for
primary calibrations and shall correspond to a size that does not exceed the largest reported particle
size that is in conformance with Annex F for secondary calibrations. The value of constant K shall be
calculated using Formula (1):
()loglHJ− og /()G−1
K =10 (1)
where G is the number of threshold settings to be used to construct the calibration curve. Intermediate
threshold settings between J and H shall be determined such that the value of each intermediate
threshold setting shall be equal to the value of its preceding channel times K. It is permissible to round
off the values of all threshold settings to the nearest value attainable by the APC, but the values of
consecutive channels shall not be the same. Record the values determined for the threshold settings in
the first column of Table 3.
6.4 Set the APC to the cumulative mode. Using at least eight different channels, set the channels such
that the threshold settings are arranged in order of increasing voltage. The settings for these channels
shall be selected from the list of threshold settings previously determined (6.3) and shall be distributed
over this range of settings.
6.5 Prepare a calibration suspension sample for analysis. Shake the sample vigorously by hand.
Agitate the sample ultrasonically for at least 30 s then shake it on a mechanical shaker for at least
1 min to disperse the dust in the liquid. Continue shaking the sample until it is to be analysed. De-
gas the sample under vacuum or ultrasonically until no surfacing bubbles are observed then analyse
immediately. Obtain five consecutive particle counts, each consisting of at least 10 mL and 10 000
particles at the smallest threshold setting. Record the particle concentrations obtained for each
threshold setting for each of the five counts in the appropriate cells of Table 2.
6.6 Calculate the mean observed number of particles counted, X, using Formula (2):
XX=⋅V (2)
where
X is the mean particle concentration, in particles per millilitre, of all acceptable counts from the
sample for a particular channel;
V is the sample volume, in millilitres, for a single count.
Calculate the total number, N, of particles counted for each channel using Formula (3):
N = 5 X (3)
The value of N shall be greater than or equal to 1 000 in order to ensure statistically significant results
for that particular channel. The value of X shall not exceed the coincidence error limit of the APC (5.3).
If the value of X exceeds the coincidence error limit, prepare dilutions of the calibration samples as in
accordance with Annex G and analyse them as described in 6.5.
Calculate D , which is the difference expressed as a percentage between the minimum, X , and
Q min
maximum, X , observed particle concentration for each channel in particles per millilitre, using
max
Formula (4):
− X
X
max min
D = ×100 (4)
Q
X
Record the threshold voltage setting, particle concentration data, X , and D for each channel in the
Q
calibration suspension worksheet in Table 2 for the appropriate sample.
Using Table C.2, find the maximum allowable D corresponding to the value of X for each channel. If the
Q
value of D is less than the maximum, then the value of X for that channel is acceptable for use. If there
Q
are at least eight channels with acceptable data, proceed to 6.7. If not, examine the results of any
unacceptable channels as follows.
Calculate D using Formula (5):
XX−
maxmin
D = (5)
XX−
0 N
where
D is the outlier test parameter;
X is the observed particle concentration of the suspected outlier (either X or X ) in particles
0 max min
per millilitre;
X is the observed particle concentration closest in value to X in particles per millilitre.
N 0
If D for a particular channel is less than 1,44, discard the related outlier data point, X , from Table 2,
0 0
then recalculate X using the remaining four data points, and use the recalculated value of X for
calibration purposes. If D for a particular channel is greater than 1,44, all data from this channel are
not acceptable and shall be discarded. If there are at least eight channels of acceptable data (using the
D and D criteria), proceed to 6.7. If not, take appropriate corrective action and repeat 6.5 to 6.6.
Q 0
If N is less than 1 000 for any channel, do not use the data for that channel. If sufficient numbers of
particles counted is the only quality criterion that is not met, change the threshold setting to correspond
to a smaller particle size that yields sufficient counts, or repeat 6.5 to 6.6 using a larger sample volume.
Do not collect and re-use primary and secondary calibration samples. Avoid the use of magnetic stirrers.
NOTE Other failures to meet the quality criteria can arise from a number of sources, including contaminated
diluent or glassware, volumetric errors, calculation errors, operating too closely to the threshold noise level of
the APC, or bubbles in the samples. Flow rate variability due to counting while the sample chamber is being
pressurized or due to other sources, also leads to problems. Particle settling can occur. Excessive agitation or
turbulence introduces bubbles into samples.
Table 2 — APC particle sizing calibration worksheet (see 6.6)
APC Model Date
Serial number Operator
Sensor type Model Noise level mV
Serial number Flow rate mL/min
First calibration suspension worksheet
First calibration suspension identification number
Channel Channel Channel Channel Channel Channel Channel Channel
1 2 3 4 5 6 7 8
Threshold setting (mV)
Count 1 (particles/mL)
Count 2 (particles/mL)
Count 3 (particles/mL)
Count 4 (particles/mL)
Count 5 (particles/mL)
X (particles/mL)
D
Q
X (particles/mL)
N
Second calibration suspension worksheet
Second calibration suspension identification number
Channel Channel Channel Channel Channel Channel Channel Channel
1 2 3 4 5 6 7 8
Threshold setting (mV)
Count 1 (particles/mL)
Count 2 (particles/mL)
Count 3 (particles/mL)
Count 4 (particles/mL)
Count 5 (particles/mL)
X (particles/mL)
D
Q
X (particles/mL)
N
Third calibration suspension worksheet
Third calibration suspension identification number
Channel Channel Channel Channel Channel Channel Channel Channel
1 2 3 4 5 6 7 8
Threshold setting (mV)
Count 1 (particles/mL)
Count 2 (particles/mL)
Count 3 (particles/mL)
Count 4 (particles/mL)
Count 5 (particles/mL)
X (particles/mL)
D
Q
X (particles/mL)
N
Table 3 — Calibration curve worksheet
Threshold
Standard
X (particles/mL)
Mean
N
setting
N uncertainty
C
(particles/mL)
(particles/mL)
mV Sample 1 Sample 2 Sample 3
6.7 Normalize the values for X recorded in Table 2 for each channel for a particular sample, using
Formula (6):
XX=⋅D (6)
NR
where
is the mean normalized particle concentration, in particles per millilitre, of the undiluted cali-
X
N
bration suspension sample for a particular channel;
is the mean particle concentration, in particles per millilitre, of all acceptable counts from the
X
sample for a particular channel (6.6);
D is the actual dilution ratio for the sample (G.8).
R
If the sample was not diluted, the value of D is 1. If the sample was diluted according to Annex G, use
R
the value of D for the sample obtained in G.8. Record the value of X for each channel in the appropriate
R
N
cells in Tables 2 and 3.
6.8 Repeat 6.4 to 6.7 two more times using different calibration suspension samples and
approximately the same D as the first sample. Choose threshold settings for each sample such that at
R
least two different samples are analysed for each of the threshold settings listed in Table 3 (6.3).
Note that a different undiluted calibration sample shall be used each time 6.4 to 6.7 is repeated to ensure
that the APC calibration curve is based on data from 3 different primary or secondary calibration
samples.
6.9 Define the relationship between particle size and threshold voltage setting using the constrained
cubic spline technique. A spreadsheet to carry out this interpolation is provided at the following URN:
https:// standards .iso .org/ iso/ 11171/ ed -5/ en.
To use the spreadsheet, open the worksheet labelled 6.9 and enter the threshold voltage settings and
corresponding values of X for each calibration suspension sample taken from the first four columns
N
of Table 3 (6.7) in the white data cells of columns A, B, C and D in order of decreasing value of threshold
voltage setting. Enter only values of X in cells for threshold settings that were actually used for a
N
given sample. Leave all other cells empty. Record in the fifth column of Table 3 the mean X for each
N
threshold setting which is displayed in column E of the 6.9 worksheet. Calculate the standard deviation
of all acceptable counts for all the samples listed in Table 2 (6.6) for each threshold setting. Calculate
the standard uncertainty for each threshold setting, using Formula (7):
sD
R
s = (7)
N
N
C
where
s is the standard uncertainty in normalized particle concentration, in particles per millilitre, of
N
the undiluted calibration suspension sample for a particular channel;
s is the standard deviation, in particles per millilitre, of all acceptable counts from all the samples
(6.6) obtained from a particular channel;
D is the actual dilution ratio for the sample (G.8);
R
N is the total number of acceptable particle counts from all samples for a particular channel
C
(i.e. 8 to 15).
Record in the approp
...
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 2022
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
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
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;
rd
— 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 .”;
t
— 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”.
iv
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.
v
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.
vi
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:
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.
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.
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.
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.
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;
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
Q
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.
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
a
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
a
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
Q
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.
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 not exceed one year. For particle sizes 30 µm(c) and smaller, use NIST calibration
suspensions (see 4.4) for primary calibrations or secondary calibration suspensions (4.15) prepared
in accordance with Annex F for secondary calibrations. For particle sizes larger than 30 µm(c), use
polystyrene latex spheres (see 4.1) for primary calibrations or use secondary calibration suspensions
prepared in accordance with Annex F for secondary calibrations.
Conduct all phases of the calibration at the same working flow rate. Determine the flow rate limits of
the APC in accordance with Annex C. Discard any data obtained at flow rates outside these limits and
repeat the corresponding part of the procedure using the proper flow rate.
Conduct the sizing calibration using the same sample volume used in 5.2. If a different volume is used,
repeat the procedure in 5.2 using the new sample volume to avoid volume measurement errors.
Determine the threshold noise level of the APC using the method in A.2 before proceeding to 6.2.
Proceed to 6.2 to calibrate for particle sizes smaller than or equal to 30 μm(c) and for secondary
calibrations for particles larger than 30 μm(c) using samples prepared in full conformance with Annex F.
The procedure described in 6.2 through 6.10 shall not be used for primary calibration at particle sizes
larger than 30 μm(c). Proceed to 6.11 for primary calibration at particle sizes larger than 30 μm(c). The
procedure described in 6.11 through 6.14 shall not be used for particle sizes 30 μm(c) and smaller.
The procedure described in 6.2 to 6.15 assumes manual calibration of an APC with at least 8 channels
that can be set at various threshold settings. Alternatively, calibration can be performed using a multi-
channel analyser (MCA) or software that follows the same procedure. If an MCA is used, the relationship
between the measured voltage of the MCA and the APC threshold setting shall be established. In general,
software and MCA methods tend to be faster and more accurate than manual methods.
Figure 2 — Sizing calibration procedure
6.2 Choose at least 16 different particle sizes from those listed in the certified particle size distribution
of the calibration suspension samples. The smallest particle size chosen shall be the smallest particle
size of interest and the largest particle size shall not exceed 30 μm(c) for primary calibrations and
shall not exceed the largest reported particle size that is in conformance with Annex F for secondary
calibrations.
Record these particle sizes and their corresponding particle concentrations from the certified particle
size distribution in the corresponding columns of the Particle Size Calibration Summary of Table 4.
6.3 Determine a minimum of 12 different threshold settings to use in constructing a calibration
curve. The first (lowest) threshold setting, J, shall be 1,5 times the threshold noise level of the APC. The
highest threshold setting, H, shall correspond to a particle size of approximately 30 μm(c) or less for
primary calibrations and shall correspond to a size that does not exceed the largest reported particle
size that is in conformance with Annex F for secondary calibrations. The value of constant K shall be
calculated using Formula (1):
()loglHJ− og /()G−1
K =10 (1)
where G is the number of threshold settings to be used to construct the calibration curve. Intermediate
threshold settings between J and H shall be determined such that the value of each intermediate
threshold setting shall be equal to the value of its preceding channel times K. It is permissible to round
off the values of all threshold settings to the nearest value attainable by the APC, but the values of
consecutive channels shall not be the same. Record the values determined for the threshold settings in
the first column of Table 3.
6.4 Set the APC to the cumulative mode. Using at least eight different channels, set the channels such
that the threshold settings are arranged in order of increasing voltage. The settings for these channels
shall be selected from the list of threshold settings previously determined (6.3) and shall be distributed
over this range of settings.
6.5 Prepare a calibration suspension sample for analysis. Shake the sample vigorously by hand.
Agitate the sample ultrasonically for at least 30 s then shake it on a mechanical shaker for at least
1 min to disperse the dust in the liquid. Continue shaking the sample until it is to be analysed. De-
gas the sample under vacuum or ultrasonically until no surfacing bubbles are observed then analyse
immediately. Obtain five consecutive particle counts, each consisting of at least 10 mL and 10 000
particles at the smallest threshold setting. Record the particle concentrations obtained for each
threshold setting for each of the five counts in the appropriate cells of Table 2.
6.6 Calculate the mean observed number of particles counted, X, using Formula (2):
XX=⋅V (2)
where
X is the mean particle concentration, in particles per millilitre, of all acceptable counts from the
sample for a particular channel;
V is the sample volume, in millilitres, for a single count.
Calculate the total number, N, of particles counted for each channel using Formula (3):
N = 5 X (3)
The value of N shall be greater than or equal to 1 000 in order to ensure statistically significant results
for that particular channel. The value of X shall not exceed the coincidence error limit of the APC (5.3).
If the value of X exceeds the coincidence error limit, prepare dilutions of the calibration samples as in
accordance with Annex G and analyse them as described in 6.5.
Calculate D , which is the difference expressed as a percentage between the minimum, X , and
Q min
maximum, X , observed particle concentration for each channel in particles per millilitre, using
max
Formula (4):
− X
X
max min
D = ×100 (4)
Q
X
Record the threshold voltage setting, particle concentration data, X , and D for each channel in the
Q
calibration suspension worksheet in Table 2 for the appropriate sample.
Using Table C.2, find the maximum allowable D corresponding to the value of X for each channel. If the
Q
value of D is less than the maximum, then the value of X for that channel is acceptable for use. If there
Q
are at least eight channels with acceptable data, proceed to 6.7. If not, examine the results of any
unacceptable channels as follows.
Calculate D using Formula (5):
XX−
maxmin
D = (5)
XX−
0 N
where
D is the outlier test parameter;
X is the observed particle concentration of the suspected outlier (either X or X ) in particles
0 max min
per millilitre;
X is the observed particle concentration closest in value to X in particles per millilitre.
N 0
If D for a particular channel is less than 1,44, discard the related outlier data point, X , from Table 2,
0 0
then recalculate X using the remaining four data points, and use the recalculated value of X for
calibration purposes. If D for a particular channel is greater than 1,44, all data from this channel are
not acceptable and shall be discarded. If there are at least eight channels of acceptable data (using the
D and D criteria), proceed to 6.7. If not, take appropriate corrective action and repeat 6.5 to 6.6.
Q 0
If N is less than 1 000 for any channel, do not use the data for that channel. If sufficient numbers of
particles counted is the only quality criterion that is not met, change the threshold setting to correspond
to a smaller particle size that yields sufficient counts, or repeat 6.5 to 6.6 using a larger sample volume.
Do not collect and re-use primary and secondary calibration samples. Avoid the use of magnetic stirrers.
NOTE Other failures to meet the quality criteria can arise from a number of sources, including contaminated
diluent or glassware, volumetric errors, calculation errors, operating too closely to the threshold noise level of
the APC, or bubbles in the samples. Flow rate variability due to counting while the sample chamber is being
pressurized or due to other sources, also leads to problems. Particle settling can occur. Excessive agitation or
turbulence introduces bubbles into samples.
Table 2 — APC particle sizing calibration worksheet (see 6.6)
APC Model Date
Serial number Operator
Sensor type Model Noise level mV
Serial number Flow rate mL/min
First calibration suspension worksheet
First calibration suspension identification number
Channel Channel Channel Channel Channel Channel Channel Channel
1 2 3 4 5 6 7 8
Threshold setting (mV)
Count 1 (particles/mL)
Count 2 (particles/mL)
Count 3 (particles/mL)
Count 4 (particles/mL)
Count 5 (particles/mL)
X (particles/mL)
D
Q
X (particles/mL)
N
Second calibration suspension worksheet
Second calibration suspension identification number
Channel Channel Channel Channel Channel Channel Channel Channel
1 2 3 4 5 6 7 8
Threshold setting (mV)
Count 1 (particles/mL)
Count 2 (particles/mL)
Count 3 (particles/mL)
Count 4 (particles/mL)
Count 5 (particles/mL)
X (particles/mL)
D
Q
X (particles/mL)
N
Third calibration suspension worksheet
Third calibration suspension identification number
Channel Channel Channel Channel Channel Channel Channel Channel
1 2 3 4 5 6 7 8
Threshold setting (mV)
Count 1 (particles/mL)
Count 2 (particles/mL)
Count 3 (particles/mL)
Count 4 (particles/mL)
Count 5 (particles/mL)
X (particles/mL)
D
Q
X (particles/mL)
N
Table 3 — Calibration curve worksheet
Threshold
Standard
X (particles/mL)
Mean
N
setting
N uncertainty
C
(particles/mL)
(particles/mL)
mV Sample 1 Sample 2 Sample 3
6.7 Normalize the values for X recorded in Table 2 for each channel for a particular sample, using
Formula (6):
XX=⋅D (6)
NR
where
is the mean normalized particle concentration, in particles per millilitre, of the undiluted cali-
X
N
bration suspension sample for a particular channel;
is the mean particle concentration, in particles per millilitre, of all acceptable counts from the
X
sample for a particular channel (6.6);
D is the actual dilution ratio for the sample (G.8).
R
If the sample was not diluted, the value of D is 1. If the sample was diluted according to Annex G, use
R
the value of D for the sample obtained in G.8. Record the value of X for each channel in the appropriate
R
N
cells in Tables 2 and 3.
6.8 Repeat 6.4 to 6.7 two more times using different calibration suspension samples and
approximately the same D as the first sample. Choose threshold settings for each sample such that at
R
least two different samples are analysed for each of the threshold settings listed in Table 3 (6.3).
Note that a different undiluted calibration sample shall be used each time 6.4 to 6.7 is repeated to ensure
that the APC calibration curve is based on data from 3 different primary or secondary calibration
samples.
6.9 Define the relationship between particle size and threshold voltage setting using the constrained
cubic spline technique. A spreadsheet to carry out this interpolation is provided at the following URN:
https:// standards .iso .org/ iso/ 11171/ ed -5/ en.
To use the spreadsheet, open the worksheet labelled 6.9 and enter the threshold voltage settings and
corresponding values of X for each calibration suspension sample taken from the first four columns
N
of Table 3 (6.7) in the white data cells of columns A, B, C and D in order of decreasing value of threshold
voltage setting. Enter only values of X in cells for threshold settings that were actually used for a
N
given sample. Leave all other cells empty. Record in the fifth column of Table 3 the mean X for each
N
threshold setting which is displayed in column E of the 6.9 worksheet. Calculate the standard deviation
of all acceptable counts for all the samples listed in Table 2 (6.6) for each threshold setting. Calculate
the standard uncertainty for each threshold setting, using Formula (7):
sD
R
s = (7)
N
N
C
where
s is the standard uncertainty in normalized particle concentration, in particles per millilitre, of
N
the undiluted calibration suspension sample for a particular channel;
s is the standard deviation, in particles per millilitre, of all acceptable counts from all the samples
(6.6) obtained from a particular channel;
D is the actual dilution ratio for the sample (G.8);
R
N is the total number of acceptable particle counts from all samples for a particular channel
C
(i.e. 8 to 15).
Record in the appropriate cells of Table 3, the values of N and s for each threshold setting.
C N
NOTE Failure to enter the threshold voltage settings in the subclause 6.9 worksheet in the proper order
results in error. The worksheet will display values of 0 for the interpolated threshold voltage settings in column
H if the threshold voltage settings in column A are not consecutive or not in order of decreasing voltage. A value
of 0 for the interpolated threshold voltage setting will also be displayed for any particle concentration that falls
outside the range of the data in column E.
6.10 Determine the threshold voltage settings that correspond to the particle concentrations for each
size selected in 6.2 using the same subclause 6.9 worksheet. Enter, in order of increasing particle size,
the size and corresponding particle concentrations from Table 4 in the blue data cells of column F and G.
The worksheet displays the interpolated threshold voltage setting corresponding to each size in yellow
column H. The values of extrapolated points are displayed as “0”. Record the interpolated threshold
voltage settings for each of these sizes in the righ
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