ISO 21501-4:2018

INTERNATIONAL ISO
STANDARD 21501-4
Second edition
2018-05
Determination of particle size
distribution — Single particle light
interaction methods —
Part 4:
Light scattering airborne particle
counter for clean spaces
Détermination de la distribution granulométrique — Méthodes
d'interaction lumineuse de particules uniques —
Partie 4: Compteur de particules en suspension dans l'air en lumière
dispersée pour espaces propres
Reference number
©
ISO 2018
© ISO 2018
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Published in Switzerland
ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Basic configuration . 3
6 Requirements . 3
6.1 Size setting error . 3
6.2 Counting efficiency . 4
6.3 Size resolution . 4
6.4 False count . 4
6.5 Maximum particle number concentration . 4
6.6 Sampling flow rate error . 4
6.7 Sampling time error . 4
6.8 Response rate . 4
6.9 Calibration interval . 4
6.10 Reporting of test and calibration results . 5
7 Test and calibration procedures . 5
7.1 Size setting . 5
7.1.1 Evaluation of size setting error . 5
7.1.2 Procedure of size setting . 6
7.2 Evaluation of counting efficiency . 9
7.3 Evaluation of size resolution .10
7.4 Evaluation of false count . .11
7.5 Estimation of coincidence loss at the maximum particle number concentration .11
7.6 Evaluation of sampling flow rate error .12
7.7 Evaluation of sampling time error .12
7.8 Evaluation of response rate .12
Annex A (informative) Counting efficiency .14
Annex B (informative) Size resolution .16
Annex C (informative) False count .17
Annex D (informative) Response rate .18
Annex E (informative) Procedure for evaluating the uncertainties of the results of the
performance tests .19
Bibliography .25
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
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on the ISO list of patent declarations received (see www .iso .org/patents).
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URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 24, Particle characterization including
sieving, Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces the first edition (ISO 21501-4:2007), which has been
technically revised.
The main changes from the previous edition are:
— Clause 4 for “Principle” and Clause 5 for “Basic configuration” have been added;
— “size calibration” and “verification of size setting” have been combined as “size setting error” in the
requirements clause;
— “Test report” (3.11 in the previous edition) has been changed to 6.10 on “Reporting of test and
calibration results”;
— information about uncertainties has been enriched and is now the subject of Annex E.
A list of all parts in the ISO 21501 series can be found on the ISO website.
iv © ISO 2018 – All rights reserved

Introduction
Monitoring particle contamination levels is required in various fields, e.g. in the electronic industry, in
the pharmaceutical industry, in the manufacturing of precision machines and in medical operations.
Particle counters are useful instruments for monitoring particle contamination in air. The purpose of
this document is to provide a calibration procedure and verification method for particle counters, so
as to minimize the inaccuracy in the measurement result by a counter, as well as the differences in the
results measured by different instruments.
INTERNATIONAL STANDARD ISO 21501-4:2018(E)
Determination of particle size distribution — Single
particle light interaction methods —
Part 4:
Light scattering airborne particle counter for clean spaces
1 Scope
This document describes a calibration and verification method for a light scattering airborne particle
counter (LSAPC), which is used to measure the size distribution and particle number concentration of
particles suspended in air. The light scattering method described in this document is based on single
particle measurements. The typical size range of particles measured by this method is between 0,1 μm
and 10 μm in particle size.
Instruments that conform to this document are used for the classification of air cleanliness in
cleanrooms and associated controlled environments in accordance with ISO 14644-1 and ISO 14644-2,
as well as the measurement of number and size distribution of particles in various environments.
The following parameters are within the scope of this document:
— size setting error;
— counting efficiency;
— size resolution;
— false count;
— maximum particle number concentration;
— sampling flow rate error;
— sampling time error;
— response rate;
— calibration interval;
— reporting results from test and calibration.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1
calibration particle
monodisperse spherical particle with a certified mean particle size, e.g. a polystyrene latex (PSL)
particle, where the certified size is traceable to the International System of Units (SI), a relative
standard uncertainty equal to or less than 2,5 %, and a refractive index that is approximately 1,59 at
the wavelength of 589 nm (sodium D line)
3.2
counting efficiency
ratio of the number concentration measured by a light scattering airborne particle counter (LSAPC) (3.4)
to that measured by a reference instrument for the same test aerosol
3.3
false count
apparent count per unit volume when a sample air containing no measurable particles is measured by
the light scattering airborne particle counter (LSAPC) (3.4)
3.4
LSAPC
light scattering airborne particle counter
instrument that measures airborne particle numbers by counting the pulses as the particles pass
through the sensing volume, and also particle size by scattered light intensity
Note 1 to entry: The optical particle size measured by the LSAPC is the light scattering equivalent particle size
and not the geometrical size.
3.5
PHA
pulse height analyser
instrument that analyses the distribution of pulse
...