Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by the counting method using an optical microscope

This International Standard specifies methods for determining the level of particulate contamination in liquids used in hydraulic systems by counting the number of particles deposited on the surface of a membrane filter using an optical microscope. It includes particle counting by two manual methods and image analysis, using either transmitted or incident lighting systems. Particle sizes greater than or equal to 2 micrometres can be sized and counted by this method, but the resolution and accuracy of the results will depend upon the optical system used and the capabilities of the operator. All hydraulic fluids with a wide range of contamination levels can be analysed according to this International Standard. However, the counting uncertainty at the larger particle sizes increases if the volume filtered is reduced to allow smaller sized particles to be counted, where a fine precipitate or a high particle concentration is present.

Transmissions hydrauliques — Pollution des fluides — Détermination de la pollution particulaire par comptage au microscope optique

La présente Norme internationale définit des méthodes permettant de déterminer le niveau de pollution particulaire des liquides utilisés dans les systèmes hydrauliques, par comptage au microscope optique du nombre de particules déposées à la surface d'une membrane filtrante. Elle traite du comptage des particules par deux méthodes manuelle et par analyse d'image, en utilisant soit une lumière transmise, soit une lumière incidente. Ces méthodes permettent de classer et de dénombrer des particules de taille supérieure ou égale à 2 micromètres, mais la résolution et l'exactitude des résultats dépend du système optique utilisé et des aptitudes de l'opérateur. Tous les liquides hydrauliques qui présentent un large éventail de niveaux de pollution sont analysables selon la présente Norme internationale. Cependant, l'incertitude de comptage aux plus grandes tailles de particules augmente si le volume filtré est réduit pour permettre le dénombrement des particules de plus petites tailles, lorsqu'on observe un léger précipité ou que la concentration des particules est élevée.

Fluidna tehnika - Hidravlika - Onesnaženje fluidov - Ugotavljanje onesnaženosti z delci - Metoda štetja delcev z optičnim mikroskopom

General Information

Status
Published
Publication Date
01-May-2002
Current Stage
9092 - International Standard to be revised
Start Date
26-Nov-2018
Completion Date
26-Nov-2018

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INTERNATIONAL ISO
STANDARD 4407
Second edition
2002-04-15
Hydraulic fluid power — Fluid
contamination — Determination of
particulate contamination by the counting
method using an optical microscope
Transmissions hydrauliques — Pollution des fluides — Détermination de la
pollution particulaire par comptage au microscope optique
Reference number
ISO 4407:2002(E)
ISO 2002
---------------------- Page: 1 ----------------------
ISO 4407:2002(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not

be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this

file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this

area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters

were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event

that a problem relating to it is found, please inform the Central Secretariat at the address given below.

© ISO 2002

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic

or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body

in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.ch
Web www.iso.ch
Printed in Switzerland
ii © ISO 2002 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 4407:2002(E)
Contents Page

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

Introduction.................................................................................................................................................................v

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

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

3 Terms and definitions ...................................................................................................................................2

4 Counting principle .........................................................................................................................................4

5 Apparatus .......................................................................................................................................................4

6 Reagent and chemicals.................................................................................................................................6

6.1 Reagent and rinsing and cleaning chemicals ............................................................................................6

6.2 Liquids for transparentizing the membrane filter (transmitted-light method) ........................................6

7 Glassware cleaning procedure ....................................................................................................................6

8 Calibration procedures .................................................................................................................................6

8.1 Microscope calibration..................................................................................................................................6

8.2 Determination of Effective Filtration Area (EFA)........................................................................................7

9 Membrane filter preparation .........................................................................................................................7

9.1 Sample preparation .......................................................................................................................................7

9.2 Blank analysis................................................................................................................................................8

9.3 Separation of contaminants by vacuum filtration......................................................................................8

9.4 Evaluation of suitability for counting ..........................................................................................................9

9.5 Mounting of membrane filters for observation under transmitted light ................................................10

10 Particle sizing and counting procedure ....................................................................................................10

10.1 Particle sizing...............................................................................................................................................10

10.2 Selection of nominal magnification ...........................................................................................................10

10.3 Statistical counting procedure...................................................................................................................10

10.4 Calculation of total count............................................................................................................................11

10.5 Verification of data ......................................................................................................................................12

11 Expression of results ..................................................................................................................................13

12 Identification statement (Reference to this International Standard)...........................................................13

Bibliography..............................................................................................................................................................14

© ISO 2002 – All rights reserved iii
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ISO 4407:2002(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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.

The main task of technical committees is to prepare International Standards. Draft International Standards adopted

by the technical committees are circulated to the member bodies for voting. Publication as an International

Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 4407 was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee SC 6,

Contamination control and hydraulic fluids.

This second edition cancels and replaces the first edition (ISO 4407:1991), which has been technically revised.

iv © ISO 2002 – All rights reserved
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ISO 4407:2002(E)
Introduction

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

enclosed circuit. The liquid is both a lubricant and power transmitting medium.

The presence of particulate contamination in the liquid interferes with its ability to lubricate and causes wear to the

components. The level of contamination in the liquid has a direct bearing on the performance and reliability of the

system, and should be controlled to a level appropriate for the system concerned.

Quantitative determination of particulate contamination requires precision in obtaining a representative sample of

the liquid and in determining the level of contamination. The method of particle counting using the optical

microscope is an accepted means of determining the extent of contamination. The accuracy of particle count data

can be affected by the techniques used.

This International Standard details procedures for the separation of particles in liquid samples by vacuum filtration

and subsequent analysis of the particles deposited on an analytical membrane filter by microscopic techniques.

The techniques involve counting using transmitted or incident light both manually and using image analysis

techniques. This International Standard specifies methods to ensure accurate and consistent results.

© ISO 2002 – All rights reserved v
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INTERNATIONAL STANDARD ISO 4407:2002(E)
Hydraulic fluid power — Fluid contamination — Determination of
particulate contamination by the counting method using an optical
microscope

WARNING — The use of this International Standard may involve hazardous materials, operations and

equipment. This International Standard does not purport to address all the safety problems associated with

its use. It is the responsibility of the user of this International Standard to establish appropriate safety and

health practices and determine the applicability of regulative limitations prior to use.

1 Scope

This International Standard specifies methods for determining the level of particulate contamination in liquids used

in hydraulic systems by counting the number of particles deposited on the surface of a membrane filter using an

optical microscope. It includes particle counting by two manual methods and image analysis, using either

transmitted or incident lighting systems.

Particle sizes W 2 µm can be sized and counted by this method, but the resolution and accuracy of the results will

depend upon the optical system used and the capabilities of the operator.

All hydraulic fluids with a wide range of contamination levels can be analysed according to this International

Standard. However, the counting uncertainty at the larger particle sizes increases if the volume filtered is reduced

to allow smaller sized particles to be counted, where a fine precipitate or a high particle concentration is present.

2 Normative references

The following normative documents contain provisions which, through reference in this text, constitute provisions of

this International Standard. For dated references, subsequent amendments to, or revisions of, any of these

publications do not apply. However, parties to agreements based on this International Standard are encouraged to

investigate the possibility of applying the most recent editions of the normative documents indicated below. For

undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC

maintain registers of currently valid International Standards.

ISO 3722, Hydraulic fluid power — Fluid sample containers — Qualifying and controlling cleaning methods

ISO 4406:1999, Hydraulic fluid power — Fluids — Method for coding the level of contamination by solid particles

ISO 4788, Laboratory glassware — Graduated measuring cylinders
ISO 5598, Fluid power systems and components — Vocabulary

ISO 14644-1:1999, Cleanrooms and associated controlled environments — Classification of air cleanliness

© ISO 2002 – All rights reserved 1
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ISO 4407:2002(E)
3 Terms and definitions

For the purposes of this International Standard, the definitions given in ISO 5598 and the following apply.

3.1
blank count

count resulting from contaminants introduced from other sources, such as reagents, cleaning of glassware and

preparation of the membrane filter (see 9.2)
3.2
calculation factor
ratio of the effective filtration area to the total area counted
3.3
effective filtration area
EFA
circular area of the membrane filter open to flow during filtration of liquid

NOTE Both the effective filtration area (EFA) and the effective filtration diameter (EFD) are determined in 8.2.

3.4
fibre

particle longer than 100 µm with a length-to-width ratio greater than or equal to 10:1

3.5
fixative liquid

liquid that, as a result of a heat curing process, causes a membrane filter to adhere to a glass base slide, resulting

in an opaque residue
3.6
grid square
square with sides of nominally 3,1 mm printed on membrane filters

NOTE Gridded membrane filters may not be suitable for counting using image analysis techniques.

3.7
image analyser

instrumentation to automatically size and count particles deposited on a membrane filter

NOTE A video image of the particle is digitally recreated based upon the difference in the grey scale contrast of the particle

and background, and the size is automatically computed. Sizing of the particle can also be undertaken on the video screen.

3.8
mountant liquid

liquid that, when heated, causes a membrane filter, previously treated with fixative liquid, to become transparent

and to adhere to the cover slip (see 5.7)
3.9
particle size
size of particle as defined by the particle's longest dimension
3.10
solvent

liquid that is physically and chemically compatible with and miscible in the sample liquid

NOTE A solvent is used for diluting the sample liquid, and can be used for cleaning and rinsing the apparatus. The solvent

should be chemically compatible with the apparatus, especially the membrane filter, and should not dissolve the particles.

2 © ISO 2002 – All rights reserved
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ISO 4407:2002(E)
3.11
statistical counting

counting and sizing particles using a proportion of the membrane filter’s surface, whereby at least 150 particles are

counted over a total of at least 10 separate locations (fields)

NOTE 1 Statistical counting requires an even distribution of particles over the complete surface, and membrane filters should

be rejected for counting if this is not achieved.

NOTE 2 Counting 150 particles gives a counting uncertainty of 8 %, and the counting uncertainty will be reduced if more

particles are counted.
3.12
unit area
proportion of membrane filter that is counted for statistical purposes

NOTE For manual counting, the unit area is defined as the area of the membrane filter bound in the horizontal plane by two

adjacent vertical membrane filter grid lines and in the vertical plane by two parallel lines either on the ocular micrometer

eyepiece or drawn on a projection screen. Examples are given in Figure 1. For image analysis, this is a fixed field of view

defined by the optical and electronic systems.
Key
1 Grid square
2 Width of grid square (mm)
3 Length of grid square (mm)
4 Full grid square
5 Unit area on a gridded membrane
6 Graticule height used for defining unit area (µm)
7 Unit area
8 Diametric unit area on ungridded membrane
9 Effective filtration diameter of membrane
Figure 1 — Examples of unit areas
© ISO 2002 – All rights reserved 3
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ISO 4407:2002(E)
4 Counting principle

A known volume of hydraulic liquid is vacuum filtered through a membrane filter to separate the contaminants from

the liquid. The particles are examined microscopically using either incident light or transmitted light, after making

the membrane filter transparent, to size and count the contaminant particles according to their largest dimension.

5 Apparatus
5.1 Drying oven, able to control temperature up to (70 ± 2) °C.

5.2 External lamp, of variable intensity, where oblique illumination of the specimen stage is required.

5.3 Filter holder, comprising:

 a funnel, 300 mL capacity with suitable calibrated volumetric graduations [e.g. (25 ± 2) mL];

 a suitable cover for the funnel (e.g. a Petri dish);
 a clamping device;
 a suitable base to support the membrane filter;

 a means of dissipating any static electricity generated during the filtering process.

5.4 Graduated cylinders, for measuring out the volume of test liquid. Either the accuracy should conform to

ISO 4788 or a sample bottle calibrated with suitable volumetric graduations can be used. The accuracy of

graduation should be ± 2 %.

5.5 Image analysing equipment, comprising a microscope base with a range of objective lenses and trinocular

head for attaching a video camera connected to a suitable video monitor. The output of the video camera is fed to a

computer which recreates a video digital image of the view, where the particles are sized and counted using

specially developed software.

Although a manual X-Y stage and focus can be used, it is recommended that these be motorized and controlled by

the software as this enables the particles to be localized.

5.6 Membrane filters, compatible with the sample liquid and any solvents or chemicals used in the processes.

Normally, the membrane filter shall be of 47 mm diameter, white, gridded (each grid square with sides

3,08 mm ± 0,05 mm and an area equal to 1/100th of the effective filtration area), with a pore size less than 1,5 µm,

used for manual counting down to 2 µm. A 47 mm diameter, white, ungridded membrane filter with a pore size less

than 1,5 µm is recommended for image analysis. Membrane filters of different diameters are permissible.

It is permissible to use membrane filters of different nominal pore size to account for the minimum size of particle to

be counted and the condition of the sample liquid. The pore size of the membrane filter should have a particle

removal efficiency of 99,9 % at the minimum size to be counted.

The colour of the membrane filter shall be chosen for maximum contrast with the particulate contamination to be

observed. For example, if most of the contaminant is translucent, transparent or white, a black membrane filter

should be considered.

5.7 Microscope glass base slides and microscope glass cover slips, for transmitted-light method only, with

dimensions greater than the diameter of the membrane filter. The thickness of the cover slip should be selected to

ensure that the particles are in focus at the magnification used.

5.8 Membrane filter holder, plastic or equivalent with lid, for retaining the membrane filter (incident-light method

only).
4 © ISO 2002 – All rights reserved
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ISO 4407:2002(E)

5.9 Microscope for particle counting, with a range of objective lenses that, in combination with the ocular

lenses, are able to resolve particles W 2 µm. The microscope shall be equipped with:

 fine and coarse focus control;

 through-the-lens lighting for the incident light method and/or a bottom lighting source for the transmitted light

method;

 a mechanical stage so that the effective filtration area of the membrane filter can be scanned;

 provision on the mechanical stage for securely holding the membrane filter holder or glass slide;

 an ocular micrometer of which the smallest division shall not subtend a distance larger than the smallest

particle to be counted at a particular magnification, and with suitable graduations.

For counting with transmitted light, the optimum equipment is a projector microscope with suitable screen, over-

eyepiece mirror and rotating superstage.

NOTE 1 For image analysis, it is preferable to have a stabilized lighting source controlled by the imaging software so that

illumination fluctuations are eliminated and automatic correction is made for any intensity drift in the lighting source.

NOTE 2 For accurate characterization of particles using the incident light method, an additional oblique lighting source may

be required (see 5.2).

Nominal magnification and optical combinations for manual counting are given in Table 1.

NOTE 3 The manufacturer of the image analysis equipment should be contacted for the magnification provided by the

trinocular head video/camera combination.
Table 1 — Nominal magnifications and optical combinations
Suggested minimum
Magnification (nominal) Ocular lens Objective lens
particle size
µm
× 50 × 10 × 5 20
× 100 × 10 × 10 10
× 200 × 10 × 20 5
× 500 × 10 × 50 2

5.10 Plastic film, 0,05 mm thick × 50 mm × 50 mm, placed between the cap and neck of the sample bottle if the

cap does not have an internal seal. The film shall be compatible with both the cleaning and sample liquids.

5.11 Sample bottles, 250 mL nominal capacity, preferably flat-bottomed and wide-mouthed with a screw cap

containing a suitable internal polymeric seal.

5.12 Sampling agitating device, suitable for redispersing the contaminant in the liquid sample. The device, such

2 2

as a laboratory bottle roller, a three-axis paint shaker or an ultrasonic bath rated at 3 000 W/m to 10 000 W/m of

base area, shall not alter the basic size distribution of the contaminant.

5.13 Solvent dispenser, a pressurized vessel that discharges solvent (see 6.1.4) through an in-line membrane

filter with a pore size not greater than 1 µm.

5.14 Stage micrometer, graduated in 0,1 mm and 0,01 mm divisions, calibrated and traceable to national

standards.
© ISO 2002 – All rights reserved 5
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ISO 4407:2002(E)

5.15 Tally counter, with sufficient sections to accumulate the numbers of particles and fields counted.

5.16 Tweezers, flat-bladed, blunt tips, of stainless steel.

5.17 Vacuum device, able to establish a vacuum of 86,6 kPa (ª 0,87 bar, 650 mm Hg).

5.18 Vacuum flask, suitable for the filter holder, and of a capacity able to filter the entire volume of sample liquid

without refilling.
6 Reagent and chemicals
6.1 Reagent and rinsing and cleaning chemicals
6.1.1 Propan-2-ol [isopropyl alcohol (IPA)].
6.1.2 Liquid detergent, without solid residue.
6.1.3 Distilled or demineralized water.
6.1.4 Solvent, for rinsing equipment and dilution samples.

Petroleum spirit (boiling point 100 °C to 120 °C) or similar is suitable if the sample liquid is a petroleum-based or

synthetic oil; alternatively distilled or demineralized water is used if the sample liquid is water-based. The solvent

shall be physically and chemically compatible with the sample liquid and apparatus.

WARNING — Exercise care when using solvents with low flash points as there could be an explosion risk.

Appropriate precautions should be taken to avoid inhalation of fumes from these solvents. Always use

suitable protective equipment. Attention is drawn to local health and safety procedures.

6.2 Liquids for transparentizing the membrane filter (transmitted-light method)
6.2.1 Fixative liquid, see 3.5.

6.2.2 Mountant liquid, see 3.8, with a refractive index similar to that of the glass cover slip.

7 Glassware cleaning procedure

7.1 Clean and validate the cleanliness level of the filtration apparatus, graduated cylinders (5.4), bottles (5.11),

glass slides and cover slips (5.7) and membrane filter holders (5.8) in accordance with ISO 3722. The final liquid

used for the flush should be either filtered petroleum spirit (or similar solvent) for petroleum based or synthetic oils,

propan-2-ol or demineralized water for water-based liquids.

7.2 The required cleanliness level (RCL) of the apparatus should be such that contaminant cannot significantly

contribute to the overall result. An RCL of less than 250 particles greater than 5 µm per 100 mL of bottle volume is

suitable for sample bottles.

All liquids used for cleaning and rinsing shall be filtered through a 1 µm or finer membrane filter.

8 Calibration procedures
8.1 Microscope calibration

8.1.1 Calibration should be carried out at least annually or whenever any major adjustment or change is made to

the optics. The stage micrometer (5.14) should be calibrated every five years.
6 © ISO 2002 – All rights reserved
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ISO 4407:2002(E)

8.1.2 For microscopes used for manual counting, select a magnification on the microscope and place the stage

micrometer on the microscope stage so that the image of the graticule is superimposed upon and aligned with the

eyepiece or trinocular graticule. Ensure that the scale and graticule are in focus.

8.1.3 Compare the two superimposed scales and align the lowest numbered division on the eyepiece graticule

so that it is coincident with one division on the stage micrometer and so that the highest graticule division falls

within the divisions of the stage micrometer. Select a suitable number of eyepiece divisions (e.g. 50) and determine

the number of corresponding divisions on the stage micrometer. Determine the length scale of the graticule

divisions at the magnification used.

8.1.4 Repeat 8.1.2 and 8.1.3 for all magnifications and record the data in a suitable calibration recording system.

8.1.5 A similar procedure to 8.1.3 shall be carried out for image analysing equipment but the individual method

may vary from instrument to instrument. Carry out the calibration in accordance with the manufacturer’s

instructions.
8.2 Determination of Effective Filtration Area (EFA)

8.2.1 This procedure should be performed before a new vacuum funnel is used for the first time, and should be

recalibrated every five years.

8.2.2 Make up a suspension of suitable staining contaminant which will identify the effective filtration area of the

membrane filter when filtered. Red oxide contaminant is suitable for this. Prepare by dispersing into a suitable

volume of solvent to give a concentration of approximately 1 mg/L and shake vigorously or mix by ultrasonics for

1 min.

8.2.3 Assemble a 1 µm filter membrane filter in the vacuum apparatus to be calibrated and clamp firmly. Vacuum

filter about 25 mL or sufficient volume of suspension to clearly stain the membrane filter, and aspirate to dryness.

8.2.4 Unclamp, remove the membrane filter and measure the diameter [effective filtration diameter (EFD)] of the

stain in at least two planes to within 0,1 mm. Average the result and calculate the effective filtration area (EFA).

Mark the funnel with a suitable code and record the result in a suitable calibration recording system.

9 Membrane filter preparation
9.1 Sample preparation

9.1.1 After noting all sample identification details, remove any tied-up or loosely attached labels ensuring that

sample identity is retained. Thoroughly clean the outside of the sample bottle, particularly around the cap, by

washing with filtered solvent dispensed from the pressurized dispenser. Take care not to force contaminant into the

cap area.

9.1.2 If the sample has been standing for a period of time, particle settlement, and hence agglomeration, will

occur. It is essential that the agglomerates are broken up, and the contaminant particles are re-dispersed evenly

within the contents of the sample before analysis.

9.1.3 Redistribute the contaminants within the contents of the bottle by either hand shaking the sample

vigorously for at least 1 min, or by using an acceptable method of mixing such as a three-axis paint shaker for at

least 5 min. The method chosen should not alter the original distribution of the contaminant.

9.1.4 If ultrasonics is used to break up any agglomerates, stand the sample container so that the level of the

liquid in the bath is either just below the fluid level in the sample bottle, or 3/4 up the side of the container,

whichever is least. The period of immersion shall not exceed 1 min. Hand shake for 30 s afterwards.

© ISO 2002 – All rights reserved 7
---------------------- Page: 12 ----------------------
ISO 4407:2002(E)
9.2 Blank analysis

9.2.1 A blank analysis should be performed before each sample analysis, unless it can be demonstrated that

acceptable blanks can be consistently obtained. If so, a blank analysis should be performed before starting a

counting programme and at least once during it.

9.2.2 Proceed as in 9.3, using solvent instead of sample liquid. Dispense a 100 mL volume of filtered solvent into

the vacuum apparatus fitted with the selected membrane filter, vacuum filter and aspirate to dryness.

9.2.3 Perform size analysis as specified in 10.3 at W 5 µm. If the count at W 5 µm exceeds the count levels given

in the note below, this indicates insufficient cleaning. Clean the apparatus again and repeat 9.2.2 to 9.2.3.

NOTE A blank count less than 10 % of the resulting count should be achieved and larger analysis volumes of sample

should be filtered if this is exceeded. A blank count of less than 100 particles sized W 5 µm in 100 mL of solvent is

recommended.

9.2.4 If high blank counts occur after recleaning, all processes should be investigated, i.e. cleaning procedure,

filtration of solvent, the preparation procedure and the environment.
9.2.5 Record the blank count on a worksheet (see Figure 2).
Key
1 10 squares
2 20 squares
3 50 squares
4 Effective filtration diameter of membrane
Figure 2 — Example of counting patter
...

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Transmissions hydrauliques -- Pollution des fluides -- Détermination de la pollution particulaire par comptage au microscope optiqueHydraulic fluid power -- Fluid contamination -- Determination of particulate contamination by the counting method using an optical microscope23.100.60Filters, seals and contamination of fluidsICS:Ta slovenski standard je istoveten z:ISO 4407:2002SIST ISO 4407:2003en01-julij-2003SIST ISO 4407:2003SLOVENSKI

STANDARD
SIST ISO 4407:2003
Reference numberISO 4407:2002(E)© ISO 2002

INTERNATIONAL STANDARD ISO4407Second edition2002-04-15Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by the counting method using an optical microscope Transmissions hydrauliques — Pollution des fluides — Détermination de la pollution particulaire par comptage au microscope optique

SIST ISO 4407:2003

ISO 4407:2002(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

ISO 2002 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 • CH-1211 Geneva 20 Tel.

+ 41 22 749 01 11 Fax
+ 41 22 749 09 47 E-mail
copyright@iso.ch Web
www.iso.ch Printed in Switzerland
ii © ISO 2002 – All rights reserved
SIST ISO 4407:2003

ISO 4407:2002(E) © ISO 2002 – All rights reserved iii Contents Page Foreword.....................................................................................................................................................................iv Introduction.................................................................................................................................................................v 1 Scope..............................................................................................................................................................1 2 Normative references....................................................................................................................................1 3 Terms and definitions...................................................................................................................................2 4 Counting principle.........................................................................................................................................4 5 Apparatus.......................................................................................................................................................4 6 Reagent and chemicals.................................................................................................................................6 6.1 Reagent and rinsing and cleaning chemicals............................................................................................6 6.2 Liquids for transparentizing the membrane filter (transmitted-light method)........................................6 7 Glassware cleaning procedure....................................................................................................................6 8 Calibration procedures.................................................................................................................................6 8.1 Microscope calibration..................................................................................................................................6 8.2 Determination of Effective Filtration Area (EFA)........................................................................................7 9 Membrane filter preparation.........................................................................................................................7 9.1 Sample preparation.......................................................................................................................................7 9.2 Blank analysis................................................................................................................................................8 9.3 Separation of contaminants by vacuum filtration......................................................................................8 9.4 Evaluation of suitability for counting..........................................................................................................9 9.5 Mounting of membrane filters for observation under transmitted light................................................10 10 Particle sizing and counting procedure....................................................................................................10 10.1 Particle sizing...............................................................................................................................................10 10.2 Selection of nominal magnification...........................................................................................................10 10.3 Statistical counting procedure...................................................................................................................10 10.4 Calculation of total count............................................................................................................................11 10.5 Verification of data......................................................................................................................................12 11 Expression of results..................................................................................................................................13 12 Identification statement (Reference to this International Standard)...........................................................13 Bibliography..............................................................................................................................................................14

SIST ISO 4407:2003
ISO 4407:2002(E) iv © ISO 2002 – All rights reserved

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. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 4407 was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee SC 6, Contamination control and hydraulic fluids. This second edition cancels and replaces the first edition (ISO 4407:1991), which has been technically revised.

SIST ISO 4407:2003

ISO 4407:2002(E) © ISO 2002 – All rights reserved v Introduction In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure within an enclosed circuit. The liquid is both a lubricant and power transmitting medium. The presence of particulate contamination in the liquid interferes with its ability to lubricate and causes wear to the components. The level of contamination in the liquid has a direct bearing on the performance and reliability of the system, and should be controlled to a level appropriate for the system concerned. Quantitative determination of particulate contamination requires precision in obtaining a representative sample of the liquid and in determining the level of contamination. The method of particle counting using the optical microscope is an accepted means of determining the extent of contamination. The accuracy of particle count data can be affected by the techniques used. This International Standard details procedures for the separation of particles in liquid samples by vacuum filtration and subsequent analysis of the particles deposited on an analytical membrane filter by microscopic techniques. The techniques involve counting using transmitted or incident light both manually and using image analysis techniques. This International Standard specifies methods to ensure accurate and consistent results. SIST ISO 4407:2003

SIST ISO 4407:2003

INTERNATIONAL STANDARD ISO 4407:2002(E) © ISO 2002 – All rights reserved 1 Hydraulic fluid power — Fluid contamination — Determination of particulate contamination by the counting method using an optical microscope WARNING — The use of this International Standard may involve hazardous materials, operations and equipment. This International Standard does not purport to address all the safety problems associated with its use. It is the responsibility of the user of this International Standard to establish appropriate safety and health practices and determine the applicability of regulative limitations prior to use. 1 Scope This International Standard specifies methods for determining the level of particulate contamination in liquids used in hydraulic systems by counting the number of particles deposited on the surface of a membrane filter using an optical microscope. It includes particle counting by two manual methods and image analysis, using either transmitted or incident lighting systems. Particle sizes W 2 µm can be sized and counted by this method, but the resolution and accuracy of the results will depend upon the optical system used and the capabilities of the operator. All hydraulic fluids with a wide range of contamination levels can be analysed according to this International Standard. However, the counting uncertainty at the larger particle sizes increases if the volume filtered is reduced to allow smaller sized particles to be counted, where a fine precipitate or a high particle concentration is present. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 3722, Hydraulic fluid power — Fluid sample containers — Qualifying and controlling cleaning methods ISO 4406:1999, Hydraulic fluid power — Fluids — Method for coding the level of contamination by solid particles ISO 4788, Laboratory glassware — Graduated measuring cylinders ISO 5598, Fluid power systems and components — Vocabulary ISO 14644-1:1999, Cleanrooms and associated controlled environments — Classification of air cleanliness SIST ISO 4407:2003

ISO 4407:2002(E) 2 © ISO 2002 – All rights reserved

3 Terms and definitions For the purposes of this International Standard, the definitions given in ISO 5598 and the following apply. 3.1 blank count count resulting from contaminants introduced from other sources, such as reagents, cleaning of glassware and preparation of the membrane filter (see 9.2) 3.2 calculation factor ratio of the effective filtration area to the total area counted 3.3 effective filtration area EFA circular area of the membrane filter open to flow during filtration of liquid NOTE Both the effective filtration area (EFA) and the effective filtration diameter (EFD) are determined in 8.2. 3.4 fibre particle longer than 100 µm with a length-to-width ratio greater than or equal to 10:1 3.5 fixative liquid liquid that, as a result of a heat curing process, causes a membrane filter to adhere to a glass base slide, resulting in an opaque residue 3.6 grid square square with sides of nominally 3,1 mm printed on membrane filters NOTE Gridded membrane filters may not be suitable for counting using image analysis techniques. 3.7 image analyser instrumentation to automatically size and count particles deposited on a membrane filter NOTE A video image of the particle is digitally recreated based upon the difference in the grey scale contrast of the particle and background, and the size is automatically computed. Sizing of the particle can also be undertaken on the video screen. 3.8 mountant liquid liquid that, when heated, causes a membrane filter, previously treated with fixative liquid, to become transparent and to adhere to the cover slip (see 5.7) 3.9 particle size size of particle as defined by the particle's longest dimension 3.10 solvent liquid that is physically and chemically compatible with and miscible in the sample liquid NOTE A solvent is used for diluting the sample liquid, and can be used for cleaning and rinsing the apparatus. The solvent should be chemically compatible with the apparatus, especially the membrane filter, and should not dissolve the particles. SIST ISO 4407:2003

ISO 4407:2002(E) © ISO 2002 – All rights reserved 3 3.11 statistical counting counting and sizing particles using a proportion of the membrane filter’s surface, whereby at least 150 particles are counted over a total of at least 10 separate locations (fields) NOTE 1 Statistical counting requires an even distribution of particles over the complete surface, and membrane filters should be rejected for counting if this is not achieved. NOTE 2 Counting 150 particles gives a counting uncertainty of 8 %, and the counting uncertainty will be reduced if more particles are counted. 3.12 unit area proportion of membrane filter that is counted for statistical purposes NOTE For manual counting, the unit area is defined as the area of the membrane filter bound in the horizontal plane by two adjacent vertical membrane filter grid lines and in the vertical plane by two parallel lines either on the ocular micrometer eyepiece or drawn on a projection screen. Examples are given in Figure 1. For image analysis, this is a fixed field of view defined by the optical and electronic systems.

Key 1 Grid square 2 Width of grid square (mm) 3 Length of grid square (mm) 4 Full grid square 5 Unit area on a gridded membrane 6 Graticule height used for defining unit area (µm) 7 Unit area 8 Diametric unit area on ungridded membrane 9 Effective filtration diameter of membrane Figure 1 — Examples of unit areas SIST ISO 4407:2003

ISO 4407:2002(E) 4 © ISO 2002 – All rights reserved

4 Counting principle A known volume of hydraulic liquid is vacuum filtered through a membrane filter to separate the contaminants from the liquid. The particles are examined microscopically using either incident light or transmitted light, after making the membrane filter transparent, to size and count the contaminant particles according to their largest dimension. 5 Apparatus 5.1 Drying oven, able to control temperature up to (70 ± 2) °C. 5.2 External lamp, of variable intensity, where oblique illumination of the specimen stage is required. 5.3 Filter holder, comprising: =a funnel, 300 mL capacity with suitable calibrated volumetric graduations [e.g. (25 ± 2) mL]; =a suitable cover for the funnel (e.g. a Petri dish); =a clamping device; =a suitable base to support the membrane filter; =a means of dissipating any static electricity generated during the filtering process. 5.4 Graduated cylinders, for measuring out the volume of test liquid. Either the accuracy should conform to ISO 4788 or a sample bottle calibrated with suitable volumetric graduations can be used. The accuracy of graduation should be ± 2 %. 5.5 Image analysing equipment, comprising a microscope base with a range of objective lenses and trinocular head for attaching a video camera connected to a suitable video monitor. The output of the video camera is fed to a computer which recreates a video digital image of the view, where the particles are sized and counted using specially developed software. Although a manual X-Y stage and focus can be used, it is recommended that these be motorized and controlled by the software as this enables the particles to be localized. 5.6 Membrane filters, compatible with the sample liquid and any solvents or chemicals used in the processes. Normally, the membrane filter shall be of 47 mm diameter, white, gridded (each grid square with sides 3,08 mm ± 0,05 mm and an area equal to 1/100th of the effective filtration area), with a pore size less than 1,5 µm, used for manual counting down to 2 µm. A 47 mm diameter, white, ungridded membrane filter with a pore size less than 1,5 µm is recommended for image analysis. Membrane filters of different diameters are permissible. It is permissible to use membrane filters of different nominal pore size to account for the minimum size of particle to be counted and the condition of the sample liquid. The pore size of the membrane filter should have a particle removal efficiency of 99,9 % at the minimum size to be counted. The colour of the membrane filter shall be chosen for maximum contrast with the particulate contamination to be observed. For example, if most of the contaminant is translucent, transparent or white, a black membrane filter should be considered. 5.7 Microscope glass base slides and microscope glass cover slips, for transmitted-light method only, with dimensions greater than the diameter of the membrane filter. The thickness of the cover slip should be selected to ensure that the particles are in focus at the magnification used. 5.8 Membrane filter holder, plastic or equivalent with lid, for retaining the membrane filter (incident-light method only). SIST ISO 4407:2003

ISO 4407:2002(E) © ISO 2002 – All rights reserved 5 5.9 Microscope for particle counting, with a range of objective lenses that, in combination with the ocular lenses, are able to resolve particles W 2 µm. The microscope shall be equipped with: =fine and coarse focus control; =through-the-lens lighting for the incident light method and/or a bottom lighting source for the transmitted light method; =a mechanical stage so that the effective filtration area of the membrane filter can be scanned; =provision on the mechanical stage for securely holding the membrane filter holder or glass slide; =an ocular micrometer of which the smallest division shall not subtend a distance larger than the smallest particle to be counted at a particular magnification, and with suitable graduations. For counting with transmitted light, the optimum equipment is a projector microscope with suitable screen, over-eyepiece mirror and rotating superstage. NOTE 1 For image analysis, it is preferable to have a stabilized lighting source controlled by the imaging software so that illumination fluctuations are eliminated and automatic correction is made for any intensity drift in the lighting source. NOTE 2 For accurate characterization of particles using the incident light method, an additional oblique lighting source may be required (see 5.2). Nominal magnification and optical combinations for manual counting are given in Table 1. NOTE 3 The manufacturer of the image analysis equipment should be contacted for the magnification provided by the trinocular head video/camera combination. Table 1 — Nominal magnifications and optical combinations Magnification (nominal) Ocular lens Objective lens Suggested minimum particle size

µm × 50 × 10 × 5 20 × 100 × 10 × 10 10 × 200 × 10 × 20 5 × 500 × 10 × 50 2 5.10 Plastic film, 0,05 mm thick × 50 mm × 50 mm, placed between the cap and neck of the sample bottle if the cap does not have an internal seal. The film shall be compatible with both the cleaning and sample liquids. 5.11 Sample bottles, 250 mL nominal capacity, preferably flat-bottomed and wide-mouthed with a screw cap containing a suitable internal polymeric seal. 5.12 Sampling agitating device, suitable for redispersing the contaminant in the liquid sample. The device, such as a laboratory bottle roller, a three-axis paint shaker or an ultrasonic bath rated at 3 000 W/m2 to 10 000 W/m2 of base area, shall not alter the basic size distribution of the contaminant. 5.13 Solvent dispenser, a pressurized vessel that discharges solvent (see 6.1.4) through an in-line membrane filter with a pore size not greater than 1 µm. 5.14 Stage micrometer, graduated in 0,1 mm and 0,01 mm divisions, calibrated and traceable to national standards. SIST ISO 4407:2003

ISO 4407:2002(E) 6 © ISO 2002 – All rights reserved

5.15 Tally counter, with sufficient sections to accumulate the numbers of particles and fields counted. 5.16 Tweezers, flat-bladed, blunt tips, of stainless steel. 5.17 Vacuum device, able to establish a vacuum of 86,6 kPa (ª 0,87 bar, 650 mm Hg). 5.18 Vacuum flask, suitable for the filter holder, and of a capacity able to filter the entire volume of sample liquid without refilling. 6 Reagent and chemicals 6.1 Reagent and rinsing and cleaning chemicals 6.1.1 Propan-2-ol [isopropyl alcohol (IPA)]. 6.1.2 Liquid detergent, without solid residue. 6.1.3 Distilled or demineralized water. 6.1.4 Solvent, for rinsing equipment and dilution samples.

Petroleum spirit (boiling point 100 °C to 120 °C) or similar is suitable if the sample liquid is a petroleum-based or synthetic oil; alternatively distilled or demineralized water is used if the sample liquid is water-based. The solvent shall be physically and chemically compatible with the sample liquid and apparatus. WARNING — Exercise care when using solvents with low flash points as there could be an explosion risk. Appropriate precautions should be taken to avoid inhalation of fumes from these solvents. Always use suitable protective equipment. Attention is drawn to local health and safety procedures. 6.2 Liquids for transparentizing the membrane filter (transmitted-light method) 6.2.1 Fixative liquid, see 3.5. 6.2.2 Mountant liquid, see 3.8, with a refractive index similar to that of the glass cover slip. 7 Glassware cleaning procedure 7.1 Clean and validate the cleanliness level of the filtration apparatus, graduated cylinders (5.4), bottles (5.11), glass slides and cover slips (5.7) and membrane filter holders (5.8) in accordance with ISO 3722. The final liquid used for the flush should be either filtered petroleum spirit (or similar solvent) for petroleum based or synthetic oils, propan-2-ol or demineralized water for water-based liquids. 7.2 The required cleanliness level (RCL) of the apparatus should be such that contaminant cannot significantly contribute to the overall result. An RCL of less than 250 particles greater than 5 µm per 100 mL of bottle volume is suitable for sample bottles. All liquids used for cleaning and rinsing shall be filtered through a 1 µm or finer membrane filter. 8 Calibration procedures 8.1 Microscope calibration 8.1.1 Calibration should be carried out at least annually or whenever any major adjustment or change is made to the optics. The stage micrometer (5.14) should be calibrated every five years. SIST ISO 4407:2003

ISO 4407:2002(E) © ISO 2002 – All rights reserved 7 8.1.2 For microscopes used for manual counting, select a magnification on the microscope and place the stage micrometer on the microscope stage so that the image of the graticule is superimposed upon and aligned with the eyepiece or trinocular graticule. Ensure that the scale and graticule are in focus. 8.1.3 Compare the two superimposed scales and align the lowest numbered division on the eyepiece graticule so that it is coincident with one division on the stage micrometer and so that the highest graticule division falls within the divisions of the stage micrometer. Select a suitable number of eyepiece divisions (e.g. 50) and determine the number of corresponding divisions on the stage micrometer. Determine the length scale of the graticule divisions at the magnification used. 8.1.4 Repeat 8.1.2 and 8.1.3 for all magnifications and record the data in a suitable calibration recording system. 8.1.5 A similar procedure to 8.1.3 shall be carried out for image analysing equipment but the individual method may vary from instrument to instrument. Carry out the calibration in accordance with the manufacturer’s instructions. 8.2 Determination of Effective Filtration Area (EFA) 8.2.1 This procedure should be performed before a new vacuum funnel is used for the first time, and should be recalibrated every five years. 8.2.2 Make up a suspension of suitable staining contaminant which will identify the effective filtration area of the membrane filter when filtered. Red oxide contaminant is suitable for this. Prepare by dispersing into a suitable volume of solvent to give a concentration of approximately 1 mg/L and shake vigorously or mix by ultrasonics for 1 min. 8.2.3 Assemble a 1 µm filter membrane filter in the vacuum apparatus to be calibrated and clamp firmly. Vacuum filter about 25 mL or sufficient volume of suspension to clearly stain the membrane filter, and aspirate to dryness. 8.2.4 Unclamp, remove the membrane filter and measure the diameter [effective filtration diameter (EFD)] of the stain in at least two planes to within 0,1 mm. Average the result and calculate the effective filtration area (EFA). Mark the funnel with a suitable code and record the result in a suitable calibration recording system. 9 Membrane filter preparation 9.1 Sample preparation 9.1.1 After noting all sample identification details, remove any tied-up or loosely attached labels ensuring that sample identity is retained. Thoroughly clean the outside of the sample bottle, particularly around the cap, by washing with filtered solvent dispensed from the pressurized dispenser. Take care not to force contaminant into the cap area. 9.1.2 If the sample has been standing for a period of time, particle settlement, and hence agglomeration, will occur. It is essential that the agglomerates are broken up, and the contaminant particles are re-dispersed evenly within the contents of the sample before analysis. 9.1.3 Redistribute the contaminants within the contents of the bottle by either hand shaking the sample vigorously for at least 1 min, or by using an acceptable method of mixing such as a three-axis paint shaker for at least 5 min. The method chosen should not alter the original distribution of the contaminant. 9.1.4 If ultrasonics is used to break up any agglomerates, stand the sample container so that the level of the liquid in the bath is either just below the fluid level in the sample bottle, or 3/4 up the side of the container, whichever is least. The period of immersion shall not exceed 1 min. Hand shake for 30 s afterwards. SIST ISO 4407:2003

ISO 4407:2002(E) 8 © ISO 2002 – All rights reserved

9.2 Blank analysis 9.2.1 A blank analysis should be performed before each sample analysis, unless it can be demonstrated that acceptable blanks can be consistently obtained. If so, a blank analysis should be performed before starting a counting programme and at least once during it. 9.2.2 Proceed as in 9.3, using solvent instead of sample liquid. Dispense a 100 mL volume of filtered solvent into the vacuum apparatus fitted with the selected membrane filter, vacuum filter and aspirate to dryness. 9.2.3 Perform size analysis as specified in 10.3 at W 5 µm. If the count at W 5 µm exceeds the count levels given in the note below, this indicates insufficient cleaning. Clean the apparatus again and repeat 9.2.2 to 9.2.3. NOTE A blank count less than 10 % of the resulting count should be achieved and larger analysis volumes of sample should be filtered if this is exceeded. A blank count of less than 100 particles sized W 5 µm in 100 mL of solvent is recommended. 9.2.4 If high blank counts occur after recleaning, all processes should be investigated, i.e. cleaning procedure, filtration of solvent, the preparation procedure and the environment. 9.2.5 Record the blank count on a worksheet (see Figure 2).

Key 1 10 squares 2 20 squares 3 50 squares 4 Effective filtration diameter of membrane Figure 2 — Example of counting pattern for 10, 20 and 50 locations 9.3 Separation of contaminants by vacuum filtration 9.3.1 Carry out the preparation procedure in accordance with 9.1 and within a controlled environment. A level of ISO class 5 or better in accord

...

NORME ISO
INTERNATIONALE 4407
Deuxième édition
2002-04-15
Transmissions hydrauliques — Pollution
des fluides — Détermination de la pollution
particulaire par comptage au microscope
optique
Hydraulic fluid power — Fluid contamination — Determination of particulate
contamination by the counting method using an optical microscope
Numéro de référence
ISO 4407:2002(F)
ISO 2002
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ISO 4407:2002(F)
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ISO 4407:2002(F)
Sommaire Page

Avant-propos .............................................................................................................................................................iv

Introduction.................................................................................................................................................................v

1 Domaine d'application ..................................................................................................................................1

2 Références normatives .................................................................................................................................1

3 Termes et définitions.....................................................................................................................................2

4 Principe de comptage ...................................................................................................................................4

5 Appareillage ...................................................................................................................................................4

6 Réactif et produits chimiques ......................................................................................................................6

6.1 Réactif et produits chimiques de rinçage et de nettoyage........................................................................6

6.2 Liquides de transparisation de la membrane filtrante (méthode en lumière transmise) .......................6

7 Mode opératoire de nettoyage de la verrerie..............................................................................................7

8 Méthodes d'étalonnage.................................................................................................................................7

8.1 Étalonnage du microscope...........................................................................................................................7

8.2 Détermination de la surface utile de filtration (SUF)..................................................................................7

9 Préparation de la membrane filtrante ..........................................................................................................8

9.1 Préparation de l’échantillon .........................................................................................................................8

9.2 Analyse à blanc..............................................................................................................................................8

9.3 Séparation des polluants par filtration sous vide ......................................................................................9

9.4 Évaluation de l’aptitude au comptage.......................................................................................................10

9.5 Montage des membranes pour observation en lumière transmise........................................................10

10 Classification des particules et méthode de comptage ..........................................................................11

10.1 Classification des particules ......................................................................................................................11

10.2 Choix du grossissement nominal ..............................................................................................................11

10.3 Méthode de comptage statistique..............................................................................................................11

10.4 Calcul du nombre total................................................................................................................................12

10.5 Vérification des résultats............................................................................................................................13

11 Expression des résultats ............................................................................................................................14

12 Phrase d'identification (Référence à la présente Norme internationale)....................................................14

Bibliographie.............................................................................................................................................................15

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ISO 4407:2002(F)
Avant-propos

L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de

normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiée aux

comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du comité

technique créé à cet effet. Les organisations internationales, gouvernementales et non gouvernementales, en

liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec la Commission

électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.

Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,

Partie 3.

La tâche principale des comités techniques est d'élaborer les Normes internationales. Les projets de Normes

internationales adoptés par les comités techniques sont soumis aux comités membres pour vote. Leur publication

comme Normes internationales requiert l'approbation de 75 % au moins des comités membres votants.

L’attention est appelée sur le fait que certains des éléments de la présente Norme internationale peuvent faire

l’objet de droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable de

ne pas avoir identifié de tels droits de propriété et averti de leur existence.

L’ISO 4407 a été élaborée par le comité technique ISO/TC 131, Transmissions hydrauliques et pneumatiques,

sous-comité SC 6, Contrôle de la contamination et fluides hydrauliques.

Cette deuxième édition annule et remplace la première édition (ISO 4407:1991), dont elle constitue une révision

technique.
iv © ISO 2002 – Tous droits réservés
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ISO 4407:2002(F)
Introduction

Dans les systèmes de transmissions hydrauliques, l’énergie est transmise et commandée par l’intermédiaire d’un

liquide sous pression circulant en circuit fermé. Ce liquide fait office à la fois de lubrifiant et de milieu de

transmission de l’énergie.

La présence d’une pollution particulaire dans le liquide entrave son aptitude à la lubrification et entraîne une usure

des composants. Il convient de maintenir le niveau de pollution dans le liquide à un degré approprié au système

considéré car il a un impact direct sur les performances et la fiabilité dudit système.

La détermination quantitative de la pollution particulaire nécessite de garantir la fidélité du prélèvement d’un

échantillon représentatif du liquide et de la détermination du niveau de pollution. La méthode de comptage des

particules avec un microscope optique est un moyen reconnu qui permet de déterminer le niveau de la pollution.

L’exactitude de la détermination quantitative des résultats du comptage des particules peut être influencée par les

techniques utilisées.

La présente Norme internationale détaille des procédures de séparation des particules dans les échantillons

liquides par filtration sous vide, puis d’analyse des particules déposées sur une membrane filtrante pour analyses

par des techniques microscopiques. Ces techniques utilisent un comptage à la lumière transmise ou incidente,

effectué à la fois manuellement et par le biais de techniques d’analyse d’images. La présente Norme internationale

définit des méthodes qui garantissent l’obtention de résultats exacts et cohérents.

© ISO 2002 – Tous droits réservés v
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NORME INTERNATIONALE ISO 4407:2002(F)
Transmissions hydrauliques — Pollution des fluides —
Détermination de la pollution particulaire par comptage au
microscope optique

AVERTISSEMENT — L’utilisation de la présente Norme internationale peut impliquer l’utilisation de

produits et la mise en œuvre de modes opératoires et d’appareillages à caractère dangereux. La présente

Norme internationale n’a pas pour but d’aborder tous les problèmes de sécurité liés à son utilisation. Il

incombe à l’utilisateur de la présente Norme internationale d’établir avant utilisation des pratiques

appropriées d’hygiène et de sécurité et de déterminer l’applicabilité des restrictions réglementaires.

1 Domaine d'application

La présente Norme internationale définit des méthodes permettant de déterminer le niveau de pollution particulaire

des liquides utilisés dans les systèmes hydrauliques, par comptage au microscope optique du nombre de

particules déposées à la surface d’une membrane filtrante. Elle traite du comptage des particules par deux

méthodes manuelle et par analyse d’image, en utilisant soit une lumière transmise, soit une lumière incidente.

Ces méthodes permettent de classer et de dénombrer des particules de taille W 2 µm, mais la résolution et

l’exactitude des résultats dépend du système optique utilisé et des aptitudes de l’opérateur.

Tous les liquides hydrauliques qui présentent un large éventail de niveaux de pollution sont analysables selon la

présente Norme internationale. Cependant, l’incertitude de comptage aux plus grandes tailles de particules

augmente si le volume filtré est réduit pour permettre le dénombrement des particules de plus petites tailles,

lorsqu’on observe un léger précipité ou que la concentration des particules est élevée.

2 Références normatives

Les documents normatifs suivants contiennent des dispositions qui, par suite de la référence qui y est faite,

constituent des dispositions valables pour la présente Norme internationale. Pour les références datées, les

amendements ultérieurs ou les révisions de ces publications ne s’appliquent pas. Toutefois, les parties prenantes

aux accords fondés sur la présente Norme internationale sont invitées à rechercher la possibilité d'appliquer les

éditions les plus récentes des documents normatifs indiqués ci-après. Pour les références non datées, la dernière

édition du document normatif en référence s’applique. Les membres de l'ISO et de la CEI possèdent le registre des

Normes internationales en vigueur.

ISO 3722, Transmissions hydrauliques — Flacons de prélèvement — Homologation et contrôle des méthodes de

nettoyage

ISO 4406:1999, Transmissions hydrauliques — Fluides — Méthode de codification du niveau de pollution

particulaire solide
ISO 4788, Verrerie de laboratoire — Éprouvettes graduées cylindriques
ISO 5598, Transmissions hydrauliques et pneumatiques — Vocabulaire

ISO 14644-1:1999, Salles propres et environnements maîtrisés apparentés — Partie 1: Classification de la

propreté de l'air
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ISO 4407:2002(F)
3 Termes et définitions

Pour les besoins de la présente Norme internationale, les termes et définitions donnés dans l’ISO 5598 et les

suivants s'appliquent.
3.1
comptage à blanc

comptage résultant de l’introduction de polluants par d’autres sources telles que les réactifs, le nettoyage de la

verrerie et la préparation de la membrane filtrante (voir 9.2)
3.2
facteur de calcul
rapport de la surface utile de filtration à la surface totale de comptage
3.3
surface utile de filtration
SUF

surface circulaire de la membrane filtrante exposée au débit du fluide pendant la filtration

NOTE En 8.2, on détermine à la fois la surface utile de filtration (SUF) et le diamètre utile de filtration (DUF).

3.4
fibre

particule de longueur supérieure à 100 µm dont le rapport longueur sur largeur est supérieur ou égal à 10:1

3.5
fixatif

liquide qui, sous l’effet d’un séchage en température, fait adhérer la membrane filtrante à une lame de verre,

donnant un résidu opaque
3.6
carré de quadrillage
carré de 3,1 mm de côté (valeur nominale) imprimé sur les membranes filtrantes

NOTE Les membranes filtrantes quadrillées peuvent ne pas convenir lorsque le comptage utilise des techniques d’analyse

d’images.
3.7
analyseur d’images

instrument permettant de classer et compter automatiquement les particules qui se sont déposées sur une

membrane filtrante

NOTE Une image vidéo de la particule est recréée numériquement à partir de la différence de contraste en niveaux de gris

entre la particule et l’arrière plan, et la taille est calculée automatiquement par l’ordinateur. La mesure de la taille de la particule

peut également se faire sur l’écran vidéo.
3.8
liquide de transparisation

liquide qui, une fois chauffé, rend transparente une membrane filtrante, ayant été préalablement traitée au fixatif, et

qui la fait adhérer à la lamelle protectrice (voir 5.7)
3.9
taille de particule

taille d’une particule telle que définie par la plus grande dimension de la particule considérée

3.10
solvant

liquide physiquement et chimiquement compatible avec l’échantillon liquide et dans lequel il est miscible

NOTE Un solvant est utilisé pour diluer l’échantillon liquide et peut servir pour nettoyer et rincer l’appareillage. Il convient

que le solvant soit chimiquement compatible avec l’appareillage, notamment la membrane, et qu’il ne dissolve pas les

particules.
2 © ISO 2002 – Tous droits réservés
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ISO 4407:2002(F)
3.11
comptage statistique

comptage et classification des particules en utilisant une proportion de la surface de la membrane filtrante où au

moins 150 particules sont comptées sur un total d’au moins 10 emplacements distincts (champs)

NOTE 1 Le comptage statistique nécessite une répartition régulière des particules sur la totalité de la surface, et il convient

de rejeter les membranes filtrantes pour comptage si ce n’est pas le cas.

NOTE 2 Le comptage de 150 particules donne une incertitude de comptage de 8 %. L’incertitude de comptage sera réduite

si l’on compte un plus grand nombre de particules.
3.12
surface unitaire
proportion de la membrane filtrante comptée à des fins statistiques

NOTE Pour le comptage manuel, la surface unitaire se définit comme la surface de la membrane délimitée dans le plan

horizontal par deux lignes verticales adjacentes du quadrillage de la membrane et dans le plan vertical par deux lignes

parallèles soit sur l’oculaire du micromètre oculaire, soit tracées sur un écran de projection. Des exemples sont donnés à la

Figure 1. En ce qui concerne l’analyse d’images, il s’agit d’un champ de vision fixe défini par les systèmes optiques et

électroniques.
Légende
1 Carré de quadrillage
2 Largeur du carré de quadrillage (mm)
3 Longueur du carré de quadrillage (mm)
4 Quadrillage complet
5 Surface unitaire sur une membrane quadrillée
6 Hauteur du graticule utilisée pour définir la surface unitaire (µm)
7 Surface unitaire
8 Surface unitaire diamétrale sur une membrane non quadrillée
9 Diamètre utile de filtration de la membrane
Figure 1 — Exemples de surfaces unitaires
© ISO 2002 – Tous droits réservés 3
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ISO 4407:2002(F)
4 Principe de comptage

Un volume connu de liquide hydraulique est filtré sous vide à travers une membrane filtrante pour séparer les

polluants du liquide après avoir transparisé la membrane. Les particules sont examinées au microscope en utilisant

soit une lumière incidente, soit une lumière transmise, pour les classer et les compter selon leur dimension la plus

grande.
5 Appareillage
5.1 Étuve, permettant de réguler la température jusqu’à (70 ± 2) °C.

5.2 Lampe extérieure, d’intensité variable, lorsqu’un éclairage oblique de la platine portant l’éprouvette est

requis.
5.3 Support de filtre, comprenant

 un entonnoir, de 300 mL de capacité ayant des graduations volumétriques étalonnées appropriées [par

exemple (25 ± 2) mL];
 un couvercle adapté à l’entonnoir (par exemple une boîte de Petri);
 un dispositif de fixation;
 une base convenable pour supporter la membrane filtrante;

 un dispositif d’élimination de l’électricité statique éventuellement générée pendant la filtration.

5.4 Éprouvettes graduées, pour le mesurage du volume de liquide d’essai. Soit l’exactitude est en conformité

avec l’ISO 4788, soit on utilise un flacon d’échantillonnage étalonné avec des graduations volumétriques

appropriées. Il convient que l’exactitude des graduations soit de ± 2 %.

5.5 Équipement d’analyse d’image, comprenant une base de microscope avec plusieurs objectifs et une tête

trinoculaire permettant la fixation d’une caméra vidéo raccordée à un écran de contrôle approprié. Le signal émis

par la caméra est entré dans un ordinateur qui recrée une image vidéo numérique de la vue, où les particules sont

comptées et classées à l’aide d’un logiciel spécialement mis au point.

Bien qu’il soit possible d’utiliser une mise au point et une platine X-Y manuelles, il est recommandé qu’elles soient

motorisées et pilotées par un logiciel car cela permet de localiser les particules.

5.6 Membranes filtrantes, compatibles avec l’échantillon liquide et les solvants ou produits chimiques utilisés

en cours de processus. Normalement, une membrane filtrante doit avoir un diamètre de 47 mm, être blanche et

quadrillée (chaque carré du quadrillage mesurant 3,08 mm ± 0,05 mm de côté et ayant une surface égale à 1/100

de la surface utile de filtration), avoir une taille des pores inférieure à 1,5 µm, et peut être utilisée pour le comptage

manuel jusqu’à 2 µm. Pour l’analyse d’images, il est recommandé d’utiliser une membrane filtrante de 47 mm de

diamètre, non quadrillée et blanche, avec une taille des pores inférieure à 1,5 µm. L’utilisation de membranes

ayant d’autres diamètres est admise.

L’emploi de membranes ayant des diamètres nominaux de pores différents est admissible pour tenir compte de la

plus petite taille de particule à compter et de l’état de l’échantillon liquide. Il convient que la membrane ait une

efficacité d’élimination des particules de 99,9 % à la plus petite taille à compter.

Il faut choisir la couleur de la membrane de manière à obtenir le plus fort contraste avec la pollution particulaire à

observer. Par exemple, si la plus grande partie du polluant est translucide, transparente ou blanche, il convient

d’envisager l’utilisation de membranes noires.
4 © ISO 2002 – Tous droits réservés
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ISO 4407:2002(F)

5.7 Lames de microscope en verre et lamelles protectrices en verre, pour la méthode en lumière transmise

uniquement, de dimensions supérieures au diamètre de la membrane filtrante. Il convient de choisir l’épaisseur de

la lamelle protectrice de manière à garantir que les particules se situent dans le plan focal au grossissement utilisé.

5.8 Support de membrane, en plastique ou l’équivalent, avec un couvercle pour maintenir la membrane filtrante

(méthode en lumière incidente, uniquement).

5.9 Microscope pour le comptage des particules, doté de plusieurs objectifs qui, avec les oculaires,

permettent de distinguer des particules W 2 µm. Le microscope doit être équipé des éléments suivants:

 une commande approchée et fine de la mise au point;

 un éclairage à travers la lentille pour la méthode en lumière incidente et/ou une source de lumière basse pour

la méthode en lumière transmise;

 une platine mécanique permettant un balayage de la surface utile de filtration de la membrane filtrante;

 un dispositif pour maintenir en toute sécurité le support de la membrane ou la lame de verre sur la platine

mécanique;

 un oculaire micrométrique dont la plus petite division ne doit pas sous-tendre une distance plus grande que la

plus petite particule à compter à un grossissement donné, et comportant des graduations adaptées.

Pour le comptage en lumière transmise, l’appareil le mieux adapté est un microscope avec projecteur équipé d’un

écran approprié, d’un miroir sur oculaire et d’une platine tournante.

NOTE 1 Pour l’analyse d’image, il est préférable de disposer d’une source lumineuse stabilisée commandée par le logiciel

d’imagerie de façon à ce que les fluctuations d’éclairage soient éliminées et que toute dérive d’intensité de la source d’éclairage

soit corrigée de manière automatique.

NOTE 2 Pour obtenir une caractérisation exacte des particules en lumière incidente, une source supplémentaire d’éclairage

oblique peut se révéler nécessaire (voir 5.2).

Le grossissement nominal et les combinaisons optiques pour le comptage manuel sont donnés dans le Tableau 1.

NOTE 3 En ce qui concerne le grossissement fourni par la combinaison tête trinoculaire/caméra vidéo, il convient de prendre

contact avec le fabricant de l’analyseur d’image.
Tableau 1 — Grossissements nominaux et combinaisons optiques
Taille de particule minimale
Grossissement
proposée
Oculaire Objectif
(nominal)
× 50 × 10 × 5
× 100 × 10 × 10 10
× 200 × 10 × 20
× 500 × 10 × 50 2

5.10 Film de plastique, de 0,05 mm d’épaisseur × 50 mm × 50 mm, intercalé entre le bouchon et le col du flacon

d’échantillonnage si le bouchon ne comporte pas de joint intérieur. Ce film doit être compatible à la fois avec le

liquide de nettoyage et avec l’échantillon.
© ISO 2002 – Tous droits réservés 5
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ISO 4407:2002(F)

5.11 Flacons d’échantillonnage, de capacité nominale 250 mL, de préférence à fond plat et col large avec

bouchon à vis muni d’un joint polymère intérieur approprié.

5.12 Agitateur d’échantillon, permettant de réhomogénéiser le polluant dans l’échantillon liquide. Ce dispositif,

tel qu’un agitateur à rouleaux de laboratoire, un agitateur à peinture triaxial ou un bain à ultrasons réglé à une

2 2

valeur comprise entre 3 000 W/m et 10 000 W/m , ne doit pas modifier la distribution granulométrique de base du

polluant.

5.13 Distributeur de solvant, récipient sous pression distribuant le solvant (voir 6.1.4) à travers une membrane

en ligne ayant une taille des pores inférieure ou égale à 1 µm.

5.14 Micromètre de platine, gradué en dixièmes et centièmes de millimètre, étalonné et pouvant être raccordé

aux étalons nationaux.

5.15 Compteur totalisateur, ayant un nombre suffisant de sections pour totaliser le nombre de particules et de

champs comptés.
5.16 Pinces, à lames plates, à extrémités émoussées, en acier inoxydable.

5.17 Appareil à vide, permettant de créer un vide de 86,6 kPa (ª 0,87 bar, 650 mm Hg).

5.18 Fiole à vide, adaptée au support de filtre, ayant une capacité suffisante pour filtrer le volume total

d’échantillon liquide sans remplissage complémentaire.
6 Réactif et produits chimiques
6.1 Réactif et produits chimiques de rinçage et de nettoyage
6.1.1 Propanol-2 [alcool isopropylique (IPA)].
6.1.2 Détergent liquide, ne laissant pas de résidu solide.
6.1.3 Eau distillée ou déminéralisée.

6.1.4 Solvant, pour le rinçage de l’appareillage et la dilution des échantillons.

L’éther de pétrole (point d’ébullition entre 100 °C et 120 °C) ou tout autre produit similaire est approprié si

l’échantillon liquide est une huile à base de pétrole ou de synthèse. Si l’échantillon liquide est à base d’eau, il y a

lieu d’utiliser de l’eau distillée ou déminéralisée. Le solvant doit être physiquement et chimiquement compatible

avec l’échantillon liquide et avec l’appareillage.

AVERTISSEMENT — Prendre les précautions appropriées lors de l’utilisation de solvants ayant des points

éclairs bas en raison du risque d’explosion et éviter d’inhaler les vapeurs émanant de ces solvants. Porter

en permanence les équipements de protection appropriés. L’attention de l’utilisateur est attirée sur les

procédures locales d’hygiène et de sécurité.

6.2 Liquides de transparisation de la membrane filtrante (méthode en lumière transmise)

6.2.1 Fixatif, voir 3.5.

6.2.2 Liquide de transparisation, voir 3.8, ayant un indice de réfraction similaire à celui de la lame protectrice

en verre.
6 © ISO 2002 – Tous droits réservés
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ISO 4407:2002(F)
7 Mode opératoire de nettoyage de la verrerie

7.1 Nettoyer et valider le niveau de propreté de l’appareillage de filtration, des éprouvettes graduées (5.4), des

flacons d’échantillonnage (5.11), des lames et lamelles protectrices en verre (5.7) et des supports de membranes

(5.8) conformément à l’ISO 3722. Il convient que le liquide final utilisé pour le rinçage soit de l’éther de pétrole filtré

(ou tout autre solvant similaire) pour les huiles à base de pétrole ou de synthèse, ou bien du propanol-2 ou de l’eau

déminéralisée pour les liquides à base d’eau.

7.2 Il convient que le niveau de propreté requis (NPR) de l’appareillage soit tel que le polluant ne puisse pas

contribuer de manière significative au résultat global. Un NPR de moins de 250 particules supérieur à 5 µm par

100 mL de volume convient pour les flacons d’échantillonnage.

Tous les liquides utilisés pour le nettoyage et le rinçage doivent être filtrés à travers une membrane d’au plus 1 µm.

8 Méthodes d'étalonnage
8.1 Étalonnage du microscope

8.1.1 Il convient de procéder à l’étalonnage au moins une fois par an ou après chaque réglage important ou

après chaque modification apportée à l’optique. Il est recommandé d’étalonner le micromètre de platine (5.14) tous

les 5 ans.

8.1.2 En ce qui concerne les microscopes utilisés pour le comptage manuel, choisir un grossissement sur le

microscope et placer le micromètre de platine sur la platine du microscope de manière à ce que l’image du repère

de visée soit superposée et alignée sur le repère de visée de l’oculaire ou du trinoculaire. S’assurer que l’échelle et

le repère de visée sont focalisés.

8.1.3 Comparer les deux échelles superposées et aligner la graduation la plus faible sur le repère de visée de

l’oculaire de manière à ce qu’elle coïncide avec une graduation sur le micromètre de platine, et de telle sorte que la

plus grande graduation du repère de visée se situe à l’intérieur des limites du micromètre de platine. Choisir un

nombre approprié de graduations d’oculaire (50, par exemple) et déterminer le nombre de graduations

correspondantes sur le micromètre de platine. Déterminer l’échelle de longueur des graduations du repère de visée

au grossissement utilisé.

8.1.4 Répéter les dispositions de 8.1.2 et 8.1.3 pour tous les grossissements et enregistrer les données dans un

système d’enregistrement approprié à l’étalonnage.

8.1.5 Un mode opératoire similaire à celui indiqué en 8.1.3 doit être suivi pour l’analyseur d’images mais la

méthode peut varier d’un instrument à l’autre. Il faut effectuer l’étalonnage conformément aux instructions du

fabricant.
8.2 Détermination de la surface utile de filtration (SUF)

8.2.1 Il convient de mettre en œuvre le présent mode opératoire avant d’utiliser pour la première fois un nouvel

entonnoir à vide, et il est recommandé d’effectuer un réétalonnage tous les 5 ans.

8.2.2 Préparer une suspension de polluant colorant approprié qui identifiera la surface utile de filtration de la

membrane filtrante (5.6) après filtration. Un polluant à l’hématite rouge convient pour ce faire. Préparer par

dispersion dans un volume approprié de solvant pour obtenir une concentration d’environ 1 mg/L et agiter

vigoureusement ou mélanger pendant 1 min au moyen d’un ag
...

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