BS ISO 4406:2021 pdf download – Hydraulic fluid power — Fluids — Method for coding the level of contamination by solid particles
3 Terms and definitions
No terms and definitions are listed in this document.
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4 Code definitions
The purpose of this code is to simplify the reporting of particle count data by converting the numbers of particles into broad classes or codes, where an increase in one code generally represents a doubling of the contamination level.
The original code, in accordance with the first edition of this document, stated the reporting at two sizes: ≥ 5 µm and ≥ 15 µm. The sizes in this document account for the use of a different calibration standard for optical automatic particle counters (APCs). The reported sizes are ≥ 4 µm(c), ≥ 6 µm(c) and 14 µm(c), as per ISO 11171. The last two of these are equivalent to the 5 µm and 15 µm particle sizes specified in the first edition.
NOTE Throughout this document, the use of µm(c) means that particle size measurements are carried out using an APC that has been calibrated in accordance with ISO 11171 or a particle contamination monitor (PCM) calibrated to ISO 21018-3 or ISO 21018-4.
Measurement of particles using an optical microscope as specified within ISO 4407 establishes the size of a particle as being equal to its longest dimension, whereas an APC derives the size of an equivalent particle from its cross-sectional area, a value different in most cases from that determined using a microscope.
The particle sizes to be reported for measurement by microscope ❓ 5 µm and ❓ 15 µm are unchanged from those specified in the first edition of this document.
4.2 Basis of code
The code for contamination levels using APCs or PCMs comprises three scale numbers that permit the differentiation of the dimension and the distribution of the particles as follows:
the first scale number represents the number of particles equal to or larger than 4 millilitre offluid;
the second scale number represents the number of particles equal to or larger than 6~millilitre of fluid: and
the third scale number represents the number of particles equal to or larger than 1 4~ millilitre of fluid.
The code for microscope counting comprises two scale numbers using 5 µm and 15 µm
4.3 Allocation of scale numbers
4.3.1 The scale numbers are allocated according to the number of particles counted per millilitre of the fluid sample (see Tohk_l ).
4.3.2 A step ratio of generally two, as given between the upper and lower limits for the number of particles per millilitre in .Tobl.e__1, has been adopted to keep the number of scale numbers within a reasonable limit and to ensure that each step is meaningful.
4.4 Determination of code using automatic particle counter analysis
4.4.1 Counting shall be undertaken in accordance with ISO 11500 or another recognized method,using an APC calibrated to ISO 11171 or a PCM calibrated to ISO 21018-3 or ISO 21018-4.
4.4.2 A first scale number shall be allocated to the number of particles equal to or larger than 4 µm(c).
4.4.3 A second scale number shall be allocated to the number of particles equal to or larger than 6 µm(c).BS ISO 4406 pdf download.