MP Filtri ICM, User Manual

Page: 76 / 82

Appendix G
76 New ISO Medium Test Dust and its effect on ISO . . .
In order that users are not confused by the changes to these standards, particularly by
reference to them in technical literature, ISO is updating 4402 to ISO 11171, and 4572
to ISO 16889.
Two standards which concern our industry are the ISO 4406 coding system and the new
ISO 16889 Multi-pass test. As APCs will henceforth count particles more accurately,
there will now be a change in the way sizes are labelled.
In the new ISO 4406:1999, new calibration sizes are used to give the same cleanliness
codes as the ‘old’ calibration sizes of 5 and 15 µm. In this way, there will be no neces-
sity to change any system cleanliness specifications. It is proposed that the cleanliness
codes (for APCs) will be formed from three 25 particle counts at 4, 6 and 14 µm, with
6 and 14 µm corresponding very closely to the previous 5 and 15 µm measurements.
This will ensure consistency in data reporting.
As the counts derived by microscope counting methods are not affected, the particle
sizes used for microscopy will remain unchanged (i.e. at 5 and 15 µm).
To clarify matters still further, ISO standards written around the new test dust will
utilize a new identifier, ‘(c)’. Hence µm sizes according to the new ISO 11171 will
be expresses as ‘µm(c)’ and Beta ratios according to ISO 16889 will be expressed as
‘Bx(c)’, e.g.‘B5(c)’.
However, it must be stressed that the only real effect users will experience will be the
improved accuracy in particle counts - there will be no change in the performance of
filters, nor in the ISO cleanliness levels that they will achieve.
The following charts shows the correlation between the old ACFTD and the new ISO
MTD.
The ICM is calibrated with ISO Medium Test Dust (to ISO 11171). The correlation
between particle sizes and the ACFTD (old standard) to the ISO MTD (new standard)
is as follows :
ACFTD <1 5 15 25 30 50 75 100
ISO MTD 4 6 14 21 25 38 50
26
70
27
25
The option of quoting just two counts of 6µm and 14µm for APCs remains.
26
Not verified by NIST
27
acftd