New Test Dust

The International Standards Organization (ISO) and Society of Automotive Engineers (SAE) have worked to find dusts to replace ACFTD. This has resulted in a new ISO Standard: ISO 12103-1. ISO Medium Test Dust (ISO MTD), having a particle size distribution close to ACFTD, has been selected as the replacement dust for calibration and testing purposes. However, although similar to ACFTD, ISO MTD produces test results that are somewhat different than ACFTD. Therefore, results of both laboratory filter performance testing (including filter efficiency and dirt holding capacity) and automatic particle counting can be significantly affected. This is an artifact of the testing only; filter performance and actual contamination levels in the field will remain the same as before.

Filter Efficiency

Revisions to the Multi-pass test method and its inclusion of both⁰ ISO MTD and the new APC calibration procedure will dramatically affect reported filter element Beta ratios. The effect will vary for different filters, depending on the influence of the test dust and the degree of change in the particle size at the filter’s rating. Generally, fine filters will appear coarser or less efficient, and coarse filters will appear finer or more efficient. Tests have been performed on Pall Machinery and Equipment standard filter media using the new Multi-pass test method, ISO 16889 (FDIS). Comparisons to results obtained from the previous ISO 4572 method are shown in Table 2.

Table 2 Comparing Laboratory Filter Ratings
Pall Filter Grade	Micron rating for Beta value
	Using ISO 4572	Using ISO FDIS 16889
	ßx = 200	ßx(c) = 200
KZ	<1	2.0
KP	3	3.8
KN	6	5.7
KS	12	9.7
KT	25	18.2

Table 3 New Filter Ratings for Pall Media using ISO 16889 (FDIS
	µm(c) rating for Beta value
Pall Media Grade	ß = 2	ß = 10	ß = 75	ß = 100	ß = 200	ß = 1000
KZ	< 2	< 2	< 2	< 2	2.0	2.5
KP	< 2	< 2	3.1	3.3	3.8	5
KN	2.1	3.4	5.0	5.2	5.7	7
KS	3.2	5.5	8.3	8.7	9.7	12
KT	7.2	11.0	15.8	16.5	18.2	22

Table 3 shows a summary of the new Pall filter ratings, µm(c), at Beta = 2, 10, 75, 100, 200, and 1000.
It should be noted that the filter’s performance in the field has not changed at all. The filter is no more or less efficient at removing harmful particles. The reported results are merely an artifact of the new procedures and methods.

Filter Dirt Holding Capacity
The replacement of ACFTD with ISO MTD in the Multi-pass test also affects retained dirt capacity values for filter elements. Capacity may be somewhat higher or lower with the new dust, depending on the specific filter being tested; however, most filters evaluated have exhibited an increase in dirt capacity of about 10% to 40% when using ISO MTD over values measured with ACFTD. Because each type of filter performs differently with ISO MTD, no general factor can be given to convert ACFTD capacities to ISO MTD capacities. It should be noted that a dirt capacity increase or decrease with ISO MTD does not imply that the filter will have a longer or shorter actual service life. In fact, there will not be a change in field service life. This reinforces the fact that dirt capacity should not be used as an indicator of field service life.

Reporting Fluid Cleanliness
The changes discussed in the previous sections will not affect the actual cleanliness of fluids in the field. However, for those operators reporting data using particle counts, the changes in APC calibration will affect laboratory particle counts for system fluids and those obtained using portable particle counters calibrated to the new standards (see Table 4).

Table 4 Typical Effect of New Calibration on Particle Counts
Particle Size, µm (old count) µm(c) (new count)	Old Count (ACFTD) (particles/mL)	New Count (NIST) (particles/mL)
2	4,170	24,900
5	1,870	3,400
15	179	105
25	40	14

Those operators reporting data using the ISO cleanliness codes will notice less effect. The adoption of a cleanliness code with 3 digits should not have an appreciable impact, as 3-digit codes have been used throughout the industry for a number of years. In addition, the change from the 5 µm and 15 µm sizes to 6 µm(c) and 14 µm(c) will not show an appreciable change in fluid contamination levels. The primary change will come from the adoption of the 4 µm(c) size. This is a new addition to the ISO standard, although a third digit at 2 µm using ACFTD has been widely used throughout industry. Since the new 4 µm(c) size equates to about 1 µm using ACFTD, particle counts on fluid samples will show a typical increase of one to two levels for this first digit of the code because there are typically more particles in the fluid at smaller particle sizes.

The change in ISO cleanliness code is illustrated in the following example:

Old 2-digit ISO Code
14 / 12
5 µm / 15 µm

Old 3-digit ISO Code
16 / 14 / 12
2 µm / 5 µm / 15 µm

New 3-digit ISO Code
17 / 14 / 12
4 µm(c) / 6 µm(c) / 14 µm(c)

Remember: regardless of the calibration method or ISO cleanliness code version used, the fluid is no dirtier or cleaner than before.

A replacement dust for ACFTD has been chosen because ACFTD is no longer being manufactured. To gain better resolution, accuracy, repeatability, and reproducibility, four new or revised ISO standards are being adopted. These changes will impact automatic particle counter calibration, particle size definition, and laboratory reporting of filter performance – both in particle removal efficiency (fine filters will appear coarser and coarse filters finer) and dirt holding capacity (capacity will likely increase). The changes will also impact laboratory reporting on system fluid cleanliness (typically a higher contamination level at smaller particle sizes). Although this will undoubtedly cause confusion, it should be remembered that this impact is merely an artifact of the testing. Actual filter performance and field fluid contamination levels will remain the same as before.