Subject to change · V 2.02.20 · EN
Page 56
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17.1.3 Cleanliness classes according to NAS 1638
Function only available from software version 2.00.15.
The NAS 1638 is divided into different size classes. 5-15µm, 15-25µm, 25-50µm, …
The particles are counted differentially and not accumulated as in ISO 4406.
The OPCom can only measure the sizes 4, 6, 14, 21 µm. Therefore, the cleanliness class is calculated only based on
NAS 1638.
A direct recalculation of NAS to ISO is not possible.
The concentrations are calculated according to the following scheme:
› Concentration NAS(5-15µm) = Concentration ISO6µm – Concentration ISO14µm
› Concentration NAS(15-25µm) = Concentration ISO14µm – Concentration ISO21µm
› Concentration NAS(25-50µm) = Concentration ISO21µm
The according NAS ordinal number is determined with the following table. The largest of the three determined NAS ordinal numbers
constitutes the result.
Concentration in particles / ml NAS 1638
Display OPCom
5-15µm 15-25µm 25-50µm
1.25 0.22 0.01 00
2.50 0.44 0.08 0
5.00 0.89 0.16 1
10.00 1.78 0.32 2
20.00 3.56 0.63 3
40.00 7.12 1.26 4
80.00 14.25 2.53 5
160.00 28.50 5.06 6
320.00 57.00 10.12 7
640.00 114.00 20.25 8
1,280.00 228.00 40.50 9
2,560.00 456.00 81.00 10
5,120.00 910.00 162.00 11
10,240.00 1,824.00 324.00 12
Even if there is no direct reference between ISO 4406 and NAS 1638, the following table may serve as an indication.
NAS ISO NAS ISO
3 - / 12 / 9 8 - / 17 / 14
4 - / 13 / 10 9 - / 18 / 15
5 - / 14 / 11 10 - / 19 / 16
6 - / 15 / 12 11 - / 20 / 17
7 - / 16 / 13
Table 38: Determination of cleanliness classes according to NAS 1638
Table 39: Comparison of ISO 4406 and NAS 1638 (approximately)
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