What Happened to NAS 1. National Aerospace Standard NAS 1. Iso 4406 To Nas 1638 Conversion TablesIt converts the particle counts at various size ranges into convenient broad base classes. The particle numbers can range from single particles to many millions therefore, a power series is used to cover the number range with a convenient number of classes. NAS 1. 63. 8 was conceived in the 1. American National Aerospace Standard in 1. No coding system existed at the time for completed systems, so it was logical that it would be applied in this area. NAS 1. 63. 8 saw widespread acceptance in the 1. It led to the development of other coding systems, the most notable being the International Organization for Standardization ISO 4. If you obtain the latest issue of NAS 1. Inactive for new designs after May 3. AS4. 05. 9C and 6. This standard should not be used with Automatic Particle Counting. This is a result of recent changes to the ISO contamination standards for automatic particle counter APC calibration. A Comparison of NAS 1638 and ISO 4406 Cleanliness Codes. The NAS system was originally developed in 1964 to define contamination classes for contamination contained. UNDERSTANDING ISO CODES ISO 4406 Chart Code More than Up toincluding 24 80000 160000 23 40000 80000 22 20000 40000 21 10000 20000 20 5000 10000. Selecting Target ISO Cleanliness Codes When setting target ISO fluid cleanliness codes for hydraulic and lubrication systems it is important keep. ISO 4406. National Aerospace Standard NAS 1638 1 is a particulate contamination coding system used in the fluid power industry to simplify the commu nication of data from. ISO 44061999 codes hydraulic uid contamination. NAS 1638 table. PPM Conversion table. NAS 1. 63. 8 and resulted in its withdrawal for newly designed systems. NAS 1. 63. 8 Contamination Classes NAS 1. The concept of the code can be seen in Table 1 and it is based upon a fixed particle size distribution of the contaminant over a size range of 5 to 1. This distribution was based on particle contamination inside delivered aircraft hydraulic components in the 1. From this basic distribution, a series of 1. This principle is a feature of many of the classes that have developed since. The method of counting the particles referenced the optical microscope method defined in ARP 5. Another method of measuring the concentration of particles is included in the standard of gravimetric analysis, which is the weight per volume mg1. L with nine codes for this rarely applied technique. Since its inception in the 1. NAS 1. 63. 8 as the proportion of larger particles 1. These relative low numbers generated significant errors in data at the larger sizes 2. Trending these sizes was fraught with problems and inaccuracies. This, and the fact that all five of the size ranges were not needed, led to the development of ISO 4. This system was originally based upon the numbers of particles at 5 m and 1. ISO standards. Another criticism of NAS 1. For this reason, and to generally improve the standard, the SAE A6 Aerospace panel developed AS4. This subsequently became de facto ISO 1. Few aircraft companies adopted this standard, and very few industrial companies even knew it existed despite the fact that it overcame the deficiencies of NAS 1. Changes To APC Calibration Method The introduction of the APC during the 1. The accuracy, repeatability and speed of analysis allowed it to be used extensively for research into the effects of dirt on components and systems. Oklahoma State University, under the direction of Prof. Ernest C. Fitch, was the main force behind the introduction of ISO 4. APCs. This was based upon the size distribution of A. C. Fine Test Dust ACFTD, a silica based test dust used in the automotive and hydraulics industry. The size distribution was derived in 1. APC was set up to record identical numbers of ACFTD particles as the microscope. A praiseworthy step because it should give identical results in theory. The notice of termination of the supply of ACFTD in 1. It also gave the overseeing ISO committee the opportunity to obtain traceability for the particle size distribution PSD of the calibration material. The lack of traceability was a problem in the 1. ISO 9. 00. 0 type quality systems. It was also embarrassing for laboratories involved with contamination testing which often had to explain why there was no traceability and control over the dust. ISO Medium Test Dust ISO MTD was the selected replacement and by the National Institute of Standards and Technology NIST, who also certified the PSD. The NIST used a Scanning Electron Microscope SEM with an Image Analysis software package to precisely identify the size and numbers of particles down to 1 m. As explained in Leonard Benchs article, How the New ISO particle Count Standard will Affect You, published in the May June 2. Practicing Oil Analysis magazine, the new size distribution differed from that in ISO 4. The most popular standard for Contamination Classes in the hydraulic systems is ISO 44061999 the standard NAS 1638. FILTRATION IN BRIEF ISO Code. The net result was that if the APC was set to the same size for example, 2 m, 5 m, etc., the APC with the new calibration would record more small particles than one calibrated to ISO 4. This is a complex issue and is fully described in ISO TRI6. Because this situation could cause an uproar within the industry when companies would have to change specifications, the ISO committee decided to take the road of least resistance and selected new size descriptors that would give the same particle counts while retaining integer sizes. The term m c is used to differentiate data obtained using the two methods. The only major difference in particle counts is likely to be at the 4 mc size, which effectively has no previous equivalent but as few organizations have cleanliness specification based upon the size, the change would be minimal. The Replacement For NAS 1. AS4. 05. 9, which was developed in 1. A Companion Booklet to be used with The Portable Fluid Analysis Kit. ISODIS 4406 CODE NAS 1638 CLASS SAE 749 CLASS 118 129 1310 149. Defining And Maintaining Fluid Cleanliness For Maximum Hydraulic. ISO, NAS and SAE. ISO 44 SAE 749 MINIMUM RECOMMENDED. Technical Paper Series. ISO has taken several steps in order to minimize confusion during the transition from old to new standards. D. The author considers AS4. Daemon Tools Lite Windows 7 64 Bit here. NAS 1. 63. 8 because it offers many benefits. The most significant changes are Uses ISO 1. APCs, leading to increased precision, and improved repeatability and reproducibility, Presents data in terms of cumulative counts X m Y m rather than interval mode X Y m this is how particle counters present the data, Introduces a cleaner class 0. Extends the size range to smaller sizes 4 mc for increased sensitivity, Allows flexibility in cleanliness specification, Gives information on how to apply it, Gives the background to the changes, and Gives guidance for sample bottle cleanliness and sampling. The basis of the code is seen in Table 3. Click here to see Table 3. Notice that the same particle numbers are used in AS4. NAS 1. 63. 8 to verify this try subtracting the 1. NAS 1. 63. 8. In the transition period, the standard applies to both methods of calibration of APCs ISO 4. Many are specified for analyzing oil samples and presenting data to NAS 1. The reasoning behind this is not entirely clear, but thought to be to separate old and new APC data. APC users are recommended to switch to the new standards. In Table 3 it can be seen that the particle counts are defined by a number relating to the quantity of particles and a letter relating to the size. This concept gives AS4. NAS 1. 63. 8 because it is often the control of the cleanliness level that specifiers require rather than a fixed distribution for example, they can specify improved control over critical sizes or relax controls over those that are not. Equally, sizes that are not critical can be omitted. There are three reporting options Specifying at single sizes AS4. B which means that only the 5 m 6 mc is subject to a cleanliness specification. Specifying for specific sizes AS4. B 6. C 5. D 4. E 4. F, note that 1 m4 mc has no specification and tighter controls are required over the larger sizes. Specifying cleanliness over the complete size range AS 4. A through F. Now What Is NAS 1. Well. not quite. NAS 1. However, users are encouraged to change to AS4. Current specifications, like those based on a single number, for instance NAS 1. Class 6, can be swapped to AS4.