Oil Analysis Lab - Mechanical and Optical Methods of Particle Analysis

PARTICLE ANALYSIS

Particle analysis is the second phase of oil analysis. This test evaluates the particulate from 5 - 100+ microns. A partical count is a totally separate test from a spectroanalysis. In many cases there are no correlation's between a particle count and the spectroanalysis. Particle Analysis is one of the most misunderstood procedures in oil analysis.

It is the purpose of this section to give a clear understanding of what type of particle tests are available, different formats of information and how to interpret the data.

Two of the most common methods of particle counting are:

AUTOMATED MECHANICAL METHOD

MANUAL OPTICAL METHOD

AUTOMATED MECHANICAL METHOD
The most common method is the automated mechanical method. This method employs a particle counting machine that uses some form of laser beam or light source to count the particulate.

* Easy to perform
* Requires limited technician training time
* Provides automatic graphing capabilities
* Fast

* Cannot count samples with high water content
* Some use high dilution factors that decrease accuracy
* No identification of particulate composition (What type of particle is it?)
* Photograph of contamination is not possible

MANUAL OPTICAL METHOD

This method is a method that follows Aerospace Recommended Practice ARP 598. In this method 50 - 100 mls of fluid is filtered through a .8 micron grided milipore patch. The particulate are then counted and identified using a high powered microscope.

* Can count samples with high water content
* Uses little or no dilution factor to increase accuracy
* Identifies the type of particulate
* Photographs of contamination are possible

* Requires highly trained staff
* No automated graphing system
* Time consuming

DATA REPORTING FORMATS

Three of the most common forms of data formats are:

* ISO - International Standard Organization
* NAS - National Aerospace Standards
* SAE - Society of Automated Engineers

These methods group the actual particulate levels into classes. The following is how each format groups particulate.

Particle size in Microns

*Particles per milliliter

SEE EXHIBIT C
FOR GREATER DETAIL

*Particle Size Range		Classes
(Microns)	0	0	1	2	3	4	5	6	7	8	9	10	11	12
5 to 15	125	250	500	1,000	2,000	4,000	8,000	16,000	32,000	64,000	128,000	256,000	512,000	1,024,000
15 to 25	22	44	89	178	356	712	1,425	2,580	5,700	11,400	22,800	45,600	91,200	184,400
25 to 50	4	8	16	32	63	126	253	506	1,012	2,024	4,050	8,100	16,200	32,400
50 to 100	1	2	3	6	11	22	45	90	180	360	720	1,440	2,880	5,760
Over 100	0	0	1	1	2	4	8	16	32	64	128	256	512	1,024
* Same as ARP 598

Size Range MICRONS	CONTAMINATION CLASS
Size Range MICRONS	0	1	2	3	4	5	6	7-10
2.5-5	P	E	N	D	I	N	G	P
5-10	2,700	4,600	9,700	24,000	32,000	87,000	128,000	E
10-25	670	1,340	2,680	5,360	10,700	21,400	42,000	N
25-50	93	210	380	780	1,510	3,130	6,500	D
50-100	16	28	56	110	225	430	1,000	I
Over 100	1	2	5	11	21	41	82	N
G

NOTE: The official recommendation of class tables by SAE is NAS 1638, not SAE 749D (Reference: SAE - ASC, Committee Meeting Minutes, Seattle 1971.)

OAL uses a combination of the laser and optical methods in our particle testing. The laser method is run to give particle size and distribution and then a filter patch is made and an optical correlation is performed to confirm or dispute the laser test. If the laser is confirmed, a photograh is taken and the results reported. If there is a conflict between the two methods, the tests are rerun. If there is still a difference the customer is called and the conditions are reviewed to get a better understanding of the situation.

It is important to understand that though there are correlation's between these two methods, the exact numbers should not be considered identical. Once a trend is developed using one type of test method, it is important not to cross methods, using one method one time and the other the next.

It is important that the method of testing, optical or laser, is known when comparing test results. If there is a big discrepancy between two test results, call the laboratory and see if they can help you find out why.