computer (PC) system [14]. When the oil sample flows through the
electromagnetic control system, wear debris is deposited on the
substrate of its concerned bright rectangular area (CBRA). A
camera then captures images on and in the CBRA for the PC system
to process off-line.
Generally, the important output parameter of OLVF is the index
of particle coverage area (IPCA) on CBRA. To obtain the binary
image of CBRA, gray color of the ferrographic image monitored by
the OLVF system was processed and sharpened intelligently by
choosing a suitable gray threshold [17]. On the binary image, the
black region represents the location of the deposited particles on
CBRA, whereas the white region indicates the absence of particle
deposition. The ratio of deposited particle coverage area to the
entire CBRA, which is denoted as the parameter of IPCA, can
represents the concentration of wear particles in a sampling oil.
Thereafter, on the basis of the measurements of the area covered
by various sizes of particles deposited with electromagnetic force,
the IPCA value was calculated on the basis of coverage area of
particles in the binary image, according to the expression defined
as follows [11]:
IPCA ¼ C
w h 100 ð2:1Þ
where C is an object pixel number of wear debris in the segmented
image of CBRA, w is the width of CBRA, and h is the height of CBRA.
As the IPCA value normally reflects the amount of deposited debris
on CBRA, its magnitude allows the identification of how the
amount of wear debris in various sampling oil changes. Hence, the
tendency of the IPCA values can be used for assessing the wear
condition of friction pairs with a simplified model relating the
parameter IPCA to wear rate of the friction pairs in running process
[18] (see Appendix A for detailed description).