1.  Technical Field
This is related to systems for optically monitoring objects suspended in flowing fluid, and more particularly, to particle monitoring systems for monitoring the presence and size of debris in oil. 
2.  Related Technology
U.S. Pat.  No.  5,572,320 to Reintjes et al.  and U.S. Pat.  No.  6,049,381 disclose in-situ fluid samplers for identifying particles in a flowing fluid with an optical near-field imaging device.  In this system, a single laser illuminator is co-located with a single viewing port and a single electronic camera, the camera output being analyzed for particulate content of the fluid with a single computer processor.  U.S. Pat.  No.  6,049,381 to Reintjes et al.  discloses a real time suspended particle monitor that uses a pulsed collimated optical source to produce a series of images of particles in a flowing fluid.  U.S. Pat.  No.  7,921,739 to Fjerdingstad et al.  discloses a real-time optical monitoring system having an automatic on line bottle sampling operation. 
U.S. Pat.  No.  8,056,400 to Reintjes et al.  discloses a system for particle entrained fluid sampling in a high pressure or high flow rate fluid flow system. 
Such sampling systems can identify the number, shape, and size of particles in fluids.  Information about the metal or other particles present in lubricating fluid, for example, can provide valuable information about wear in the machinery or other system being lubricated.