I have used Hiac particle counters on some of the active filtration systems we make, when the customers' request them. The one I like is the PM-4000. It can be purchased in several forms depending on the type of application, that is, where the driving pressure is coming from. One variation has the sensing head located at the collection point and the display unit mounted remotely. The connection between them is a piece of plastic fiber optic cable. It is a very simple system to connect and it is very reliable. If you need help working with the Hiac unit or the Parker I-count system, email or call me.
Here is a link to Hiac:
http://www.hachultra.com/index.php/hachultra/hach_ultra_brands/hiac