Atonometrics offers many products and system configurations for measuring soiling losses on PV arrays, including systems using the RDE300i PV module measurement unit, Mars soiling sensors, RC22 PV reference cells, and automatic washing of reference cells. Configuring the correct system for your needs involves choosing from a number of options, including measurement devices and cables.
For a detailed guide to your options and accessory configurations, see document 880100 "Soiling Products Ordering Guide", available at the link at the bottom of this page.