Abstract: A cleaning apparatus (10) for a radiation source assembly (35) in a fluid treatment system is described. The cleaning apparatus comprise cleaning chamber (20) and a second chamber (25, 30) independent of the cleaning chamber which defines a fluid (typically water) buffer layer to obviate or mitigate cleaning fluid from the cleaning chamber leaking into the fluid being treated. The fluid treatment system is particularly useful for us in clean water applications in which ultraviolet radiation is used to treat the water while having the advantages of in situ cleaning of the radiation source when it becomes fouled.

Abstract: There is disclosed an optical radiation sensor system. The system includes a sensor device and a cleaning device. The sensor device detects and responds to radiation from a radiation field and includes a surface that is movable with respect to the radiation field between a first position in which the surface is in the radiation field and a second position in which at least a portion of the surface is out of the radiation field. The cleaning device operates to remove fouling materials from at least a portion of the surface in the second position. The cleaning device may be a chemical cleaning device, a mechanical cleaning device or a combined chemical/mechanical device.