Ultraviolet intensity sensor for Trojan UVMax D, E and F-PLUS systems. A UV intensity sensor reads the germicidal output actually reaching the water at 254 nm, which is the only direct evidence that the reactor is still delivering its validated dose. Lamp output falls with age and quartz sleeves foul, and both show up here before they show up anywhere else, so the controller alarms on this reading rather than on lamp hours alone. One sensor covers all three models in the PLUS range. Contact us if you are unsure whether this part fits your UV system.