The UV intensity sensor reports the UV-C actually reaching the water. That is the measured variable a disinfection duty is controlled and alarmed on — not lamp hours and not lamp current — so a sensor that has drifted or fouled will under-report a healthy plant or, more seriously, over-report a failing one. This is the UCI sensor, supplied complete with its 20 × 2.5 mm sealing O-ring — the seal is included because it is renewed whenever the sensor is disturbed, and a leak at this position wets and ends the sensor. Wedeco designates the sensor type UCI; the designation is carried here exactly as the manufacturer states it. Wedeco was founded in Herford, Germany in 1976 and is now a Xylem brand.