Employing solid-state Coulometric sensor delivery of direct O2 measurement optimized for sensitivity and safety, DF-500 ultra-trace oxygen analyzers are optimized for semiconductor, LED, and specialty gas applications that depend on exceptional ultra high purity (UHP) gas quality. Models DF-550E and DF-660E use Coulometric E-sensor to respectively measure down to 200 and 75 ppt. All models feature graphical menu interface as well as stable and firmware-optimized measurement capability.