AST Model SRX-CA60-RTS % Oxygen Sensor, a galvanic type micro fuel cell, replaces AII Model GPR-11-60-RTS industrial % oxygen sensor used in GPR-20, GPR-2000, GPR-25, GPR-2500, GPR-25XP and GPR-28. SRX-CA-60RTS has 60 months life in air yet offers a fast response. Sensor is designed, developed and manufactured in the USA.