SRZ-MA333 PPM Oxygen Sensor – Replacement to Analytical Industries Model XLT-12-333 PPM oxygen sensor. Its proprietary electrolyte formulation offers excellent compatibility with sample gas containing acid gases such as CO2 and trace levels of H2S and SO2. All sensors are gas tested for output, stability and recovery from air to low PPM levels before shipment. Sensor is designed, developed and manufactured in the USA.