O2S-FR-T2-18C/B/A is a zirconia oxygen sensor with a sensitive element made of zirconia. It utilizes two zirconia disks, with a sealed chamber in between. One disk functions as a reversible oxygen pump, sequentially filling the sample gas and evacuating the small space. The other disk measures the oxygen partial pressure difference ratio, yielding the corresponding sensor voltage. When the zirconia disks operate as an oxygen pump, the required 700 °C temperature is generated by a heating element (the matching circuit board O2I-FLEX-092 provides heating and linear analog output functionality.).