In reply to Ary Wibisono:
The measurement of Oxygen cannot be ignored. You need the O2 measurement to ensure you stay on the "good" side of the combustion curve , i.e. you want some amount of O2 to be present. Too much O2, you waste energy , to little and heater goes lean and have a rich mixture in the flu.
Typically coal fired power plant would control O2 at best 3.0 to 3.5% O2 . For a natural gas fired burner the control point on O2 can be taken down to 1.0-1.5% .
The COe sensor by definition is CO equivalent , it may respond to a certain degree to other components( refer to the vendors data sheet for this detail). Whether CO or COe , the measurement does have meaning when looking at poor combustion e.g. due to poor burner condition or poor mixing of the fuel air in the burner section of the process heater . ON large process heaters i.e. ethylene furnace for example . Three O2/ Coe analysers probes can be placed across the heater to profile burner performance. As a practical example you can have two of these analyser probes indicating minimal COe ( less than 50ppm ) and one indicating 1500ppm this infers an issues with a burner section in the furnace.