Methods of Measuring O 2

 Orsat - Oxygen absorption into a liquid results in a change in volume. Chemical, only. Indication, only, No electrical output. Not suitable for continuous operation. Extractive  Chemical Cell - Used in portable analyzers. Inexpensive electrolytic cell is consumed by the measurement. Not suitable for continuous use in Flue Gas conditions. Extractive.  Paramagnetic - Oxygen is affected by magnetic fields. Suitable for continuous use in combustion service, but requires a clean, dry, extracted sample.  Zirconium Oxide - The ZrO 2 solid fuel cell has become the industry standard for measuring combustion O 2.

Product Overview - In Situ O 2 Probe

Zirconium Oxide Sensing Cell Permits In Situ Probe Design

ZrO2 Sensing Cell  Steel Cell Holder  Disc-type ZrO 2 Cell

Theory of Operation - ZrO 2 Fuel Cell F Flue gases Heater Cell Flange ZrO 2 cell Cell lead wire T/C Cell contact pad Diffusion element

How Does it work? Theory of Operation - Normal ZrO 2 O 2 Cell 20.95% O 2 Flue Gas 2% O 2 porous platinum electrodes cell contact pad and lead wire (positive charge) C (1357 F) Nernst Equation EMF = KT log10 (P1/P2) + C O2O2 O MV +53MV Heater Signal varies with the O 2 partial pressure difference between the reference and flue gas sides of the cell Cell tube ZrO 2 disc Thermocouple

Theory of Operation Like a Thermocouple, the Cell Generates It’s own MV Signal Theory of Operation Like a Thermocouple, the Cell Generates It’s own MV Signal Nernst Equation EMF = KT log10 (P1/P2) + C Where: P2 is the partial pressure of the oxygen in the measured gas on one side of the cell. P1 is the partial pressure of the oxygen in the reference gas on the other side. T is the absolute temperature. C is the cell constant. K is an arithmetic constant. For best results, use clean, dry, instrument air (20.95%) as a reference gas.

 Output is inverse and logarithmic. –Signal increases at the low O 2 levels commonly experienced in combustion processes. –Accuracy is stated as a “percent of reading,” as opposed to the conventional “percent of full scale.” Accuracy actually improves at lower O 2 levels.  Sensing cells operate well at elevated temperatures, permitting the “in situ” design. Response is fast.  Net/Wet Measurement  Sensing cells are robust. Cell life can easily exceed 3-5 years. Sulfur is the major cause of shortened cell life. ZrO 2 “Fuel Cell” Technology is Clearly Favored for Flue Gas Analysis

Output is Inverse and Logarithmic