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Methods of Measuring O 2

Methods of Measuring O 2. 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

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Methods of Measuring O 2

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  1. Methods of Measuring O2

  2. Methods of Measuring O2 • 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 ZrO2 solid fuel cell has become the industry standard for measuring combustion O2.

  3. Product Overview - In Situ O2 Probe

  4. Zirconium Oxide Sensing CellPermits In Situ Probe Design

  5. ZrO2 Sensing Cell • Steel Cell Holder • Disc-type ZrO2 Cell

  6. Theory of Operation - ZrO2 Fuel Cell Cell Flange Heater Diffusion element ZrO2 cell T/C Cell contact pad Cell lead wire 1550F Heater Flue gases

  7. How Does it work?Theory of Operation - Normal ZrO2 O2 Cell Heater 736 C (1357 F) Signal varies with the O2 partial pressure difference between the reference and flue gas sides of the cell 20.95% O2 Cell tube O2 O2-- -53MV Thermocouple Flue Gas 2% O2 +53MV ++ cell contact pad and lead wire (positive charge) ZrO2 disc Nernst Equation EMF = KT log10 (P1/P2) + C porous platinum electrodes

  8. Theory of OperationLike 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.

  9. ZrO2 “Fuel Cell” Technology is Clearly Favored for Flue Gas Analysis • Output is inverse and logarithmic. • Signal increases at the low O2 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 O2 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.

  10. Output is Inverse and Logarithmic

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