Glossary
Wet Measurement
Gives the true concentration in the gas stream as opposed to "dry" measurement which drops out most or all of the condensable components thus, altering the sampled composition. Wet measurement is inherent in in-situ sensing while while some degree of "drying" occurs in most all extraction configurations.
In-Situ
The measurement is taken "in place" as opposed to moving the sample to the sensor which generally alters the sample's natural state.
Excess Oxygen
is the oxygen remaining in the flue gas after all the fuel has been consumed in the combustion reaction. Thus, it is the residual that remains in excess to the perfect ratio of fuel and air (oxygen).
Stoichiometric
is used to describe the conditions when the theoretical amount of air (oxygen) and fuel are present to have complete combustion, leaving no residual fuel or oxygen in the flue gas.
Inferred or Empirical Measurement
of process conditions, as in combustion off-gases, is normally used when a direct reading of the constituent of interest is difficult or considered impractical. The technique can be successfully used in many applications. However, the quality of the measurement is easily compromised by the constantly changing nature (transient conditions) of real-time operation. This is primarily due to the analyzer being calibrated to specific steady state conditions.
Oxygen Depletion
is used to describe an atmosphere where the free oxygen (O2) is less than the reference or source. In combustion, the reference or source is typically air which is 20.95% O2 (as free oxygen molecules). During the combustion reaction, O2 is being combined with carbon (C) and/or hydrogen (H2) thus "depleting" the free O2 molecules. Reducing or fuel-rich atmospheres have free O2 molecules present in proportion to the magnitude of the reducing state of the combustion gases. Zirconium Oxide is sensitive to this "depleted" amount of O2 molecules down to the sextillionth (-21 power). More . . .
ODel
is a proprietary scale developed by Zirtek as a Unit of Measure of the magnitude of the reducing state of the combustion atmosphere. It is based on the direct measurement of the depleted oxygen using the Nernst equation to reconcile the millivolt signal generated by the zirconium oxide and the sensor temperature into engineering units. The scale spans both PPM and % levels of combustibles as shown in the accompanying graphic.