Table of Contents
Advertisement
For measuring oxygen in non-combustibles gases, the calibration of an
analyzer is obtained from the formula:
E = A * T * Log
Where A is a constant, T is the cell temperature on an absolute scale (°C +
273) and O
Unk% is the unknown oxygen concentration of the gas to be
2
analyzed, and which is calculated by the analyzer.
Because of the high operating temperature of the cell, combustible
gases that are present may burn. When this occurs, the cell will gener-
ate a higher than expected millivolts and cause the display to indicate
NOTE
less oxygen than is actually in the gas.
Hydrocarbons
When hydrocarbons are present in the gas sample, a combustion process
occurs when this gas sample is exposed to the high temperature of the
zirconia cell. An indication that hydrocarbons may be present in the gas
sample is that the oxygen reading will be lower than expected. For ex-
ample, if a calibration gas cylinder has an oxygen value of 20 ppm and 5
ppm of hydrogen (balance nitrogen), the oxygen analyzer will read 17.5
ppm of oxygen. The reduction of oxygen is due to the combustion process
where 5 ppm of hydrogen will combine with 2.5 ppm of oxygen to form
water. Thus, the oxygen analyzer will read 17.5 ppm rather than the actual
20 ppm oxygen. Note that the amount of oxygen reduction is dependent
on the type of hydrocarbons present in the sample gas.
AT = 48.0 at 695°C
20.9%
O
Unk%
AT = 54.4 at 824°C
2
|
Overview
1-3
Advertisement
Table of Contents
