
Instruction Manual
After the calibration procedure of Section
If the analyzer exhaust port is vented through a suitable absolute backpressure regulator, barometric pressure changes do not affect the percent oxygen readout. However, if the analyzer exhaust port is vented directly to the at- mosphere, any change in barometric pressure after instrument standardization will result in a directly proportional change in the indicated percentage of oxygen. This effect may be compensated in various ways. If desired, correction may be made by the following equa- tion:
True % Oxygen = (Pst/Pan)(Indicated % Oxy- gen)
Where:
Pst = Operating pressure during standardization
Pan = Operating pressure sample analysis
Example: U.S. Units
Pst = 760 mm Hg Pan = 740 mm Hg Indicated % O2
True % O2 = (760/740)(40%) = 41.1% O2
Example: S.I. Units
Pst = 101 kPa
Pan = 98.2 kPa
Indicated % O2 = 40%
True % O2 = (101/98.2)(40%) = 41.1%
O2
Model 755R
The appropriate calibration interval will depend on the accuracy required in the particular application, and is best determined by keeping a calibration log. If the analyzer exhaust port is vented directly to the atmos- phere, the greatest source of error is normally the variation in barometric pressure. If de- sired, effects of barometric pressure variation can be minimized by calibrating immediately before taking readings, for example, at the beginning of each shift.
Rosemount Analytical Inc. A Division of Emerson Process Management |