Instruction Manual

748213-S April 2002

3-8 ROUTINE OPERATION

After the calibration procedure of Section 3-4 (page 3-1), admit sample gas to the analyzer at the same pressure and the same flow rates used for the zero and span gases. The instrument will now continuously indicate the oxygen content of the sample gas.

3-9 EFFECT OF BAROMETRIC PRESSURE CHANGES ON INSTRUMENT READOUT

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

3-10 CALIBRATION FREQUENCY

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.

3-8 Operation

Rosemount Analytical Inc. A Division of Emerson Process Management