Emerson 7003M - Manual (Page 14)

Operator Manual
748223-K
June 2002
1-2 Description and Specifications Rosemount Analytical Inc. A Division of Emerson Process Management
Model 7003M
1-4 CONDITIONS AFFECTING MEASUREMENT
Oxygen measurement is affected by the
following:
• Composition of the sampled gas
• Sample and calibration gas pressures
• Environment of sensor, cable and
analyzer
Each must be considered when calibrating
and operating the analyzer to obtain accurate
measurements.
a. Gas Composition
Any substance in the sample that
significantly interferes or "poisons" the
sensor oxygen reading should be
removed by a chemical and/or
mechanical sample handling system (see
Section 5-2 on page 5-1). If ambient air is
not used as the span gas, the
composition of calibration gases should
also be representative of the sample.
The sample and calibration gases must
meet certain specifications (see
Specifications in Preface) to ensure
accurate measurement. Physical
parameters that affect measurement
include:
• Pressure
• Humidity
• Temperature
• Gas composition
Also refer to Section 5-2 on page 5-1 for
additional information about how gas
conditions affect the oxygen
measurement.
b. Sample and Cal Gas Pressures
The sample and calibration gases may be
at different pressures as long as the
pressure of each remains constant. Any
variation in the pressure of either gas will
result in an incorrect output reading of the
same proportion.
Two methods of sample calibration are
recommended:
1. Calibrate at the sample pressure, or
2. Calibrated at a different pressure, and
enter the two pressure in the analyzer
(Section 4-2c on page 4-4)
Refer to Section 5-2 on page 5-1 for a
more detailed discussion of the
relationship between gas pressures and
apparent oxygen concentration.
c. Environmental Factors
If radio frequency interference (RFI)
normally occurs in the operating
environment, the sensor cable should be
electrically shielded during installation.