Instruction Manual

748213-S April 2002

Model 755R

RANGE % OXYGEN

RECOMMENDED ZERO

RECOMMENDED SPAN

STANDARD GAS

STANDARD GAS

 

0 to 1

Nitrogen

0.9% O2, balance N2

0 to 2.5

Nitrogen

2.3% O2, balance N2

0 to 5

Nitrogen

4.5% O2, balance N2

0 to 10

Nitrogen

9% O2, balance N2

0 to 25

Nitrogen

Air (20.93% O2)

0 to 50

Nitrogen

45% O2, balance N2

0 to 100

Nitrogen

100% O2

Table 3-1. Calibration Range for Various Zero-Based Operating Ranges

a.Oxygen Equivalent Value of Gases

For computation of background correc- tions, the analyzer response to each component of the sample must be shown. Table 3-2 (page 3-6) lists the percentage oxygen equivalent values for many com- mon gases.

The percentage oxygen equivalent of a gas is the instrument response to the given gas compared to the response to oxygen, assuming that both gases are supplied at the same pressure .

Example: Zero Based Range

In equation form:

 

%O2 Equivalent of Gas =

 

Analyzer Response to Gas

X 100%

Analyzer Response to O2

 

To select a random example from Table 3-2, if analyzer response to oxygen is +100%, the response to xenon would be -1.34%.

The oxygen equivalent of a gas mixture is the sum of the contribution of the individual gas components.

At lower range limit, i.e., 0% oxygen, composition of sample is 80% CO2, 20% N2.

From Table 3-1 (page 3-4), the % oxygen equivalents are CO2. -0.623 and N2, -0.358%.

% oxygen equivalent of mixture =

0.8x (-0.623) + 0.2 x (-0.358) = (-0.4984) + (-0.0716) = -0.570% Oxygen

b.Computing Adjusted Settings for Zero and Span Controls

During instrument calibration, adjusted values may be required in setting the ZERO and SPAN controls to correct for the magnetic susceptibility of the background gas.

The quantities are defined as follows:

BGGst = Oxygen equivalent of background gas in standard gas (see Table 3-2, page 3-6)

BGGs = Oxygen equivalent of background gas sample (see Table 3-2, page 3-6)

OP = operating pressure. Unless special pressure corrections are to be made, the zero stan- dard, span standard and sample gases must all be admitted at the same pressure.

3-4 Operation

Rosemount Analytical Inc. A Division of Emerson Process Management