Emerson 3000 manual System Configuration, Features

Instruction Bulletin

106-300NE Rev. 3.4 May 2000

World Class 3000

The equipment measures oxygen percent- age by reading the voltage developed across a heated electrochemical cell, which consists of a small yttria-stabilized, zirconia disc. Both sides of the disc are coated with porous metal electrodes. When operated at the proper temperature, the millivolt output voltage of the cell is given by the following Nernst equation:

EMF = KT log10(P1/P2) + C

Where:

1.P2 is the partial pressure of the oxygen in the measured gas on one side of the cell,

2.P1 is the partial pressure of the oxygen in the reference gas on the other side,

3.T is the absolute temperature,

4.C is the cell constant,

5.K is an arithmetic constant.

NOTE

For best results, use clean, dry, instrument air (20.95% oxygen) as a reference gas.

When the cell is at operating temperature and there are unequal oxygen concentra- tions across the cell, oxygen ions will travel from the high partial pressure of oxygen side to the low partial pressure side of the cell. The resulting logarithmic output voltage is approximately 50 mV per decade. Be- cause the magnitude of the output is pro- portional to the logarithm of the inverse of the sample of the oxygen partial pressure, the output signal increases as the oxygen concentration of the sample gas decreases. This characteristic enables the oxygen analyzer to provide exceptional sensitivity at low oxygen concentrations.

Oxygen analyzer equipment measures net oxygen concentration in the presence of all the products of combustion, including water vapor. Therefore, it may be considered an analysis on a "wet" basis. In comparison with older methods, such as the Orsat ap- paratus, which provides an analysis on a "dry" gas basis, the "wet" analysis will, in general, indicate a lower percentage of

oxygen. The difference will be proportional to the water content of the sampled gas stream.

c.System Configuration

The equipment discussed in this manual consists of two major components; the oxy- gen analyzer (probe), and the heater power supply.

Probes are available in five length options, giving the user the flexibility to use an in situ penetration appropriate to the size of the stack or duct. The options on length are 18 inches (457 mm), 3 feet (0.91 m), 6 feet (1.83 m), 9 feet (2.74 m), or 12 feet

(3.66 m).

The heater power supply (HPS) provides an interface to the electronics package and contains a transformer for supplying proper voltage to the 44 Vac and 115 Vac probe heaters. The enclosure has been designed to meet NEMA 4X (IP56) specifications for water tightness; an optional enclosure to meet Class 1, Division 1, Group B (IP56) explosion-proof is also available.

The oxygen analyzer is connected to the HPS and electronics package using seven wires housed within the connecting system cable.

d.Features

1.Unique and patented cell protection action that automatically protects sensor cell when analyzer detects reducing atmospheres.

2.Output voltage and sensitivity increase as the oxygen concentration decreases.

3.In situ, non-sampling analyzer.

4.Field replaceable cell.

5.Analyzer constructed of rugged 316 LSS for all wetted parts.

1-2 Description Rosemount Analytical Inc. A Division of Emerson Process Management