Emerson 4000 manual Section Description and Specifications, System Overview

Oxymitter 4000

Instruction Manual

IB-106-340 Rev. 3.0 December 2003

SECTION 1

DESCRIPTION AND SPECIFICATIONS

1-1 COMPONENT CHECKLIST OF TYPICAL

SYSTEM (PACKAGE CONTENTS)

A typical Rosemount Oxymitter 4000 Oxygen Transmitter should contain the items shown in Figure 1-1.Record the part number, serial num- ber, and order number for each component of your system in the table located on the first page of this manual.

Also, use the product matrix in Table 1-1at the end of this section to compare your order num- ber against your unit. The first part of the matrix defines the model. The last part defines the various options and features of the Oxymitter 4000. Ensure the features and options specified by your order number are on or included with the unit.

1-2 SYSTEM OVERVIEW

a.Scope

This Instruction Bulletin is designed to supply details needed to install, start up, operate, and maintain the Oxymitter 4000. Signal conditioning electronics outputs a 4-

20 mA signal representing an O2 value and provides a membrane keypad or fully func- tional Local Operator Interface (optional) for setup, calibration, and diagnostics. This same information, plus additional details, can be accessed with the HART Model 275/375 handheld communicator or Asset Manage- ment Solutions (AMS) software.

b.System Description

The Oxymitter 4000 is designed to measure the net concentration of oxygen in an indus- trial process; i.e., the oxygen remaining after all fuels have been oxidized. The probe is permanently positioned within an exhaust duct or stack and performs its task without the use of a sampling system.

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 volt- age 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 air on the opposite side of the cell.

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, in- strument air (20.95% oxygen) as the reference air.

When the cell is at operating temperature and there are unequal oxygen concentra- tions across the cell, oxygen ions will travel from the high oxygen partial pressure side to the low oxygen partial pressure side of the cell. The resulting logarithmic output voltage is approximately 50 mV per decade. The output is proportional to the inverse logarithm of the oxygen concentration. Therefore, the output signal increases as the oxygen con- centration of the sample gas decreases. This characteristic enables the Oxymitter 4000 to provide exceptional sensitivity at low oxygen concentrations.

The Oxymitter 4000 measures net oxygen concentration in the presence of all the prod- ucts of combustion, including water vapor. Therefore, it may be considered an analysis on a “wet” basis. In comparison with older methods, such as the portable apparatus, which provides an analysis on a “dry” gas basis, the “wet” analysis will, in general, indi- cate a lower percentage of oxygen. The dif- ference will be proportional to the water content of the sampled gas stream.

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