Broadley Technologies 14 Manuál s instrukcemi stáhnout pdf (Strana 4)

Model 14 Oxygen Analyzer

Chapter1:

Introduction

1.1 Introduction

The Model 14 Dissolved Oxygen Analyzer is a single-

channel analyzer for the measurement of dissolved oxy-

gen in fermentation vessels and bioreactors, as well as

in municipal applications.

1.2 Principle of Operation

The measurement of dissolved oxygen is based on the

well-known Clark cell principle. An oxygen-permeable

membrane isolates the electrodes from the sample,

thus eliminating the need for sample conditioning.

Other reducible or oxidizable ions do not interfere,

because they cannot pass through the gas-permeable

membrane.

A constant voltage supply powers two electrodes, main-

taining each at a constant potential. A platinum work-

ing electrode (cathode) reduces the dissolved oxygen

to hydroxyl ions :

+ 2H

O + 4e

= 4OH

A large silver counter electrode (anode) provides the

oxidation reaction:

4Ag

+ 4Cl

= 4AgCl + 4e

The reduction of oxygen is the current limiting reac-

tion, thus making the cell current linearly proportional

to the dissolved oxygen concentration.

Electrochemical reactions and diffusion rates are tem-

perature-sensitive. The measuring cell, therefore, is

equipped with a temperature sensor which allows an

automatic temperature compensation.

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Broadley Technologies 14 Manuál s instrukcemi Strana 4