Teledyne 3220 - Multi-channel oxygen monitor system - Manual (Page 24)

2 Operational Theory Model 3220
Teledyne Analytical Instruments 10
2.5 Micro-fuel Cell
The oxygen sensor used in the Model 3220 Oxygen Monitor is a
Micro-fuel Cell designed and manufactured by Teledyne Analytical
Instruments. It is a sealed plastic disposable electrochemical transducer.
The active components of the Micro-Fuel Cell are a cathode, an
anode, and the 15% aqueous KOH electrolyte in which they are
immersed. The cell converts the energy from a chemical reaction into an
electrical current in an external electrical circuit. Its action is similar to
that of a battery.
There is, however, an important difference in the operation of a
battery as compared to the Micro-Fuel Cell. In the battery, all reactants
are stored within the cell, whereas in the Micro-Fuel Cell, one of the
reactants (oxygen) comes from outside the device as a constituent of the
gas being monitored or sampled. The Micro-Fuel Cell is therefore a
hybrid between a battery and a true fuel cell. (All of the reactants are
stored externally in a true fuel cell.)
2.5.1 Anatomy of a Micro-Fuel Cell
The Micro-Fuel Cell is a cylinder only 1 1/4 inches in diameter and 1
inch thick. It is made of extremely inert plastic, which can be placed
confidently in practically any environment or sample stream. It is
effectively sealed, although one end is permeable to oxygen in the
monitoring or sampling environment. The other end of the cell is a contact
plate consisting of two concentric foil rings. The rings mate with spring-
loaded contacts in the sensor block assembly and provide the electrical
connection to the rest of the analyzer. Figure 2-1 illustrates the external
features.
Figure 2-4: Micro-fuel Cell