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Teledyne Analytical Instruments
2-2
2 Operational Theory Model OT-2 System
2.2 Micro-Fuel Cell Sensor
2.2.1 Principles of Operation
The oxygen sensor used in the Model OT-2 System is a Micro-
fuel Cell designed and manufactured by Analytical Instruments. It
is a sealed plastic disposable electrochemical transducer.
The key components of the Micro-Fuel Cell are a diffusion
barrier in the form of a thin membrane, a cathode, an anode, and
an electrolyte in which they are immersed.
Oxygen from the sample gas diffuses through the thin mem-
brane and is reduced at the cathode. As a result, an electrical
current is produced that is proportional to the concentration of
oxygen in the sample gas.
The choice of electrolyte, and hence the sensor type, de-
pends on the exact constituents of the sample gas. For sample
gases that contain a high concentration of CO
2
, for example, an
acid electrolyte will be the more optimal choice.
2.2.2 Anatomy of a Micro-Fuel Cell
The Micro-fuel Cell is approximately 1¼ inches in diameter.
The cell body is made of an inert plastic that is compatible with a
wide variety of sample streams. Oxygen from the sample gas
diffuses through a thin membrane located at one end of the
sensor. The other end of the cell is a contact plate consisting of
two concentric foil rings. The rings mate with spring-loaded con-
tacts in the sensor block assembly and provide the electrical
connection to the rest of the analyzer. Figure 2-1 illustrates the
external features.
Figure 2-1: Micro-Fuel Cell