Micro-Fuel Cell Sensor; Sample System - Teledyne 3160 Operating Instructions Manual

2.1.1 Micro-Fuel Cell Sensor

The Micro-Fuel Cell is a sealed plastic disposable oxygen transducer that mea-
sures 1¼ inches in diameter and is ¾ inch thick. Inside of the cell are a cathode and
anode immersed in 15% aqueous KOH electrolyte. At one end of the sensor is a
Teflon diffusion membrane; the other end is sealed with a polyethylene membrane. At
the rear of the cell is a contact plate consisting of two concentric foils. The foils mate
with spring-loaded contacts in the sensor block assembly and provide the electrical
connection to the rest of the analyzer.
The sensing cathode, located beneath the diffusion membrane, has a surface area
2
of 2.48 cm . The sample gas enters the sensor block through an inlet tube between the
cathode and the sensor block cap, diffuses through the Teflon membrane, and any
oxygen in the sample gas is reduced on the surface of the cathode by the following
mechanism:
O + 2H O + 4e
2 2
When the oxygen is reduced at the cathode, lead is simultaneously oxidized at the
anode by the following mechanism.
2Pb 2Pb
The electrons released at the surface of the anode flow to the cathode surface via
an external circuit. This current is proportional to the amount of oxygen. It is mea-
sured and used to determine the oxygen concentration in the gas mixture.
The overall reaction for the fuel cell is:
2Pb + O
2
The output of the fuel cell is limited by the amount of oxygen in the cell at any
one time, and the amount of stored anode material. In the absence of oxygen, there is
no current generated.

2.1.2 Sample System

The sample system delivers gases to the Micro-Fuel Cell sensor from the ana-
lyzer rear panel inlet. Depending on the mode of operation either a sample or zero gas
is delivered.
The Model 3160 sample system is designed and fabricated to ensure that the
oxygen concentration of the gas is not altered as it travels through the sample system.
The following list of sample system and analyzer features are among those
available, but the exact configuration depends on the standard options incorporated.
Paragraph 1.3 contains a list of the standard variations on the basic model.
– – – – – – – – – –
4OH
+2 – – – – –
+ 4e
2PbO
TELEDYNE ANALYTICAL INSTRUMENTS
Operational Theory 2 Operational Theory 2
Operational Theory 2 Operational Theory 2 Operational Theory 2
(cathode)
(anode)
2-3