Teledyne 335 - Analog control room monitor for personnel safety - Manual (Page 7)

2-1 TELEDYNE ANALYTICAL INSTRUMENTS
Oxygen Alarm Monitor Operational Theory 2
Operational Theory
2.1 Method of Analysis
The analysis is specific for oxygen, i.e., the measuring cell will not
generate an output current unless oxygen is present in the sample gas.
Thus, the instrument has an absolute zero and no zero gas is required to
operate the analyzer.
The measuring cell has the ability to respond accurately to the pres-
ence of oxygen irrespective of flowrate. TAI recommends using ambient
air as a span gas or, if that is not possible, using a known calibration gas of
about 80% of the range of interest value.
The measuring cell (U.S. Patent #3,429,796) is a solid-state mainten-
ance-free structure that carries a TAI guarantee for performance and usable
life. The cell consumes oxygen from the gas surrounding it and generates
a proportional microampere current. The low level signal is then amplified
by a solid-state operational amplifier. The resulting DC signal is suitable
for driving a high impedance recording device, a temperature compen-
sation circuit for the cell and an integral 0-100µA meter. The output signal
is linear over the specified ranges of analysis.
2.2 Micro-Fuel Cell Sensor
2.2.1 Principles of Operation
The oxygen sensor used in the Model 335 is a Micro-Fuel Cell (MFC)
designed and manufactured by TAI. It is a sealed plastic disposable elec-
trochemical transducer.
The active components of the MFC are a cathode, an anode and the
15% aqueous Potassium Hydroxide (KOH) electrolyte in which they are
immersed. The cell converts the energy from a chemical reaction into an
electrical potential that can produce a current in an external electrical
circuit. Its action is similar to that of a battery.