Our oxygen sensors are
galvanic cell sensors that have a lead
anode, a gold cathode, an acid electrolyte and a Teflon
membrane. The current flow between the electrodes is
proportional to the oxygen concentration being measured. An
internal bridge resistor is used to provide a mV output.
Being a galvanic cell type sensor, a small amount of oxygen
is consumed in the reaction in order to produce the current
flow and subsequent mV output. The oxygen consumption was
measured to be 2.2 µmol O2 per day when the O2 concentration
was 20.95% (3240 mmol) at 23 C.
The mV output responds to the partial pressure of oxygen in
air. The standard units for partial pressure are kPa.
However, gas sensors that respond to partial pressure are
typically calibrated to read out in mole fraction of the gas
in air, which has units of moles of oxygen per mole of air.
These units can be directly converted to % O2 in air or ppm
O2 in air.
Gas sensors read out in percent because this value does not
change with temperature or pressure. The concentration of
oxygen in our atmosphere is 20.95%, and this value, to 4
significant digits, has not changed for decades. This means
that we are surrounded by calibration gas for this sensor
(provided you are not breathing on the sensor when it is
being calibrated. Our exhaled breath is about 17% oxygen).
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ABOUT
APOGEE OXYGEN SENSORS
