Panametrics CGA 351, User Manual, Page: 10 / 119

Chapter 1.
4 CGA 351 User’s Manual
In the annular sample space, the gas is heated to the same 700°C at which the zirconium oxide oxygen sensor is
maintained. A mV signal is generated. This signal is proportional to the logarithm of the ratio of the oxygen
concentration in the sample gas to the oxygen concentration in a reference gas contacting the outer electrode. In
the display electronics, the logarithmic signal can be read directly in unlinearized form, or it can be converted to a
0/4–20 mA, 0–2 V, or Namur linearized signal before display.
Note: A temperature above 650°C is required for proper operation of the oxygen sensor. Also, ambient air is the
usual reference gas on the outside of the zirconium oxide sensor.
The sensor furnace also generates the convective flow that circulates the sample gas through the sample path.
Pushed from behind by the hot gases still in the furnace, the hot sample gas in the sensor furnace rises out of the
furnace and cools. The cooled sample gases then pass through the outlet port, where they are carried away by the
main gas flow.
A platinum coating on the end of the ceramic tube and the zirconium oxide oxygen sensor ensures that all
oxidation/reduction reactions in the sample gas reach equilibrium. It is therefore possible to measure such
parameters as excess oxygen in air/fuel mixtures and equilibrium oxygen in reducing atmospheres such as
hydrogen.