GE CGA 351, Руководство пользователя

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December 2004
1-4 General Information
Principles of Operation
A gas sample is drawn into the inlet port of the analyzer by gas
diffusion and a gentle convective flow. The sample gas then flows
through a ceramic inlet tube and into the annular space between the
inlet tube and the inside of the zirconia oxygen sensor. The flowmeter
on the outlet port and the needle valve on the inlet port are used to
adjust the sample flow rate to 1,000 ± 150 cc/min (2.1 ± 0.3 SCFH).
In the annular sample space, the gas is heated to the same 700°C at
which the zirconia 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. Using
the digital panel meter (DPM) 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 zirconia 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 zirconia
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.
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