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2.1 THE ZIRCONIA SENSOR
The transmitter input is provided for a solid electrolyte oxygen probe, which
contains a zirconia element and thermocouple. The probe is designed to be inserted into
a boiler or furnace exit gas flue or similar process. A 1234 sensor is designed to be
installed outside of the flue or process. Sampling lines and filters are not required for in-
situ probes but they are required for 1234 sensors. When a sampling line is required, the
sample flows to the sensor under process pressure in most applications. In applications
where the process pressure is negative or neutral, a suction pump will be required. A
reference air pump is provided in the 9060 oxygen Analyser. The internal construction of a
probe or sensor is shown as follows.
The heater control in the 9060 Analyser consists of a time proportioning
temperature controller and solid state relay so that the thermocouple junction is controlled
to over 700°C (1300°F). Probes operating in a combustion environment above 650°C
(1200°F) do not require a heater. When exposed to different oxygen partial pressures at
the outside and inside of the sensor, an EMF (E) is developed which obeys the Nernst
equation:
RT
4F log e ⎝ ⎜
E (millivolts) =
Where T is the temperature (K) at the disc (>650°C (1200°F)), R is the gas constant, F is
the Faraday constant and (PO 2 ) INSIDE and (PO 2 ) OUTSIDE are the oxygen partial
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DESCRIPTION
Schematic View of a Zirconia Sensor Assembly
⎛
(PO 2 ) INSIDE
(PO 2 ) OUTSIDE
9060-Zirconia Analyser
⎞
⎟
⎠
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