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XZR250 User’s Manual
20
97528
Issue 5, May 2019
OPERATION
5 OPERATIONAL CONSIDERATIONS
5.1 Environments
The application in which the zirconium oxide oxygen sensor is operating influences the
life of the sensor. To ensure the sensor does not fail prematurely, the following should
be noted:
5.1.1 Operating in Aggressive and Humid Environments
When operating the sensor in warm, humid environments it is important the sensor
remains at a higher temperature than its surroundings, especially if there are corrosive
components in the measurement gas. During operation this is not an issue as the heater
operates at 700°C, however this means when the sensor or process is being powered
down the sensor heater must be the last thing to be turned off after the temperature of
the surroundings have suitably cooled.
Failure to adhere to these rules will result in condensation forming on the sensing
element. When the sensor is re-powered the water will evaporate, leaving behind
corrosive salts which very quickly destroy the sensing element.
5.1.2 Protecting from Excessive Moisture
In environments where excessive moisture is likely the sensor should be protected from
water reaching the very hot sensor cap as this can cause massive temperature shocks
to the cell and heater. For this reason, the probe must be installed in a horizontal or
downward angled position to prevent moisture from filling the gas sampling tubes and
coming into contact with the sensor. This is also true when the sensor head is removed
for inspection or maintenance.
5.1.3 Using the Sensor with Silicones
Zirconium oxide oxygen sensors are damaged by the presence of silicone in the
measurement gas. Vapors (organic silicone compounds) of RTV rubbers and sealants
are the main culprits and are widely used in many applications. These materials are
often made of cheaper silicones, that when heated still outgas silicone vapors into the
surrounding atmosphere. When these vapors reach the sensor, the organic part of the
compound will be burned at hot sensor parts, leaving behind a very fine divided Silicon
Dioxide (SiO
2
). This SiO
2
completely blocks the pores and active parts of the electrodes.
If RTV rubbers are used we advise using high quality, well cured materials. Guidance
can be provided on request.
5.2 Cross Sensitivity
Gases or chemicals that have an influence on the life of the sensor or on the measuring
results are listed in the following sub-sections.