© 2010 SST Sensing Ltd 10
DS0074 Rev 7
O2I
-
Flex
Oxygen Interface
SENSOR OPERATING TIPS
To get the best performance from the O2I-Flex interface it is important that the attached oxygen sensor is installed and
maintained in the correct manner. The following two pages outline some useful sensor operating tips and a list of gases
and materials that must be avoided to ensure a long sensor life.
Operating the Sensor in Aggressive Humid Environments:
When operating the sensor in warm, humid environments it is important the sensor remains at a higher temperature
than it’s surroundings, especially if there are corrosive components in the measurement gas. During operation this is not
a problem due the 700
°
C generated by the heater, but this means when the sensor or application 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. Ideally the sensor should be left powered at all times in very humid environments.
Failure to adhere to the above will result in condensation forming on the heater and sensing cell as these will be the first
components to cool due to their connections to the outside world. When the sensor is re-powered the condensation will
evaporate, leaving behind corrosive salts which very quickly destroy the heater and cell as illustrated below. Note how
the sensor’s external metalwork looks completely normal.
Protecting from Water Droplets:
In environments where falling water droplets are likely the sensor should be protected from water falling directly onto the
very hot sensor cap as this can cause massive temperature shocks to the cell and heater. Popular methods include a
hood over the sensor cap or for the sensor to be mounted in a larger diameter cylinder.
At a very minimum the sensor cap should be angled downwards in the application as this will deflect any falling moisture
and prevent the sensor cap from filling with water.
Using the Sensor With Silicones:
SST Sensing’s oxygen sensors, like all other Zirconium Dioxide sensors, are damaged by the presence of silicone in the
measurement gas. Vapours (organic silicone compounds) of RTV rubbers and sealants are the main culprits and are
widely used in many applications. These materials which are often applied as a liquid or gel still outgas silicone vapours
into the surrounding atmosphere even after they have cured. When these vapours 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 silicone cannot be avoided in the application we advise using high quality, high temperature cured materials which do
not outgas when subsequently heated. SST can provide guidance if there is concern about use of silicone within the
application.
When installing the sensor do not use any lubricants or grease which may contain silicone.
In addition to silicones other gases which may interfere will the sensor are listed overleaf.
