It is a question we are asked frequently: How to make oxygen sensors have a long life? There are many things we can do, but also, more importantly, there are many chemicals and gases we can try to avoid to prevent contaminating your oxygen sensor and having to replace it sooner rather than later.
Many oxygen sensors have cross sensitivity issues associated with them therefore it is important to know the root cause of the cross sensitivity in order to avoid environments that may pollute your zirconium dioxide oxygen sensor.
There are specific gases and chemicals that have a negative influence on SST’s Zirconium Dioxide Oxygen Sensors, particularly on the life of the sensors or on the performance results. Therefore, in this article we will explain how to make oxygen sensors have a long life and will detail what gases and chemicals to avoid when using SST’s Oxygen Sensors.
Small amounts of combustible gases will be burned at the hot Pt-electrode surfaces or AI₂O₃ filters of the sensor. In general, combustion will be stoichiometric as long as enough oxygen is available, the sensor will measure the residual oxygen pressure which leads to a measurement error. The sensor is note recommended for use in applications where there are large amounts of combustible gases present and an accurate oxygen measurement is required. Gases investigated by SST are as follows;
- H₂(Hydrogen) up to 2%; stoichiometric combustion
- CO (Carbon Monoxide) up to 2%; stoichiometric combustion
- CH₄ (Methane) up to 2.5%; stoichiometric combustion
- NH₃ (Ammonia) up to 1500ppm; stoichiometric combustion
Vapours from metals such as Zn (Zinc), Cd (Cadmium), Pb (Lead), Bi (Bismuth) will have an effect on the catalytic properties of the Pt-electrodes. Exposing the Zirconium Dioxide Oxygen Sensors to these metal vapours must be avoided.
Halogen and Sulphur Compounds
Small amounts (<100ppm) of Halogens and/or Sulphur compounds have no effect on the performance of the oxygen sensors. Higher amounts of these gases will, in time, cause readout problems or, especially in condensing environments , corrosion of sensor parts. Gases investigated by SST are listed below;
- Halogens, F₂ (Fluorine), Cl₂ (Chlorine)
- HCL (Hydrogen Chloride), HF (Hydrogen Fluoride)
- SO₂ (Sulphur Dioxide)
- H₂S (Hydrogen Sulphide)
- Freon gases
- CS₂ (Carbon Disulfide)
Long time exposure to reducing atmospheres may in time impair the catalytic effect of the Pt-electrodes and must be avoided. Reducing atmospheres are defined as an atmosphere with very little free oxygen and where combustible gases are present. In this type of atmosphere oxygen is consumed as the combustible gases are burned.
Many customers get SST’s Oxygen Sensors confused with Bosch Lambda oxygen sensors that are mainly used in automotive combustion applications. SST’s oxygen sensors were developed for boiler combustion control applications. Life tests have been performed in;
- A laboratory atmosphere
- Exhaust gases of natural gas fired boilers
- Exhaust gases of light oil
In summary, SST’s Zirconium Dioxide Oxygen Sensors have cross sensitivity when particular gases, substances and chemicals are present within the atmosphere. In order to get the maximum performance and prolonged lifetime from the zirconium dioxide oxygen sensors, take into consideration all of the information covered in this article.
Please note, these are all the gases, chemicals and substances SST have performed tests in, if the gas that is present within your application environment is not on the list above, we would recommend testing the sensor for a period of time to ensure it works to its maximum potential.