How does an oxygen sensor work?

An oxygen sensor, often referred to as an O2 sensor, is a device that measures the concentration of oxygen in a gas mixture, typically in the context of automotive exhaust gases or other industrial applications. It plays a crucial role in ensuring efficient combustion, reducing emissions, and optimizing performance. There are different types of oxygen sensors, but the most common type used in automotive applications is the zirconia-based electrochemical sensor. Here's how it works:

  1. Zirconia-Based O2 Sensor:

    • Structure: The sensor consists of a ceramic body made of zirconia, which serves as an electrolyte. There are two electrodes on either side of the zirconia ceramic: a reference electrode and a sensing electrode.

    • Principle of Operation: Zirconia is an oxygen ion conductor. At high temperatures (typical operating temperature for zirconia sensors is around 600 to 800°C), zirconia becomes permeable to oxygen ions. The sensor operates based on the difference in oxygen concentration between the exhaust gas and the reference air.

    • Electrochemical Reaction: When a voltage is applied across the sensing and reference electrodes, oxygen ions from the exhaust gas move through the zirconia ceramic from the side exposed to the exhaust gas (hot side) to the reference air side (cool side). This movement of oxygen ions generates a voltage across the electrodes.

    • Voltage Output: The generated voltage is proportional to the difference in oxygen concentration between the exhaust gas and the reference air. A high concentration of oxygen in the exhaust gas results in a low voltage output, while a low concentration of oxygen leads to a high voltage output.

    • Control System Integration: The voltage output of the oxygen sensor is sent to the engine control unit (ECU) of the vehicle. The ECU uses this information to adjust the air-fuel mixture by controlling the amount of fuel injected into the engine. The goal is to maintain a stoichiometric air-fuel ratio (the ideal ratio for complete combustion) for optimal efficiency and reduced emissions.

  2. Wideband Oxygen Sensors:

    • Structure: Wideband oxygen sensors are more advanced than traditional zirconia-based sensors. They use a combination of a pump cell and a reference cell in a closed-loop configuration.

    • Principle of Operation: The pump cell actively pumps oxygen ions across a diffusion barrier, maintaining a constant oxygen partial pressure on one side. The reference cell is used as a reference point, and the difference in oxygen ion concentration between the two cells is measured.

    • Advantages: Wideband sensors offer higher accuracy and faster response times compared to traditional sensors. They can accurately measure both rich and lean air-fuel mixtures, making them suitable for modern engines with varying operating conditions.

Overall, oxygen sensors, whether zirconia-based or wideband, play a critical role in providing feedback to the engine control system to ensure optimal combustion efficiency, reduced emissions, and improved fuel economy.

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