Oxygen Measurement with Electrochemical Sensors

How does an electrochemical sensor work?

An electrochemical oxygen sensor consists of two electrodes in an electrolyte. Oxygen passes through a permeable membrane, reaches the working electrode and is reduced there. This reaction produces an electric current proportional to the amount of oxygen reaching the sensor. Concentration is calculated by measuring the current.

In liquid applications, the sensor is placed in a sample flow cell and measures dissolved oxygen (DO) in the water. In the gas phase, a small cell module measures the O₂ percentage in a gas mixture; sensors of this type can be offered as an option on multi-gas analyzers.

What the electrochemical sensor measures and where it is used

The method is used to measure oxygen in both liquid and gas:

• Dissolved oxygen in boiler feedwater, condensate and demineralized water lines (corrosion control)
• Aeration control at wastewater treatment plants
• O₂ measurement in flue gas and process gas applications
• Short-term oxygen tracking with portable instruments

Where the electrochemical sensor works well and where it struggles

Electrochemical sensors offer simple, small and economical measurement, with low power consumption and a fast response. Special probe designs are available for the low concentration range in trace-level dissolved oxygen applications.

Limitations: because the sensor contains an electrolyte and membrane, it is a consumable; it ages and must be renewed periodically. Calibration should be checked frequently. Changes in sample flow, temperature and pressure affect the result. Contamination or damage to the membrane compromises the response.

Choosing an instrument for the electrochemical sensor

When selecting, the measurement phase (liquid or gas), concentration range, sample flow and expected sensor life are assessed. Sensor and membrane replacement interval, maintenance kit stock and calibration frequency should be included in the operating plan. During commissioning, Tetra configures the flow cell, probe and calibration arrangement according to site conditions.

Tetra and electrochemical sensor analyzers

Tetra supplies, installs, calibrates and services electrochemical sensor analyzers in Türkiye. The product range includes the Thermo Orion 1816DO low-level dissolved oxygen analyzer (with an electrochemical probe and stainless steel flow cell) and the Thermo Scientific 60i multi-gas analyzer, which offers an oxygen sensor option. Paramagnetic analyzers are also provided for percent-level O₂ measurements that require the paramagnetic method.