Dissolved Oxygen Sensors

Dissolved oxygen is one of the most important parameters in water treatment, food & beverage, pharmaceutical, energy, and biotechnology processes. Endress+Hauser’s dissolved oxygen sensors help effectively control aeration, fermentation, and water quality, ensuring stable processes and energy savings.

With over 35 years of experience, Endress+Hauser offers a diverse portfolio of dissolved oxygen sensors suitable for all operating conditions — from pure water and wastewater to applications in hazardous environments or those requiring high hygienic standards.

Measuring principle of Dissolved oxygen sensors

1. Electrochemical method (Amperometric principle)

Dissolved oxygen sensors operate based on the electrochemical principle, consisting of a working electrode and a counter electrode surrounded by an electrolyte solution and protected by a semi-permeable membrane.

When a direct current (DC) voltage is applied between the two electrodes, oxygen molecules in the solution diffuse through the membrane and undergo a reduction reaction at the working electrode, generating a current proportional to the amount of oxygen present in the environment. The counter electrode serves to maintain the redox balance, ensuring stable operation of the system.

The measured current intensity is directly proportional to the partial pressure of oxygen, allowing the Liquiline transmitter to calculate and display the dissolved oxygen (DO) concentration in units of mg/L or ppm.

Advantages of the electrochemical method:

• • Proven technology.

  • High accuracy and long-term stability.

  • Suitable for a wide range of measurement ranges and environmental conditions.

Measuring principle of dissolved oxygen sensors based on the electrochemical method

2. Optical method (Fluorescence quenching principle)

Dissolved oxygen sensors based on the optical principle operate using fluorescence quenching. The sensor consists of an LED light source, a photodiode detector, and an oxygen-permeable membrane that interfaces with the measured environment.

This membrane contains marker molecules that, when illuminated by orange or green light from the LED, emit red fluorescent light. Dissolved oxygen molecules in the environment diffuse through the membrane and bind to the marker molecules, reducing both the intensity and duration of the fluorescence emission.

The photodiode detects these changes and converts them into an electrical signal. The intensity and lifetime of the fluorescence are proportional to the partial pressure of oxygen in the environment. The Liquiline transmitter then calculates and displays the dissolved oxygen (DO) value in units of mg/L, ppm, or % saturation.

In applications involving high temperatures or cleaning and sterilization cycles (CIP/SIP), optical sensors are equipped with a reference LED to compensate for the aging of the measuring LED, ensuring long-term accuracy and reliability.

Advantages of the optical method:

• • Completely optical measurement system, no need for electrolyte solution.

  • Fast response time and high reliability.

  • Low maintenance requirements, no need for periodic electrode membrane replacement.

  • Stable signal and extended device lifespan in demanding applications.

Measuring principle of the dissolved oxygen sensor using the optical method

Advantages of Endress+Hauser Dissolved oxygen sensors:

✅ Suitable for all applications and process conditions.

✅ Flexible choice of measuring technology (electrochemical or optical).

✅ Compact design, easy to install in pipes, tanks, or CIP/SIP piping systems.

✅ Integrated with Memosens – Liquiline technology, featuring a user-friendly interface for easy operation and maintenance.

✅ The products meet high-quality standards, undergoing rigorous testing and certification before delivery.

Applications of Endress+Hauser Dissolved oxygen sensors

Endress+Hauser dissolved oxygen sensors are widely used across various industries:

• • Water & wastewater treatment: Control aeration in activated sludge tanks and monitor residual oxygen.

  • Food & beverage: Control fermentation processes to ensure stable flavor and color.

  • Pharmaceuticals & biotechnology: Ensure optimal oxygen conditions for cell culture.

  • Energy: Monitor oxygen levels in boiler feedwater to prevent pipeline corrosion.

Accurate measurement and monitoring of dissolved oxygen are core factors for process control and product quality. Depending on the application and operating conditions, users can choose between optical methods (low maintenance, long-term stability) and electrochemical methods (fast response, suitable for low DO). With a diverse range of sensors and advanced Memosens technology, Endress+Hauser offers efficient, reliable, and cost-effective DO measurement solutions for all industries.

Portfolio of Endress+Hauser Dissolved oxygen sensors

Installation of Dissolved oxygen sensors