Several commonly used oxygen sensors

What is an oxygen sensor? How does an oxygen sensor work? While there are many types of oxygen sensors, the way they work to measure oxygen can be classified into one of three ways:

chemical reaction that releases electrons in the presence of oxygen

Change in the intensity of light emitted by a fluorescent material when exposed to oxygen

Zirconia heated at high temperatures has the ability to carry oxygen ions

Each type of oxygen sensor has advantages and disadvantages. They are used in many applications and industries including automotive, health and medical, industrial, food and beverage packaging, pharmaceuticals, and more. Each sensor uses a different type of oxygen sensor that is suitable for the application or environment.

Note that most oxygen sensors are designed to measure oxygen concentrations from 0 to 25% by volume or oxygen in breathable air. However, there are also specialized oxygen sensors that can measure 100% oxygen.

Below are the specific types of oxygen sensing technology currently in use. Note that each is suitable for one or more specific applications.

1.Electrochemical oxygen sensor:
The electrochemical oxygen sensor is primarily used to measure the oxygen content in ambient air. These sensors rely on chemical reactions within the sensor to generate an electrical output that is proportional to the oxygen level. Some electrochemical sensors are self-powered, producing their own analog current, which makes them suitable for battery-powered applications such as underwater diving equipment, handheld personal safety devices, ventilators, respiratory sensors, and blood sugar sensors.

Electrochemical sensors are favored for their advantages such as lower power requirements, lower detection limits, and reduced susceptibility to interference from other gases. They are also generally more affordable compared to other types of sensors.

One challenge with electrochemical oxygen sensors is that their performance is influenced by temperature-dependent chemical processes. Temperature compensation is necessary to ensure accurate readings under varying environmental conditions.

Another limitation of electrochemical oxygen sensors is that the chemical reaction within the sensor deteriorates over time, typically between 1 and 3 years, depending on the sensor's design. Storing the sensor in an oxygen-free environment does not extend its lifespan. As the sensor ages, it requires frequent recalibration and becomes less accurate compared to newer sensors.

2.Fluorescent oxygen sensor:
Fluorescent oxygen sensors operate based on the principle of fluorescence quenching caused by oxygen. They utilize light sources, photodetectors, and light-emitting materials that respond to light. In many applications, fluorescent oxygen sensors are replacing electrochemical sensors.

The principle of fluorescence quenching by molecular oxygen has been known for a long time. When certain molecules or compounds are exposed to light, they fluoresce, emitting light energy. However, in the presence of oxygen molecules, the light energy is transferred to the oxygen molecules, resulting in reduced fluorescence. By using a known light source, the detected decrease in fluorescence is inversely proportional to the concentration of oxygen molecules in the sample gas.

Some sensors employ a time-based approach, where fluorescence is measured twice within a known time interval. By comparing the decrease in fluorescence over time (fluorescence quenching), simpler sensor designs can be achieved.

Fluorescent oxygen sensors find applications in various fields, including medical facilities, lasers, imaging systems, and optical fibers. They offer advantages such as higher sensitivity, wider dynamic range, distributed configuration, and multiplex transmission capabilities compared to other sensor types.

3. Zirconia oxygen sensor

The zirconia oxygen sensor is an oxygen sensor similar to an electrochemical method. Zirconium dioxide is coated with a thin layer of platinum electrode. At high temperatures (>650C), stable zirconium oxide (ZrO2) exhibits two mechanisms:

1. ZrO2 partially dissociates to produce mobile oxygen ions, thus forming a solid electrolyte of oxygen. The zirconium oxide disk is covered with a transparent electrode connected to a constant DC current, allowing ambient oxygen ions to pass through the material, thereby releasing an amount of oxygen at the anode proportional to the delivered charge (electrochemical pumping).

2. Two different ion concentrations at both ends of the electrolyte will produce a potential, also known as the Nernst voltage. The magnitude of the voltage is proportional to the natural logarithm of the ratio of two different ion concentrations.