Oxygen Sensing Technologies

Luminescence optical oxygen sensor

The optical sensor, developed, patented, and manufactured by PST, is low-cost, low power and long-lasting oxygen sensor that measures the partial pressure of oxygen, ranging 0-3000ppO2, and temperature as well as the optional barometric pressure allowing the oxygen concentration to be calculated ranging from 0 to 25% O2, with a high accuracy of <2% fully scale of ppO2.

The sensor itself contains no lead of liquid electrolytes and therefore 100% RoHS compliant. With simple connections allowing connections directly to a microcontroller with UART communications so additional signal conditioning circuity required.

The sensor is built into a few compact options, flow through sensor body that allows push on fittings, a diffusion bases sensor with a PTFE filter membrane that allows the passive movement of O2 through as well as OEM options.

Galvanic Electrochemical

Galvanic sensors , generally consist of four elements: a membrane, an electrolyte, a lead anode and a cathode. As the sample gas comes into contact with the sensor it diffuses through the membrane and any oxygen present reacts with the electrolyte conducting electrons to the cathode, generating a current.

The more O2 the stronger the current and the signal it generates. There are several classes of sensor available, engineered to offer the optimum performance and maximum sensor life for the desired measurement ranges.

Sensor variants include Pico-Ion and MS sensors for parts per billion oxygen; XLT sensors for CO2 and acid gas backgrounds; -H sensors for use with H2 or He backgrounds.

Advantages

  • Measuring ranges available: 0 to 50 ppb up to 0 to 100% O2
  • Cost effective
  • Small with low power consumption
  • Simple to use and calibrate, in most cases with air
  • Can measure trace oxygen in the presence of hydrocarbons or in flammable gases such as hydrogen


  • Solid-state ceramic electrochemical sensors operate on a very similar principle to the galvanic type. Solid-state oxygen sensors measure the O2 concentration by counting the number of electrons flowing through the circuit. The circuit is connected between the sensor’s cathode and its anode electrodes. A polarizing DC voltage is used to facilitate the flow of electrons. Oxygen from the sample gas is sensed at the cathode electrode by diffusing through the barrier covering the cathode. Oxygen molecules that come into contact with the cathode are reduced according to an electrochemical reaction.


    The oxygen ions, O2, migrate through a solid-state electrolyte. The oxygen ions are converted back to molecular oxygen at the anode electrode. The electrochemical oxidation reaction that takes place at the anode between the cathode and anode is proportional to the concentration of oxygen in the sample gas. This current is measured by the analyzer’s electronics, and the oxygen concentration is displayed.

    Advantages

  • Very chemically resistant
  • Long operating life span
  • Zirconia

    PST’s Zirconium Oxide Sensors

    A dome shaped block of Zirconium dioxide (ZrO2) is coated on the inner and outer sides with a thin porous platinum layer. The Zirconium dioxide acts as a solid electrolyte and is doped with yttrium oxide which enhances the thermal and mechanical stability, and electrical characteristics. The platinum porous layer acts as an electrode, allowing oxygen ions to pass through into the ZrO2 electrolyte.

    One side of the assembly is exposed to the sample gas, whereas the other side is exposed to a reference gas (typically air).

    The entire assembly is heated above 600°C to maximise the ion conductivity of the ZrO2 electrolyte. This allows fast movement of oxygen ions from a higher concentration of oxygen to a lower one. The movement of oxygen ions across the zirconium oxide produces a voltage between the two electrodes, the magnitude of which is based on the oxygen partial pressure differential created by the reference and sample gas.

    MSRS Sensor Cells

    MSRS stands for Metallic Sealed Reference Sensor, and is a technology unique to PST’s oxygen sensors. The equilibrium state of solid metal oxide is used as a reference. This allows accurate operation irrespective of the quality of the ambient air (which is typically used as the reference gas), and negates the requirement for a “zero” calibration gas.

      Advantages of MSRS:
    • Capable of measuring oxygen in a wide variety of applications
    • Resistant to pollution (in stack gases) and remains sensitive in clean gases
    • The measurement is stable, especially when compared to electrochemical sensors
    • Only one calibration gas is required

    MIPS Sensor Cells

    PST’s MIPS (Micro-Ion-Pump Sealed reference) cells are a perfect economical solution for percentage level oxygen measurement. The sealed reference cell conveniently does not require a supply of reference gas.

    The cell is constructed from two Zirconium Dioxide (ZrO2) squares, each coated with a thin porous layer of platinum which serves as the electrodes. The platinum electrodes provide the catalyst necessary for the measured oxygen to dissociate, allowing the oxygen ions to be transported through the ZrO2.

    The two ZrO2 squares are separated by a platinum ring which forms a hermetically sealed sensing chamber. At the outer surfaces there are two further platinum rings which, along with a centre platinum ring, provide the electrical connections to the cell.

    Two outer alumina (Al2O3) discs filter and prevent any particulate matter from entering the sensor and also remove any un-burnt gases. This prevents contamination of the cell which may lead to unstable measurement readings.

    A heater coil surrounds the sample cell, heating it above 600°C to maximise the ion conductivity of the Zirconium Dioxide. An outer sintered stainless steel cap filters larger particles and dust, and protects the sensor from mechanical damage.

    Thermo-Paramagnetic

    PST’s Thermo-paramagnetic oxygen sensor offers excellent measurement stability in combination with a robust construction without moving parts.

    The sample chamber has a strong central magnetic field, which attracts paramagnetic gas components, drawing the sample gas in and causing a localised increase of pressure. Two pairs of high accuracy temperature sensors measure the sample gas temperature at different points in the chamber.

    A temperature gradient within the chamber creates an area of low pressure towards the edges of the magnetic field, inducing a flow of sample gas referred to as “magnetic wind”. The magnetic wind has a cooling effect on the temperature sensors, increasing the temperature difference between each pair as it passes across them.

    Higher oxygen concentrations in the sample gas result in increased pressure inside the magnetic field. This in turn results in stronger magnetic wind, further increasing the temperature difference between the temperature sensors in each pair.

    The oxygen concentration in the sample gas is a function of the temperature difference between the temperature sensors in each pair.

    Paramagnetic Oxygen Sensing Technology

    Paramagnetic oxygen sensing is a highly accurate and reliable method for precise oxygen concentration measurement across a range of critical applications. This technology harnesses the unique magnetic properties of oxygen molecules, which are attracted to magnetic fields—a phenomenon not observed with most other gases.


    Principle of Operation


    Paramagnetic measurement technology utilizes the fundamental property of oxygen being diamagnetic. In the presence of a uniform magnetic field, oxygen molecules exhibit a torque due to the differential magnetic susceptibility. This principle is exploited using a sensor design, commonly known as a "dumbbell" setup, where a suspended assembly of glass bulbs filled with nitrogen gas experiences a rotational force in an oxygen-containing environment. This movement is proportional to the oxygen concentration and is detected optically and electronically.


    Design and Components

  • Magnetic Field: Permanent magnets create a strong, uniform magnetic field essential for the operation.
  • Sensor Assembly: Typically, a lightweight dumbbell-shaped sensor is used, which rotates in response to oxygen’s magnetic influence.
  • Detection Mechanism: Sophisticated optical and electronic systems are employed to measure the displacement of the sensor, translating this movement into a precise oxygen level reading.
  • Advantages

  • High Accuracy and Sensitivity: This technology excels in environments where precise gas measurement is crucial, providing top-tier sensitivity and accuracy.
  • Selective Measurement: Highly selective for Oxygen due to its unique paramagnetic property.
  • Durability and Stability: Unlike other sensing technologies that might degrade due to material consumption or exposure, paramagnetic sensors maintain accuracy over extended periods, requiring minimal recalibration.
  • Non-Consumptive Measurement: As the method does not consume oxygen, it is ideal for continuous monitoring applications, providing real-time data without altering the gas being measured.


  • Applications

    Paramagnetic sensors are indispensable in measurements that require rigorous monitoring and control of oxygen levels. These include:

  • Safety: Reliable accurate measurement of Oxygen deficiency for process control. Often a component in the safety control mechanism for a process.
  • Gas Quality: to ensure Oxygen concentration meets the process requirement.
  • Medical: Ensuring the correct oxygen mix in anesthesia and respiratory systems.
  • Industrial: Monitoring and controlling combustion in power generation and manufacturing processes to optimize efficiency and minimize emissions.
  • Environmental: Assessing air quality and detecting leaks in processes involving oxygen.