Galvanic sensors generally consist of four elements: a membrane, electrolyte, a lead anode and a cathode. As oxygen comes into contact with the sensor it pushes through the membrane and reacts with the electrolyte, generating a current. Electrochemical sensors are cost-effective, small with low power requirements and they are also simple to use. They can measure trace oxygen in the presence of hydrocarbons or in flammable gases such as hydrogen
The thermo-paramagnetic sensor uses a combination of paramagnetic and thermal conductivity techniques to accurately measure the oxygen content within a process gas. Oxygen is a paramagnetic gas, which means that it is attracted to a magnetic field. It is this property that can be exploited to help determine the level of oxygen in many background gases. The magnetic susceptibility of oxygen decreases inversely with its temperature. The thermo-paramagnetic analyzer uses a temperature-controlled measuring chamber to create a flow of the process gas (known as a ‘magnetic wind’) between a pair of thermistors. This ‘magnetic wind’ alters the equilibrium temperature between the thermistors. The resulting change in the electrical resistance produces a signal that is proportional to the oxygen concentration in the sample gas.
Zirconium-oxide sensors are based on the principle of a solid-state electrochemical cell. A layer of yttria-stabilized zirconium oxide is typically heated to between +600°C and +700°C, allowing oxygen ions to pass through it from a higher concentration to a lower concentration. The movement of ions produces an electromotive force which is used to determine the oxygen concentration. The greater the differential of oxygen on either side, the higher the voltage produced, allowing measurements from 100% to less than one part per million. We offer three types of Zirconium-oxide based sensors: Metallic sealed reference sensor (MSRS), micro ion pump sensor (MIPS) and air-referenced zirconia.
Metallic Sealed Reference Sensor (MSRS)
The MSRS sensor contains a metallic sealed reference which eliminates the need for reference air, and ensures reliable measurements. The sensor technology was developed to measure oxygen levels in gas in extreme conditions, so is robust enough to withstand extreme heat and highly corrosive gases. These properties, combined with the design of the sample probe, make the MSRS very effective for high-temperature applications (up to +1300°C) such as flue-gas analysis.
Micro Ion Pump Sensor (MIPS)
The MIPS offers a compact, cost-effective percentage level oxygen sensor. The sensor can operate in temperatures up to +400°C, or higher if combined with an extractive sample probe . It has a different approach to our MSRS in that it continuously ‘pumps’ oxygen ions from the sample around the sensor into a sealed chamber and back out again depending on the direction of the DC current applied. The pumping is controlled so that the pressure inside the chamber is always less than the ambient oxygen pressure outside the chamber.
Air Referenced Zirconia
The majority of Zirconia sensors use ambient or compressed air as a reference, but function in a similar way to our MSRS and MIPS cells. Air-referenced sensors are ideal for laboratory and clean industrial applications.
The phase shift of fluorescence light due to oxygen present in the sample gives an indication of the oxygen concentration. The sensor measures the partial pressure of oxygen (ppO2) which, along with the internal sensor temperature is communicated serially to the host microcontroller. Non-depleting, maintenance-free optical sensor offer significant reduction in maintenance complexity and frequency. Does not consume the analyte which is particularly important for low ranges. The patented technology allows PST to produce a sensor that provides low power operation with longer lifetime.