Analytical Instrumentation

Oxygen Analyzer Working Principle: Paramagnetic Type

  • Accurate measurements of gas composition must be made continuously for many industrial operations. 
  • These readings help technicians in maximizing productivity and provide important safety information. 
  • For example, oxygen measurements are frequently used to find transmission line leaks and adjust the fuel-to-air ratio in combustion operations. 
  • A comprehensive range of O2 analyzers is provided by Paramagnetic O2 Analyzers to ensure that facilities are always operating from accurate data. 
  • For measuring low oxygen concentrations in combustible, high-pressure, or high-humidity mixtures, our paramagnetic O2 gas analyzers are perfect.
  • The paramagnetic oxygen analyzers better than traditional analyzers because of an innovative magnetic flow ratio technique. 
  • One of the advantages of these analyzers over zirconia oxygen analyzers is their ability to measure oxygen concentrations in combustible gas mixtures in a low range with high accuracy. 
  • They can also be utilized for measurement in process gasses with high pressure, high temperature, high dust content, and/or high humidity when the right sample systems are in place. 

Paramagnetic oxygen analyzers employ several different methods for accurate oxygen concentration measurement:

  1. The Magnetic Proportional Flow Rate Method.
  2. The Magnetic Wind Method.
  3. The Magnetic Force Method in dumbbell configuration.
  4. The Magnetic Force Method using pressure sensors.
Magnetic Proportional Flow Rate Method: Paramagnetic Oxygen Analyzer
  • This method operates on the principle that oxygen molecules are paramagnetic, meaning they are attracted to magnetic fields. 
  • In the setup, the sample gas is divided into two streams within a ring-shaped gas flow path. 
  • Similarly, an auxiliary gas is also split into two streams. 
  • Each stream is equipped with a thermistor to monitor its flow rate. 
  • One of the auxiliary gas streams is exposed to a magnetic field generated by a magnet.
  • When the sample gas containing oxygen flows through the chamber, the paramagnetic oxygen molecules are drawn towards the magnetic field, thereby reducing the flow rate of the auxiliary gas stream exposed to the magnetic field. 
  • This reduction in flow rate is proportional to the concentration of oxygen in the sample gas. 
  • By comparing the flow rates of the two auxiliary gas streams using the thermistors, the oxygen concentration can be accurately determined. 
  • This method is valued for its rapid response time and robustness against external disturbances like vibration and shock.
Magnetic Wind Method: Paramagnetic Oxygen Analyzer
Magnetic Wind Method: Paramagnetic Oxygen Analyzer 1
  • In the magnetic wind method, a gas sample is introduced into a chamber containing a heating wire surrounded by a magnetic field. 
  • Oxygen molecules in the sample gas are attracted towards the heating wire, where the magnetic field is strongest. 
  • As the oxygen molecules reach the heating wire, they are heated and lose their magnetic susceptibility. 
  • This causes them to rise upwards due to the cooler gas entering from below, creating a phenomenon known as “magnetic wind.” 
  • The intensity of this magnetic wind is directly proportional to the concentration of oxygen in the sample gas.
  • To compensate for environmental factors such as temperature changes, a reference chamber identical to the measurement chamber but lacking a magnetic field is employed. 
  • By measuring the change in resistance in the heating wires caused by the magnetic wind, the oxygen concentration in the sample gas can be accurately determined. 
  • However, this method can be sensitive to fluctuations in ambient temperature and changes in gas composition.
Magnetic Force Method (Dumbbell Type): Paramagnetic Oxygen Analyzer
  • In this method, a dumbbell-shaped object with low magnetic susceptibility is suspended within a magnetic field. 
  • When the sample gas containing oxygen is introduced into the vicinity of the dumbbell, the oxygen molecules are attracted towards the point of maximum magnetic field strength, causing the dumbbell to deflect slightly in the opposite direction. 
  • This deflection of the dumbbell is detected using a light source and reflector attached to the suspension wire.
  • The resulting signal is used to generate a current that is proportional to the oxygen concentration in the sample gas. 
  • This method offers a wide dynamic range and is less affected by the presence of background gasses. 
  • However, it may be susceptible to contamination and corrosion, and it has lower resistance to mechanical disturbances compared to other methods.
Magnetic Force Method (Pressure Sensor Type): Paramagnetic Oxygen Analyzer
  • In this method, the oxygen concentration is determined by measuring the differential pressure generated when the sample gas and an auxiliary gas come into contact within a magnetic field. 
  • The pressure difference is directly proportional to the disparity in magnetic susceptibilities between the gasses. 
  • To maintain a constant oxygen content in the auxiliary gas, an electromagnet intermittently excites the magnetic field.
  • Small voltages resulting from the pressure difference are detected using a condenser microphone or micro flow sensor. 
  • Despite requiring an auxiliary gas, this method offers a fast response time and minimal interference from background gasses. 
  • However, it may be influenced by fluctuations in ambient temperature and gas composition.
Interference Gas Compensation in Paramagnetic Oxygen Analyzers
  • Paramagnetic oxygen analyzers utilize the paramagnetic property of oxygen to measure oxygen concentration. 
  • Still, this characteristic can be somewhat present in gasses other than oxygen, which could cause inaccuracies when measuring oxygen concentrations.
  • The analyzers compensate for these errors, which are particularly noticeable at low oxygen concentrations between 0% and 1%, by using methods that take advantage of the difference in density between the sample gas and a reference gas. 
  • The interference faults brought on by the paramagnetic characteristics of process gasses are successfully controlled by this adjustment.
  • In practice, the sample gas is divided into streams within a gas path, with an auxiliary gas introduced at the center and flowing in separate streams. 
  • Even if the auxiliary gas doesn’t contain oxygen, the presence of paramagnetic gasses can influence the flow rates in these streams, leading to errors. 
  • Adjusting the cell angle (cell attitude) can compensate for these errors. For instance, if a gas with lower magnetic susceptibility, like carbon dioxide (CO2), passes through the measurement cell, tilting the cell angle alters the flow rate of the auxiliary gas, counteracting any deviations in the measurement.
  • Every analyzer goes through a final tuning process based on the density and magnetic properties of the sample gas before deployment. 
  • The measurement cell angle is then corrected by this adjustment and saved in the analyzer’s memory. 
  • To ensure precise compensation during installation, users align the measuring cell angle using a bubble level that is integrated inside the device.
  • Accurate determination of the amount of oxygen present in flammable, high-pressure, or high-humidity gas mixtures.
  • Fast responses allow industrial processes to be adjusted in real time.
  • Durability against stress and vibration from the outside.
  • Wide dynamic range that can adapt to different operating circumstances.
  • Minimal interference from background gasses, ensuring accurate readings.
  • Compensation mechanisms for interference gasses, enhancing measurement accuracy.
  • Flexible uses in a range of industrial environments, including as leak detection and combustion operations.
  • Sensitivity to environmental factors such as temperature fluctuations and changes in gas composition.
  • Subject to corrosion and contamination; frequent maintenance is necessary to maintain longevity and accuracy.
  • Considerable complexity in setup and calibration, requiring experienced professionals for correct installation and use.
  • Dependency on auxiliary gasses for several measuring techniques, which raises the expense and complexity of operations.
  • Greater initial expenditure than with certain conventional oxygen analyzers, however over time, increased performance and accuracy might make this expense beneficial.

Frequently Asked Questions

  • The magnetic attraction of oxygen molecules is determined by the paramagnetic measuring principle. 
  • Oxygen molecules are attracted to magnetic fields, which can cause detectable changes in the characteristics of an oxygen-containing gas sample. 
  • This makes it possible to accurately determine the gas mixture’s oxygen concentration.
  • Combustion processes: Optimizing fuel-to-air ratios for efficient combustion and emissions control.
  • Industrial safety: Continuous monitoring of oxygen levels to prevent hazardous conditions, such as oxygen depletion.
  • Environmental monitoring: Monitoring oxygen levels in air and water to assess environmental quality and detect pollution.
  • Power plants: Ensuring optimal combustion efficiency and minimizing emissions in coal-fired, natural gas, or biomass power plants.
  • Petrochemical refineries: Monitoring oxygen levels in various process streams to optimize combustion processes and ensure safety.
  • Chemical manufacturing: Controlling oxygen levels in reactors and process streams to maintain desired reaction rates and product quality.
  • Steel production: Monitoring oxygen levels in blast furnaces and converters to optimize steelmaking processes and reduce energy consumption..

Paramagnetic oxygen analyzers measure low oxygen concentrations quickly and reliably in dynamic industrial situations. However, zirconia oxygen analyzers are better for high, stable oxygen levels but have slower response times and are more sensitive to environmental variables. Both types of analyzers have advantages and are chosen for specialized applications.

ParameterParamagnetic Oxygen AnalyzerZirconia Oxygen Analyzer
Measurement PrincipleOperates on the paramagnetic properties of oxygen molecules.Operates based on the electrochemical reaction of oxygen with zirconium dioxide.
Measurement RangeSuitable for measuring low oxygen concentrations.Typically used for measuring higher oxygen concentrations.
ApplicationIdeal for combustible, high-pressure, or high-humidity gas mixtures.Commonly used in applications where oxygen levels are relatively high and stable.
Response TimeGenerally offers fast response times.Response times may vary but are generally slower compared to paramagnetic analyzers.
RobustnessRobust against external disturbances like vibration and shock.Sensitive to external factors such as temperature and pressure variations.
MaintenanceMay require less maintenance due to robust design.Requires periodic calibration and maintenance due to sensor degradation over time.
CostInitial investment may be higher but justified by performance.Typically lower initial cost but may incur higher maintenance costs over time.
AccuracyProvides high accuracy for low oxygen concentrations.Offers accuracy within its measurement range but may struggle with low concentrations.
CompatibilitySuitable for various industrial applications.Commonly used in stationary combustion applications.

In many sectors, paramagnetic analyzers accurately monitor oxygen levels. They monitor oxygen levels to minimize risks, improve operations for efficiency and lower emissions, maintain product quality in manufacturing, and measure pollution levels to safeguard the environment.

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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