Common online measurement methods for determining the oxygen concentration | traces of oxygen | oximetric
Paramagnetic sensor for 0-100% O2
These oxygen sensors use the paramagnetic property of the oxygen atom. Oxygen can be influenced (accelerated and decelerated) by magnetic fields and loses this property above ~300°C.
Paramagic sensors work quickly and without wear and have a very long service life. There are virtually no cross-sensitivities to other gases.
Measuring principle: Paramagnetic (partial pressure measurement with a rotating glass jacket).
The sensor is heated to 55°C. Oxygen is one of the few gases with pronounced paramagnetic properties that are used for the measurement as follows: A small glass dumbbell, filled with nitrogen, is suspended in an inhomogeneous magnetic field in the measuring cell. The rest position of the system is determined by a light beam, a mirror on the dumbbell and a photo detector. The glass jacket is diamagnetic and tends to twist out of the magnetic field. The paramagnetic oxygen molecules in the measurement gas, on the other hand, are drawn into the magnetic field, which displaces the glass dumbbell or causes it to rotate in the other direction. This rotation is canceled by an opposing magnetic field, which is generated around the glass dumbbell with the help of a coil, whereby the necessary current intensity depends on the signal from the photo detector. The difference between the coil current when pure nitrogen flows through the measuring cell and the coil current when the measuring gas is flowing is proportional to the oxygen concentration in the measuring gas.
Areas of application:
- Monitoring of medical oxygen or medical gases
- Measurement of residual oxygen in all types of combustion systems
- Indoor air monitoring to protect people and goods
- Monitoring of the oxygen content in fermentation tanks and biochemical fermenters
- Monitoring of the oxygen content in digester gases
- Monitoring the atmosphere in fruit stores and greenhouses
- Process gas measurement for continuous monitoring of the required or permissible oxygen content
- Monitoring of smoldering and fire gases
- Monitoring of vehicle emissions and internal combustion engines
- Monitoring of protective gases
- Monitoring of tunnel and tunnel air
- Measurement of residual oxygen in protective atmospheres of systems or packaging in the food industry
- Bio and landfill gas monitoring
- Measurement of residual oxygen in processes
- Air monitoring in the animal barn
- Air monitoring in training simulators
- Residual oxygen in the glazing industry
Electrochemical sensor for the %- and ppm-range
An electrochemical oxygen sensor is a specific type of fuel cell. If the potassium hydroxide in the measuring cell comes into contact with oxygen, a chemical reaction takes place. This results in an electrical current that flows through a resistor between the anode and cathode. The current is proportional to the oxygen concentration.
The service life of the measuring cell is limited. The measurement method is ideal for detecting traces of oxygen, but is also suitable for the percentage range.
We recommend the use of electrochemical sensors in Ex areas or generally anywhere where flammable components are present in the gas flow.
The measuring device is not subject to any noteworthy wear, only the fuel cell has to be replaced regularly (normal cycle approx. 3-4 years).
We work together with the company ProChem Analytik when it comes to electrochemical oxygen measurements.
Areas of application:
- Semiconductor industry
- Gas manufactures
- Metal industry
- Chemical industry
- Heat treatment
Potentiometric O2 zirconium oxide probes for the %- and ppm range
Conventional λ-probes from the automotive sector have the decisive disadvantage that the unregulated heating and ceramic cover layers, which promote the diffusion of certain gases, can result in considerable measurement errors. The company ZIROX builds high-precision potentiometric oxygen measuring cells. The measuring cells SS27 / MS27 have an integrated regulated heating and primary electronics. The core of the probe is the proven potentiometric drift and calibration-free ZIROX measuring cell. Due to the construction of the probe, measurements with high accuracy and reliability are possible.
To obtain favorable values for the oxide ion conductivity of the zirconium dioxide and to avoid interfering reactions due to imbalances with combustible components of the measuring gas, the measuring cell is heated up to 750 ° C. A thermocouple on the measuring cell determines the current measuring temperature. A constant measuring temperature is guaranteed by an electronic control circuit.
Areas of application:
Oxygen measurements in protective gases
- Exhaust gas analysis in combustion systems, large engines and combined heat and power plants
- Combustion optimization in small combustion systems
- Furnace gas measurements in heat treatment plants
- Optimization of landfill and biogas incineration plants
- Monitoring of industrial processes under protective and forming gas atmosphere
General information on the λ probe
The λ-probe measures the residual oxygen concentration in exhaust gases and is used, for example, to optimize the combustion process and the efficiency in internal combustion engines. But they are also used in waste incineration plants, steel works and coal-fired power plants.
A distinction is made between two measuring principles: (1) voltage of a solid electrolyte (NERNST probe) and (2) change in resistance of a ceramic (resistance probe). Most oxygen probes are designed as NERNST probes, named after their inventor Walther Nernst. These use a solid, ceramic electrolyte that conducts oxygen ions as a membrane (zirconium oxide). A voltage (measured variable) arises on the membrane, which is dependent on the difference in the oxygen content of the gases on both sides.