Siemens 7MB3000 Series Operating Instructions Manual

Also see for SIPROCESS GA700: Compact operating instructions Quick start Operating instructions Operating instructions Compact operating instructions

Measuring principleIn contrast to other gases, oxygen is highly paramagnetic. OXYMAT 7 analyzer modules use thisphysical property to determine the oxygen concentration in gases.Oxygen molecules in an inhomogeneous magnetic field always move toward the higher fieldstrength. This results in a higher oxygen concentration where the field strength is higher(higher oxygen partial pressure). If two gases with differing oxygen content come togetherin a magnetic field, a partial pressure difference arises between them. The measuring effectis therefore always based on the difference in the oxygen content of the two gases. The twogases are referred to as the sample gas and the reference gas.How it worksTo measure oxygen in the OXYMAT 7, the reference gas (nitrogen, air or oxygen) flows throughtwo reference gas channels ④ into the measuring chamber ⑥. One of these partial flows entersthe measuring chamber in the area of the magnetic field ⑦. If the sample gas contains nooxygen, the reference gas flows freely into the sample chamber. However, if the sample gascontains oxygen, the oxygen molecules concentrate in the area of the magnetic field. Thereference gas can then no longer flow freely into the sample chamber. There is a slight build-upof dynamic pressure, which depends on the concentration of oxygen in the sample gas. In anoscillating magnetic field, oscillating pressure is also generated and this results in alternatingflow. This alternating flow is converted into an alternating current signal by two microflowsensors ③ located between the reference gas channels ④.The microflow sensors ③ consist of two nickel-plated grids each, which are arrangedtogether with two further nickel-plated grids to form a measuring bridge. The alternatingflow results in a change in the resistance of the nickel-plated grids. The resulting offset in thebridge is a measure of the concentration of oxygen in the sample gas.The microflow sensors ③ are surrounded by reference gas. This arrangement protects themfrom corrosion by the sample gas.Vibrations at the installation site can interfere with the measured signal, for example, largefluctuations in the output signal. Two additional optional microflow sensors ⑪ serve asvibration sensors and thus compensate for the undesirable behavior.Description4.4 OXYMAT 7Wall-mounted device30 Operating Instructions, 07/2023, A5E31930403-AB