Siemens SIPROCESS GA700 - Option modules

Measuring principle
In contrast to other gases, oxygen is highly paramagnetic. OXYMAT 7 analyzer modules use this
physical property to determine the oxygen concentration in gases.
Oxygen molecules in an inhomogeneous magnetic 󹪝eld always move toward the higher 󹪝eld
strength. This results in a higher oxygen concentration where the 󹪝eld strength is higher
(higher oxygen partial pressure). If two gases with di󹪜ering oxygen content come together
in a magnetic 󹪝eld, a partial pressure di󹪜erence arises between them. The measuring e󹪜ect
is therefore always based on the di󹪜erence in the oxygen content of the two gases. The two
gases are referred to as the sample gas and the reference gas.
How it works
To measure oxygen in the OXYMAT 7, the reference gas (nitrogen, air or oxygen) 󹪞ows through
two reference gas channels ④ into the measuring chamber ⑥. One of these partial 󹪞ows enters
the measuring chamber in the area of the magnetic 󹪝eld ⑦. If the sample gas contains no
oxygen, the reference gas 󹪞ows freely into the sample chamber. However, if the sample gas
contains oxygen, the oxygen molecules concentrate in the area of the magnetic 󹪝eld. The
reference gas can then no longer 󹪞ow freely into the sample chamber. There is a slight build-up
of dynamic pressure, which depends on the concentration of oxygen in the sample gas. In an
oscillating magnetic 󹪝eld, oscillating pressure is also generated and this results in alternating
󹪞ow. This alternating 󹪞ow is converted into an alternating current signal by two micro󹪞ow
sensors ③ located between the reference gas channels ④.
The micro󹪞ow sensors ③ consist of two nickel-plated grids each, which are arranged
together with two further nickel-plated grids to form a measuring bridge. The alternating
󹪞ow results in a change in the resistance of the nickel-plated grids. The resulting o󹪜set in the
bridge is a measure of the concentration of oxygen in the sample gas.
The micro󹪞ow sensors ③ are surrounded by reference gas. This arrangement protects them
from corrosion by the sample gas.
Vibrations at the installation site can interfere with the measured signal, for example, large
󹪞uctuations in the output signal. Two additional optional micro󹪞ow sensors ⑪ serve as
vibration sensors and thus compensate for the undesirable behavior.
Description
4.4OXYMAT 7
Wall-mounted device
30 Operating Instructions, 07/2023, A5E31930403-AB