In contrast to almost all other gases, oxygen is paramagnetic. This property is utilized as a
measuring effect by the OXYMAT 61 channel.
Due to their paramagnetism, oxygen molecules in an inhomogeneous magnetic field always
move in the direction of increased field strength. When two gases with different oxygen
contents meet in a magnetic field, a pressure difference is produced between them.
In the case of OXYMAT 61, one gas (1) is a reference gas (N2, O2 or air), the other is the
sample gas (5). The reference gas is introduced into the sample chamber (6) through two
channels (3). One of these reference gas streams meets the sample gas within the area of a
magnetic field (7). Because the two channels are connected, the generated pressure
difference creates a flow. This flow is converted into an electric signal by a microflow sensor
(4). The pressure difference is proportional to the difference in the oxygen content of sample
and reference gas.
The microflow sensor consists of two nickel-plated grids, which are heated to approximately
120 °C. Together with two supplementary resistors they form a Wheatstone bridge. The
pulsating flow results in a change in the resistance of the Ni grids. This leads to an offset in
the bridge which is proportional to the oxygen content of the sample gas.
Because the microflow sensor is located in the reference gas stream, the measurement is
not influenced by the thermal conductivity, the specific heat or the internal friction of the
sample gas. This also provides a high degree of corrosion resistance because the microflow
sensor is not exposed to the direct influence of the sample gas.
A magnetic field with alternating strength (8) prevents detection of the background flow in the
microflow sensor, enabling measurement to be performed independent of the sample
chamber position and thus also independent of the location where the gas analyzer is used.
The sample chamber is directly in the sample channel and has a small volume, and the
microflow sensor is a low-lag sensor. This results in a very fast response time for the