thermistors. One thermistor of each pair located inside the
magnetic field and the other thermistor of each pair located
outside the field. Because the thermistors are electrically
heated, a temperature gradient is thus created within the
magnetic field.
Figure 2 below shows the arrangement of the two thermistor
pairs.
A small portion of the sample gas flow is allowed to
diffuse from the lower chamber into the upper chamber
of the measurement cell. If the sample gas contains
a paramagnetic gas such as oxygen, it is attracted to
the magnetic field, causing the sample gas pressure to
become locally higher in the center of the chamber. At the
same time, the sample gas pressure is slightly lower near
the thermistors because the high thermistor temperature
causes the paramagnetic properties of oxygen to decrease.
This slight gradient in sample gas pressure causes the
sample gas to flow outward from the center of the magnetic
field and over the thermistors. As a result, the inner, wind-
generating thermistors decrease in temperature as they
lose heat to the magnetic wind. This causes a temperature
gradient between the cooler inner thermistors and the
warmer outer thermistors.
gure 2: Typical XMT1000 labels (stainless
Figure 1: Measuring cell flow schematic
Figure 2: Arrangement of the thermistor pairs
2
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