Mindray PM-7000, Service Manual

Page: 36 / 82

Chapter 2 Principles
24
1. Send the gas to be measured to a sampling chamber;
2. Use an optical infrared filter, select a specific band of infrared, and transmit it
through the gas;
3. Measure the infrared that gets through the gas to obtain the gas concentration.
For a given volume, the higher the gas concentration is, the more absorbed infrared is,
and the less the infrared that gets through the gas is. For the measurement of multiple
gases, multiple infrared filters are required in the AG module.
The oxygen does not absorb the infrared within the above-mentioned wave band.
Therefore, the oxygen is measured based on its paramagnetism. Inside the transducer of
the O
2
module, there are two crystal balls full of nitrogen. They are suspended in the
symmetrical magnetic field, and designed to point to the strongest outgoing part of the
magnetic field. Outside the balls is the paramagnetic oxygen. Therefore, the balls are
forced, by the relatively stronger paramagnetic oxygen, out of the magnetic field. The
moment of the force acting on the balls is proportional to the paramagnetic strength as
well as to the concentration of the paramagnetic oxygen.