A fast differential paramagnetic O2-sensor

A differential oxygen sensor using the paramagnetic principle in a pneumatic bridge configuration has been constructed and tested. The signal being picked up with a differential pressure transducer is generated in a measuring cell with a strong magnetic field being switched on and off with a frequency of 110 Hz. The output signal is a DC-voltage proportional to the O2 concentration difference between the two gases to be measured. A response time of 130 ms has been obtained. A special emphasis on the mechanical design was put to minimize the internal magneto-mechanical noise and to attenuate the external pressure and vibration interference. To eliminate the relatively strong temperature dependence of the paramagnetic effect a compensation circuit was designed as an integral part of the sensor. In performance investigations linearity, stability, noise, humidity and pressure effects as well as sensitivity for other gases were studied.