Patent ID: 6520001
Filing Date: 2003-02-18
Classification: G01N

Abstract:
An apparatus for measuring the concentration of oxygen in an unknown or sample gas by comparison with a reference gas, comprising:a sample chamber with an inlet and an outlet, a valving system which connects either the sample or the reference gases to the inlet, a source of low pressure connected to the outlet which tends to draw one or the other into the chamber, a magnetic circuit for generating a flux path, one or more coils of wire surrounding the flux path in the magnetic circuit, control means for the valves, amplification and detection of induced voltages in the coil(s), which detected signal is a representation of the difference of magnetic susceptibility of the reference and test gases, in which the chamber is in the form of an annulus, with inner and outer pole pieces made of soft iron enclosed on the sides by a non magnetic material and in which the control and detection system includes an integrator for the signal from the coil, and in which the integrated signal is synchronously multiplied by a periodic signal of the same frequency as valve operation to produce a detected signal to reject noise and spurious signals.