Magnetic displacement transducer system having a magnet that is movable in a tube whose interior is exposed to a fluid and having at least one magnetometer outside the tube

摘要

A magnetic displacement transducer system for measuring the movement of a member includes an elongated permanent magnet which is mechanically coupled to the member so that the magnet moves parallel to its axis. A magnet-position sensor assembly, which includes at least one magnetometer having an elongated ferromagnetic core with a coil wrapped around it, is positioned adjacent the magnet so that the axis of the core and coil intersects the axis of the magnet at right angles. A pair of wires carry a sinusoidal excitation current to the assembly, convey the second harmonic from the assembly, and deliver a DC biasing current to the assembly in order to null the component of the permanent magnet's field that is perpendicular to the axis of the magnet. The value of the DC biasing current is measured to obtain the displacement of the member. The transducer may be employed in a differential pressure gauge for use within the containment building of a nuclear power plant, in which case it is desirable to know the temperature at the gauge. The same pair of wires that conduct the excitation current, the second harmonic, and the DC biasing current may be used to measure the DC resistance provided by the coils in the assembly so that the temperature can be determined based upon the thermal coefficient of resistance.