| 摘要 |
An inductive magnet sensor has two identically wound magnetic antennae connected in series, out of phase, spaced axially from one another, and placed outside and parallel to the axis of a magnetic pipe so that induced noise voltages from the symmetrical noise magnetic flux of the pipe mostly cancel, leaving the responsiveness of the antennae undiminished to sense the non-symmetrical magnetic flux from a permanent magnet or a signal from a transmitter passing through the pipe. The enhanced signal of each of these antennae is then resistively attenuated, one fixed and the other adjustable, to further enhance the cancellation after placement of the sensor outside of the pipe. This balance adjustment improves the signal to noise ratio of the combined signal and the sensor is adjustably resistively attenuated to set the gain to enhance the dynamic range after mounting on the pipe. This balanced and attenuated signal is then assessed to determine whether sufficient induction by the magnetic flux from the permanent magnet or from the transmitter in either antenna or the region in between qualifies as a legitimate sensing event. If so, an appropriate indicator such as an LED is energized to indicate the passage of the magnet or transmitter.
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