Electronic sensor for static magnetic field
First Claim
1. A magnetic field sensor comprising a resonant circuit including a coil and whose resonant frequency varies with the strength of a magnetic field which passes through the coil, means for applying an energizing signal to said resonant circuit for a predetermined time interval, means for defining a sensing window which begins following the cessation of said energizing signal and ends at a predetermined time thereafter, and means for detecting whether the signal level at a selected point in the resonant circuit crosses a threshold level during said sensing window.
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Abstract
A magnetic field sensor including a resonant circuit having a coil. The resonant frequency varies with the strength of the magnetic field which passes through the coil. The resonant circuit is energized for approximately one-half cycle of the resonant frequency which characterizes the circuit in the absence of a magnetic field. During a sensing window of predetermined duration which then immediately follows, the voltage across the coil is examined for a zero crossing. A zero crossing will occur only in the presence of a magnetic field whose amplitude exceeds a threshold value.
74 Citations
9 Claims
- 1. A magnetic field sensor comprising a resonant circuit including a coil and whose resonant frequency varies with the strength of a magnetic field which passes through the coil, means for applying an energizing signal to said resonant circuit for a predetermined time interval, means for defining a sensing window which begins following the cessation of said energizing signal and ends at a predetermined time thereafter, and means for detecting whether the signal level at a selected point in the resonant circuit crosses a threshold level during said sensing window.
- 7. A magnetic field sensor comprising a resonant circuit including a coil and whose resonant frequency varies with the strength of a magnetic field which passes through the coil, means for applying an energizing signal to said resonant circuit for a predetermined time interval, said resonant circuit operating to ring following the cessation of the energization thereof, means for sensing a resulting signal level at a selected point in the resonant circuit following the cessation of the energization thereof, and means for determining whether said signal level as a function of time, following the cessation of the energization of said resonant circuit, is that expected in the presence of a magnetic field whose strength exceeds a predetermined level.
Specification