Speed insensitive wheel detector
AssigneeGeneral Signal Corporation
InventorDavid Birnbaum
Life of this patent
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Abstract
An apparatus for detecting the presence and/or direction and/or velocity of a moving ferromagnetic element is provided. A sensing coil is placed in coupling relationship with a bi-stable ferromagnetic wire to provide a signal in response to a change in polarity of the core of the bi-stable wire. The core polarity changes in response to element presence as the element constitutes a magnetic shunt causing a change in magnetic flux density and/or direction in the air gap of a magnetic circuit in which the bi-stable wire is situated. The sensor is substantially insensitive to element velocity. Modified structures provide for fail-safe operation.
Claims14
In a detector of the class wherein the presence of a member having magnetic properties alters a magnetic circuit such that there is a change in the magnetic flux between the faces of opposing pole pieces of the magnetic circuit, the combination with said structure of:
- (a) a bi-stable ferromagnetic device situated between the faces of the pole pieces, said device having a core portion and an outer shell portion of relatively low and high coercivity, respectively;
- (b) said change of magnetic flux being effective for reversing the polarity of said low coercive core;
- (c) a sensing coil in coupling relationship with said bi-stable ferromagnetic device for responding to the flux change resulting from the reversal of the polarity of said core by producing an output signal;
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- (d) a separate winding coupled to one of said pole pieces and connected to a source of a.c. potential of sufficient magnitude that the magnetic flux between said faces of the opposing pole pieces reverses direction at a rate proportional to the frequency of the a.c. potential for causing said sending coil to produce output signals in response to each flux reversal.
In a system for railroad wheel detection of the class wherein the entrance and exit of a ferromagnetic railroad wheel alters a magnetic circuit and changes the direction of the magnetic flux between the faces of opposing pole pieces, the combination with said structure of:
- (a) a bi-stable ferromagnetic device having a core portion and an outer shell portion of relatively low and high coercivity, respectively, situated between the faces of the opposing pole pieces;
- (b) said magnetic flux, when said magnetic circuit is altered, being effective to alter the magnitude and/or magnetic polarity of said low coercive core;
- (c) a sensing coil in coupling relationship with said bi-stable ferromagnetic device for producing an output pulse in response to each magnetic polarity reversal of said core and
- (d) wherein said sensing coil produces first and second output pulses in response to the entrance and exit, respectively, of the railroad wheel in said detection system.
A motion and direction sensing system comprising in combination:
- (a) a control air gap in a magnetic circuit arranged and oriented with respect to the path of a moving magnetic member for sequentially producing a first and second flux flow in first and second directions in said control air gap in response to the motion of said magnetic member along the path;
- (b) a bi-stable ferromagnetic device having a core portion and a shell portion of relatively low and high coercivity, respectively, situated in said control air gap for responding to said flux flow in said control air gap;
- and
- (c) a sensing coil in coupling relationship with said bi-stable ferromagnetic device for producing first and second output pulses of first and second polarities, respectively, in response to a change of direction of flux in said core.
A motion detection system comprising in combination:
- (a) a magnetic circuit including a control air gap;
- (b) circuit means coupled to said magnetic circuit for alternately producing a flux of first and second opposing directions in said control air gap;
- (c) a bi-stable ferromagnetic device situated in said control air gap and having a core and shell portions of relatively low and high coercivity, respectively, with at least said core responding to the direction of the flux in said control air gap by becoming magnetically polarized in accordance with the direction of the flux in said control air gap;
- (d) a sensing coil in coupling relationship with said ferromagnetic device for producing an output pulse in response to each reversal of magnetic polarity of said core;
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- (e) said magnetic circuit arranged and oriented with respect to the path of a moving magnetic member for altering the flux in said magnetic circuit and introducing a flux in a first direction in said control air gap of sufficient magnitude to terminate the production of flux reversals in said control air gap by said circuit means when said magnetic member is in a first predetermined relationship with respect to said magnetic circuit.
Dependencies are inferred from the claim text.