RAILWAY WHEEL SENSOR

• US 3,721,821 A
• Filed: 12/14/1970
• Issued: 03/20/1973
• Est. Priority Date: 12/14/1970
• Status: Expired due to Term

• Current Assignee: ABC Rail Corp.
• Original Assignee: Carl G. Blanyer
• Inventors: Blanyer, Carl G.
• Primary Examiner(s): Hoffman, Drayton E.
• Assistant Examiner(s): Libman, George H.
• Application Number:
  US05/097,602
• Time in Patent Office: 827 Days
• Field of Search: 246/249 340/258R,285 324/179
• US Class Current: 246/249
• CPC Class Codes: B61L 1/10 actuated by electromagnetic radiation; actuated by particle radiation
• CPC Class Codes: G01P 13/045 with speed indication
• CPC Class Codes: G01P 3/66 using electric or magnetic means G01P3/80 takes precedence; measuring short time intervals G04F8/00, G04F10/00

Abstract

A railway wheel sensor, for detecting passage of a railway wheel, comprising two tuned pickup coils of large surface area having vertically oriented axes, spaced longitudinally of a railway rail with magnetic fields through which the wheel flange passes successively, the coils being connected in a bridge circuit excited by a high frequency signal, and a synchronous detector coupled to the bridge and to the excitation source, all mounted in a small, compact non-magnetic housing.

Claims

1. A railway wheel sensor comprising:

a housing, formed of non-magnetic material in at least its upper portion and adapted for mounting adjacent a railway rail below the head of the rail in position to clear the flange of a wheel moving along the rail;

two matched electrical sensing coils, each tuned to a given operating frequency, mounted in the upper portion of said housing with their axes oriented vertically and spaced from each other in a direction longitudinal to said rail, for generating two electromagnetic fields of essentially identical configuration in the space above said housing traversed by the flange of a wheel moving along the rail;

a bridge circuit, mounted in said housing, said sensing coils being connected in two adjacent arms of the bridge;

excitation means, in said housing, for applying a continuous balanced excitation signal to said bridge circuit at approximately said given frequency; and

synchronous detector means, mounted in said housing and electrically coupled to said bridge and to said excitation means, for detecting variations in the relative signal strengths in the arms of the bridge containing the sensing coils, caused by detuning of the individual coils upon movement of a wheel flange into the field space above said housing, and for generating a control signal indicative of the wheel flange movement through the field space.

2. A railway wheel sensor according to claim 1, in which said detector means comprises a pair of synchronous detectors and a differential amplifier, producing a control signal varying in polarity sequence in accordance with the direction of movement of a railway wheel traversing the rail.

3. A railway wheel sensor according to claim 2, in which each of said synchronous detectors is a diode bridge detector coupled to an input of said differential amplifier by a resistance-capacitance low-pass filter, so that the filtered signal input to the differential amplifier approaches the amplitude of a full-wave detector.

4. A railway wheel sensor according to claim 1, in which said housing is of resilient molded elastomer materiaL permitting substantial distortion of the housing without permanent deformation.

5. A railway wheel sensor according to claim 4, in which the remaining principal components of the sensor, other than said coils, are mounted upon a relatively flexible circuit board mounted within said housing.

6. A railway wheel sensor according to claim 1, in which each sensing coil is a low-inductance high-Q coil having a damping resistor connected in parallel therewith to afford a drift-stabilized sensing inductance.

7. A railway wheel sensor according to claim 1, in which said excitation means comprises an oscillator and in which said tuned sensing coils constitute frequency-determining elements for said oscillator.

8. A railway wheel sensor according to claim 7, in which said sensing coils are of flat configuration, each having horizontal dimensions approximating the maximum possible horizontal displacement of a railway wheel flange from the head of the rail and a substantially smaller vertical dimension.

9. A railway wheel sensor according to claim 7, in which said excitation oscillator has two output terminals connected to two respective opposed corners of said bridge, at opposite ends of the two bridge arms comprising said coils, constituting the input terminals of said bridge, said sensor further comprising an automatic gain control circuit for maintaining the amplitude of excitation of said bridge within a given limited range.

10. A railway wheel sensor according to claim 9, in which said oscillator comprises a cross-coupled differential amplifier, in which the remaining two arms of said bridge comprise matched resistors connected to respective ones of the source and drain electrodes of a field-effect transistor, and in which said automatic gain control circuit comprises a filter amplifier having its input connected to said output terminals of said bridge and having its output connected to the gate electrode of said field-effect transistor.

11. A railway wheel sensor according to claim 9, and further comprising a constant-current reference circuit connected to one output terminal of the bridge at the junction of said sensing coils, said constant-current source comprising an auxiliary bridge including two matched resistances connected in series across said sensing coils, and a transistor having its control electrode connected to an output terminal of the auxiliary bridge, its input electrode connected to an intermediate stage in said excitation means, and its output electrode connected to said one output terminal of the principal bridge.

12. A railway wheel sensor according to claim 11, in which said reference circuit is also connected to said automatic gain control circuit to maintain balanced operation in said oscillator.