Motion transducer

• US 5,399,967 A
• Filed: 03/15/1993
• Issued: 03/21/1995
• Est. Priority Date: 03/13/1992
• Status: Expired due to Term

• Current Assignee: British Gas Trading Limited (Centrica PLC)
• Original Assignee: British Gas Trading Limited (Centrica PLC)
• Inventors: Carscadden, Ian A.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): PHILLIPS, ROGER
• Application Number:
  US08/031,359
• Time in Patent Office: 736 Days
• Field of Search: 324/235, 324/207.2, 324/207.11, 324/207.12, 324/207.24, 324/207.25, 324/207.21, 338/32 H, 338/32 R
• US Class Current: 324/207.2
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06

Abstract

A motion transducer for measuring the displacement of, for example, shafts in gas control modules. The shaft 14 carries two magnets 10, 12 each of hollow cylindrical form, the magnet 10 presenting a south pole everywhere over its external cylindrical face and the magnet 12 presenting a north pole everywhere over its external cylindrical face. The shaft 14 moves vertically past an array of Hall-effect sensors 18-24 to produce sinusoidal voltage outputs at the sensors. The outputs are combined in a summing amplifier (FIG. 3). The combined output is not affected by rotation of the shaft and magnets nor by tilting or sideways displacement of the axis 16 of the shaft. That is because no matter what the rotational position is the sensors are always subjected to the same magnetic field and, if the shaft tilts or is displaced sideways an increased field at some sensors is compensated by a decreased field at others.

(FIG. 1 is suggested as the accompanying drawing).

Claims

1. A motion transducer comprising magnetised ferromagnetic material which is capable of motion past an array of Hall-effect sensors positioned in a common plane at points on a circle, said motion being along a straight axis transverse to said plane in which said circle lies, said axis being displaceable from a true position normal to said plane through the centre of said circle to a displaced position within said circle, said magnetised material being in the form of a hollow cylinder having a central longitudinal axis coincident with said straight axis, and comprising external and internal faces, and said material being magnetised so that said external face everywhere presents a magnetic pole of a first polarity and said internal face everywhere presents a magnetic pole of a second polarity, each sensor having an output when the magnetised material moves past the sensors and the transducer also comprising means by which said output may be combined with each other said output to yield a combined output representative of said motion, the value of said combined output being unaffected by any rotation of said hollow cylinder of magnetised material about said straight axis either in said true position or in said displaced position, said sensors being located in the array such that each said output is equal to each other said output in response to said motion along said straight axis in said true position and said combined output being unaffected by said motion along said straight axis in said displaced position, any increase in said output from any sensor or sensors closer to said displaced position of said straight axis being compensated for by reduced output from a sensor or sensors more remote from said displaced position of said straight axis, said output having the form of part of a sine wave and said motion being such that said output has a substantially linear relationship with said motion.

2. A transducer according to claim 1, the magnetised material comprising a first hollow cylinder and a second hollow cylinder, each said cylinder having a central longitudinal axis coincident with said straight axis, said cylinders being positioned in contact with one another, said first cylinder comprising a first external face and the first cylinder being magnetised so that said first external face everywhere presents a magnetic pole of a first polarity, said second cylinder comprises a second external face and the second cylinder being magnetised so that said second external face everywhere presents a magnetic pole of a second polarity.

3. A transducer according to claim 1, there being four sensors in said array at points on said circle which points are equiangularly distributed around said circle.

4. A transducer according to claim 1, wherein the magnetised material comprises flexible material.

5. A transducer according to claim 1, wherein the magnetised material is formed around a common shaft.