Magetoelastic force transducer

• US 4,823,621 A
• Filed: 04/29/1988
• Issued: 04/25/1989
• Est. Priority Date: 04/30/1987
• Status: Expired due to Fees

• Current Assignee: Asea Brown Boveri AB (ABB Limited)
• Original Assignee: Asea Brown Boveri AB (ABB Limited)
• Inventors: Sobel, Jarl, rnholmer, Lars
• Primary Examiner(s): Ruehl, Charles A.
• Assistant Examiner(s): Chen, Hollis T.
• Application Number:
  US07/188,204
• Time in Patent Office: 361 Days
• Field of Search: 73/862.69, 73/DIG. 2, 335/215
• US Class Current: 73/862.69
• CPC Class Codes: G01L 1/125 by using magnetostrictive means magnetostrictive sensors H10N35/101
• CPC Class Codes: G01L 1/127 by using inductive means G01L1/122, G01L1/125 take precedence
• CPC Class Codes: Y10S 73/02 Magnetostrictive

Abstract

A magnetoelastic force transducer comprising two identical, cylindrical bodies defining a hollow magnetic core and held together by means of a force-transmitting stud bolt has its measuring and excitation windings located in the core. The interior of the core is constructed such that a thin cylindrical tubular wall is formed opposite to a respective measuring winding in each one of the bodies, whereby when the core is force-loaded via the stud bolt a compressive stress arises in one of these tubular walls and a tensile stress arises in the other. To eliminate a possible measurement signal at zero applied force a magnetically asymmetric center pole in the form of a punched disk of a soft-magnetic material and having the same diameter as the core and having a foil of a similar material secured on one side is located between the bodies. The hickness of the foil determines the magnitude of the signal adjustment.

Claims

1. A magnetoelastic force transducer comprising a closed core of a solid magnetoelastic material provided with two excitation windings adapted to be supplied with alternating current, and two measuring windings adapted to be connected to a measuring device capable of sensing the electricl signal induced therein by the excitation winding s and changes in said induced signal caused by forces applied ot the core;

the closed core including two centrally and axially connected cylindrical bodies each having

(a) outwardly-directed end surfaces in which a respective first hole is provided centrally and axially, the axial length of said holes being shorter than the axial length of the respective body;

(b) respective second threaded holes provided axially in the remaining central part of the body; and

(c) an axially extending and concentrically located annular space in each said body;

a force-transmitting member extending with clearance through the first providd hole in one of said bodies and being threadedly engaged in each of said second holes provieed in the bodies by means of a threaded end thereof,

the measuring and excitation windings being located in the annular spaces provided within the core,

and between the two bodies a magnetically asymmetrical center pole is arranged provided with a center hole surrounding said threaded end of the force-transmitting member.

2. A froce transducer according to claim 1, in which said center pole consists of a circular disk of soft-magnetic material with a glued-on foil of soft-magnetic material.

3. A force transducer according to claim 1, in which a bobbin is provided in the annular spaces, which bobbin includes two bobbin halves held together by a waist portion, the center pole being provided with a diametrical slot adapted to slide around the waist portion.

4. A froce transducer according to claim 2, in which a bobbin is provided in the annular spaces, which bobbin includes two bobbin halves held together by a waist portion, the center pole being provided with a diametrical slot adapted to slide around the waist portion.

5. A force transducer according to claim 1, in which a bobbin is provided in the annular spaces, which bobbin includes two separate bobbin halves and the center pole consists of an apertured circular disc.

6. A force transducer according to claim 2, in which a bobbin is provided in the annular spaces, which bobbin includes two separate bobbin halves and the center pole consists of an apertured circular disc.

7. A force transducer according to claim 2, in which the ratio of the thickness of the disk to the thickness of the foil is of the order of 2.5:

1.

8. A force transducer according to claim 7, in which the foil has a thickness of about 100 microns.

9. A froce transducer comprising a hollow magnetic core, an excitation winding for magnetically exciting the core and a measuring winding for sensing the magentic excitation in a force-loaded part of the core, the core being formed from a first cylindrical cup-shaped core part and an identical second cylindrical cup-shpaed core part, which cylindrical cup-shaped parts when assembled together define an enclosed volume in which the excitation and measuring windings are located to surround said force-loaded part which is defined by conjoined central parts of the two cylindrical cup-shaped parts,

a disk of magnetic material is located between the core parts to provide a center pole, which center pole has different magentic properties on the side of the disk facing the first core part and on the side of the disk facing the second core part, whereby the center pole differently influences the magnetic excitation of the conjoined central parts of the two core parts.

10. A force transducer according to claim 9, in which the disk making the center pole has a layer of foil secured thereto to provide the different magnetic properties on the two sides.