Non intrusive and dynamic method for measuring a distance or the variation thereof through dielectrics

• US 7,064,559 B2
• Filed: 03/25/2002
• Issued: 06/20/2006
• Est. Priority Date: 03/23/2001
• Status: Expired due to Term

• Current Assignee: VibroSystM Inc. (Gestion Marius Cloutier, Inc.)
• Original Assignee: VibroSystM Inc. (Gestion Marius Cloutier, Inc.)
• Inventors: Pronovost, Jean, Cloutier, Marius, Bissonnette, Marc
• Primary Examiner(s): Nguyen, Vincent Q.
• Assistant Examiner(s): ZHU, JOHN X
• Application Number:
  US10/468,148
• Publication Number:
  US 20040135588A1
• Time in Patent Office: 1,548 Days
• Field of Search: 324/658, 324661-664, 324/671, 324/71.1, 324/690, 324/772
• US Class Current: 324/662
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: G01B 7/14 for measuring distance or clearance between spaced objects or spaced apertures G01B7/30 takes precedence
• CPC Class Codes: G01H 11/00 Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by detecting changes in electric or magnetic properties

Abstract

A non intrusive method and system for the dynamic measurement of a distance, or the variations over time thereof, constituting the thickness, or the variations thereof, of a thin compressible dielectric material located between one or several other closely spaced solid dielectric layers of constant thickness and a conductive or semi-conductive surface. This is achieved by positioning a capacitive sensor on the external layer of the dielectric material, the sensor being composed of two parallel plates electrically insulated from one another, feeding the first plate with a high frequency signal, measuring the voltage and current value over time generated by the high frequency signal between the plate of the sensor which is closest to the surface of the outer layer of dielectric material, and deducting the above distance or variations thereof.

Claims

1. A method for measuring the vibrations of a stator bar of an electric generator while in use, said vibrations corresponding to a distance to be measured over a period, said electrical generator having a layer of compressible dielectric substance wherein said layer of dielectric substance is sandwiched anywhere between several parallel layers of solid and fixed dielectric substances having each a constant but not necessarily identical permittivity, said layers being closely but variably spaced from a grounded conductive or semi-conductive surface, said stator bar acting as said grounded conductive or semi-conductive surface, said distance is an air gap between a stator-side surface of a tightening wedge of said stator bar and a rotor-side surface of said stator bar, the method comprising:

using a capacitive sensor installed from the outside, and without modifying the existing arrangement of parallel dielectric layers, on a rotor-side surface of said tightening wedge which is adjacent or forms part of an external surface of the first layer of said solid dielectric substances which is furthest from the grounded conductive or semi-conductive surface, said sensor being composed of a first conductive or semi-conductive plate which is parallel to the parallel layers of dielectric substances, said first plate being furthest from said first layer, and a second parallel superimposed conductive or semi-conductive plate which is nearest said first layer and electrically insulated from the first plate, and both plates being parallel to the parallel layers of dielectric substances;

feeding said first plate of said sensor a high frequency signal;

measuring over time the values of the current generated by said high frequency signal between the second plate and the grounded conductive or semi-conductive surface which faces the dielectric layers;

wherein the measured current varies as an inverse function of the thickness of said compressible dielectric substance, thereby enabling the determination of the amplitude of the variations of thickness of said compressible dielectric substance and hence said distance.

2. The method according to claim 1 wherein the compressible dielectric substance is one of air and gas.

3. The method according to claim 1, further comprising deducting from the variations of said current, the changes over time of the permittivity existing between the outer surface of the first dielectric layer and the facing surface of the grounded conductive or semi-conductive component due to the variation in thickness of said layer of compressible dielectric substance.

4. The method according to claim 3 allowing the detection of the passage or the measurement of the change of level of a fluid in front of a capacitive sensor, said passage or change of level occurring in an empty space located anywhere between parallel solid layers of dielectrics and a conductive or semi-conductive surface, whereby said sensor detects the change in permittivity caused by the beginning and by the end of the passage of the fluid in said space or by the arrival of the level of the fluid in the detecting zone of said space.

5. An apparatus for measuring the vibrations of a stator bar of an electric generator while in use, said vibrations corresponding to a distance to be measured over a period, said stator bar acting as a grounded conductive or semi-conductive surface, said distance is an air gap between a stator-side surface of a tightening wedge of said stator bar and a rotor-side surface of said stator bar, the apparatus comprising:

a capacitive sensor installed on a rotor-side surface of said tightening wedge, said sensor being composed of a first conductive or semi-conductive plate, said first plate being furthest from said stator-side surface of the tightening wedge, and a second conductive or semi-conductive plate which is nearest stator-side surface of a tightening wedge and electrically insulated from the first plate, and both plates being parallel to the rotor-side surface of said stator bar;

a high frequency signal generator for feeding said first plate of said sensor a high frequency signal while said electric generator is in use;

a current detector for measuring over time the values of the current generated by said high frequency signal between said second plate and the grounded conductive or semi-conductive surface which faces said stator-side surface of the tightening wedge;

a treatment unit receiving the measured current, wherein the measured current varies as an inverse function of said distance, thereby enabling the determination of said distance over a period and hence said vibrations.

6. A method for measuring the vibrations of a stator bar of an electric generator while in use, said vibrations corresponding to a distance to be measured over a period, said stator bar acting as a grounded conductive or semi-conductive surface, said distance is an air gap between a stator-side surface of a tightening wedge of said stator bar and a rotor-side surface of said stator bar, the method comprising:

using a capacitive sensor installed on a rotor-side surface of said tightening wedge, said sensor being composed of a first conductive or semi-conductive plate, said first plate being furthest from said stator-side surface of the tightening wedged, and a second conductive or semi-conductive plate which is nearest stator-side surface of a tightening wedge and electrically insulated from the first plate, and both plates being parallel to the rotor-side surface of said stator bar;

feeding said first plate of said sensor a high frequency signal while said electric generator is in use;

measuring over time the values of the current generated by said high frequency signal between said second plate and the grounded conductive or semi-conductive surface which faces said stator-side surface of the tightening wedge;

wherein the measured current varies as an inverse function of said distance, thereby enabling the determination of said distance over a period and hence said vibrations.