APPARATUS FOR MONITORING THE AIR GAP IN ROTARY ELECTRICAL MACHINES USING MAGNETIC FIELD PLATES OR MAGNETO DIODES

• US 3,743,934 A
• Filed: 05/06/1971
• Issued: 07/03/1973
• Est. Priority Date: 05/20/1970
• Status: Expired due to Term

• Current Assignee: Rudolf Risch
• Original Assignee: Rudolf Risch
• Inventors: Risch, Rudolf
• Primary Examiner(s): Corcoran, Robert J.
• Application Number:
  US05/140,928
• Time in Patent Office: 789 Days
• Field of Search: 324/34R,34PS,34E,34D,158MG 340/282 318/490 73/462,71.4 323/94H 338/32R,32H
• US Class Current: 324/224
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: G01R 31/343 in operation

Abstract

The present apparatus monitors the width of an air gap between the rotor and stator of an electrical machine by bridge circuit means which comprise magnetic field responsive probes located in the stator, preferably adjacent to the air gap. Each probe comprises a magnetic field responsive impedance element, such as a Hall-generator, and a temperature responsive ohmic resistance element. The probes are connected in pairs to form said bridge means, whereby monitoring output signals are produced between diagonally opposite bridge terminals, which are evaluated by, for example, a peak voltage rectifier and an indicating instrument.

Claims

1. In an apparatus for monitoring an air gap by means of magnetically responsive temperature compensated probes, especially in rotary electrical machines having a rotor and a stator defining said air gap therebetween to normally have a predetermined width, said stator including teeth facing said air gap and distributed about the stator in accordance with a given pole pitch, the improvement comprising at least four magnetic field responsive probes forming two pairs of adjacent probes located in said stator teeth immediately adjacent to said air gap so that adjacent probes forming a pair are spaced from each other by one pole pitch at the most, one pair of probes being arranged diametrically opposite the other pair of probes, each of said four magnetic field responsive probes comprising at least one magnetic field plate having a magnetic field responsive impedance and at least one further probe element having an ohmIc, temperature responsive resistance, a bridge circuit having first (A), second (B), third (C), and fourth (D) branches, conductor means for interconnecting said branches to form power input terminals (20, 22) between the first and third branch, and between the second and fourth branch, as well as output terminals (19, 21) between the first and second branch and between the third and fourth branch, power supply means connected to said power supply terminals, and signal evaluating means connected to said output terminals for evaluating said monitoring signals which indicate the width of said air gap, further conductor means connecting in series with each other the magnetic field responsive field plates of adjacent probes of each pair, and further conductor means connecting in series with each other the ohmic, temperature responsive probe elements of adjacent probes of each pair, whereby each series connection of adjacent probe elements extends over one pole pitch at the most, and means connecting each series connection of field plates and series connection of ohmic elements (126, 127, and 136, 137;

124, 125 and 134,

     135) of adjacent probes of each pair in diagonally opposite bridge circuit branches, whereby a mean gap monitoring magnetic field value is ascertained over the respective pole pitch.

2. The apparatus according to claim 1, wherein said ohmic, temperature responsive resistance probe element has a temperature coefficient corresponding in magnitude to the respective coefficient of the magnetic field plate, and wherein said temperature coefficients have opposite sense.

3. The apparatus according to claim 1, wherein said signal evaluating means comprise a peak voltage rectifier having two input terminals and output means, said two rectifier input terminals being connected to said bridge output terminals (19, 21).

4. The apparatus according to claim 3, wherein said signal evaluating means comprise, in addition to said peak voltage rectifier, an indicating means connected to said output means of said peak voltage rectifier.

5. The apparatus according to claim 3, wherein said signal evaluating means further comprise threshold signal responsive means having a sensitivity which is adjustable for responding to different threshold values, and means for connecting the threshold signal responsive means to the rectifier output means, whereby monitoring signals representing a predetermined air gap deviation from said given width are ascertained by triggering said threshold responsive means.

6. The apparatus according to claim 1, wherein the maximum number of series connected magnetic field responsive probes corresponds to the number of grooves per pole pitch in said electrical machine.

7. The apparatus according to claim 1, wherein said magnetic field responsive impedance probe element is a magnetic diode.

8. The apparatus according to claim 1, wherein said magnetic field responsive impedance probe element and said temperature responsive ohmic resistance probe element in each of said magnetic field responsive probes are electrically insulated from each other.

9. The apparatus according to claim 1, wherein said ohmic, temperature responsive resistance probe element is arranged in close thermal contact with the magnetic field responsive impedance element.

10. The apparatus according to claim 1, further comprising electrically insulating encapsulating means in which two probe elements forming a pair are embedded.