Apparatus for monitoring the air gap in rotary electrical machines using magnetic field plates or magneto diodes

Claim 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.