GB871669A - Transducing apparatus - Google Patents

Abstract

871,669. Electromagnets. FOXBORO CO. Sept. 9, 1959 [Sept. 15, 1958], No. 30842/59. Class 35. [Also in Group XXXVIII] In a device for producing, electromagnetically, a torque to balance that produced by a variable force to be measured, e.g. a force produced by the differential pressure across an orifice type flow-meter, the magnetic circuit is provided with two sets of air gaps, one producing the main balancing torque, the magnetic circuit including materials of low hysteresis and a second set of air gaps producing a small opposing torque, the magnetic circuit including materials having high hysteresis so that the resultant torque has negligible hysteresis. The development of the restoring torque on the armature is illustrated in Fig. 9, which shows the armature 62 which rocks about 66 surrounded by coil 88, the magnetic circuit being completed by parts 74 and 78. A steady magnetic flux indicated at 104, 106, 108 and 110 is maintained between parts 74 and 78 by permanent magnets 84 and 86, Fig. 6 (not shown). Flux due to current in coil 88 is indicated at 112, 114 and 116 and it can be seen that with flux in the direction indicated by the arrows the flux in the main gaps, i.e. between the armature and poles 72, 76, 80 and 82 will produce an anti-clockwise torque on armature 62 while flux in the auxiliary gaps 96 and 98 will produce a clockwise torque, this clockwise torque will be comparatively small with regard to the anti-clockwise torque but having comparatively high hysteresis since parts 92 and 94 of armature 62 are of ordinary steel having high hysteresis while the remaining parts of the magnetic circuit are of material having low hysteresis the net effect being that the hysteresis effects of the two torques will cancel. In an alternative form, Fig. 11 (not shown), the auxiliary poles of high hysteresis material are attached to the coil pole-pieces rather than the armature.