. Practical wireless telegraphy; a complete text book for students of radio communication . he commutator acts to main-tain in the same direction the flow of current through the two sides of the armature , the upper half of the armature will always be a south pole while the lowerhalf will be a north pole, irrespective of the speed at which the armature revolves. Now it would have no effect on the general direction of rotation if the connections from the source of current to the motor werereversed because the polarity of the fluxin both the armature and the field poleswould b
. Practical wireless telegraphy; a complete text book for students of radio communication . he commutator acts to main-tain in the same direction the flow of current through the two sides of the armature , the upper half of the armature will always be a south pole while the lowerhalf will be a north pole, irrespective of the speed at which the armature revolves. Now it would have no effect on the general direction of rotation if the connections from the source of current to the motor werereversed because the polarity of the fluxin both the armature and the field poleswould be reversed accordingly and be-cause the strain of the two magnetic fieldswould have the same general directionthe motor would revolve in the same di-rection as before. Careful considerationof this fact reveals that in order tochange the direction of rotation of thearmature, the flow of current^ must bereversed independently in either thearmature or field VOLT j^.j^^ generators, motors may have ^- lfiSi?iS„orMa^eficFiefdst a^MoVor. either series, shunt, or compound wind-. 30 PRACTICAL WIRELESS TELEGRAPHY. ings. The type known as the diflferential wound motor appears in Fig. 29 and will bedescribed further on. 39. The Effect of Counter Electromotive Force.—When a motor armatureis set into motion by an external current, the loops of wire composing its coils cut throughthe magnetic field and induce a reverse electromotive force counter to that which originallycaused the motion. This back pressure is known as counter electromotive force which gov-erns directly the speed of a motor. The difference between the impressed and the countervoltage determines the actual flow of current in the armature and the counter voltage isproportional to the speed of the armature, the number of armature wires and the strengthof the magnetic field which is enclosed. The speed of a motor supplied with current at constant pressure varies directly with thecounter electromotive force and
Size: 2044px × 1223px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjecttelegra, bookyear1917
