units such as yarn storage feeder devices which operate to store yarn temporarily for use by user means such as a loom application_number US 46583583 A description a system is shown in fig1 for detecting and monitoring erratic operation of the rotary electromagnetic armature of a d c motor 15 coupled to a variable voltage d c power soruce 16 by means of the brush commutator or slipring assemblies 17 18 the d c power source rectifies and filters current from an a c power line source 19 by means of a silicon controlled rectifier duty cycle control circuit 20 other conventional power supplies including batteries could be used in accordance with the present invention motor 15 may be alternatively a series wound universal a c d c motor operable from an a c power source or another device having a rotary electromagnetic member coupled to a power source by a brush and commutator or slipring such as a generator erratic behavior of motor 15 precedes motor failure and is indicated when abnormal current occurs such as from weak or improperly operating brush bias springs or nearly worn out brushes etc this abnormal current is accompanied by high frequency impulses and thus in accordance with the present invention is separated from any lower frequency electromagnetic waves occuring in normal operation of the motor by the build.