A method and apparatus for slowing back spin of a rod string of a progressing cavity pump powered by an electric motor when power is lost. Pulse direct current voltage into the windings of the electric motor powering the progressing cavity pump to magnetize a stator of the electric motor thereby reducing the rotational speed of a rotor of the electric motor and consequently the rotational speed of the back spinning rod string of the progressing cavity pump.

In a tape drive system, a dynamic brake control circuit provides dynamic braking for slowing and stopping an associated tape reel and motor system in the event of a power failure. Upon sensing a power failure, the electrical energy stored in a capacitor supplies electrical energy to enable the control circuit, which in turn supplies a controlled conductive path for the flow of a dynamic braking current due to the back electromotive force signal generated by the motor, to effect the controlled dynamic braking of the drive motor to a stop.

An apparatus comprising, in combination, an AC motor, a solid state switch controlling the AC motor, the solid state switch switchable between an on state in which an electric current flows through the solid state switch and an off state in which electric current does not flow through the solid state switch, the solid state switch characterized by a turn off time such that, when the solid state switch is switched between the on state and the off state, at least a portion of the electric current flows through the solid state switch during the turn off time, a first switch circuit for switching off the solid state switch to prevent the electric current from flowing to the AC motor, a diode bridge coupled across the AC motor, a second switch circuit for controllably switching the diode bridge between an active state in which electric current may flow through the diode bridge and an inactive state in which electric current may not flow through the diode bridge, a control circuit for controlling the second switch circuit to switch the diode bridge into an active state a predetermined time period after the solid state switch is turned off, said predetermined time period longer than the turn off time of the solid state switch and shorter than an EMF degradation time, wherein back EMF of the AC motor is rectified into a DC current and injected back to the AC motor to provide high torque braking of the AC motor while avoiding a short circuit condition.

The invention relates to a method for enhancing the dosing precision of a dosing pump which is driven by an asynchronous motor via an eccentric gear. The supply of the motor is cut off approximately half a cycle time before a desired dosing pause period or stoppage. The motor freewheels afterwards for part of the cycle time, before a direct voltage is applied to it for approximately a quarter cycle time, such that an eddy current is induced in the rotor, which produces an antipolarized magnetic field which brakes the rotor.

Arrangement for winding of an electric cable which arrangement comprises a rotatable drum from which the cable is arranged to be wound off manually, and an electric motor (M) arranged to be connected to a first circuit for driving the drum in the winding direction and arranged to be rotated by the drum during unwinding of the cable. A second circuit (M,1,3,4) comprises besides the motor (M) also a contact means (1) arranged to be closed when the motor (M) is inoperative. During unwinding of the cable from the drum the motor generates a braking moment which increases with the speed of rotation of the motor. The second circuit preferably comprises a voltage dependent switch (3), preferably a Zener-diode, which is arranged to be closed when the voltage generated by the motor (M) during the unwinding exceeds a value corresponding to a predetermined speed of rotation of the drum and, as a consequence, of the motor.