Electrical motor circuits

Claim 2

A circuit comprising a motor, a control circuit for energising the motor with pulses of current, a safety circuit for monitoring selected elements of the control circuit and a relay for disabling the motor, in which the safety circuit is oscillatory at a relatively high frequency and includes at least one closed loop and means for disabling the loop on the occurrence of predetermined conditions in the control circuit; and in which the said relay is operative to disable the motor in the absence of oscillation by the oscillatory safety circuit.

Claim 3

A circuit according to claim 1 in which the control circuit includes a thyristor in series with the motor and a sensing circuit coupled to sense the motor''s armature current and provide an output dependent thereon, in which the oscillatory safety circuit includes two alternative oscillatory loops, means for disabling one of the loops when said thyristor is conductive and means for disabling the other loop when said output reaches a preset level.

Claim 4

A circuit according to claim 1 in which the said relay is normally open and energised and is arranged when closed to short circuit together the ends of two opposed series field windings of the motor.

Claim 5

A circuit comprising a direct current motor with an armature and at least one field winding; a control circuit for energising the motor with pulses of current, said control circuit including a first thyristor in series with said field winding; means for rendering said thyristor intermittently conductive; means for sensing current in said armature; switch means having an open energised state and a closed de-energised state, said switch means effecting disabling of said motor when in said closed de-energised state; a safety circuit comprising an oscillator having first and second alternative feedback loops; bias means coupling said thyristor to said first loop for disabling same on conduction of said thyristor; further bias means coupling said means for sensing to said second loop for disabling same on occurrence of a predetermined level of armature current; and means coupling said oscillator to said switch meAns for de-energising said switch means in the absence of oscillation by said oscillator.

Claim 6

A circuit comprising a direct current motor with an armature and at least one field winding; a control circuit for energising the motor with pulses of current, said control circuit including a first thyristor in series with said field winding; means for rendering said thyristor intermittently conductive; means for sensing current in said armature; switch means having an open energised state and a closed de-energised state, said switch means effecting disabling of said motor when in said closed de-energised state; a safety circuit comprising an oscillator having first and second alternative feedback loops; bias means coupling said thyristor to said first loop for disabling same on conduction of said thyristor; further bias means coupling said means for sensing to said second loop for disabling same on occurrence of a predetermined level of armature current; and means coupling said oscillator to said switch meAns for de-energising said switch means in the absence of oscillation by said oscillator.

Claim 7

A circuit according to claim 4 in which said motor has two series field windings which are jointly coupled at one end to the armature and said switch means includes a relay for connecting the other ends of the windings together.

Claim 8

A circuit comprising a direct current source, a direct current motor with an armature and two opposed series field windings having first ends jointly coupled to the armature and second ends, current chopper circuits between each of said second ends and said source of direct current, means for selecting one or other of said current chopper circuits for operation, means for supplying pulses to one or other of said windings selectively, and a relay having an open energized state and a closed de-energized state, said relay in said closed state connecting said second ends together.

Claim 9

A circuit comprising a direct current source, a direct current motor with an armature and two opposed series field windings having first ends jointly coupled to the armature and second ends, current chopper circuits between each of said second ends and said source of direct current, means for selecting one or other of said current chopper circuits for operation, means for supplying pulses to one or other of said windings selectively, and a relay having an open energized state and a closed de-energized state, said relay in said closed state connecting said second ends together.