Motor speed detector

Claim 1

A method for detecting rotational speed of a motor, comprising the step of: (a) producing a first signal comprising real tachometer pulses responsive to revolution of rotor armature segments of said motor and false tachometer pulses responsive to extraneous non-rotor components of said motor, both said real and false tachometer pulses increasing in amplitude with increasing rotational speed of said motor, (b) producing a second signal with amplitude representative of the maximum amplitude of said real tachometer pulses, (c) producing a third signal with amplitude less than that of said second signal and exceeding the maximum expected amplitude of said false tachometer pulses, and (d) comparing said first and third signals to discriminate against said false tachometer pulses and produce a fourth signal that is directly proportional to the rotational speed of said motor as represented solely by said real tachometer pulses.

Claim 2

A method for detecting rotational speed of a motor, comprising the step of: (a) producing a first signal comprising real tachometer pulses responsive to revolution of rotor armature segments of said motor and false tachometer pulses responsive to extraneous non-rotor components of said motor, both said real and false tachometer pulses increasing in amplitude with increasing rotational speed of said motor, (b) producing a second signal with amplitude representative of the maximum amplitude of said real tachometer pulses, (c) producing a third signal with amplitude less than that of said second signal and exceeding the maximum expected amplitude of said false tachometer pulses, and (d) comparing said first and third signals to discriminate against said false tachometer pulses and produce a fourth signal that is directly proportional to the rotational speed of said motor as represented solely by said real tachometer pulses.

Claim 4

A system for detecting rotational speed of a motor, comprising: (a) a magnetic sensor, responsive to the rotational motion of said motor for producing a plurality of real tachometer pulses in response to the revolution of rotor armature segments of said motor past said magnetic sensor as well as a plurality of false tachometer pulses in response to the movement of extraneous non-rotor components of the motor past said magnetic sensor, both said real and false tachometer pulses increasing in amplitude as the rotational speed of said motor increases, (b) a capacitor to which said real and false tachometer pulses are applied, said capacitor charging to the level of the largest amplitude tachometer pulses, (c) a resistive divider across said capacitor, said resistive divider providing a trip level signal that is a select percentage of the voltage across said capacitor, said percentage being selected such that the trip level signal always exceeds the largest amplitude false tachometer pulse expected for the particular rotational speed of said motor, (d) means for establishing a reference signal that is representative of the amplitudes of said real tachometer pulses for the minimum rotational speed of said motor at which none of said false tachometer pulses are produced, (e) a comparator, (f) means for applying said trip level signal to a first input of said comparator when it exceeds said reference signal, and (g) means for applying said real and false tachometer pulses to a second input of said comparator, said comparator producing output pulses in response to real tachometer pulses that exceed said trip level signal and discriminating against false tachometer pulses that do not exceed said trip level signal, said output pulses being thereby directly proportional to the rotational speed of said motor.

Claim 5

A system for detecting rotational speed of a motor, comprising: (a) a magnetic sensor, responsive to the rotational motion of said motor for producing a plurality of real tachometer pulses in response to the revolution of rotor armature segments of said motor past said magnetic sensor as well as a plurality of false tachometer pulses in response to the movement of extraneous non-rotor components of the motor past said magnetic sensor, both said real and false tachometer pulses increasing in amplitude as the rotational speed of said motor increases, (b) a capacitor to which said real and false tachometer pulses are applied, said capacitor charging to the level of the largest amplitude tachometer pulses, (c) a resistive divider across said capacitor, said resistive divider providing a trip level signal that is a select percentage of the voltage across said capacitor, said percentage being selected such that the trip level signal always exceeds the largest amplitude false tachometer pulse expected for the particular rotational speed of said motor, (d) means for establishing a reference signal that is representative of the amplitudes of said real tachometer pulses for the minimum rotational speed of said motor at which none of said false tachometer pulses are produced, (e) a comparator, (f) means for applying said trip level signal to a first input of said comparator when it exceeds said reference signal, and (g) means for applying said real and false tachometer pulses to a second input of said comparator, said comparator producing output pulses in response to real tachometer pulses that exceed said trip level signal and discriminating against false tachometer pulses that do not exceed said trip level signal, said output pulses being thereby directly proportional to the rotational speed of said motor.