System for controlling motor speed

摘要

A motor has a shaft carrying a dielectric disk on whose edge is fitted an undulating iron ring formed with a plurality of angularly equispaced points that pass beneath a magnetic detector head that generates a sinusoidal voltage signal having a frequency proportional to the rotation velocity of the shaft. This sinusoidal signal is clipped at a minimum signal level and then fed to an amplifier once it has passed through a resonant circuit tuned to a frequency corresponding to the desired motor rotation speed. The output side of this resonant circuit is connected via a capacitor and variable resistance to the input of a Schmitt trigger which operates a relay controlling the motor so as to maintain the motor speed within a desired range.