PURPOSE: To make it possible to calculate motor torque easily and precisely by finding the slip factor of an induction motor by measuring a pulse signal proportional to the rotation speed of the induction motor.
CONSTITUTION: Contactless adjacent sensor 9 is provided for rotation detection of rotary shaft 8 of induction motor 7 to generate a pulse signal of a frequency proportional to its rotation speed, and the signal is divided by divider 10. Pulse generating circuit 12 generates a pulse signal of a frequency proportional to a power frequency, and divider 13 divides it. A reference clock pulse generated by high- frequency oscillator 14 is led to gate circuit 15 and on the basis of this reference clock pulse, gating operation between both pulse signals of dividers 10 and 13 is performed. Then, arithmetic is carried out by up-and-down counter 16 and latch circuit 17 to find the slip factor of induction motor 7, and from the result, a signal corresponding to the motor torque can be obtained.
OKUNO TOSHIYUKI
NAKANO TOSHIO
