The rotational speed of a DC motor is directly proportional to the mean value of its supply voltage when operated under pulsed condition. If the motor is operating at a frequency 'f' and at an operating voltage of say +24V DC, then the pulse amplitude from the driver has to be 24V DC under all conditions at the given frequency. Under these conditions the speed is dependent on the duty cycle of the pulses from the driver. This type of circuit provides complete speed control from minimum to maximum speeds at reasonably high torque. The trainer makes use of a chopper circuit for speed control.

This trainer has all the facilities to vary the speed of the DC motor, observe wave forms at different test points in the circuit, namely at the output of oscillator, amplifier, driver, and at motor terminals. A recording of these observations in terms of amplitudes, pulse width, shape of pulses will provide a good understanding of how speed control can be achieved at different speeds.

This trainer is intended to demonstrate the speed control of a permanent magnet DC motor. This motor is mechanically coupled to a Tacho-Generator. Changing the voltage of armature from 0 to 24VDC controls the DC motor speed. As the voltage varies, the armature current increases and in turn the speed increases.

The change in armature voltage can be changed in this trainer

• Either by varying a potentiometer by DC voltage control or
  
• By pulse width modulated CHOPPER DRIVE, or
  
• It is possible to provide external pulses modulation from your circuitry also for exciting the motor. This external pulse modulation can be provided from any external controller like Microprocessor trainers Model MPT-85 or MPT-J-85 or MPT-86, Microcontroller trainer Model MCT-31, PLC trainer Model IM-29 or and Data Acquisition System Trainer Model DAS-1.