Speed Control of A DC Motor Using PLC and PIC Microcontroller

A Programmable Logic Controller (PLC) is a specialized computer like device used in industrial process control, replacing banks of electromagnetic relays. Here, the speed of a Permanent Magnet Direct Current (PMDC) motor is controlled under load condition by a PID Controller simulated in the PLC Platform using the Siemens step S7 software. The PLC used is Siemens CPU224XPsi. The reason behind the PID to be implemented in the PLC program is for the system to have a better response and less error. The loading on the PMDC motor is through eddy current braking. As the loading on the motor cannot be quantified, observations were made for specific loading positions. The performance of the motor was examined under three conditions- (i) Motor without feedback and without controller, (ii) Motor with feedback without controller and (iii) Motor with feedback and controller. The performance of a PMDC motor was also studied through actual hardware implementation. Here a Peripheral Interface Controller (PIC) Microcontroller is used to integrate a number of functions like optical method of measurement and display of speed of the motor, feedback and implementation of the PID controller. The transistor-based motor drive is activated by variable Pulse Width Modulation (PWM) output from the microcontroller.