Using PLC for custom-design of a PID/PWM program to control a heater temperature

Abstract

This is a practical approach to control a continuous-time process variable (temperature) using a discrete controller (PLC) and a custom-designed software control algorithm and hardware interface, in a closed-loop system. Unlike the conventionally known technique of transforming a digital control action into a proportional analogue one by a D/A converter followed by power amplifier, the control action was formed internally by the PLC as a PID/PWM signal, which was used to trigger the power stage. This approach helped reducing the error due D/A conversion, maximized utilization of the PLC and reduced total cost. The control system is realized by utilizing the heater of the training board (RGT1), manufactured by DL-lorenzo Company and it simulates an analogue heating control system. The PLC is Siemens Simatic S7-214 model. An experimental result has shown that the control algorithm functions perfectly. © 2007 Science Publications.