PLC-based industrial temperature controller with different response times

This work presents a temperature control of industrial ovens using block FB58 “TCONT_CP” from the Siemens S7-300 PLC, which is evaluated by the OB35 interrupt. Two plants were considered. The first plant was a small industrial oven made of aluminum of size 1.5 cm × 5 cm and taking in 60 W of heat. The second plant was a large industry oven with a 0.125 m3 capacity, capable of exuding 1500 W of heat. Both experiments were controlled by the same Block Command and ovens were tested separately. The Cohen-Coon PID tuning method was firstly applied to both plants, with a separate controller values being obtained for each plant. These values were kept fixed throughout the experiments. A tailored approach was adopted whereby a pulse gen was used in conjunction with the PID control for the small plant; whereas a control zoning was used for the larger plant. Result show that the tailored approach yielded significant improvements in settling times compared to a conventional PID controller.