In this article will be shown how to design a PID regolator with Scilab, for temperature control in a industrial oven used for metal harding. The temperature regolation’s target is to hold the real temperature inside the oven as near as possible to the time dependent value generated by the PLC software ( the operator put in the software just the values of initial and final temperatures and period duration for each segment of temperature’s curve ).
The setpoint temperature, hence, follow a curve programmed with ramps and flat segments till the final value of 1020°C and at the end of the automatic cycle the temperature falls in very short time to material’s harding. The system measures the temperature inside the oven with a K Thermocouple connected to a specific module of PLC. The oven heating is possible with a SCR Driver module that drives heating resistor inside the oven. The heating phase is make in vacuum environment and so the heat trasfer is possible through irradiance. The Power sent to the resistors is regolated by the analog driver input, connected to the PLC analog 4 - 20 mA output.
The PID controllerr is used in the PLC software in order to receive the measured temperature, the setpoint temperature and to generate the power level for the Resistors Driver. In this way the PID response allows the temperature following.
Scilab Simulation of whole system ( Process and Control ) and temperature / power trends are compared to show the results.