'Control of an industrial process using PID control blocks in automation controller

摘要

Many continuous industrial processes can be controlled using programmable automation controllers for digital implementation of classical PID control. For this type of applications, a PID control block has been developed for use in the programming environment PCWorx. Two types of PID control of tank level are discussed: single point control and cascade control. The single point control uses a single PID controller to regulate tank level using a single measurement for feedback being tank level itself. The PID controller output determines the state of the feed valve. The system has limitations in reacting to variations in output flow, which is to be regarded as a system disturbance. The cascade control uses two PID controllers for a better performance of the level control. The master controller is the level controller using the level setpoint and measurement to determine the setpoint for the slave controller driving the input flow valve. Measurements of input and output flow are taken into account, enabling the system to faster respond to output flow disturbances. Both types of control have been implemented using the PID control block in PCWorx for programming a Phoenix Contact PLC. The physical system, tank level control, was simulated in the process simulation environment ProcesSim running on the host PC. This virtual process environment enables the automation engineer to implement and test a PLC program controlling a process without having the actual installation physically available. Results of the PID controllers implemented within a Phoenix Contact PLC type ILC 150 ETH, linked to the simulated process in ProcesSim are presented.