Concept and Application of PID Control and Implementation of Continuous PID Controller in Siemens PLCs

Background/Objectives: The main objectives are to define the concept and application of PID control in parallel structure of PID controller and to describe implementation of the continuous PID controller in SIMATIC STEP 7. Methods/Statistical Analysis: Various designs of PID controllers in SIMATIC STEP 7 are available for different kinds of feedback control systems. Parallel structure is used in the algorithm of PID controllers in Siemens PLCs. In this study PID controller with the continuous control function block FB41 (CONT_C) is analyzed. Programming with PID controller in Siemens PLCs with continuous Manipulated Variable output and the option of influencing the Manipulated Value manually is thoroughly discussed. Findings: PID controller is the most common form of feedback control and it can be found in all the areas where control loops exist. The simplicity of understanding of the PID algorithm is one of its advantages but due to a wide range of systems and different manufacturers of control systems with various design and tuning methods of PID controllers in their products, the implementation process gets complicated. This difficulty is reduced by using several kinds of PID controllers for different types of systems in Siemens control systems. FB41 is a function block of continuous PID controller which was designed for Siemens PLCs to provide control performance with analog signals; it can function both in a manual and automatic mode.The most important part of FB41 functioning is addressing of the analog Input and Output in this function block. The results of P, I, D, PI, PD and PID controller implementation in FB41 have been compared. Applications/Improvements: This continuous control function block can be used in different kinds of control loop systems where analog input is sensed and analog output is required.