IMPLEMENTATION OF CASCADE CONTROL USING A PROGRAMMABLE LOGIC CONTROLLER

The aim of the project is to implement cascade control using a Programmable
Logic Controller (PLC). The PLC module has been successfully used for
ON/OFF control in sequential processes. However in this project the PLC has to
be configured to accept and monitor a variable input and to supply a variable
output ( 4mA to 20mA) signal in-order to control a final element (e.g. control
valve). The significance of this project is to make a comparison between a PLC
and a distributed control system (DCS) in terms of controllability and system
simplicity. The project requires familiarization in the field of plant process
control and instrumentation since it involves the design and implementation of a
cascade loop. The cascade controller has been designed to control the level of a
liquid in a distillation tower. Familiarization with the PLC hardware and software
is another important aspect of the project and took up the bulk of the project time.
The final result of the project shows that the PLC is a versatile controller that is
able to perform PID control effectively with a relatively simple system. The PLC
PID control system is flexible therefore it can be configured to implement any
type of control loop e.g. Cascade control.