Lesson 2 - Principles of Process Control
This lesson explores exactly what process control is and explains why it is important. It examines the various levels within process control systems and identifies the associated equipment. It also takes a detailed look at the various automation communication and control elements.
Preface
Process control plays a crucial role in any modern-day operation. As it can be used at many different levels, it is thus important to understand the level at which you are operating.
So, what exactly is a process? A process is a series of action or operations imparting change on an item or product. In a brewery, many smaller processes are taking place to get us from grain to glass, e.g. from the raw material to having a beer in bottle on its way to the customer. These processes include crushing, heating, mixing, cooling, storing, and filtering, to name but a few. Within each of these processes, there are many things we can control.
This brings us to process control, which is the method we employ to control the steps within the process.
So, what is the importance of process control? To answer this, consider what you would want out of a process. Your answer is likely to be the best quality product, at the lowest cost, with the highest throughput, all delivered in a safe manner. This brings us to the aims of process control.
Process control aims to:
-
Reduce variability and produce a consistent product that meets specification.
-
Increase efficiency by optimising throughput and input costs.
-
Ensure the safety of employees, equipment, and the environment.
Let us now identify the various components of a process control system, or PCS.
-
The process (otherwise we would have nothing to control).
-
Sensors or instruments that provide information about what is happening in the process. (We will cover process instruments in detail in the Process Instrumentation lesson.)
-
Control systems that act on the information, based on the parameters in it.
-
Control elements, which are the components in the process that the control system can use to control the process.
-
The communication network that links everything together.
Before we continue, let us make one more distinction between controlling a process and controlling a variable. Controlling a process can involve lots of steps and be carried out by sequence control, whereas controlling a variable can have various mechanisms, including a process control loop.
Let us now explore the processes in more detail.