PLC & SCADA SYSTEMS: Quick Reference Guide

The programmable logic controller represents a key factor in industrial Automation. Its use permits flexible adaptation to varying processes as well as rapid fault finding and error elimination.

This book has detailed Project that explain the practical concept of PLC & SCADA Systems and it will be useful for Students, Technicians and design professionals. This Guide explain the each topic with real time projects and case studies

This textbook explains the design of a programmable logic controller and its interaction with peripherals. It gives details of the different type of PLC’s available and why one is chosen over another.

The book has a whole section detailing the different ways a PLC can be programmed, and gives example of each programming method such as Ladder Logic

In the interest of continual further improvement, all readers of this book are invited to make contributions by way suggestions, ideas and constructive criticism.

If you use PLC & SCADA combination the advantages you have is you have better monitoring and control of the plant and also you have access to the information the way you want. SCADA enables engineers, supervisors, managers and operators to view and interact with the workings of entire operations through graphical representation of their production process.  SCADA runs on a PC and is generally connected to various PLCs and other peripheral devices. It enables you to generate applications for the most demanding requirements of plant engineers, operators, supervisors and managers tailored precisely to the needs of each plant. SCADA constantly gathers data from the plant in real-time, stores and processes it in the database, evaluates and generates alarms, displays information to plant operators, supervisors and managers and can issue instructions to PLCs on the plant floor.

Programmable Logic Controller, or PLC, is more or less a small computer with a built-in operating system (OS). This OS is highly specialized to handle incoming events in real time, or at the time of their occurrence.  The PLC has input lines where sensors are connected to notify upon events (e.g. temperature above/below a certain level, liquid level reached, etc.), and output lines to signal any reaction to the incoming events (e.g. start an engine, open/close a valve, etc.).  The system is user programmable. It uses a language called “Relay Ladder” or RLL (Relay Ladder Logic). The name of this language implies that the control logic of the earlier days, which was built from relays, is being simulated

The PLC is primarily used to control machinery. A program is written for the PLC which turns on and off outputs based on input conditions and the internal program. In this aspect, a PLC is similar to a computer. However, a PLC is designed to be programmed once, and run repeatedly as needed. In fact, a crafty programmer could use a PLC to control not only simple devices such as a garage door opener, but their whole house, including switching lights on and off at certain times, monitoring a custom built security system, etc.  Most commonly, a PLC is found inside of a machine in an industrial environment. A PLC can run an automatic machine for years with little human intervention. They are designed to withstand most harsh environments.

SCADA systems typically implement a distributed database, commonly referred to as a tag database, which contains data elements called tags or points. A point represents a single input or output value monitored or controlled by the system. Points can be either “hard” or “soft”. A hard point represents an actual input or output within the system, while a soft point results from logic and math operations applied to other points. (Most implementations conceptually remove the distinction by making every property a “soft” point expression, which may, in the simplest case, equal a single hard point.)