SCADA Basics

A SCADA Basics 101 Overview

SCADA systems are an important part of modern day industries. A SCADA system operates over coded signals in communication channels for monitoring and control of remote equipment.

Modern day SCADA systems combine data acquisition systems to inquire the status of remote equipment for display or recording purposes.

PLC Basics and its role in the SCADA Systems

PLCs stand for Programmable Logic Controllers. These are used for monitoring inputs. Depending on the statistics from these inputs, decisions are taken for automating machines or processes. In most conventional systems, PLC controllers usually preside as the central part of the process control systems. With the help of PLC, it becomes possible to connect multiple systems to the central computer for running more complex problems.

PLC units are programmable solid-state electrical interfaces which manipulate, execute and monitor process states and communication systems at a very fast speed. The basis of PLC operation in the programmable data over an integral microprocessor-based machine. PLC unit can receive and transmit input and output for electrical signals for practically all kinds of mechanical or electronic systems. With this flexibility, these units are used as interfaces in setups with large and complex work-flows. PLCs are usually programmed over relay ladder logic. When combined with the SCADA systems, they can operate effectively in an industrial environment.

Following are the advantages of PLC controllers

  • Tough, designed for withstanding temperature, vibrations, noise and humidity
  • Interfaces for input and outputs already inside the controller
  • Easily programmable with simple, easily comprehensible programming language.

SCADA Programming Basics

SCADA systems usually work toward monitoring and controlling entire sites, systems or complexes which are spread out over vast areas. On the most basic level, the host control functions are restricted to the overriding at the basic or supervisory levels. For instance, PLC unit can control the flow of coolant water through one part of the industrial process. However, the SCADA system will prompt the operators for changing the set point for the flow, enabling alarm conditions and creating and logging events for record and display. The feedback loop usually passes through the PLC or RTU while SCADA handles the overall loop performance.

Telemetry Basics

Simple Telemetry System
Simple Telemetry System

Telemetry is the measurement of remote quantities or variables. Telemetry is crucial to measuring these remote variables in cases where either the variable is distant or either the variable is inaccessible.

Elements of Basic Telemetry

  • Sensor or Transducer: This converts the physical variable which has to be measured into an electrical parameter such as inductance, variable resistance or capacitance or an electrical signal such as current or voltage.
  • Signal Conditioner -1: This is used for converting electrical output from a transducer into an electrical signal which is compatible with the transmitter.
  • Transmitter: This transmits the information signal coming from signal conditioner-1 to the receiving end.
  • Signal Transmission Medium: Link which connects the transmitting end with the receiving end.
  • Receiver: Used for reception of signals coming from the transmitter and recovering information.
  • Signal Conditioner-2: The receiver output is processed with this for driving the device.
  • End Device: This appears at the end of the system and performs analog indication, digital storage and display, closed loop control and data processing.


MODBUS is an application layer protocol. It is based on client and server architecture and was published by Modicon. MODBUS is primarily employed in industrial implementations.

The protocol follows a client-server architecture where a client requests data from the server or request the server to perform some action. The process in initiated by sending a request representing the transaction to be performed. The transaction performed by MODBUS shows the process used by the controller for requesting access for another device, how to respond to requests from other devices and detection of errors and their reporting. For all contents of the message fields, the protocol establishes a similar format for layout. During communication on MODBUS, the protocol also determines how to send device address to each controller, recognize the issues and messages address to it, implement the action to be taken and retrieve data and other information contained inside the message.

Controllers in MODBUS communicate working on a master and slave technique. In this technique, only a single device called as the master can initiate query or transactions. The slaves on the other hand, respond by providing the requested data or performing the task as assigned to them by the master. Some of the typical master devices include programming panels and host processors. Some of the slaves include programmable controllers.

Elements of SCADA Programming

The mode of programming depends on the system. In some setups, logic chains are designed which are performed when trigger events occur. These setups are common in the manufacturing industry.

In larger setups such as power utilities, railways, etc., the networks are large scale. The SCADA systems used here are simple interfaces with little programming as most of the modules will already be developed beforehand. The preferred mode of creating modules is the C language or the derived programming language. However, the SCADA PLCs are flexible and easily programmable. While the SCADA modules require maintenance, the PLCs need to be programmed to suit the needs of the specific industry they are installed in.

Basics of SCADA training

Most modern day SCADA training programs follow a specific format for the training. This includes the overview, class and conclusion, preferably wrapping up with certifications from industry. The courses are flexible enough so that they can be acclimatized with the business needs.

The training courses focus over the principles behind SCADA, Industrial Network Security, Industrial Control Systems, Securing Infrastructure Networks for Smart Grid as well as SCADA engineering. Some of the other highlights of these training modules includes basics of SCADA systems, its architectures, security vulnerabilities, communication protocols and theory of operations. With proper SCADA training, employees can understand the potential benefits of applying SCADA systems into their domain.