A commonly asked question of people who are new in the control engineering world is just that–“What is the difference between PLC and SCADA?”

Scada For Dummies Pdf
Scada For Dummies

The difference between them is that the PLC is hardware based and SCADA is software based. While both fall under the category of “control systems”, SCADA provides greater capability than the PLC with the help of several components.

7 Siemens PLCs Siemens makes several PLC product lines in the SIMATIC® S7 family. They are: S7-200, S7-300, and S7-400. S7-200 The S7-200 is referred to as a micro PLC because of its small size. The S7-200 has a brick design which means that the power supply and I/O are on-board.
SCADA stands for Supervisory Control And Data Acquisition. As the name indicates, it is not a full control system, but rather focuses on the supervisory level. As such, it is a purely software package that is positioned on top of hardware to which it is interfaced, in.

Optimally, you would want to use the capabilities of both types of control systems in order to meet design expectations while becoming more cost-efficient (in the long run).

SCADA’s connectivity Modbus TCP IP TCP Function code – reading/writing coils/registers Address - offset into register list Length - number of bits and coils Data – what you want to put to the device UnitID – which unit under the same IP address. SCADA stands for Supervisory Control and Data Acquisition; it is an industrial computer-based control system employed to gather and analyze the real-time data to keep track, monitor and control industrial equipments in different types of industries. Consider the application of SCADA in power systems for operation and control. SCADA Basics Theory Lecture no 1Twitter: Tutorial For Beginners.This video explains the basic concept of SCADA.E- Le.

Table of Contents

1 What is SCADA?
- 1.1 Components of SCADA systems
  - 1.1.2 Remote Terminal Unit
3 Where is SCADA used?
4 When SCADA is NOT used
- 4.1 Safety-Instrumented Systems

What is SCADA?

SCADA stands for Supervisory Control And Data Acquisition. It is a technology that enables the user to collect historical information from multiple facilities (even distant ones) and even supervise the control operations.

Of course, the historical information acquired from the whole data gathering system (usually from sensors and outcomes) are visualized by the user in order to perform a control decision on his discretion.

Usually, these data are analyzed statistically in order to optimize processes and/or systems. An example would be profit optimization for a production line.

Lately, SCADA systems have used the concept of Machine Learning or even Deep Learning to process data and automatically perform control decisions for the system.

The Learning system can act as a “brain” that can be taught about desirable or undesirable outcomes for a system based on VERY specific conditions of inputs and other parameters. It’s like the “most raw (hence, inferior) version” of Artificial Intelligence.

Scada For Dummies Pdf

Components of SCADA systems

A SCADA system is much more of a large-scale system than that of PLC systems. At the center of a SCADA system is the operator, whereas, in PLC control systems, the center is the PLC itself.

Central Control Unit

The operator has access to a visualization unit, usually called VDU or Video Display Unit in order to show real-time data regarding the conditions in the monitored facilities of the whole SCADA control system. These are provided to the operator via a Server computer (the “sink” of all data).

PLC systems, at large, operate independently even without the help of computers because the controller IS a computer itself. This makes a large difference between a PLC control system and a SCADA control system as SCADA systems cannot work using just the central component alone (of course, the statement assumes that there are input and output devices present). More on that later.

Remote Terminal Unit

The Server computer is connected to different distant control units called RTU or Remote Terminal Unit. Usually, the server computer connects to these RTUs through a transmission media.

These RTUs are the ones connected to the physical facilities of a process inside a SCADA system. The RTU pre-processes the data before sending it to the Server via transmission media.

Going back to my previous point, the PLC does not require any other interface for the input and output devices to become part of the system. SCADA systems require Remote Terminal Units to do so.

Then, what is the difference between the PLC and the RTU?

Good point. Both certainly have overlaps but in terms of how they can be controlled, as well as what tasks they were designed to do, they become much more different than you think.

RTUs are usually designed for remote communications between the server and itself. It is most commonly a pre-processor of the data that it receives from the connected devices, as well as a device to relay the command messages that come from the Server.

PLCs, on the other hand, are designed to actually control the devices in its immediate surroundings based on the PLC programming. The PLC does not rely on any other condition other than the signals that come from the connected input devices. However, the PLC does not concern itself of recording or relaying the data regarding the processes involved.

Hence, the RTUs are more inclined towards a manually operated type of control. In spite of being reliant on commands, RTUs have the advantage of being controlled REMOTELY as well as intelligently through careful decisions that are based on DATA.

On the other end of the spectrum, PLCs are more inclined towards an automated type of control. They only rely on the instantaneous conditions of the input devices connected but are more capable of controlling output devices without much supervision.

Transmission Media

In this context, transmission media refers to a dedicated communication medium between two Terminal Units–the Main Terminal Unit (Server) and the RTU.

Scada For Dummies

Fiber-optic cables are usually used for SCADA systems, while some use regular Digital Subscriber Lines (DSL) to interconnect the RTUs to the main server computer. Radio technology is also used. Hence, almost every communication technology available can technically be utilized for SCADA systems.

Modems

It is worth noting that the digital information can not be directly sent from one computer to another without modifying the signals in such a way that it would be able to propagate through the air/cables with minimal error and highest fidelity.

This is where modems are used. Modems stand for “Modulator-Demodulator”. Modulators transform a signal into a media-friendly form, and Demodulators transform that same signal back into the original signal.

Using these communication devices, SCADA systems are easily connected as a Local Area Network. What this means is you can easily control the processes in a SCADA system without you being physically present in the actual facility. You just need to send out control commands using the Server computer and you’re done.

PLC SCADA systems

Even though we wanted to differentiate the two systems in this post, some people may also ask if PLC and SCADA systems could work together.

PLC systems can work UNDER a SCADA system. With proper communication interfaces, usually Ethernet, you can definitely make a PLC control system work under a SCADA system.

Where is SCADA used?

The two systems, in terms of just controlling several devices and processes, can absolutely rival each other even in terms of capabilities: the SCADA is able to perform very well remotely and the PLC is able to perform very well locally.

However, when it comes to safety systems and product measurement systems, the convenience of SCADA may not be reliable.

That said, SCADA has a wide range of applications–not to mention they are also BIG areas of application. Here they are:

Hydroelectric Power Plants

These power plants have plenty of small hydroelectric generators which are grouped together. Based on the power demands, they are t