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SCADA (Supervisory Control and Data Acquisition) is a system that collects data from various sensors at a factory, plant, or in other remote locations and sends this data to a central computer that then manages and controls the data.

SCADA is a term that is used broadly to portray control and management solutions in a wide range of industries. Some of the industries where SCADA is used are Water Management Systems, Electric Power, Traffic Signals, Mass Transit Systems, Environmental Control Systems, and Manufacturing Systems. There are many parts in a working SCADA system. A SCADA system usually includes signal hardware (input and output), controllers, networks, user interface (HMI), communications equipment, and software. All together, the term SCADA refers to the entire central system. The central system usually monitors data from various sensors that are either in close proximity or off site (sometimes miles away).
For the most part, the brains of a SCADA system are the Remote Terminal Units (RTU). The Remote Terminal Units consists of a programmable logic converter. The RTU are usually set to specific requirements. However, most RTU allow human intervention. For instance, in a factory setting, the RTU might control a conveyor belt’s setting and humans can change or override the speed at any time. In addition, any changes or errors are usually automatically logged and/or displayed. Most often, a SCADA system monitors and makes slight changes to function optimally. SCADA systems are considered closed loop systems and run with relatively little human intervention.
One of SCADA’s key processes is its ability to monitor an entire system in real time. Data acquisitions including meter reading, checking sensor statuses, etc. that are communicated at regular intervals depending on the system facilitate this. Besides the data that the RTU uses, data is also displayed to a human that interfaces with the system to override settings or make changes when necessary.
SCADA can be seen as a system with many data elements called points. Usually, each point is a monitor or sensor and can be hard or soft. A hard data point can be an actual monitor, while a soft point can be seen as an application or software calculation. Data elements from hard and soft points are always recorded and logged to create a time stamp or history
 
User Interface (HMI)
A SCADA system includes a user interface called a Human Machine Interface (HMI). The HMI of a SCADA system is where data is processed and presented to be viewed and monitored by a human operator. This interface usually includes controls where the individual can interface with the SCADA system.
HMIs are an easy way to standardize the facilitation of monitoring multiple RTUs or PLCs (programmable logic controllers). RTUs or PLCs run a pre programmed process, but monitoring each of them individually can be difficult because they are spread out over the system. Because RTUs and PLCs historically had no standardized method to display or present data to an operator, the SCADA system communicates with PLCs throughout the system network and processes information that the HMI easily disseminates.
HMIs can also be linked to a database, which can use data gathered from PLCs or RTUs to provide graphs on trends, logistic info, schematics for a specific sensor or machine, or even make troubleshooting guides accessible. In the last decade, practically all SCADA systems include an integrated HMI and PLC device, making it extremely easy to run and monitor a SCADA system.
 
SCADA Software and Hardware Components
SCADA systems are an extremely advantageous way to run and monitor processes. They are great for small applications such as climate control or can be effectively used in large applications such as monitoring and controlling a nuclear power plant or mass transit system.
SCADA can come in open and non-proprietary protocols. Smaller systems are extremely affordable and can either be purchased as a complete system or can be mixed and matched with specific components. Large systems can also be created with off the shelf components. SCADA system software can also be easily configured for almost any application, removing the need for custom made or intensive software development.

Data Acquisition
First, the systems you need to monitor are much more complex than just one machine with one output. So a real-life SCADA system needs to monitor hundreds or thousands of sensors. Some sensors measure inputs into the system (for example, water flowing into a reservoir), and some sensors measure outputs (like valve pressure as water is released from the reservoir).
Some of those sensors measure simple events that can be detected by a straightforward on/off switch, called a discrete input (or digital input). For example, in our simple model of the widget fabricator, the switch that turns on the light would be a discrete input. In real life, discrete inputs are used to measure simple states, like whether equipment is on or off, or tripwire alarms, like a power failure at a critical facility.
Some sensors measure more complex situations where exact measurement is important. These are analog sensors, which can detect continuous changes in a voltage or current input. Analog sensors are used to track fluid levels in tanks, voltage levels in batteries, temperature and other factors that can be measured in a continuous range of input.
For most analog factors, there is a normal range defined by a bottom and top level. For example, you may want the temperature in a server room to stay between 60 and 85 degrees Fahrenheit. If the temperature goes above or below this range, it will trigger a threshold alarm. In more advanced systems, there are four threshold alarms for analog sensors, defining Major Under, Minor Under, Minor Over and Major Over alarms.

Data Communication
 Early SCADA networks communicated over radio, modem or dedicated serial lines. Today the trend is to put SCADA data on Ethernet and IP over SONET. For security reasons, SCADA data should be kept on closed LAN/WANs without exposing sensitive data to the open Internet.
Real SCADA systems dont communicate with just simple electrical signals, either. SCADA data is encoded in protocol format. Older SCADA systems depended on closed proprietary protocols, but today the trend is to open, standard protocols and protocol mediation.
Sensors and control relays are very simple electric devices that cant generate or interpret protocol communication on their own. Therefore the remote telemetry unit (RTU) is needed to provide an interface between the sensors and the SCADA network. The RTU (Remote Telemetry Unit) encodes sensor inputs into protocol format and forwards them to the SCADA master; in turn, the RTU (Remote Telemetry Unit) receives control commands in protocol format from the master and transmits electrical signals to the appropriate control relays.


What RTU (Remote Telemetry Unit) Features Do You Need?

How do you find the right RTU (Remote Telemetry Unit)? Heres 5 essential features to look for …
1. Discrete alarms: Monitor device failures, intrusion alarms, beacons, and flood and fire detectors.
2. Analog alarm inputs: Monitor voltage, temperature, humidity and pressure.
3. Control relays: Operate remote site equipment directly from your SCADA master.
4. Redundant backup communication: Backup serial ports and/or internal modems will keep your monitoring online even during a LAN failure.
5. Redundant backup power inputs: Dual power inputs and battery backup keep monitoring online, even during power failures.
DPS Telecom offers RTUs that meet all these requirements - and offer local visibility via Web browser, email and pager notification, and more.
 
Data Presentation
The only display element in our model SCADA system is the light that comes on when the switch is activated. This obviously wont do on a large scale - you cant track a lightboard of a thousand separate lights, and you dont want to pay someone simply to watch a lightboard, either.
A real SCADA system reports to human operators over a specialized computer that is variously called a master station, an HMI (Human-Machine Interface) or an HCI (Human-Computer Interface).
The SCADA master station has several different functions. The master continuously monitors all sensors and alerts the operator when there is an "alarm" - that is, when a control factor is operating outside what is defined as its normal operation. The master presents a comprehensive view of the entire managed system, and presents more detail in response to user requests. The master also performs data processing on information gathered from sensors - it maintains report logs and summarizes historical trends.
An advanced SCADA master can add a great deal of intelligence and automation to your systems management, making your job much easier.
 
Control
Unfortunately, our miniature SCADA system monitoring the widget fabricator doesnt include any control elements. So lets add one. Lets say the human operator also has a button on his control panel. When he presses the button, it activates a switch on the widget fabricator that brings more widget parts into the fabricator.
Now lets add the full computerized control of a SCADA master unit that controls the entire factory. You now have a control system that responds to inputs elsewhere in the system. If the machines that make widget parts break down, you can slow down or stop the widget fabricator. If the part fabricators are running efficiently, you can speed up the widget fabricator.
If you have a sufficiently sophisticated master unit, these controls can run completely automatically, without the need for human intervention. Of course, you can still manually override the automatic controls from the master station.
In real life, SCADA systems automatically regulate all kinds of industrial processes. For example, if too much pressure is building up in a gas pipeline, the SCADA system can automatically open a release valve. Electricity production can be adjusted to meet demands on the power grid. Even these real-world examples are simplified; a full-scale SCADA system can adjust the managed system in response to multiple inputs.
SCADA can do a lot for you - but how do you make sure that youre really getting the full benefits of SCADA? Evaluating complex systems can be tricky - especially if you have to learn a new technology while still doing your everyday job.
But youve got to be able to make an informed decision, because the stakes are incredibly high. A SCADA system is a major, business-to-business purchase that your company will live with for maybe as long as 10 to 15 years. When you make a recommendation about a permanent system like that, youre laying your reputation on the line and making a major commitment for your company.
And as much as SCADA can help you improve your operations, there are also some pitfalls to a hasty, unconsidered SCADA implementation:
• You can spend a fortune on unnecessary cost overruns
• Even after going way over budget, you can STILL end up with a system that doesnt really meet all your needs
• Or just as bad, you can end up with an inflexible system that just meets your needs today, but cant easily expand as your needs grow
So lets go over some guidelines for what you should look for in a SCADA system.
 
The Two Most Important Components of Your SCADA System
Although you need sensors, control relays and a communications network to make a complete SCADA system, its your choice of a master station and RTUs that really determine the quality of your SCADA system.
 
A Brief Note on Sensors and Networks
Sensors and control relays are essentially commodity items. Yes, some sensors are better than others, but a glance at a spec sheet will tell you everything you need to know to choose between them.
An IP LAN/WAN is the easiest kind of network to work with, and if you dont yet have LAN capability throughout all your facilities, transitioning to LAN is probably one of your long-term goals. But you dont have to move to LAN immediately or all at once to get the benefits of SCADA. The right SCADA system will support both your legacy network and LAN, enabling you to make a graceful, gradual transition.