SCADA SYSTEMS BASICSSupervisory Control And Data Acquisition•Definition and Examples of SCADA systems•Designing a SCADA system(interface and sensors)•Building a SCADA system using LABVIEW 2013•Implementation and Troubleshooting

BY WINNIE MBAU

SCADA Definition and ExamplesS-Supervisory, C-Control And Data Acquisition

A SCADA system is an automated centralized monitoring and control function/system for processes

with data logging capability used to control and monitor geographically dispersed sites over long-

distance communications networks, including monitoring alarms and processing status data.

Based on information received from remote stations, automated or operator-driven supervisory

commands can be pushed to remote station control devices, which are often referred to as field

devices= control local operations such as opening and closing valves and breakers, collecting data

from sensor systems, and monitoring the local environment for alarm conditions

SCADA systems are typically used in industries such as electric, water, oil and gas, transportation,

chemical, pharmaceutical, pulp and paper, food and beverage, textile industry and other discrete

manufacturing processes.

SCADA systems are also used in distribution systems such as water distribution and wastewater

collection systems, oil and gas pipelines, electrical power grids, and railway transportation systems.

FEATURES OF A SCADA SYSTEM Dynamic Process

Graphic –HMI

Alarm History

Real time trend

&Historical Time Trend

Data base connectivity

Device Connectivity

Script and Security

Device Connectivity

FUNCTIONS OF A SCADA SYSTEM

A SCADA system performs four functions:

1. Data acquisition- Using sensors (either digital or analog) that are directly interfaced with the managed system.

2. Networked data communication- remote telemetry units (RTUs). These are small computerized units deployed in the field at specific sites and locations that report to SCADA master units (ie larger computer consoles that serve as the central processor for the SCADA system)

3. Data presentation- HMI Human machine Interface

4. Control- control relays that are directly interfaced with the managed system can be switched ON/Off from the Central processor AND PLCs.

Data Acquisition

Networked Data

Communication

Data Presentation Control

ARCHITECTURE OF SCADAPower supply

Digital or Status inputs

Analog inputsDigital (control)

outputsAnalog outputs

Software and logic control

• IED communications• Master communicationsCommunications

Architecture cont

HARDWARE •CLIENT LAYER man machine interaction•DATA SERVER Layer handles process data control activities. This is where PLCs are connected.

SOFTWARE•SERVERS responsible for data acquisition and handling

COMMUNICATIONS •INTERNAL COMMUNICATIONS server to sever & server to client

•ACCESS TO DEVICES data servers poll controllers at user defined intervals.

INTERFACING

RTU remote terminal unit (RTU) is a microprocessor-controlled electronic device that interfaces objects in the physical world to a distributed control system or  SCADA (supervisory control and data acquisition) system by transmitting telemetry data to a master system, and by using messages from the master supervisory system to control connected objects. Another term that may be used for RTU is remote telecontrol unit.

PLC in SCADA system(PLCs) connect to sensors in the process and convert sensor signals to digital data. PLCs have more sophisticated embedded control capabilities than RTUs. PLCs do not have telemetry hardware, although this functionality is typically installed alongside them. PLCs are sometimes used in place of RTUs as field devices because they are more economical, versatile, flexible, and configurable.

HMIHuman Machine InterfaceHMI is the apparatus or device which presents processed data to a human operator, and through this, the human operator monitors and interacts with the process. The HMI is a client that requests data from a data acquisition server.

ADVANTAGES

Flexible simple reliable

Efficient with less manpow

er

Portable and cost

efficient

Self-checking

and readabili

ty

Alarming-Early Fault

Detection

Data logging

DISADVANTAGES Network Security Risks

Lack of trained personnel

Initial capital investments

DESIGN AND IMPLEMANTATION OF SCADA SYSTEMS

Consider a simple system where an alarm goes on when the water level of a tank reaches maximum. The operator has the ability to switch off the pump at the sound of the alarm 500meters away. SCADA systems are basically the same. However you need to monitor more complex machines with more than one output. So a real-life 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).

Some are analog sensors, which can detect continuous changes defined by a bottom and top level.. 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 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.

Cont… Data Communication is required to monitor multiple systems from a central

location, so you need a communications network to transport all the data collected from your sensors.

Early SCADA networks communicated over radio, modem or dedicated serial lines. Today, more and more data is being transmitted over optical fiber using SONET.

SONET (Synchronous Optical NETworking) is a standardized protocol that transfers digital information over fiber optic networks. For security reasons, data should be kept on closed LAN/WANs without exposing sensitive data to the open Internet.

Real SCADA systems don't communicate with just simple electrical signals, either. Data is encoded in protocol format.

Sensors and control relays are very simple electric devices that can't 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 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..

APPLICATION AREAS OF SCADAPower Oil & Gas water and waste managementProcess Industries including petrochemicals,

fertilizers, cement, paper and pulp, steel industries, and aluminum plants.

LABVIEW 2013Basic SCADA Level program.

WINCC98