SCADA systems are used to monitor and control geographically dispersed assets and processes. They integrate data acquisition systems with data transmission systems and HMI software to provide centralized monitoring and control for numerous process inputs and outputs. SCADA systems consist of field devices like RTUs and PLCs that connect to sensors and convert signals to digital data, communication systems to transfer data between field devices and central host computers, central host computers that process information and present it through HMIs, and HMIs for operators to monitor and control the entire system from a central location.

1. Supervisory Control and Data
Acquisition Systems

2. What is SCADA?
✓ It is a control system architecture that uses computers, networked data
communications and graphical user interfaces for high-level process supervisory
management, but also uses other peripheral devices such as programmable logic
controllers (PLC) and discrete PID controllers to interface to the process plant or
machinery.
✓ SCADA is not a 100% controller, it is just a software which has to be linked
with other controllers. Ultimately it is connected to PLC/PID/DCS systems
which in turn are connected to field instruments. Hence it can be said that it is
not a full control system, but rather focuses on the supervisory level.
✓ SCADA is an automation remote monitoring and control system. As stated
in its name, SCADA is applicable in any automation operation that requires
supervisory control and real-time data acquisition.

3. ✓ It works like a supervisor who supervises the entire plant area, if needed it also
controls the process as well as it converts the data segments for storing process
values i.e. level, pressure, switch positions, density, temperature, messages, etc.
✓ SCADA systems integrate data acquisition systems with data transmission systems
and HMI software to provide a centralized monitoring and control system for
numerous process inputs and outputs.
✓ SCADA systems are designed to collect field information, transfer it to a central
computer facility, and display the information to the operator graphically or
textually, thereby allowing the operator to monitor or control an entire system from
a central location in real time
✓ These systems can be relatively simple, such as one that monitors environmental
conditions of a small office building, or very complex, such as a system that
monitors all the activity in a nuclear power plant or the activity of a municipal
water system.

4. Data acquisition is the process of sampling signals that measure real world
physical conditions and converting the resulting samples into digital numeric
values that can be manipulated by a computer.

5. Need of SCADA
✓ Previously without SCADA, an industrial process was entirely controlled by
PLC, CNC, PID or microcontrollers which were programmed in certain
languages or codes.
✓ These codes were either written in assembly language or relay logic without any
true animation of the process running.
✓ Thus, to make the understanding of process easy with the help of true animations,
SCADA came into existence.
✓ Also, there are many places like hazardous area, unhygienic places, hilly areas
etc. where a person cannot be send regularly but the process has to be watched
continuously or it should be controlled. In such places SCADA is needed.

6. SCADA system consist of:
1.field data interface devices 2.communications system
3.central host computer server 4.Human Machine Interface

8. ✓ RTU- Remote terminal Unit
✓ MTU – Master terminal unit

10. Field Data Interface Devices
RTUs/PLCs/PACs:
✓ Remote terminal units (RTUs) connect to sensors in the process and convert
sensor signals to digital data. They have telemetry hardware capable of
sending digital data to the supervisory system, as well as receiving digital
commands from the supervisory system.
✓ Programmable logic controller (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.

11. Selection of RTUs:
✓ survive an industrial environment. Rugged construction and ability to
withstand extremes of temperature and humidity.
✓ have sufficient capacity to support the equipment at a site
✓ have a secure, redundant power supply for 24/7 working, support
battery power
✓ have non volatile memory (NVRAM) for storing software and/or
firmware.
✓ have a real-time clock to accurately date/time stamp reports
✓ have a watchdog timer to ensure that the RTU restarts after a power
failure.

12. ✓ RTUs are considered more suitable for wider geographical telemetry, the
reason being that RTUs use wireless communication; PLCs are more
suitable for local control, for example, for assembly lines in factories, light
fixtures, amusement rides, etc. PLCs are specially designed for output
arrangements and multiple inputs. They have electrical noise immunity,
vibration and impact resistance, varied temperature ranges, etc.
➢ Examples of wired telemetry media used in SCADA systems include leased
telephone lines and WAN circuits.
➢ Examples of wireless telemetry media used in SCADA systems include
satellite (VSAT), licensed and unlicensed radio, cellular and microwave.

13. ✓ A data acquisition server is a software service which uses industrial protocols
to connect software services, via telemetry, with field devices such as RTUs
and PLCs. It allows clients to access data from these field devices using
standard protocols.

14. Communications System
The communications network is intended to provide the means by which data
can be transferred between the central host computer servers and the field-
based RTUs. The Communication Network refers to the equipment needed to
transfer data to and from different sites.
1) Wire line communication
2) Radio
3) Satellite communication
4) Fiber optic communication

15. A central host computer server
✓ The central host computer or master station is most often a single computer or
a network of computer servers that provide a man-machine operator interface
to the SCADA system.
✓ The computers process the information received from and sent to the RTU
sites and present it to human operators in a form that the operators can
work with. Operator terminals are connected to the central host computer
by a LAN/WAN so that the viewing screens and associated data can be
displayed for the operators.
✓ A human–machine interface or HMI 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.

16. Human Machine Interface
✓ Operator workstations are most often computer terminals that are
networked with the SCADA central host computer.
✓ The central host computer acts as a server for the SCADA application, and
✓ The operator terminals are clients that request and send information to
the central host computer based on the request and action of the operators.

17. Basic functions of SCADA:
1) Channel scanning
2) Conversion into engineering units
3) Data processing
Channel scanning: The Micro processor scans the channels to read the data,
this process is called polling . In polling, the action of selecting a channel and
addressing it, is the responsibility of processor . The channel selection may be
sequential or in any particular order decided by designer . It is also possible to
assign priority to some channels over others:
In channel scanning:
✓ sending channel address to multiplexer
✓ Sending start convert pulse to ADC
✓ Reading the digital data.

18. Conversion into engineering units: The data read from the output of ADC
should be converted to the equivalent engineering units before any analysis is
done or data is sent for display or printing.
DATA Processing: The data read from output of ADC for various channels
is processed by micro processor to carry out limit checking and
performance analysis . For limit checking the highest and lowest limits for
each channel are stored in array . when any of the two limits is violated for
any channel, appropriate action like alarm generation , printing is
initiated.

19. SCADA Architectures
SCADA systems have evolved in parallel with the growth and sophistication
of modern computing technology. The three generations of SCADA systems:
✓ First Generation – Monolithic
✓ Second Generation – Distributed
✓ Third Generation – Networked

20. Monolithic SCADA Systems
When SCADA systems were first developed, the concept of computing in general
centred on “mainframe” systems. Networks were generally non-existent, and
each centralized system stood alone. As a result, SCADA systems were
standalone systems with virtually no connectivity to other systems.

21. Distributed SCADA Systems
The next generation of SCADA systems took advantage of development of
Local Area Networking (LAN) technology to distribute the processing across
multiple systems. Multiple stations, each with a specific function, were
connected to a LAN and shared information with each other in real-time.

22. Networked SCADA Systems
In the case of a networked design, the system may be spread across more than
one LAN network and separated geographically. Several distributed
architecture SCADAs running in parallel, with a single supervisor and
historian, could be considered a network architecture. This allows for a more
cost effective solution in very large scale systems.

23. Features of SCADA
✓ Dynamic Representation : It explains about the representation of various
symbols of the field instruments present in tools library which can be utilized
in SCADA applications.
✓ Database Connectivity : SCADA doesn’t have its own database. Hence, for
storage, it depends on databases available in the market like VB, SQL, Excel or
SAP.
✓ Device Connectivity : SCADA is not a 100% controller so it can’t run the
process alone. Hence, it is connected to PLC or DCS.
✓ Alarms : Using SCADA, in the field area, alarms are generated for warnings
or to keep the process in limits. The format consists of date, time, status,
priorities, etc.

24. ✓ Trends : Also called as XY Plotters or Data Loggers. It represents the values in
wave format and plots with reference to time. It is categorized as Real time and
Historical trend.
✓ Scripts : It is the combination of logical operators written in a statement. It is
used to run the applications made or stimulate before the final execution.
✓ Security : It is provided, in SCADA, as a whole as well as individually.
✓ Recipe Management : It explains that we can maintain various recipes of
different process and can implement it. All the recipes are stored in a single
server and can be fetched by any client server from any area to run the process.
✓ Networking : It explains that we can share SCADA applications on LAN or
internet and exchange of data is also possible.

25. ✓ The system provide facility to store large amount of data.
✓ The data can be displayed in various formats as per user requirements.
✓ It provides interface to connect thousands of sensors across wide region for
various monitoring and controlling operations.
✓ It is possible to obtain real data simulations with the help of operators.
✓ Many types of data can be gathered from RTUs connected with the master unit.
✓ With the advanced protocols and application software’s, the data can be
monitored from anywhere and not just from local site.
✓ The redundancy of units are incorporated in the SCADA system in order to have
backup in the event of faults or failures. This makes system more robust.
✓ It is fast in obtaining response.
✓ It is scalable and flexible in adding additional resources.
✓ It is used in wide industries and departments including telecommunications,
energy, transportation, oil & gas, water, military, meteorological etc.
Advantages

26. Disadvantages
✓ PLC based SCADA system is complex in terms of hardware units and
dependent modules.
✓ As the system is complex, it requires skilled operators, analysts and
programmers to maintain SCADA system.
✓ Installation costs are higher.
✓ The system increases unemployment rates.
✓ The system supports use of restricted software's and hardware equipment's.

27. SCADA v/s DCS
✓ SCADA is event driven while DCS is state driven system.
❑ A SCADA considers changes of state as the main criteria for the data gathering.
❑ DCS systems consider the process variable's present state to be the main criteria
driving the DCS and tasks are generally run sequentially, rather than event
driven.
✓ RTUs for SCADA while DCS uses PLC/controllers.
✓ DCS is process oriented and SCADA systems are data-gathering oriented.
✓ DCS is always connected to its data source so it doesn't need to maintain
database of current values. While SCADA needs to get secure data and control
and hence it maintains database of last known good values for prompt
operator display.

28. ✓ PLC is a hardware which is directly in contact with the field instruments. It
works according to the logic stored in its memory. While SCADA is a
software which shows the output and feedback in visual manner.
✓ A programmer can write the program as per client requirement in PLC where
input can sense the field equipment's while output can activate it.
✓ While in SCADA the programmer designs the animation as per PLC
programming and field equipment position, then establishes communication
between SCADA & PLC.
SCADA v/s PLC