SCADA control systems provide graphical representations of
your machine, process or plant, Data logging, Trends, Alarm
generation and Reporting to allow simplified management of your
system and ultimately process improvement.
We have more than 20 years experience in providing these
systems. Our systems are able to be viewed locally or
anywhere else on the planet utilising secure internet
communications. Alarms can be sent via SMS or Email to mobile
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SCADA stands for supervisory control and data
acquisition. It generally refers to an industrial control system: a computer
system monitoring and controlling a process. The process can be industrial,
infrastructure or facility-based as described below:
Industrial processes include those of manufacturing, production, power
generation, fabrication, and refining, and may run in continuous, batch,
repetitive, or discrete modes. Infrastructure processes may be public or
private, and include water treatment and distribution, wastewater collection and
treatment, oil and gas pipelines, electrical power transmission and
distribution, Wind Farms, civil defence siren systems, and large communication
systems. Facility processes occur both in public facilities and private ones,
including buildings, airports, ships, and space stations. They monitor and
control HVAC, access, and energy consumption.
Common system components
A SCADA System usually consists of the following subsystems:
- A Human-Machine Interface or HMI is the apparatus which presents process
data to a human operator, and through this, the human operator monitors and
controls the process.
- A supervisory (computer) system, gathering (acquiring) data on the
process and sending commands (control) to the process.
- Remote Terminal Units (RTUs) connecting to sensors in the process,
converting sensor signals to digital data and sending digital data to the
- Programmable Logic Controller (PLCs) used as field devices because they
are more economical, versatile, flexible, and configurable than
- Communication infrastructure connecting the supervisory system to the
Remote Terminal Units.
Supervision vs. control
There is, in several industries, considerable confusion over the differences
between SCADA systems and distributed control systems (DCS). Generally speaking,
a SCADA system usually refers to a system that coordinates, but does not control
processes in real time. The discussion on real-time control is muddied somewhat
by newer telecommunications technology, enabling reliable, low latency, high
speed communications over wide areas. Most differences between SCADA and DCS are
culturally determined and can usually be ignored. As communication
infrastructures with higher capacity become available, the difference between
SCADA and DCS will fade.
The term SCADA usually refers to centralized systems which monitor and
control entire sites, or complexes of systems spread out over large areas
(anything between an industrial plant and a country). Most control actions are
performed automatically by Remote Terminal Units ("RTUs") or by programmable
logic controllers ("PLCs"). Host control functions are usually restricted to
basic overriding or supervisory level intervention. For example, a PLC
may control the flow of cooling water through part of an industrial process, but
the SCADA system may allow operators to change the set points for the flow, and
enable alarm conditions, such as loss of flow and high temperature, to be
displayed and recorded. The feedback control loop passes through the RTU or PLC,
while the SCADA system monitors the overall performance of the loop.
Data acquisition begins at the RTU or PLC level and includes meter readings
and equipment status reports that are communicated to SCADA as required. Data is
then compiled and formatted in such a way that a control room operator using the
HMI can make supervisory decisions to adjust or override normal RTU (PLC)
controls. Data may also be fed to a Historian, often built on a commodity
Database Management System, to allow trending and other analytical auditing.
SCADA systems typically implement a distributed database, commonly referred
to as a tag database, which contains data elements called tags or
points. A point represents a single input or output value monitored or
controlled by the system. Points can be either "hard" or "soft". A hard point
represents an actual input or output within the system, while a soft point
results from logic and math operations applied to other points. (Most
implementations conceptually remove the distinction by making every property a
"soft" point expression, which may, in the simplest case, equal a single hard
point.) Points are normally stored as value-timestamp pairs: a value, and the
timestamp when it was recorded or calculated. A series of value-timestamp pairs
gives the history of that point. It's also common to store additional metadata
with tags, such as the path to a field device or PLC register, design time
comments, and alarm information.
Human Machine Interface
A Human-Machine Interface or HMI is the apparatus which presents process data
to a human operator, and through which the human operator controls the process.
An HMI is usually linked to the SCADA system's databases and software programs,
to provide trending, diagnostic data, and management information such as
scheduled maintenance procedures, logistic information, detailed schematics for
a particular sensor or machine, and expert-system troubleshooting guides.
The HMI system usually presents the information to the operating personnel
graphically, in the form of a mimic diagram. This means that the operator can
see a schematic representation of the plant being controlled. For example, a
picture of a pump connected to a pipe can show the operator that the pump is
running and how much fluid it is pumping through the pipe at the moment. The
operator can then switch the pump off. The HMI software will show the flow rate
of the fluid in the pipe decrease in real time. Mimic diagrams may consist of
line graphics and schematic symbols to represent process elements, or may
consist of digital photographs of the process equipment overlain with animated
The HMI package for the SCADA system typically includes a drawing program
that the operators or system maintenance personnel use to change the way these
points are represented in the interface. These representations can be as simple
as an on-screen traffic light, which represents the state of an actual traffic
light in the field, or as complex as a multi-projector display representing the
position of all of the elevators in a skyscraper or all of the trains on a
An important part of most SCADA implementations is alarm handling. The system
monitors whether certain alarm conditions are satisfied, to determine when an
alarm event has occurred. Once an alarm event has been detected, one or more
actions are taken (such as the activation of one or more alarm indicators, and
perhaps the generation of email or text messages so that management or remote
SCADA operators are informed). In many cases, a SCADA operator may have to
acknowledge the alarm event; this may deactivate some alarm indicators, whereas
other indicators remain active until the alarm conditions are cleared. Alarm
conditions can be explicit - for example, an alarm point is a digital status
point that has either the value NORMAL or ALARM that is calculated by a formula
based on the values in other analogue and digital points - or implicit: the
SCADA system might automatically monitor whether the value in an analogue point
lies outside high and low limit values associated with that point. Examples of
alarm indicators include a siren, a pop-up box on a screen, or a coloured or
flashing area on a screen (that might act in a similar way to the "fuel tank
empty" light in a car); in each case, the role of the alarm indicator is to draw
the operator's attention to the part of the system 'in alarm' so that
appropriate action can be taken. In designing SCADA systems, care is needed in
coping with a cascade of alarm events occurring in a short time, otherwise the
underlying cause (which might not be the earliest event detected) may get lost
in the noise. Unfortunately, when used as a noun, the word 'alarm' is used
rather loosely in the industry; thus, depending on context it might mean an
alarm point, an alarm indicator, or an alarm event.
SCADA solutions often have Distributed Control System (DCS) components. Use
of "smart" RTUs or PLCs, which are capable of autonomously executing simple
logic processes without involving the master computer, is increasing. A
functional block programming language, IEC 61131-3 (Ladder Logic), is frequently
used to create programs which run on these RTUs and PLCs. Unlike a procedural
language such as the C programming language or FORTRAN, IEC 61131-3 has minimal
training requirements by virtue of resembling historic physical control arrays.
This allows SCADA system engineers to perform both the design and implementation
of a program to be executed on an RTU or PLC. A Programmable automation
controller (PAC) is a compact controller that combines the features and
capabilities of a PC-based control system with that of a typical PLC. PACs are
deployed in SCADA systems to provide RTU and PLC functions. In many electrical
substation SCADA applications, "distributed RTUs" use information processors or
station computers to communicate with protective relays, PACS, and other devices
for I/O, and communicate with the SCADA master in lieu of a traditional RTU.
Since about 1998, virtually all major PLC manufacturers have offered
integrated HMI/SCADA systems, many of them using open and non-proprietary
communications protocols. Numerous specialized third-party HMI/SCADA packages,
offering built-in compatibility with most major PLCs, have also entered the
market, allowing mechanical engineers, electrical engineers and technicians to
configure HMIs themselves, without the need for a custom-made program written by
a software developer.
The RTU connects to physical equipment. Typically, an RTU converts the
electrical signals from the equipment to digital values such as the open/closed
status from a switch or a valve, or measurements such as pressure, flow, voltage
or current. By converting and sending these electrical signals out to equipment
the RTU can control equipment, such as opening or closing a switch or a valve,
or setting the speed of a pump.
The term "Supervisory Station" refers to the servers and software responsible
for communicating with the field equipment (RTUs, PLCs, etc), and then to the
HMI software running on workstations in the control room, or elsewhere. In
smaller SCADA systems, the master station may be composed of a single PC. In
larger SCADA systems, the master station may include multiple servers,
distributed software applications, and disaster recovery sites. To increase the
integrity of the system the multiple servers will often be configured in a
dual-redundant or hot-standby formation providing continuous control and
monitoring in the event of a server failure.
For some installations, the costs that would result from the control system
failing are extremely high. Possibly even lives could be lost. Hardware for some
SCADA systems is ruggedized to withstand temperature, vibration, and voltage
extremes, but in most critical installations reliability is enhanced by having
redundant hardware and communications channels, up to the point of having
multiple fully equipped control centres. A failing part can be quickly
identified and its functionality automatically taken over by backup hardware. A
failed part can often be replaced without interrupting the process. The
reliability of such systems can be calculated statistically and is stated as the
mean time to failure, which is a variant of mean time between failures. The
calculated mean time to failure of such high reliability systems can be on the
order of centuries.
Communication infrastructure and methods
SCADA systems have traditionally used combinations of radio and direct serial
or modem connections to meet communication requirements, although Ethernet and
IP over SONET / SDH is also frequently used at large sites such as railways and
power stations. The remote management or monitoring function of a SCADA system
is often referred to as telemetry.
This has also come under threat with some customers wanting SCADA data to
travel over their pre-established corporate networks or to share the network
with other applications. The legacy of the early low-bandwidth protocols
remains, though. SCADA protocols are designed to be very compact and many are
designed to send information to the master station only when the master station
polls the RTU. Typical legacy SCADA protocols include Modbus RTU, RP-570,
Profibus and Conitel. These communication protocols are all SCADA-vendor
specific but are widely adopted and used. Standard protocols are IEC 60870-5-101
or 104, IEC 61850 and DNP3. These communication protocols are standardized and
recognized by all major SCADA vendors. Many of these protocols now contain
extensions to operate over TCP/IP. It is good security engineering practice to
avoid connecting SCADA systems to the Internet so the attack surface is reduced.
RTUs and other automatic controller devices were being developed before the
advent of industry wide standards for interoperability. The result is that
developers and their management created a multitude of control protocols. Among
the larger vendors, there was also the incentive to create their own protocol to
"lock in" their customer base. A list of automation protocols is being compiled
Recently, OLE for Process Control (OPC) has become a widely accepted solution
for intercommunicating different hardware and software, allowing communication
even between devices originally not intended to be part of an industrial
Trends in SCADA
There is a trend for PLC and HMI/SCADA software to be more "mix-and-match".
In the mid 1990s, the typical DAQ I/O manufacturer supplied equipment that
communicated using proprietary protocols over a suitable-distance carrier like
RS-485. End users who invested in a particular vendor's hardware solution often
found themselves restricted to a limited choice of equipment when requirements
changed (e.g. system expansions or performance improvement). To mitigate such
problems, open communication protocols such as IEC IEC 60870-5-101 or 104, IEC
61850, DNP3 serial, and DNP3 LAN/WAN became increasingly popular among SCADA
equipment manufacturers and solution providers alike. Open architecture SCADA
systems enabled users to mix-and-match products from different vendors to
develop solutions that were better than those that could be achieved when
restricted to a single vendor's product offering.
Towards the late 1990s, the shift towards open communications continued with
individual I/O manufacturers as well, who adopted open message structures such
as Modbus RTU and Modbus ASCII (originally both developed by Modicon) over
RS-485. By 2000, most I/O makers offered completely open interfacing such as
Modbus TCP over Ethernet and IP.
The North American Electric Reliability Corporation (NERC) has specified that
electrical system data should be time-tagged to the nearest millisecond.
Electrical system SCADA systems provide this Sequence of events recorder
function, using Radio clocks to synchronize the RTU or distributed RTU clocks.
SCADA systems are coming in line with standard networking technologies.
Ethernet and TCP/IP based protocols are replacing the older proprietary
standards. Although certain characteristics of frame-based network communication
technology (determinism, synchronization, protocol selection, environment
suitability) have restricted the adoption of Ethernet in a few specialized
applications, the vast majority of markets have accepted Ethernet networks for
With the emergence of software as a service in the broader software industry,
a few vendors have begun offering application specific SCADA systems hosted on
remote platforms over the Internet. This removes the need to install and
commission systems at the end-user's facility and takes advantage of security
features already available in Internet technology, VPNs and SSL. Some concerns
include security, Internet
connection reliability, and latency.
SCADA systems are becoming increasingly ubiquitous. Thin clients, web
portals, and web based products are gaining popularity with most major vendors.
The increased convenience of end users viewing their processes remotely
introduces security considerations. While these considerations are already
considered solved in other sectors of Internet services, not all entities
responsible for deploying SCADA systems have understood the changes in
accessibility and threat scope implicit in connecting a system to the Internet.
PLC's Supported Include
Simatic S7 - 200
Simatic S7 - 300
Direct Logic / KOYO
Software Tools Available Include
KOYO Direct Logic
Direct Soft 5
Omron CX One
Omron CX Programmer
Mitsubishi GX Developer