A SCADA System Assessment
Introduction Supervisory Control and Data Acquisition (SCADA) is
a process control system that enables a site operator to monitor
and control processes distributed among various remote sites.
Such systems can be used to monitor and control land, air or
water pollution control equipment, or just about any
manufacturing process.
A properly designed SCADA system saves time and money by
eliminating the need for service personnel to visit each site
for inspection, data collection/logging or make adjustments.
Real-time monitoring, system modifications, troubleshooting,
increased equipment life and automatic report generating are
just a few of the benefits that come with today’s SCADA systems.
As technology continues to advance, such systems will be the
operating standard for process control. But from hundreds of
system providers available today, which one will a facility
choose to partner with and why?
Choosing a system provider that will design a system applicable
to an operator’s needs can be an overwhelming, confusing task.
With little or no knowledge of SCADA and telemetry systems and
an incomplete pre-system assessment, decisions can include
costly mistakes. Too often the decisions are based upon:
Price: The quality of system components and workmanship may
suffer when vendors low-bid to win the contract. The vendor may
then indiscriminately cut costs to make a profit. Proprietary
equipment – If proprietary, closed-protocol equipment is
installed in the system, the customer can be forced to pay
inflated prices and face the possibility of future equipment
integration problems due to obsolete or irreplaceable
components, company shutdowns and a lack of support when it
comes time for repair.
Excessively complex or customized equipment: If the SCADA system
is too complex to understand, operate and support, the only
recourse is to purchase expensive training and/or service
contracts, which do not always guarantee prompt and professional
service.
Years of experience or knowledgeable expertise: There are a host
of reputable SCADA providers, with years of experience and
knowledgeable expertise, who have designed systems that are too
broad or expensive. Experience and knowledge are important but
only as a starting point when selecting a vendor.
Sales people and/or flashy marketing: Effective sales and
marketing strategies are meant to produce top-of-mind results.
Avoid being lured or pressured into a purchase. Be equipped and
make a sound decision based on all factors that affect optimum
system performance.
These and other costly mistakes can be avoided through
knowledge, understanding and careful assessment. Some will only
need to consider Tables A and B of this article. Others, with
little or no SCADA knowledge, will need to familiarize
themselves with more background information.
A Brief History SCADA began in the early 1960s as an electronic
system operating as input/output transmissions between a master
station and a remote station. The master station would receive
data through a telemetry network and then store the data on
mainframe computers.
In the early 1970s, distributed control systems (DCS) were
developed to control separate remote subsystems and in the
1980s, with the development of the microcomputer, process
control could be distributed among remote sites. Further
development enabled DCS to use programmable logic controllers
(PLC), which have the ability to control sites without taking
direction from a master.
In the late 1990s, SCADA systems were built with DCS
capabilities and systems were customized based on certain
proprietary control features built in by the designer. Now, with
the Internet being utilized more as a communication tool, SCADA
and telemetry systems are using automated software with certain
portals to download information or control a process.
Engineered SCADA systems today not only control processes but
are also used for measuring, forecasting, billing, analyzing and
planning. Today’s SCADA system must meet a whole new level of
control automation while interfacing with yesterday’s obsolete
equipment yet remain flexible enough to adapt to tomorrow’s
developments.
Whether the requirement is a new system or upgrading an older
one, it is important to know the system components before
deciding on who to talk with and what equipment is needed for a
particular application.
System Components The four major SCADA system components include
the Master Terminal Unit (MTU), the Remote Terminal Unit (RTU),
communication equipment and SCADA software.
The MTU is located at the operator’s central control facility
and provides a man-machine software interface, two-way data
communication and monitoring/control of remote field devices.
The RTU, located at a remote site, gathers data from field
devices (pumps, valves, alarms, etc.) into memory until the MTU
initiates a send command. The central processing unit within the
RTU receives a data stream via hardware equipment protocol. When
the RTU sees its specific address embedded in the protocol, data
is interpreted and the CPU directs the specified action to take.
The protocol used can be open like Modbus, TCP/IP or a
proprietary closed protocol. Some RTUs, called “smart PLCs” or
remote access PLCs, provide remote programmable functionality
while retaining the communications capability of an RTU. These
devices are designed to perform control functions, check site
conditions, re-program anytime from anywhere, and have any alarm
or event trigger a call to a personal computer without any
direction from the MTU.
The way the MTU/RTU transmission network or topology is set up
can vary, but the system must feature uninterrupted,
bi-directional communication in order to properly function.
Methods to accomplish this include private medium, where the end
user owns, operates, licenses and services the medium, and/or
public medium, where the customer pays for a monthly, per time
or volume use.
The first method for private media transmission includes wire
lines or buried cable and modems, and is usually limited to low
bandwidth. When it makes sense for a company to string or bury
its own communication cable between sites, companies should
consider staffing requirements necessary to support the
technical/maintenance aspects of the system.
The second method to consider is wireless transmission and
includes spread spectrum, microwave or VHF/UHF radios.
Spread Spectrum is license-free and available to the public in
the 900 MHz and 5.8 GHz bands. Some spread spectrum radios have
the ability to re-strengthen signals for the next radio in line.
These repeater radios are used to span distances and generally
have built-in error correction, encryption and other features,
making them a reliable, secure and long-lasting solution for
network communication.
Microwave radio transmits at high frequencies through parabolic
dishes mounted on towers or on top of buildings. This media uses
point-to-point, line-of-sight technology and communication may
become interrupted at times due to misalignment and/or
atmospheric conditions.
VHF/UHF radio (good for up to 30 miles) is an electromagnetic
transmission with frequencies of 175 MHz-450 MGz-900 MHz
received by special antennas. A license from the FCC must be
obtained and coverage is limited to special geographical
boundaries.
Public media transmission includes services offered by a local
telephone or cable company, and in some systems and/or
subsystems, it may provide a more suitable method for data
transfer. The Public Switch Telephone Network, Generally
Switched Telephone network, and the Cellular network are dial-up
services suitable for occasional use. If a 24-hour permanent
connection for analog data transmission between two or more
locations is needed, the Private Leased Line should be
considered. The Digital Data Service with DSL and ISDN, systems
recently popularized by broadband/cable Internet, should be
considered for high speed/low error rate, computer-to-computer
applications. WiFi equipment utilizes broadband as well, but on
a time-share basis when it makes sense to use the infrastructure
of another company. PCS/CDPD service, provided by cellular
companies and Low Earth Orbit or geosynchronous satellites can
also be used for continuous communication.
Finally, the employment of an easy-to-use SCADA software
package, commonly know as the human machine interface (HMI),
installed on PC hardware provides a reliable representation of
the real system at work. An HMI allows the operator to view
virtually all system alerts, warnings and functions as well as
change set points and analyze, archive or present data trends.
Some common HMI software packages include Cimplicity (GE-Fanuc),
RSView (Rockwell Automation), IFIX (Intellution) and InTouch
(Wonderware). Most of these software packages use standard data
manipulation/presentation tools for reporting and archiving and
integrate well with Microsoft Excel, Access and Word. Collected
data can also be sent to Web servers that dynamically generate
HTML pages to be viewed on the operator’s LAN or published to
the Internet.
The Microprocessor Option With this basic understanding of SCADA
system components, a facility may want to consider utilizing a
microprocessor and/or PLC-based SCADA system over a basic RTU or
a proprietary system for the following reasons:
Microprocessors (MPs), like MTUs, can continuously collect,
process and store data, operating independently from the MTU
through “intelligent” programming. In addition, by utilizing a
microprocessor-based level meter, a SCADA system provides both a
master and local display that automatically gathers, processes
and reports data necessary to comply with local, state and
federal regulations in formats that integrate well will
Microsoft Excel, Access and Word.
Microprocessors can provide security and monitoring of door
switches, heat and motion detectors. Managers/operators can be
informed 24 hours a day through automatic e-mail, paging and
dial-up call features. Multiple users can easily be added and,
if open architecture protocol is used, future equipment can
easily be integrated. Since MPs have no moving parts, they are
extremely reliable and can be designed to be repairable with
components that any local electrical distributor supplies.
Microprocessor-based SCADA systems can reduce the number of
man-hours needed for on-site visual inspections, adjustments,
data collection and logging. Continually monitoring and
troubleshooting potential problems increases equipment life,
reduces service calls, reduces customer complaints and increases
system efficiency. Simply put, open-architecture,
microprocessor-based SCADA systems are an excellent means for
process control facilities to save time and money.
Review The return on investment and benefits produced by a
properly engineered microprocessor-based SCADA system far
outweigh the initial investment if the right equipment is chosen
and installed correctly. But from the hundreds of SCADA system
providers to choose from, one poor decision may lead down the
path to countless frustrations, inefficiencies and unnecessary
expenses.
Hopefully, by conducting a pre-SCADA system assessment,
facilities will be better equipped to avoid such problems . . .
This is an edited version of the company’s Pre-SCADA Assessment
white paper. For a full copy, visit
www.epgco.com/scada-assessment.html or contact Randy Dennison at
800-443-7426
About the author:
Randy Dennison is Marketing Manager for NBT, EPG Companies Inc.
SCADA and telemetry division. NBT manufacturers SCADA and
Telemetry equipment for the Water and Wastewater Industry as
well as for landfills and remediation sites. For more
information, call 800-443-7426 or go to www.nbtinc.com or
www.epgco.com
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