A SCADA SYSTEM ASSESSMENT

This valuable SCADA system information is intended to help educate and equip you for future SCADA and/or telemetry system decisions. INTRODUCTION Supervisory Control and Data Acquisition (SCADA) is a process control system that enables a site operator to monitor and control processes that are distributed among various remote sites. 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, automatic report generating . . . these are just a few of the benefits that come with today’s SCADA system. As technology continues to advance, SCADA systems will be the operating standard for any processing site. But from the hundreds of system providers available today, which one will you choose to partner with and why? Choosing a SCADA system provider that will design a system applicable to your needs can be an overwhelming, confusing task. With little or no knowledge of SCADA and telemetry systems and an incomplete pre-system assessment, decisions made can be costly mistakes. Too often the decisions are based on . . . 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 as “standard” for 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. Excessively Complex or Customized Equipment: If the SCADA system installed 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. Keep it simple wherever possible. Years of Experience or Knowledgeable Expertise: Be careful! 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 determining what vendor is right for you. Sales People and/or Flashy Marketing: Effective sales and marketing strategies are meant to produce “top-of-mind” results. Don’t be lured or pressured; 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 knowing, understanding, and carefully assessing your particular needs. For some, that may mean skimming through this article and then focusing on Table A and B below. For others, with little or no SCADA knowledge, you should read and become familiar with the following background information. A BRIEF HISTORY SCADA began in the early sixties as an electronic system operating as Input/Output (I/O) 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 seventies, Distributed Control Systems (DCS) were developed to control separate remote subsystems and in the eighties, with the development of the microcomputer, process control could be distributed among remote sites. Further development enabled the DCS to use Programmable Logic Controllers (PLC), which have the ability to control sites without taking direction from a master. In the late nineties, 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. Good 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, interfacing with yesterday’s obsolete equipment yet flexible enough to adapt to tomorrow’s changes. Whether you need a new system or are upgrading an older one, it is important to know the system components before you decide on who to talk with and what equipment you will need for your 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, located at the operator’s central control facility, enables two-way data communication and control of remote field devices. The RTU, located at the remote site, gathers data from field devices (pumps, valves, alarms, etc.) in memory until the MTU initiates a send command. The central processing unit (CPU) 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, Transmission Control Protocol and Internet Protocol (TCP/IP) or a proprietary closed protocol. Some RTUs, called “smart PLCs” or Remote Access PLCs (RAPLC) provide remote programmable functionality while retaining the communications capability of an RTU. These devices are designed to perform control, check site conditions, re-program anytime from anywhere and have any alarm or event trigger a call to your personal computer without any direction from the MTU. The way the MTU/RTU transmission network (topology) is set up can vary but they must have uninterrupted, bi-directional communication for the system to function properly. 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 to string or bury your own communication cable between sites, consider the 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 5.8GHz 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 175MHz-450MGz-900MHz 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 your local telephone or cable company and in some systems and/or subsystems may provide a more suitable method for data transfer. The Public Switch Telephone Network (PSTN), Generally Switched Telephone network (GSTN) and the Cellular network are dial-up services suitable for occasional use. If you need a 24-hour permanent connection for analog (continuously varying signal) data transmission between two or more locations, the Private Leased Line (PLL) should be considered. The Digital Data Service (DDS) with the Digital Subscriber Lines (DSL) and Integrated Service Digital Network (ISDN) 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 (LEO) or Geosynchronous satellites can also be used for continuous communication. Finally, the use 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. The HMI allows the operator to view virtually all system alerts, warnings, and functions as well as change set points, analyze, archive or present data trends. 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 Local Area Network (LAN) or published to the Internet. The Microprocessor Option Now that you have a basic understanding of the SCADA system components, you may want to consider utilizing a microprocessor (MP) and/or a PLC-based SCADA system over a basic RTU or a proprietary system for the following reasons: MPs, like MTUs, can continuously collect, process and store data, operating independently from the MTU through "intelligent" programming. In addition, by utilizing the EPG LevelMaster™ microprocessor-based level meter (pictured), you can have a robust SCADA system with 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. MPs can provide security and monitoring of door switches, heat and motion detectors. Managers/operators can be informed 24 hours a day through automatic email, 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. MP-based SCADA system 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, MP-based SCADA systems are an excellent means for process control facilities to save time and money. IN REVIEW The ROI (return on investment) and benefits produced by a properly engineered MP-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 you down the path to countless frustrations, inefficiencies and unnecessary expenses. Hopefully this Pre-SCADA system assessment will help you avoid such a decision. Begin by answering the questions in Table A and consider the principles offered in Table B. If you do, you will be further equipped to purchase an appropriate SCADA system that will provide years of cost-effective, dependable process control while leaving you open for tomorrow’s options. Table A - Questions to Consider General SCADA System 1. What features/benefits will SCADA perform at the master/remote site? 2. What type of SCADA system/hardware is presently installed? (proprietary, outdated, etc.) 3. How many sites, stations and dependant users does your present/future system require? 4. Will remote station collect data independently from master station? 5. Will master station control local input/output and back up operations? 6. Will the present/future system communicate with additional (LAN, Internet, etc.) points? 7. Considering the present/future software used, is it fully documented, easy to learn/use and likely to have future support? 8. Does present/future budget need to change for higher ROI? 9. What aspect of SCADA requires further investigation? The Field Equipment 1. Rate the performance standards of each site and all field equipment. Are they reliable and cost-effective? 2. What present equipment needs replacing? 3. What present/future process needs expansion, monitoring and control? 4. What are the future equipment/expansion needs? 5. Can new equipment integrate well with the present system? 6. What is the present/future maintenance and service arrangement? Will it change with new equipment? Will you assign your own maintenance personnel or contract out? 7. What are your present costs for operation, personnel, field inspection, maintenance, repair, travel time, gas, report generating, etc? Is it cost-effective? How will it change with a new SCADA system? The Communication Path 1. What telemetry network or communication path is presently installed? a. Topology: (Point-to-Point, Point-to-Multipoint, Multipoint-to-Multipoint) b. Transmission Mode: (Hardwire, Telephone, Fiber Optics, Radio/Microwave) 2. What are the transmission modes available and if changes are made, how will that affect vendor service charges - at each site? 3. What topology and transmission mode is best suited and cost-effective for present/future application? 4. What are the distances and obstacles to span between the control center and each present/future site? The Protocol (Encoding/Decoding) 1. What protocol (open, closed) is used (present/future) and will it integrate well with future equipment? 2. Is there complete documentation? 3. Do you need multi-vendor software to communicate with a variety of manufacturer's equipment? 4. What protection and safeguards are needed/used to keep out hacking, tampering, sabotage, and other unauthorized use. (Consider security issues) Table B - SCADA Equipment Purchasing Principles 1. Must be supplied by a reputable, established, customer-focused manufacturer. 2. Must use open architecture, (Modbus) protocol to keep future integration options open. 3. Must be non-proprietary, proven technology that integrates well with existing/future equipment. 4. Must be cost-effective, easy to learn/use, reliable and not cause disruptions to the every day business operation. 5. Must be supportable, well documented and designed to use locally supplied electrical components. NBT equipment uses the open architecture Modbus protocol, is well documented, and will integrate into any existing system. For over 20 years we’ve been manufacturing dependable, cost-effective process control solutions for thousands of industry professionals. If you have any questions or would like to talk to a Data Acquisition, SCADA or Telemetry hardware specialist, please give us a call at 800-892-5303. We look forward to partnering with you. Top of page © 2009, Nota Bene Technology, 19900 County Rd. 81, Maple Grove, MN 55311

A properly designed SCADA system saves time and money . . .

Don’t be lured or pressured; be equipped and make a sound decision . . .

. . . it is important to know the system components . . .

The MTU . . . enables operator interface . . .

The RTU . . . gathers data from field devices (pumps, valves, alarms, etc.) in memory until the MTU initiates a send command.

The HMI allows the operator

to view virtually all system alerts, warnings and

functions . . .

MPs, like MTUs, can

continuously collect,

process and store data . . .

LevelMaster microprocessor-based level meter

Managers/operators can be informed 24 hours a day through automatic email . . .

SM800 Series MP Communications Controller

THE HIGH VOLTAGE TEST

The high voltage test (also called dielectric strength test or hipot test) can be made in AC or DC. If the high voltage test is made in DC, it is then combined with insulation ; if the high voltage test is made in AC, it is then, this is then, more stressful for the sample and made according to the sketch below.

Measurement of high voltage test under alternating current is performed using an alternating voltage (50Hz) adjustable to an effective 50V to 1,500V. As is the case with direct current, the high voltage test detects any sudden rise of current up to a programmed threshold.

The short circuit test is maintained by default. The rise time is more than 500 ms and the application time at least one period.

Warning: The high voltage test under alternating current is penalised by the capacitive value of the tested equipment. It must be remembered that the generator power is limited to 5 mA.

The term SCADA stands for Supervisory Control And Data Acquisition. A SCADA system is a common process automation system which is used to gather data from sensors and instruments located at remote sites and to transmit and display this data at a central site for either control or monitoring purposes. The collected data is usually viewed on one or more SCADA Host computers located at the central or master site.

A real world SCADA system can monitor and control hundreds to hundreds of thousands of I/O points. A typical Water SCADA application would be to monitor water levels at various water sources like reservoirs and tanks and when the water level exceeds a preset threshold, activate the system of pumps to move water to tanks with low tank levels.

Common analog signals that SCADA systems monitor and control are levels, temperatures, pressures, flow rate and motor speed. Typical digital signals to monitor and control are level switches, pressure switches, generator status, relays & motors.

There is typically another layer of equipment between the remote sensors and instruments and the central computer. This intermediate equipment exists on the remote side and connects to the sensors and field instruments. Sensors typically have digital or analog I/O and these signals are not in a form that can be easily communicated over long distances. The intermediate equipment is used to digitize then packetize the sensor signals so that they can be digitally transmitted via an industrial communications protocol over long distances to the central site.

Typical equipment that handles this function are PLC's (Programmable Logic Controllers) and RTU’s (Remote Terminal Units). These devices employ de- facto standard industrial data communication protocols such as Modbus, AB-DF1, and DNP3.0 to transmit the sensor data. Typical physical interface standards are Bel 202 modem, RS-485 & RS-232.



The SCADA Host is usually an industrial PC running sophisticated SCADA MMI (Man Machine Interface) or HMI (Human Machine Interface) software. This software is used to poll the remote sites and store the collected data in its centralized SQL or Oracle database. Logic can be configured in the SCADA Host software which then monitors and controls plant or equipment. The control may be automatic, or initiated by operator commands.

Data acquisition is accomplished firstly by the RTU's or PLC's scanning the field inputs connected to the RTU / PLC. This data is usually collected at a polling rate configured by the operator. The polling rate is determined by the number of sites, the amount of data at each site, the maximum bandwidth of the communication channel and the minimum required display and control time.

Once the data has been acquired at sent to the SCADA Host, the MMI software will scan the acquired data (usually at a slower rate.) The data is then processed to detect preset alarm conditions, and if an alarm is present, an alarm message will flash on the operator screen and added to an alarm list. The operator must then acknowledge this alarm. There are 3 common types of data collected:

• Analog - used for trending
• Digital (on/off) - used for alarming
• Pulse (i.e. revolutions of some kind of meter) - accumulated /counted

The primary operator interface is a set of graphical screens which show a representation of the equipment being monitored. Real-time data is displayed numerically or graphically as changing bars, circles, lines or other shapes over a static background.

As the acquired data changes in real-time, the bar, circle, line or other representative shape is updated. For instance, an analog level increase may be displayed as a lengthening of the representative vertical bar or a valve graphic may look open to represent that it is open. A typical MMI will have a nested tree structure of many such screens, usually with the many overview screen on the first page with the most relevant data displayed. There are then links that go to other pages. Users can easily configure the type of I/O point, communication protocol driver, polling rate, alarm thresholds and notifications, trend process data as well as configure the User and Operator screens.

Next generation SCADA MMI software such as NetSCADA include all these functions in one convenient easy to use and cost effective package and also have seamless internet integration enabling many clients to securely view the collected data anywhere on the internet. A flexible SCADA Host can easily expand to handle additional future remote sites and I/O points.

SCADA communications can employ a diverse range of both wired (lease line, dial-up line, fiber, ADSL, cable) and wireless media (licensed radio, spread spectrum, cellular, WLAN or satellite). The choice depends on a number of factors that characterize the clients existing communication infrastructure.

Factors such as existing communications infrastructure, available communications at the remote sites, data rates and polling frequency, remoteness of site, installation budget and ability to accommodate future needs all impact the final decision. In complex SCADA architectures, there can be a variety of both wired and wireless media and protocols involved to get data back to the central monitoring site.

SCADA systems differ from DCS's (Distributed Control Systems) which are generally found in plant sites. While DCS's cover the plantsite, SCADA systems cover much larger geographic areas. Often SCADA Systems are required to interface to a plantsite DCS if there are remote sensors, instruments or motors and pumps that must be controlled/monitored by the plantsite DCS.

Certain types of applications like those in Oil & Gas, Electrical & Water Utilities, Water & Wastewater and Environmental Monitoring inherently require SCADA communications because of the remoteness of the assets (i.e. Oil wells, water wells, generator stations). Furthermore, due to the remoteness many of these often require the use of wireless communications. In these cases, the traditional solution is to add a radio modem stage to the standard SCADA architecture shown above.



Next generation Wireless SCADA equipment such as Bentek Systems SMX-900 or UNICON IP offers another level of integration by placing the wireless communications and RTU functionality together in the same package.



In addition to this higher level of integration, next-generation SCADA equipment such as the IP100 also support TCP/IP, UDP or other IP based communications protocols as well as strictly industrial protocols such as Modbus TCP, Modbus over TCP or Modbus over UDP all working over private radio, cellular or satellite networks. The IP100 can act as an Ethernet Serial gateway to enable older legacy serial equipment to connect to TCP/IP networks. Coupled with Host software such as NETSCADA, this enables implementation of powerful IP based SCADA networks over mixed cellular, satellite systems and land line systems.