Supervisory Control and Data Acquisition (SCADA) systems integrate data acquisition systems with data transmission systems and graphical software in order to provide a centrally-located "monitor and control" system for numerous process inputs and outputs. Specifically, SCADA systems are designed to collect information, transfer it back to a central computer, and display the information to the operator(s), thereby allowing the operator to monitor and/or control an entire system from a central location in real time. Based on the sophistication and setup of the individual system, control of any individual system, operation, or task can be automatic, or it can be initiated by operator commands. For example, a SCADA system could allow a water treatment system operator to continuously monitor the dissolved oxygen (DO) content of a reservoir, and to take action if DO levels suddenly drop to an alarm state (e.g. in the event of contamination by an organic). From a more specifically security-related perspective, SCADA systems could integrate data from cameras, motion sensors, security lights, or other security devices, and provide all of this information to a central security monitoring location, allowing an operator to evaluate all of these data at once.

This may allow an operator to manually turn on cameras at a remote site when SCADA reports that an on-site motion sensor has been tripped. In contrast to providing information that allows operators to manually respond to system parameters, SCADA systems may also be programmed to automatically perform necessary analysis and control for a system. For example, SCADA can cause a booster pump to start automatically to add chlorine to a system if a chlorine sensor indicates chlorine concentrations are below a threshold value.

SCADA systems have been used to control water and wastewater infrastructure, as well as power generation systems, electrical systems, and hazardous waste treatment facilities, for many years. The uniqueness of a SCADA system relative to other process control systems is SCADA's ability to monitor and control remote processes. Other process control equipment, such as Distributed Control Systems (DCSs), which have long been used in factories and in other industrial applications, is designed to control processes within a plant or application that require high processor power for the many analog functions with a given application. However, with the increased processing power and capabilities now available in programmable logic controllers (PLCs), the outfitting of remote sites or processing equipment with remote telemetry units (RTUs) presents a viable, cost effective solution in water and wastewater automation control. The PLC-based RTU allows communication between the outlying equipment and a central processing unit (CPU), and therefore allows a SCADA system to control both local and remote equipment and processes.

SCADA systems consist of both hardware and software. Typical hardware includes a computer/CPU placed at a central location, communications equipment (radio, telephone line or satellite), and one or more RTUs or sensors. The CPU stores and processes the information from RTU inputs and outputs, while the RTU/sensor PLC controls the local function. The communications hardware allows the transfer of information and data back and forth between the CPU and the RTUs and sensor inputs. The software is programmed to tell the system what and when to monitor, what parameter ranges are acceptable, and what response to initiate should the parameters go outside acceptable values. SCADA software is designed to be configured for a user's specific application. Since existing hardware is not always compatible with the SCADA software, limited-functionality, off-the-shelf RTU hardware packages that have been specifically designed to interface with SCADA software are also available.

The figure below shows the setup of a typical SCADA system. Data, such as the water level in a water tank, are generated by instrumentation (RTUs or sensors) set up at remote sites. In this example, the water level is monitored constantly, and this information is transmitted through a communications network back to a central monitoring station. Once these data are received at the central monitoring location, they can be evaluated by an operator, who can take manual actions regarding the water level, if necessary. If the SCADA system is more advanced, it could provide automatic feedback to the water tank. For example, if the measured water level is below some threshold value, the SCADA system could send a signal back and turn on a pump to fill the tank, etc.

SCADA systems can be designed to measure a variety of equipment operating conditions and parameters (e.g. tank levels, temperature, voltage, current, or volumes and flow rates), or water quality parameters (e.g. pH, turbidity, and chlorine residual), and to respond to changes in these parameters either by alerting operators or by modifying system operation through a feedback loop. Thus, these systems can be useful in monitoring and operating an entire water/wastewater system without having personnel physically visit each process or piece of equipment on a daily basis to check it and/or to ensure that it is functioning properly. SCADA systems can also be used to automate certain functions, so that they can be performed without needing to be initiated by an operator (for example, injecting chlorine in response to periodic low chlorine levels in a distribution system, or turning on a pump in response to low water levels in a storage tank). As described above, in addition to process equipment, SCADA systems can also integrate specific security equipment, such as cameras, motion sensors, lights, data from card reading systems, etc., thereby providing a clear picture of what is happening at areas throughout a facility. Finally, SCADA systems also provide constant, real-time data on processes, equipment, location access, etc., which allows the necessary response to be made quickly. This can be extremely useful during emergency conditions, such as when distribution mains break or when potentially disruptive BOD spikes appear in wastewater influent.

Because these systems can monitor multiple processes, equipment, and infrastructure, and can provide quick notification of, or response to, problems or upsets, SCADA systems typically provide the first line of detection for atypical or abnormal conditions. For example, a SCADA system connected to sensors that measure specific water quality parameters in a public water system could be designed to respond when these water quality parameters are measured outside of a specific range. A real-time customized operator interface screen could display and control critical system monitoring parameters.

The system could transmit warning signals back to the operators, such as by initiating a call to a personal pager. This might allow the operators to initiate actions to prevent contamination and disruption of the water supply. Further automation of the system could ensure that the system initiated measures to rectify the problem. Preprogrammed control functions (e.g. shutting a valve, controlling flow, increasing chlorination, or adding other chemicals) can be triggered and operated based on SCADA utility.

The Ohio River Valley Water Sanitation Committee (ORSANCO), which operates programs to improve water quality in the Ohio River and its tributaries, has set up a SCADA feedback system to monitor its system for volatile organic carbon contamination. The Advanced Measurement Initiative (AMI) uses four monitoring stations equipped with online gas chromatographs to analyze for twenty-one contaminant compounds every two hours. The data is transmitted to station operators located in a different location, allowing the operators to monitor the station remotely. If any of these contaminant concentrations exceeds a predetermined concentration (set at 5 micrograms/liter), station operators notify ORSANCO of a potential problem, which may allow ORSANCO to take remedial actions.

A variety of different SCADA systems are commercially available. These systems vary in their complexity from sophisticated networked systems with real-time controls linking numerous remote sites equipped with RTUs to several central monitoring systems, to simple alarm feedback systems installed at one or more sites. On-line systems can be equipped with control, signal, and alarm systems that notify the operator of abnormal conditions, and some may be tied into feedback loops that can provide real-time control, such as automatically adjusting chemical usage at a treatment plant or activating a back-up pump station.

In selecting SCADA systems, important factors to consider include:

(1) Numbers of Input/Output (I/O) Points, Analog and Discrete:

The SCADA system links all RTU and associated I/O and connection points under a systematic design to meet all of the requirements and monitoring functionality. Therefore, the level of sophistication selected for a particular application is a function of the level of information needed by the operator. Key factors that influence the selection of a SCADA system include the numbers of data points (I/Os and connection points) to be monitored and the method and quantity of data to be archived. For example, one of the most important steps in selecting specific devices/components for a SCADA system is identifying the specific equipment and/or processes that the system will monitor. In building a customized SCADA system, many utilities begin by first preparing a list of assets associated with the particular utility (i.e., pump stations, storage tanks, reservoirs, treatment process, or any other asset to be monitored), and then identifying the operational parameters, water quality parameters, and types of monitoring that are key to that specific operation. Each of the assets would have at least one input into the SCADA system. This input would allow the pertinent information from that asset to be sent to the CPU, and would identify it as coming from that particular asset. Once the information from a particular asset is input into the CPU, the input information would be processed vs. internal logic to determine whether outputs were required. Potential outputs would be based on the types of responses that the user chooses to program based on the inputs. For example, there may be output connections that control pumps, lights, alarms, locks, etc. As described above, a specific input (such as a sensor reporting low chlorine concentration) may be designed to generate a specific output (such as turning on a pump).

(2) Data Transmission and Communication Network:

Data transmission can be provided via two primary channels - hardwired and wireless. Hardwired systems are physically connected to each other through wires or fiber optic cables. Wireless systems are not physically connected. In these systems, the transmissions take place from the originator to the receiver over radio waves, satellite, or microwave frequencies. Both hardwired and wireless systems can transmit voice and data communications. However, security experts recommend not mixing the two data types on one line or channel, because current technology prioritizes voice information over data transmission, thus interrupting the data flow. Thus, data transfer will not occur until the lines are clear of voice communications.

Three important considerations when choosing the appropriate type of transmission system are the speed of transmission, the amount of data that can be transferred, and the cost. For example, the transmission of photographic images of a plant (for example, surveillance camera data) may require a greater data transmission and storage requirements than the transmission of text data (for example, the on/off status of a pump). Data transmission and speed are related to the available bandwidth for the transmission. This, in turn, is related to the size of the size of the conduit; the larger the conduit, the more bandwidth is available, and thus the faster the transmission or speed. However, the higher the speed, the higher the costs. It should be noted that costs will include both upfront capital improvement costs and reoccurring monthly fees/costs.

Another important consideration in choosing a communications network is its security. Specific security concerns regarding data transmission methods include ensuring that the communication method is available (ensuring that the communication method is functioning and free to transmit data), as well as ensuring that the communication is not altered during transmission (ensuring the integrity of the communication), and ensuring that unauthorized parties do not intercept the communication (ensuring the confidentiality of the communication). Specific security aspects of different types of communications technologies, as well as discussions of general security aspects of hardwired vs. wireless communications methods will be discussed in a future Product Guide.

As described above, there are a wide range of specific SCADA options available to a system designer once the system's needs have been defined. SCADA systems can be set up to communicate using a range of media, including telephone lines, radio, internet, cellular, or satellite interfaces. Whether using hardwired or wireless technology, current SCADA systems can report alarms using pre-specified custom voice, pager, fax, or even e-mail communications. If a system uses a portable design, SCADA can use a cellular phone for communication. Additionally, an operator can use a laptop computer to access the SCADA system by dial-up means or via the Internet, both of which can be password protected. It should be noted that the topography of the area may be a factor for wireless systems. Any wireless system using a frequency of 900 MHz or more requires a direct line of site between antennas for data transmission. Hilly terrain requires high antennas that can transmit the signal above interfering topography. This terrain may also require repeater stations to retransmit the signal and keep it strong. These additional requirements add to the capital cost of the system.

(3) Control Features:

As described above, the control function of SCADA system is achieved through use of PLCs. PLCs use a programming language called "relay ladder logic," which is capable of executing programs to control the operation of the system (e.g. turning a pump on or off). Ladder logic is the most widely used control language today. In a PLC-based SCADA system, a full set of standard ladder logic instructions are built into the system, along with counters, timers, and even analog capabilities for performing tasks such as turning on/off pumps and screens, and opening/closing valves etc.

Certain advanced SCADA systems are capable of communication with PLCs that can implement control programs created using both ladder logic programs and more advanced C-programs. C-programs can run independently of ladder logic programs, and can handle complex calculations and manipulation of system data, and any dynamic control algorithms that may be too complex for ladder logic. Building both programs into one system allows information to be shared between components, increasing dynamic control of the system. This can be critical depending on system complexity and the needs of a specific application. For example, SCADA may be designed to control a variable speed pumping application that is to operate at its most efficient point on the pump curve at any given flow in the specified range. This operation requires each pump curve to be entered with the system curve. The program superimposes the system curve on the pump curve to determine the most efficient means of operating with one, two, or even three pumps depending on the size and number of pumps in the system. This part of the program is performed using the C program, while the start/stop and speed control is performed in the ladder logic program. Both types of control programs are displayed on the SCADA software.

For more information on PLCs, see the Electronic Controllers/Program Logic Controllers Product Guide.

(4) Software and Security Issues:

Selecting the appropriate SCADA system software is very important. Security experts recommend that the software program be capable of performing every task needed to operate and maintain the system.

The SCADA software typically runs on IBM PC or compatible computers under Microsoft Windows 95, 98, NT or 2000 operating systems. Software packages compatible with other operating systems (e.g. UNIX) are also available. However, software for these systems would be proprietary and would be more expensive than PC-based systems. These packages would typically be used for SCADA systems at larger facilities.

The SCADA software typically provides a graphical user interface (GUI) to program and display all pertinent operational parameters, including, but not limited to, system configuration, polling ("polling" is reading data from, and communicating with, two or more sites individually), data-logging, and alarming. The PLC software includes the ability to build control programs (e.g. using a ladder logic editor or a C-program editor). A screen editor is usually included to create dynamic graphical displays capable of showing the value of selected process parameters in real time.

Vendors have included various security options in their products to deter possible security problems. These include:

(5) General Security Issues:

Because SCADA systems can provide automatic control of a system, system security is an important consideration. The primary security vulnerabilities for SCADA systems are the communication links, the computer software, and power sources for the various system components. Discussions of security considerations for communications and SCADA software were provided above. Protection of power sources for individual system components will be dependent on the power sources used in the system. However, security can be improved by ensuring that there are backup power systems for emergency situations.

Costs for SCADA systems can be divided into hardware costs, software costs, and installation costs.

Costs for SCADA hardware systems can vary greatly depending on the level of system sophistication, the total number of individual components (e.g. data acquisition systems and RTUs) and the communication method (e.g. modem, analog or digital wireless depending on the topography).

Cost ranges for SCADA components are provided below.

Data acquisition systems (e.g. data loggers), which are components of an RTU, can range from over $2,000 to more than $5,000. For example, the YSI 6200 Data Acquisition System (DAS), which manages remote real-time data collection through sensor sampling, data buffering/storage, and cellular and radio telemetry to a base station, costs approximately $2,700.

With control functions available on buoy platform, Apprise Technologies' Enviro FX with Remote Underwater Sampling Station (RUSS) dynamic profiler costs approximately $5,900. The more sophisticated systems may include additional instruments and functionality. Please also refer to Product Guide "Sensors for Monitoring Chemical, Biological, and Radiological Contamination" for information on specific sensors.

In terms of power supply, solar power components will generally add another $600 to the base cost of a system (versus a typical AC power connection). However, the low power operation of this type RTU allows significant cost savings to be achieved over time vs. a typical AC power connection.

The cost for a communication network depends on the communication method (e.g. hardwired or wireless) and the number of RTUs from which data must be communicated to the CPU. Data transmission by phone modem is often the least expensive of the communications options and offers low upfront capital costs, although it has monthly fees associated with each line. For example, it costs approximately $700 to set up a hardwired connection to a data logger (e.g. YSI 6200 system). Installing a hardwired line also represents a major upfront expenditure, which can range from $15/foot under ideal circumstances to as much as $200/foot under less ideal conditions (e.g. difficult terrain/ground). Wireless transmission service (either analog or digital) can range from $1,400-$3,900 or more for the same RTU, depending on the antenna configuration and if any repeaters are required (as described above, a repeater is an intermediate radio system that communicates to several RTU's in an area that otherwise does not have a good signal with the master radio. The master radio communicates to the repeater radio which communicates the surrounding remote RTU's).

The cost for wireless data components typically range from $3,500 for one Ethernet port (a communication protocol), with moderate speed to $10,000 or more for a high speed application serving multiple sites. Installation costs can range from 25 to 35 percent of equipment cost depending again upon the location and system nodes.

The cost of a commercially available RTU ranges from $800 for a basic model to $9,200 for an advanced model. The important features influencing the cost of an RTU are the number of I/Os, the type of communication used, the type of PLC processor selected, and the installation configuration. Advanced models usually require additional options relative to base models in order to be functional for all design features. System controller (the PLC CPU) costs range from $1,500 to $2,000. The important features of a system controller influencing its cost are PLC model, I/O count, method of communication, antenna height, and functionality.

Manufacturers, engineering design firms or a reputable systems integrator will be able to provide an estimate for a full package SCADA system (e.g., CPU with GUI, RTU and communication options). Given the potentially different levels of system complexity, the cost can range from $4,000-$14,000 per application at one site.

Manufacturers of SCADA hardware sometimes provide SCADA software. The price of the software depends on the level of application complexity (e.g. the number of database points and the number of I/Os, or "tags"). The programming of a given application will vary widely, and thus cost is often project-specific. For example, the cost for Wonderware SCADA software licenses ranges from $750 for 100 tags to $4,500 for an unlimited tag version. This cost is typical for SCADA software.

Typically, the configuration of the software is an additional cost, and can be approximately $500 per point. MIKE NET-SCADA software, which can monitor up to 50 pipe connections, costs $1,200. This software also has the capability to generate scenarios to simulate system operation. There are other similar software and hardware manufacturers. A list of these manufacturers/vendors is included at the end of this document.

In addition, software and hardware may be purchased from different vendors, as long as the specific combination between software and hardware is fully compatible.

Specialized expertise is needed for installation, setup, and routine checks for a SCADA system. Remote monitoring instruments require periodic inspection and maintenance in order to operate reliably. Routine maintenance may include a visual inspection of the field instruments and RTUs, a check for any visual damage, a check of all terminations for tightness, and dusting/cleaning of all equipment. The communications network and the central processing unit must also be inspected periodically. These maintenance requirements will add slightly to the costs of operating a SCADA system.