SUPERVISORY CONTROL & DATA ACQUISITION (SCADA)

What is SCADA?     Issues     Solutions

SCADA systems combine specialized computer hardware and software to monitor and control many types of processes and operations – from manufacturing to power generation to water and wastewater treatment, collection and transmission.

In water-related processes, a SCADA system is used to control equipment (e.g., pumps and valves) based on predetermined events and/or logic. The system also collects information from measuring devices (instruments) to determine the status of a process or equipment. This information is used by a centralized control station to initiate commands automatically based on specific conditions, a series of events or a threshold. Operators can also monitor processes and initiate control actions from a workstation.

There are four elements of a SCADA system:

1. Instruments: These devices are used to collect information about a specific condition. Various instruments might measure water quality (turbidity), flow rates, reservoir levels, etc.
2. Field Control Components: The purpose of a Remote Terminal Unit (RTU) or Programmable Logic Controller (PLC) is to initiate an action (e.g., start or stop) at a pump, valve, etc. RTUs and PLCs provide varying abilities to execute “closed-loop control,” independent of direction from an operator or SCADA master station. These components can also be controlled by the master station.
3. Communications: A network (hardware and software) transmits data and commands between the central control room and field components – across a treatment plant, distribution or collection system, or the length of a transmission pipeline. These networks can be wireless, radio-based or based on wire or fiber-optic cable.
4. Master Station and Human-Machine Interface (HMI): Users interface with the system via SCADA workstations. The software presents processes via a graphic display to the operator, provides status and alarms, allows manual control of elements and gathers data for historical analysis and reporting. Large systems may have a separate data historian for long-term archiving.

Issues
Most U.S. water and wastewater utilities have progressed through multiple generations of process automation and control systems. Process changes, system expansion, technical obsolescence and/or the desire for higher levels of process automation and optimization cause many utilities to consider system replacements or major upgrades. The following issues typically are addressed in a SCADA system replacement or upgrade project:

• Users' needs related to system functionality, user interface, remote system access, reports
• Standardization of control system components to reduce maintenance and training costs and to simplify system design
• Maximizing the useful life of existing automation investments
• Uninterrupted system operation during implementation and start-up
• Complete and accurate documentation, accessible from a web-based tool, for system components
• Automatic control strategies to better control chemical and power utilization and to relieve operators of labor-intensive activities
• Process instrumentation that is rugged, accurate and easy to maintain
• Flexible system design that minimizes component obsolescence and supports straightforward expansion for system growth
• Seamless integration with other utility information systems including CMMS, CIS, GIS, LIMS, etc.
• Matching the organization’s business requirements and the system’s ability to address those requirements

Westin has developed a rigorous, methodical approach to successfully delivering system projects. While specific SCADA applications are unique, Westin’s field-proven SCADA system delivery methodology helps to ensure project success. This methodology is explained further in the other SCADA sections of this web site.