SCADA improves citys monitoring system
By the mid-1990s, it was apparent that Albany, Ga., had a serious problem. The SCADA (Supervisory Control and Data Acquisition) network at its aging wastewater treatment plant was failing and needed to be replaced.
The system, installed in 1981, monitored alarm conditions at 80 unattended lift stations and an additional 18 stations devoted to collection of stormwater. Because the city of 78,000 was sending about 20 million gallons per day through the system to the plant, it was critical that the SCADA system work properly.
Consequently, the city chose Revere Control Systems, Birmingham, Ala., to provide a new system. Installation began in July 1996 and was completed in about six months. The new system includes a central communications processor and remote terminal units (RTUs) from Schaumburg, Ill.-based Motorola. The RTUs feature two-way FM radio communication; their store-and-forward feature allows each RTU to act as a relay station, extending signals to units that are unable to reach the central site directly because of distance or line-of-sight obstructions.
The central processor, located in the treatment plant, communicates with a Pentium-based PC. The PC runs under Windows NT software and is dedicated as a SCADA system with an operator interface configured with Factory Link software from U.S. Data, Richardson, Texas. An Ethernet connection allows a similarly configured PC in the nearby shop building to access the same system.
Under the previous system, two stations that pumped combined wastewater and stormwater had electrically activated gate valves to divert water to the nearby Flint River during flood emergencies. The RTU at each station had two discrete inputs to monitor gate positions and two discrete outputs to control the opening and closing of the gates. Those gates are no longer used, and the combined sewers have been separated.
We did a sort of bare-bones installation to begin with, but we wanted the capability for expansion, says Albany Superintendent Larry Wert. The program and the units can do much more than what were currently asking of them.
The expansion capability was a major requirement for the RTUs. Each can be expanded in modular fashion to accommodate additional discrete and analog signals for conditions such as flow rate, motor temperature and vibration. Each also can handle a variety of intelligent local control functions, such as periodic actuation of ventilator fans, that might be implemented at a later time. The system as installed could have up to 246 RTUs. Our old system was hard to fix because everything was proprietary, says Site Manager Brian Johnson. We were looking for something we could depend on, with off-the-shelf parts. This system fits our profile, and its flexible, so we can expand it over a period of time.