Flexibility and Room to Grow

The central communication processor is a Motorola MCP-M located in the wastewater treatment plant. It communicates via a Modicon, Inc. MODBUS connection with an Intel PentiumŪ-based PC used by operating personnel in the main building. The computer is dedicated to a SCADA host and operator interface system configured by Revere U.S. Data's Factory LinkŪ under Microsoft Windows NTŪ. Via an Ethernet connection, the same Factory Link system is accessed by a similar computer in the maintenance office in the nearby shop building. That computer is used by personnel of U.S. Filter Operating Services, which maintains the treatment plant and lift stations by contract with the City. Each RTU closely resembles the central unit shown in Figure 4, incorporating a Series 200 CPU and typically, a 16DI input module. The RTUs report changes in monitored variables soon after occurrence. In addition, the central unit polls all remotes every 15 to 20 minutes to verify communications.

One major advantage of the Motorola RTUs is that they have a "store-and-forward" capability for relaying messages to and from designated peers. Thus, for example, having an RTU near the top of a hill can save the expense of a relay station for other RTUs in the valley beyond. The MOSCAD units act as programmable controllers (PLCs) with built-in two-way radio communication. They can readily be expanded in modular fashion to incorporate additional discrete and analog signals such as flow rate, motor temperature, and vibration. That was a major requirement for this application. The RTUs can also handle a variety of intelligent local control functions that might be implemented in the future, such as periodic actuation of ventilator fans. The network can accommodate up to 246 RTUs.

In summary, U.S. Filter's site manager Brian Johnson said, "Any kind of power surge or transmitter lockup would take our old system out for a while, and it was hard to fix because everything was proprietary. We were looking for something we could depend on, with off-the-shelf parts. Revere's system fits our profile for now, and it's flexible, so we can expand it over a period of time."

A status display screen for a lift station showing water levels and site security information.

Motor controls at a lift station are raised to keep them above flood levels

These centrifugal pumps are located in the dry well underneath a lift station.