In 1998, Seattle Public Utilities (SPU) recognized a problem in achieving Y2K compliance. During a Y2K analysis on pump station equipment, Senior Software Engineer Dan Pflager found problems in the software and hardware. He also reported that much of the field equipment was obsolete or unsupported.
New regulations from the Department of Ecology also required the pump station network to quantify an overflow at any given permitted site. The older monitoring and data collection equipment in place at the time could not accomplish that task.
SPU decided a new system was needed to meet the regulatory requirements, to avoid any potential for a Y2K incident, and to update the legacy equipment. SPU searched for a system that could provide more data from field equipment, add intelligence to the remote sites to compute and log lift station flow rates, and increase the accuracy of data during overflow events.
Systems Interface, a Seattle-based system integrator company, obtained the bid to design the new SCADA system. Although SPU?s detailed specifications fit several manufacturers, Robert Schommer, Municipal Business Manager with Systems Interface, recommended Allen-Bradley hardware.
ProSoft, a supplier of protocol emulation modules for the Allen-Bradley products, was contacted to provide integration services using the specified Modbus protocol.
?A large number of SCADA projects in the oil and gas and water/wastewater industries have been specified with the Modbus protocol,? said Doug Sharratt, President and Lead Developer for ProSoft. ProSoft chose its RTU-5/03 processor, developed jointly by ProSoft and Allen-Bradley. The processor has been modified to include the Modbus slave protocol.
The new telemetry system consists of a hot backup, redundant, dual processor Master Telemetry Unit (MTU) which talks to Remote Telemetry Units (RTU) at each of SPU?s 72 sewer pump stations. Since there are two processors, one in primary mode and one on stand-by, should one processor fail the other will take control, thereby assuring that the RTU?s never lose contact with headquarters. Should the worst-case scenario happen and contact is broken, the RTUs have the capability of making decision for their station until contact is re-established.
?ProSoft?s Modbus Communication Modules function independently of the PLC, sharing the task of communications and allowing the processor module to concentrate on control and data functions,? said John Stephenson, Project Manager for Systems Interface.
The RTUs monitor the pump station activities and control the operation of the sewage removal equipment consisting of either pumps or air compressors. Each RTU is polled by the MTU through U.S. West telephone lines. The MTU also contains a telephone dialer that is programmed to announce system alarms, thereby allowing SPU staff to track the data and respond to emergency situations.
SPU is using the same RTU equipment for each of its four types of pump stations. The only difference is in what features of the program are active for the particular station an RTU is controlling.
This new system is far different from the previous legacy system, which could not track or control any station flow rates.
?Technically speaking,? said Pflager in an interview with the Seattle Times, ?they [were] just modems ... that have no smarts at all.?
The new SCADA system is scheduled for completion in late October. System testing was completed on June 30 and a successful simulation of the system was run to catch and correct any defects. The new system passed all compliance tests.
Seattle Public Utilities will be adding two more remote telemetry sites for the combined sewer overflow stations soon. These sites will also use the Allen-Bradley/ProSoft solution.
About the Author: Danetta York is the Marketing Specialist for ProSoft Technology, Inc.
