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Breathing New Life Into a Legacy SCADA System

 

The Town of Derry in New Hampshire had been running its wastewater monitoring system on a mix of old and new - and potentially Y2K noncompliant - computer applications. In the fall of 1999, when the town set out to upgrade its Supervisory Control and Data Acquisition (SCADA) system, it faced the challenge of adapting the new system to its existing remote telemetry units (RTUs).

The Town of Derry transfers two million gallons of wastewater daily through eight wastewater pumping stations to serve 13, 500 users. The central wastewater treatment facility has three lagoons with biological treatment, a remote blower building to aerate the lagoons, wet wells and a 14-inch pressurized line to the Merrimac River nine miles away.

 

This SCADA System integrates 13 remote pumping stations with 650 points under one software program.

 

Communication between the remote pumping stations is handled by older Aquatrol 1500 RTUs and a single Allen-Bradley SLC/503 programmable logic controller (PLC) at a newer pumping station. Data is transmitted through a Motorola Maxar 80 and Maxtrac radios over a single radio channel to the central system. A Control Microsystems ScadaPack PLC recently replaced a local I/O rack at the facility.

Prior to the fall of 1999, the town had been using proprietary and unsupported Prosoft software under the iRMX operating system to monitor the remote stations. This software had proven to be stable, but increasingly difficult to use and maintain over the years. A second computer had been dedicated to paging software from a different supplier. This array of unsupported hardware and software, together with the risk of Y2K noncompliance and the lack of a clear system-upgrade path, led the town to seek a new SCADA system.

The Town of Derry turned to local system integrator IAN Technology Solutions for an open systems-based SCADA system that could accommodate their requirements without replacing the existing Aquatrol RTUs.

Operations can be monitored and controlled from a desktop computer.
Operations can be monitored and controlled from a desktop computer.

 

"It was a particular challenge to accommodate switching between three protocols - the Aquatrol, Allen-Bradley and ScadaPack," said Andrew Ian, owner of IAN Technology Solutions. "The limitation of only one radio channel made the project even more daunting."

The solution was a flexible and customizable operator interface software package (Visual Tag System from Trihedral Engineering of Bedford, Nova Scotia, Canada). The software allows the superintendent to monitor and control operations from a central Pentium II desktop computer running Windows NT. The new SCADA system integrates 13 remote pumping stations with 650 points under one software program on one computer, over one radio channel with three protocols. The existing Aquatrol RTUs could be kept because Trihedral developed a new Aquatrol 1500 device driver enabling the town to add new PLCs to the system.

"We saved a lot of money by not replacing the existing RTUs," said Ron Robinson, the town's mechanical technician.

 

"The old Aquatrol system couldn't run on a fast computer so upgrades were going to be difficult. Now with the SCADA system, we only have to send two technicians to inspect the remote systems once per week, and this meets state requirements."

The new SCADA system performs at a higher level in monitoring and controlling valves, pump sequences and oxygen levels. Operators select pump sequencing control of wet wells at the wastewater treatment plant, while the ScadaPack PLC does the actual control. Reporting, alarming and paging to alphanumeric pagers also are generated through the new system, and the town receives daily, weekly and monthly reports on run time and the number of starts for each pump, air compressor and bubbler.

"It was a long process, but we got excellent value for our money," said Tom Carrier, Derry's water and wastewater superintendent. The town plans to add two new water pumping stations to the system this year.

An open systems-based SCADA system could accommodate all the project requirements without having to replace the existing RTUs.
An open systems-based SCADA system could accommodate all the project requirements without having to replace the existing RTUs.

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