Town's SCADA System Based on Open Protocols

A recent lift station telemetry project in the town of Somers, Wis., illustrates a trend away from proprietary SCADA protocols to systems based on open protocols. Somers is an urbanized township of more than 8,300 on Lake Michigan, adjacent to the City of Kenosha. It needed a SCADA telemetry system to integrate four existing lift stations with four older lift stations recently acquired from a nearby district that disbanded.

"While the town's lift station included a dialer that terminated at the town shop, the system they inherited included four lift stations with no remote function. The town wanted a dialer at each of the lift stations. We did an evaluation of the old lift stations and recommended a radio telemetry system to include all lift stations," said Crispell-Snyder Senior Engineering Technician Dean Logterman. Crispell-Snyder serves as engineer to the town.

"They just had alarm lights outside on existing lift stations they inherited from the old sanitary district," said Mike Bewick, Project Engineer for Altronex, the electrical integration division of L.W. Allen, a full service distributor based in Madison, Wis.

Apart from a lack of integration in the SCADA system, the existing lift stations were designed in such a way that problems were more likely.

"The older equipment would experience failures when things like the floats would fail, or the lead pump would fail. On a couple of the stations, the bubbler tubes ran off air compressors and if the compressor goes out you're totally out of luck. You're basing your system on a piece of hardware that has a limited life cycle," Bewick said. "The Sigma submersible transducers we used allow the operator to see levels in wet wells - and were put in four of the lift stations."

The new master panel uses a polling system, Bewick said.

"It calls out to each site for its information and when it gets to the last site it starts over. The master PLC is an AB Slick 503 processor, and that processor works in conjunction with AB RS Logix Software. All the communication ladders and all that logic is completed internally," he said.

The open architecture of the system will allow the town to add functionality in the future, including monitoring of flow from all stations.

"The PLC being used can send four analog signals back, and each fixed PLC can send 12 discreet alarms. All we'd need to do is add wires and do a little programming," Bewick said. "New lift stations can also be added, as the current master panel can handle up to 256 remotes."

That will become a key feature this year as the town plans a new lift station to the west of the four lift stations it inherited.

Equipment protection and cost were both taken into consideration in the surge protection system, according to Bewick. The town installed Square D lightning surge protectors and metal oxide varesters, but did not go with the most expensive equipment available.

"There is certainly such a thing as overkill - they make varesters that cost up to $2,500. The components we used cost $100 together - which is appropriate since we only have $2,000 in equipment behind them," Bewick said. "Each remote site does have an uninterruptible power supply (UPS). This provides a battery backup so a customer can differentiate between a power failure and a data communication failure. The UPS also conditions the power, taking out some of the spikes and sags."

Major components at the remote lift station sites include:

MDS Digital Synthesized Data Radios - UHF Radio Transceivers operating at 453 mhz.
Allen Bradley Micrologix 1000 fixed I/O programmable logic controller/remote telemetry unit.
Allen Bradley SLC 5/03 modular, expandable I/O programmable logic controller/remote telemetry unit.
Operator interface including 4-line X 20-character LCD alphanumeric keypad displaying wetwell level and providing set points at all four lift stations.

Major components at the town hall master panel include:

MDS Digital Synthesized Data Radios - UHF Radio Transceivers operating at 453 mhz.
Allen Bradley SLC 5/03 fixed I/O programmable logic controller/central telemetry unit.

The town hall master panel also includes an automatic telephone dialer with 96 logic controller virtual channels and 4-dry contact inputs, and a TCP Quickpanel with RS485 protocol Verbatim Gateway VFLC-4L-96 modem. An Okidata Model 184 Dot Matrix printer was installed for alarm printouts.

The lift station function is monitored on a 10.5 inch TFT color operator interface touchscreen which displays:

System overview
Menu screen
Individual lift station screens
Run time and flow total screens
Total run times and flow total screens
System alarm screen
Time and data screen

Configuration A Key Process

Unlike proprietary SCADA systems that generally include Fieldbus components that are designed to work together and require little or no configuration, components included in the Somers telemetry project had to be configured to work with the rest of the design. This involved programming of individual components to perform various tasks, and then the configuration necessary to get the hardware to function in the field.

"The actual process of putting in the telemetry system took two weeks. Then we spent another 6 weeks tweaking it to do what we wanted it to do," said Somers Public Works Foreman George Stoner. "We did the installation in the fall, when there were no leaves on the trees. The real challenge came in spring when we started getting data failures as the trees leafed out and blocked the signal from the antennae. One of the signals also went over a power substation, which took some additional configuration."

Despite the faster configuration times possible with proprietary Fieldbus systems, most communities are better off with open-source, Bewick said.

"This (open source) is what general industry uses. It's tough as nails and we have a very low failure rate," he said.

But the real argument that many municipalities use against the idea of proprietary SCADA systems is the lack of choice, Bewick said.

"They (proprietary SCADA companies) have a rep and you'll have to buy those products through the rep. If the customer has some problem with that representative, they really can't go anywhere else. With an open design like the Somers telemetry system, if the customer gets disgruntled with our company for any reason, they can go to any Allen-Bradley rep and buy the same components."