Harford County DPW uses UtiliNet radios to improve their Wastewater Telemetry System

Harford County DPW, a public utility providing water and wastewater services for a county in Maryland, chose to implement a spread spectrum UtiliNet radio network that would meet their current needs and also take them into the future through the radio network’s capacity, expandability, and flexibility.

The challenge
By the early 1990s, it was obvious to Maryland’s Harford County that they needed to improve their Wastewater Telemetry System to monitor wastewater pumping stations for alarms. The company had discontinued the product and spare parts were difficult to obtain. In addition, it did only the most basic of telemetry functions. It could not interrogate all of the stations, had no control capabilities, no data storage or retrieval, and no data conversion. In addition, the radio-based Secode system communicated using audible tones over the same channel that the water and sewer department used for voice communication with repair crews and field staff.

In 1994, Harford County contracted with a consulting firm to investigate a solution. Harford County and their consultant looked at several alternatives.

The solution
Harford County chose to implement an open architecture, PLC-based system using a Spread Spectrum Landis+Gyr UtiliNet radio network. The system would meet their current needs and take them into the future through the radio network’s capacity, expandability, and flexibility. In addition, county supervisors and managers received the benefits of improved information flow and availability.

The consultation firm reviewed telephone systems and radio systems. The radio-based network was preferred because it was more reliable and had lower annual costs. They looked at VHF/UHF radios, 900 MHz multiple address system radios, and 900 MHz spread spectrum. From these, the UtiliNet spread spectrum radio was selected.

Spread spectrum
The spread spectrum radios were recommended by the consultation firm because they communicate over an unlicensed band and do not use a dedicated frequency like other radios. Instead, the data is spread across many different frequencies and encodes specifically so that only the receiving station can decode the message. It does not require FCC licensing for operation. Another advantage is that they are well-suited to SCADA applications.

Mesh topology
However, this is where UtiliNet radios had the advantage. With the mesh topology, each radio is intelligent enough to know where it is in terms of location and neighboring radios; to know how to combine transmissions from adjacent radios, build information packets to perform store-and-forward data transmission and be able to selectively transmit to surrounding radios in the mesh in order to seek a path free from temporary interference, site disruptions or signal outages. The UtiliNet radios met these requirements – the only one on the market at this time to do these intelligent activities.

The results
Harford DPW now has a UtiliNet radio network that covers 53 pumping stations, servicing an equivalent population of about 100,000 people. The network consists of 81 radios, 53 single radios at the pumping stations, four repeater sites, four meter sites, and 20 radios at ten core sties that also act as repeaters. The radio network is easily scalable to add pumping stations, repeaters, and core sites to accommodate future growth.

Harford DPW now monitors three times the quantity of data with the new system. Monitored points include: run and fail status of all pumps and generators; power; high wetwell level; station flooding; intrusion alarms; and analog points for flow (instant and totalized) and levels. “I particularly like the automatic rerouting that the radios do, as well as the report-by exception features. We can know immediately when there is a problem, rather than having to wait for the round-robin polling technique to complete. The software also makes it possible for us to look inside the network to see what is happening,” said Joel Caudill, P.E. Process Engineer.

The added value of the new system is that it improves their ability to monitor the wastewater pumping system with minimal effort and it provides valuable insights into the performance and efficiency of the pumping systems.

Now, if an alarm comes in to the central facility and is not acknowledged by someone, a page is sent to field personnel. Also, the supervisors use laptop computers with the HMI software and use cell phones to dial in to the main server and track the status of pumping stations from anywhere.

“In the future, we expect to accommodate the flow growth and connection growth by adding less personnel and systems than would otherwise be required. The UtiliNet radios make scalability possible,” Caudill said.