Oak Brook Case Study
Background
The existing Supervisory Control And Data Acquisition (SCADA) system for the Village of Oak Brook, IL included Remote Telemetry Unit (RTU) data collection hardware that was outdated at best. Data was collected via dedicated telephone lines. The master utilized a polling sequence calling each RTU sequentially. The original RTUs were installed in the late 1970’s and additional RTU stations were added over the following twenty years. In 2000 a computer system running a modern Human Machine Interface software package was successfully integrated with the existing RTU hardware with the majority of the control functions residing in the computer.
The Village of Oak Brook receives water from the Du Page Water Commission (DWC). Oak Brook’s fresh water supply system consists of two 250,000 gallon elevated tanks, two pumping stations with in ground reservoirs, three wells (for emergency purposes), one receiving/pressure adjusting station and one inline booster station. The two pumping stations and the receiving station receive water from DWC. During low demand periods the pumping stations regulate the water flow from DWC based on elevated tank levels. The control was sluggish. A full polling cycle took 25 seconds to complete. The elevated tank levels were transmitted to the Master Control Panel (MCP), control functions were calculated, and data was then retransmitted out to the pumping stations. Elevated tank data updates to the pumping stations took up to one minute. This severely limited the operation of the flow control. Local pressure and flow control were available but not preferred. Telephone line failures caused numerous problems for the Village.
Solution and Results
Automatic Control Services proposed an upgrade to Programmable Logic Controller (PLC) based RTUs and the installation of a private wireless communications system. Operator Interface Terminals (OIT) would be installed at the remote stations and provide data monitoring and system control from each station. The communications between the stations would be Ethernet based utilizing a 3.65 GHz lightly licensed radio system. This radio frequency provides high bandwidth and is capable of handling large amounts of data. The polling method of data collection would be eliminated.
The Village of Oak Brook now enjoys a true Distributed Control System. Elevated tank data is sent directly to the pumping stations with two second updates. All control functions reside in the local PLCs. The SCADA computer and the local OITs communicate directly with each station collecting data and sending control setpoint modifications as needed. A computer system failure will not severely limit system operations. All system control can be managed from the computer and any of the four main stations via the OITs. As an added bonus, with the 3.65 GHz radio system in place the Village of Oak Brook has the capability of adding video security at all of the water system locations.