RTU System Streamlines Pumping, Level Control
The city of Martinsville, Va., recently installed a wireless SCADA system to help improve the performance of its water treatment and distribution system, replacing a control system that was more than 15 years old.
Three years ago the city began by installing a Zetron Model 1700 Controller and Model 1708 RTUs at three of its sites. The system has since been expanded to include 10 RTUs: two Model 1716s and eight Model 1708s.
The city?s main water source is the Martinsville Reservoir, which lies some four miles north of town. From this site 6 million gallons of water per day is pumped to a filtration plant located in the city?s northern outskirts. At the reservoir pump station three 100 horsepower pumps are controlled by a Model 1716 RTU. Two of the pumps are fitted with variable speed drives that are controlled by a 1-5 volt signal. An analog output from the Model 1716 allows operators at the filtration plant to control the pumps? variable speed drives. The flow of water coming into the filtration plant can then be adjusted to match the flow leaving the plant.
Clean water from the filtration plant is pumped to storage tanks in six different locations around Martinsville: NY Avenue, Tank Street, Bethel Lane, Grandview, and Industrial Park.
The new SCADA system has been installed by GCS Electronics & Communications, based in Martinsville.
?In the past they would run the pumps wide open for a couple of hours and then they?d have to shut them off,? said Giles Smith, owner of GCS. ?Once the water levels started getting low they?d have to run the pumps wide open again for a couple of hours. They were in a constant battle trying to adjust the chemicals going into the water to compensate for the flow. Now they have a slide gauge on a computer screen. By clicking their mouse on the slide gauge they can adjust the pump speed up and down to achieve a level that exactly matches their output.?
Digital In, Digital Out
The reservoir pumping station provides digital inputs and outputs to the Model 1716 RTU to turn the pumps on and to provide feedback to indicate when the pump contractors have pulled-in and the variable speed drives have reached the requested speed. A three-phase monitor also provides an alert to operators at the filtration plant if at least one phase of the incoming electrical service is lost.
Digital In, Digital Out
The system controls two smaller pumping systems. During periods of drought ? when the Martinsville Reservoir cannot supply all the demands of the city ? water is pumped from the Leatherwood Creek pump station. In addition, the Bethel Lane tank site uses a small pump to send water on to the Grandview site. Model 1708 RTUs are used at each of the tank sites to provide water level and battery level readings.
Digital In, Digital Out
?Each tank has an analog input,? Smith said. ?Some tanks have a drop-in ultrasonic transducer; others have a pressure transducer at a point in the bottom of the tank. In both cases it provides a 4-20 mA input so we actually have a reading in feet. All the sites have battery backup and one of the inputs is battery level. If power goes out and the battery voltage falls below a certain level an alarm written in the software goes off to let them know.?
Digital In, Digital Out
Parts of the SCADA system are being used to monitor things other than those related to fresh water supply. To the south of the city the Smith River is dammed at one point to provide hydroelectric power. To protect delicate ecosystems above and below the dam, the USGS has a gauging station that monitors the river level.
Digital In, Digital Out
?The state environmental agency requires the city to maintain the river water at a certain level,? Smith said. ?The USGS gauging station had strip recorders. Every couple of months or so USGS personnel would stop by to collect the strip charts and send the city a report. That worked fine normally, but during some dry periods in the summer they could have a critical situation where the water level dropped too low and caused environmental problems.?
Digital In, Digital Out
The gauging station now has a Model 1708 powered by a solar panel and battery backup. One input on the RTU is used for a pressure sensor (4-20mA) to indicate river level, and the other input is used to monitor battery voltage. By providing an instantaneous report of the water level, operators at the hydroelectric dam know when to open or close the dam to keep the river at a certain level.
Store and Forward
Using UHF Simplex radios, the 10 RTUs communicate with the controller at the water filtration plant. The Model 1700 is connected via a modbus option to a PC running the system software. According to Smith, the filtration plant is in the worst location in the city from a radio perspective. As a result, direct communication is only possible with two of the tank sites. To get around this problem, GCS is using the Model 1708?s ?store and forward? capability. The Grandview Road Water Tank is located at a relatively high elevation. The Model 1708 RTU at that location is used like a repeater to store and forward data from the outlying sites.
Store and Forward
?The Manager of the Water Filtration Plant, Andy Lash, wrote a modbus interface in visual Basic for the system,? Smith said. ?All data is therefore recorded and stored in a database format. Since the system has been implemented, tank fluctuations are easy to monitor. Andy also has plans to allow limited access to the data on the SCADA system through a remote dial-up connection for real-time monitoring from a remote PC.?
Suitcase Monitor
GCS Electronics also built the city a portable monitoring station packaged in a plastic equipment suitcase. The suitcase contains a Model 1708 RTU, a power supply, a radio, and a portable antenna tube. The portable station can be set up anywhere in the city to take pressure readings using a 4-20mA signal from a pressure sensor. The portable monitoring station was built to allow temporary monitoring so the information can be sent back to the water filtration plant and allow the generation of a database.