By Victor Garcia
Fourteen seconds is not the type of performance you want from an automobile going zero to 60. But for a wireless radio system gathering data from more than 70 sites spanning 85 square miles, at extremely varied terrain levels, 14 seconds is the crème de la crème of performance.
The geographical representation is that of the Padre Dam Municipal Water District, located in Eastern San Diego County, which serves several communities from Santee to Alpine. Its terrain ranges from an elevation of 100 feet to 2,600 feet. Padre Dam MWD decided to go wireless with ProSoft Technology Industrial Hotspot Radios in mid-2010, because it was becoming difficult to maintain its then-current system.
Its old system, which used RS-232, had a maximum baud rate of 4,800 and took some 90 seconds to get data from all sites. The software to drive the original radio system was a custom program written in C Programmable by outside contractors.
"The original authors of the program were no longer available," said Rich Mellor, Padre Dam MWD SCADA Technician. "There was a great desire to replace the system with one that could be installed and maintained with in-house staff, eliminating dependence on outside contractors."
Between the difficulty maintaining the old system and its speed of response, Padre Dam officials knew it was time to upgrade. After a path study was performed with relatively few issues, installation and configuration of the radios went smoothly, Mellor said.
"Along with the radios, we replaced the entire Remote Terminal Unit, including new MicroLogix 1400 PACs, power supplies, terminal blocks and wiring," he said.
There were some challenges with the terrain.
"There are many natural and man-made difficulties, which made line of site an almost impossibility, even though some of our sites are on the highest points around the county," Mellor said. "Using some ingenuity and the radio's repeater ability, we were able to use some of the 900MHz radios as repeaters allowing us to pass information through very difficult terrain."
ProSoft Technology's wireless engineers came on site for two days to assist Padre Dam officials with the field study and verify connectivity. After the study, Prosoft helped Padre Dam MWD evolve the system by creating "backbone" communications using their 2.4GHz radios.
Nine radios were linked in a circular pattern which allowed Padre Dam to drive communications in either direction should a failure of one radio ever occur. Seven of the nine 2.4GHz radios are positioned at key sites around the district working with the local 900MHz radio and PLC to transfer the RTU data gathered back to the office at high speeds. The final two radios are at the office collecting data and storing it in a ControlLogix PLC.
At some of Padre Dam's remote locations there is no AC power. It was decided to go solar in those remote locations.
"This was a learning curve, between the size of the panels and the type of batteries. Parabolic antenna mounting also became an issue due to size, angle needed, mounting them back to back, and providing a weatherproof splitter to tie them into a single radio," Mellor said.
The wireless radios were phased in overtime.
"We had to be careful to not interrupt operations too much," Mellor said. "Water delivery and storage is a balancing act between demand and weather."
Collecting data from 70 sites in a mere 14 seconds allows the Padre Dam Municipal Water district to respond immediately should one of its Remote Terminal Units shut down. And that happened in April.
"A person driving near one of our RTUs lost control, hit a hydrant and completely destroyed our RTU. Within a just a few seconds, the HMI recorded an alarm of low pressure and total loss of communications with that site," Mellor said.
Knowing what happened and where the incident took place was quick and easy, he added.
About the Author: Victor Garcia is the staff writer for ProSoft Technology. Prior to working for ProSoft, he was a journalist for six years.
