The City of Carlsbad SCADA system monitors transport, and distribution of purchased water from lakes and reservoirs to the city; and reclamation of treated water.
“We started using Opto as an experiment,” Pagakis said. “Years ago, we were using outdated technologies like tone telemetry and later, a mix of I/O modules and systems from other vendors. Special drivers had to be created to make everything communicate and it had become very complicated and unwieldy.”
The SNAP systems — which communicate with each other and back to the control center through a combination of radio, serial, and Ethernet links — are used to monitor, control, and acquire data from all of the city’s water and reclaimed water systems. Pagakis regulates all water transport, monitors an independent water treatment plant, and controls the chemical dosing of ammonia and chlorine that cleans the water. In total, these activities incorporate more than 1000 I/O points distributed across the city’s command and control center and numerous remote sites.
“Currently, the SCADA system encompasses three large reservoir impounds, 14 reservoirs, and 20 pressure-reducing stations used to monitor more than 500 miles of distribution pipeline,” Pagakis said.
Significantly, all of the monitoring and data acquisition functions are performed not by a single (or even multiple) central controllers, but by local I/O processors (or “brains”) distributed at pump stations and other points across the city’s infrastructure. These brains communicate to I/O located on the same rack and perform functions normally reserved for an expensive PLC.
For example, the brain takes valve readings from the analog input modules and performs scaling calculations to convert a voltage measurement into a percentage. So, for a typical 4-20 mA analog input module, a measurement of 12 volts would result in a reading of 50%. To have this scaling and engineering unit conversion take place locally, at the I/O level, relieves the main controller from extra processing, while also providing control center personnel the convenience of being able to view and interpret easy-to-understand units of measure (i.e., percentages as opposed to voltages.)
Distributing intelligence in this manner also provides a safeguard in case there’s an interruption in the operation of one of the main controllers. The brain can be instructed to continue to record measurements and perform calculations, and operators can continue to view this data from the control center’s HMI.
