Project Description

SCADA is an acronym for supervisory control and data acquisition. As the name implies the “supervisory” component does not do direct control of equipment and process but rather oversees the operation of the plant. What accomplishes the direct control are devices known as programmable logic controllers or PLCs.

Further examination of the term SCADA reveals that there is a component that does data acquisition. The data acquired includes many of the operating parameters within the plant along with the operating history of pumps, blowers, flows, valves, etc. The acquired data is utilized by the utility to generate information about the plant and then to take actions based upon this information. It can be said that the purpose of the SCADA system is to produce actionable information or information upon which decisions can be made and actions taken.

Situation

The utility was successfully operating the wastewater plant but it was very difficult to quantitatively understand where any improvements could be made. So another early project undertaken was the implementation of the SCADA system not only for the wastewater plant but also for the potable water system.

It was clearly understood that the first SCADA implementation was to provide actionable knowledge. Equipment and process changes would then be performed to improve the efficiency of the processes. In addition, it was understood that additional controls would be added in the form of instrumentation, PLCs and additional SCADA capability as the utility gained greater insight and became more efficient.

Problem

As mentioned above there was little useful information available about the operation of the wastewater plant and precious little that could be done while in that state.

Implication

Without understanding the true state of the wastewater process and the efficiency of the plant any actions taken to reduce costs and improve efficiency would be hit-and-miss. Not the best way to spend the hard earned money of the Kachina Village residents.

Need Payoff

As part of the SCADA implementation the real-time dissolved oxygen instruments (see above) were incorporated into the new PLC which was to control the blowers. The aeration blowers were now under control of the PLC and the performance information was gathered by the SCADA system.

Results

The aeration blowers were placed under automatic control of the PLC and the PLC turned the blowers on and off based upon the DO levels in the aeration basins. The aeration system was now operating in a closed loop fashion and providing performance information (blower runtime and DO levels) and history.

Two very important things were accomplished by this project. The utility now had some limited visibility into the effectiveness of the process and the power consumption within the plant was beginning to come under “knowledge based” control not “guessing” control.