The Many Faces of SCADA

The electrical controls team at Tri-Tech has worked on SCADA systems for many years, providing a knowledgeable and experienced team which you can trust with your processes. Continue reading for more information about the opportunities available for utilizing SCADA and automation for process control.

A BRIEF HISTORY OF SCADA

Historically SCADA systems have been used to monitor processes, provide information to the operator, and provide a remote venue for the operator to control the process. This was especially advantageous for processes that spanned a large geographic area such as refineries, municipal water and wastewater treatment systems, and other similar applications. The monitoring and reporting functions of SCADA systems typically include “Run, Stop, and Alarm status”, “Real time reporting of variable data” (Flow, Temperature, Level, Pressure, pH, O2, ORP…), and the like. This is critical information that an operator requires to make the decisions which keep the process running correctly.

With some exceptions, the majority of the decision making was left to the operator(s). Those exceptions include such things as lead-lag operation of redundant equipment, startup upon failure of redundant equipment and systems, etc. The challenge has always been for the operator to be observing ALL of the information, in real time, when it begins to change so that the process doesn’t stray too far from normal conditions before corrections can be made.

REAL-TIME DATA COLLECTION

Since not all changes happen at a rate that is easily recognizable as being a problem, tools must be implemented that will identify and display trends. As operators learn their processes, over time they discover that trends often give an early warning of impending problems. Values plotted on a graph in real time paint “pictures” that are repeatable and become identifiable at a glance. The chart recorder was an early method of data collection which served this purpose.

The problem for chart recorders was that since they were limited to a relatively small number of data points, they could operate at only one resolution per data point. Additionally, they stored their data on a paper media which had to be changed periodically and then filed. Retrieval of data was cumbersome at best.

As SCADA systems became increasingly sophisticated, they began to offer the ability to integrate multiple sub-systems of varying manufacturers. They also allowed for real-time data collection, storage, and display of an ever-increasing number of data points in a digital format. Graphical displays allow for uninterrupted viewing of plotted data, as well as the ability to change the resolution displayed (zoom in and out) without changing data itself, nor interrupting the data collection effort.

STATISTICAL PROCESS CONTROL

Statistical Process Control (SPC) really came into its own once the technology advanced to the point of being able to accurately monitor and record, in real time, many data points. When a process begins to fail, a look at the “history” of all data, displayed simultaneously will show what variables first began to change, causing the process to fail. This is valuable information, allowing the operator to quickly discern and correct problems before they become catastrophic.

The alternative to using SPC was to implement a correction based upon the experience of the operator; wait for a result to see if the correction solved the problem; and if that didn’t work, try something else. It is important to note that different operators may come to different conclusions as to how the problem needs to be corrected which can further compound the problem and delay the correction. There is also the concern that the stability of the process could depend on one or two experienced individuals, with little or no backup plan otherwise.

THE AUTOMATION OF SCADA

With SPC, the cost-effective use of large number of data and/or I/O points now made it possible to have eyes on all aspects of the process at all times. As more and more is learned about the process, automated corrections can be implemented into the programming, along with notification features that will inform the operator that a correction was implemented. This liberates the operator to perform other necessary tasks and allows them to venture farther from the process.

For example: a wastewater plant that processes storm water as well as sanitary sewage is affected by sudden storm surges. The operator has to be vigilant to monitor the weather. In a large municipality a local rainstorm may go undetected by the operator and the subsequent increase in the influent flow rate may not arrive at the plant for hours after the actual event. If automatic corrective action is programmed into the SCADA system, it will recognize the sudden increase in flow and based upon the trend implement a pre-defined corrective action, averting the problems associated with high influent flow rates. Then it will notify the operator of the action taken.

SCADA IN PROCESS DEVELOPMENT

Having the ability to monitor and record a large number of data points in real time is a priceless tool in developing a new or modifying an existing process.

For example: a client has invented a new process whereby they take whole scrap tires and gasify them to produce an alternative fuel source for a boiler. The process has been proto-typed on a small scale to verify the technology. Now when that process has been up-scaled to allow a continuous feeding of tires into the process, there is a lot at stake. Every minute the new process does not operate correctly costs money.

The process has to be observed from many points of view. Problems must be identified and resolved quickly. Something happening in one part of the process may affect another seemingly unrelated part of the process. Subtle changes in variables can cause the process to fail. The cause of these subtle changes must be identified and corrected in short order.

The latest technology in SCADA allows us to cost-effectively monitor and record ALL of the variables in real time. When a problem occurs we can view all of the data, in parallel, simultaneously. Observing the trends in this manner enables us to quickly observe what changed first and the subsequent changes that followed and in what order. This allows the root problem(s) to be identified and corrected, instead of treating the issue symptomatically.

IN CONCLUSION

SCADA, as it exists today, is a problem solving tool. It is well worth the investment. Sometimes that is not readily apparent because you are not experiencing the problems, and bearing the cost that would be present were it not doing its job. If you already have a SCADA system, it may be prudent to continuously look for ways to automate the control of the processes, and notify the operator of impending problems and automatic corrections to the process.

The engineering staff at Tri-Tech have many years of experience in working with different SCADA systems and automation. Please give us a call at 937.306.1630 to talk more about our SCADA capabilities.