You know you’re getting old when you start replacing control systems that you designed/installed earlier in your career.  I don’t feel that old, but the grey in my beard tells me otherwise.  I have been providing design and integration services for water/wastewater SCADA systems for over 19 years now, and see a common thread in the life cycle of a SCADA system:  SCADA servers need to be replaced about every 5 years and the industrial control hardware (PLCs, operator interface terminals and telemetry) should be replaced about every 15 years.  Why replace them? Servers typically run out of warranty and parts become harder to find after about 5 years, while more industrial control hardware usually has a longer life span of about 15 years, at which time manufacturers have a new product available and are looking to stop supporting the old.  In addition to the hardware/software simply becoming unserviceable, as with anything else technology related, new systems typically provide far more functionality and other benefits to make your job easier.


When I first started doing this job in the late 90’s-early 2000’s, I was involved with the first generation of water/wastewater SCADA system replacements.  Many water/wastewater SCADA systems were installed in the mid to late 80’s and were proprietary systems (such as Aquatrol) with rudimentary controls. Although functional, the older proprietary systems didn’t have the flexibility or functionality of newer PLC/HMI-based systems.  These systems typically used thumb-wheel switches for adjusting setpoints, digital displays to view instrument readings, maybe a silk-screen graphic (pretty cool but a pain to modify), and phone lines for communication to remote sites.  These first generation systems worked well until the early 2000’s (15-year mark) at which time they became obsolete, didn’t provide the functionality for more sophisticated control logic, and needed to be replaced.  I consider this the transition from the first generation to second generation SCADA systems.  

Silk-Screen Graphic Display


The second generation  SCADA systems introduced PLC-based controls and SCADA software to allow graphical representation of the process system on a computer screen.  These systems were far more flexible and functional than the first generation systems:

  • Control logic could be configured in the PLC program as opposed to being hard-wired.
  • Computer graphics were used to display process information and allow control parameters to be modified, trends in the SCADA software eliminating the need for old paper chart recorders, and database reporting systems could replace the clipboard and paper used to collect data manually.
  • Alarm software provided more flexible methods for alarm management and notification.
  • Digital radio systems provided another telemetry option that could be more reliable than old, leased phone lines that used 30-year old copper wires.

This second generation of SCADA systems was much more flexible and provided far more functionality than first generation systems.  

Allen-Bradley SLC PLC


We’re now moving on to the third generation of SCADA systems that have even more functionality than the second generation systems installed 15+ years ago.  You’re probably thinking your SCADA system wasn’t installed that long ago, but the reality is that if you haven’t had a recent upgrade, it’s likely time to start budgeting for a SCADA system upgrade.  The older proprietary systems from the 80’s were replaced in the early 2000’s with PLC-based systems (typically Allen-Bradley SLC PLCs or PLC-5s, GE 90-30 PLCs, or similar).  GE 90-30 PLCs are now obsolete, Allen-Bradley PLC-5 units are also obsolete, and the writing is on the wall for the Allen-Bradley SLC Series PLCs.  In addition, software enhancements over the last 15 years allow for more functionality than the second generation systems:

  • Enterprise historians provide more flexible and user-friendly data analysis tools.
  • Tablets and smartphones provide highly portable means for remote access.
  • Newer theories in graphic screen development provide operators with better situational awareness and detection of abnormal conditions, and allow for reduced training time for new staff.
  • Aggregating data from multiple data sources for dashboard displays or comparison using trends is feasible.

Enterprise Historian Client 

Control systems are a critical part of water and wastewater treatment operations.  They allow process equipment to operate automatically without operator intervention based on information from field instrumentation and devices, as well as provide notification to operations staff of equipment and process system alarms.  As reliance on automated processes grows, maintaining reliable and serviceable control systems becomes even more critical. These systems should be replaced using a planned approach, before becoming obsolete.  When performing a major upgrade of a SCADA system, in addition to simply replacing the hardware, you should also consider improving the functionality and finding ways that allow you to do your job more effectively by using enhanced SCADA tools such as information management and remote access.

With the vast number of options available in new SCADA systems, consider using an experienced SCADA engineer/consultant to help determine what hardware and software best fit your needs for your next upgrade.  Moving forward with a major SCADA system upgrade can be costly, so proper planning is essential to enable you get the most “bang for your buck” out of your upgraded system.