Supervisory Control and Data Acquisition (SCADA) is a broad term that can be applied to a variety of control system components and functions as it pertains to manufacturing and process systems. Our focus to today will be on the software layer of a SCADA system that exists between the controller interacting with the field devices and the people who operate the manufacturing systems. There are four major technical functions, graphical representation of automated systems, data storage, and annunciation. Just as important as the technical functions of a SCADA system are the standards used to develop and maintain the system along with key performance indicators (KPIs). Development standards and KPI’s represent the bookends that create a robust software platform and drive business objectives.
The ability for a SCADA system to monitor and track performance of a manufacturing or process system is key realizing long-term business objectives. Monitoring and reporting on performance does not have to be complex. Your typical SCADA graphic resembles a Piping and Instrumentation Diagram (P&ID), plenty of pressures, speeds, temperatures and status feedback shown on the graphical display. This is useful information when trouble shooting, changing over or starting up a production system. Once that system is running these screens provide more comfort than value. Maintaining the speed of a pump or temperature of a system may be a critical control point for a process, however these individual readings and status points fail to define performance. Performance measurement requires that these standalone values be combined to create a KPI. A KPI can be the rate of production per unit of time, efficiency of fuel used per unit of work done and raw material variance expressed in a unit such as pounds or dollars. There is a high probability that the SCADA system is already monitoring the raw value to create the KPIs, they require only a bit of math to create and some graphical housekeeping to create a place to display them. Place these values in a consistent location across numerous screens and work them into shift transition meetings and continuous improvement efforts. Adding KPIs to a trending graphic can assist in looking at performance over extended periods of time. Corelate KPI’s with production logs or at shift change while shift details are fresh to identify what caused performance to drop or soar. The more attention a KPI is given the faster it will improve.
"There is a high probability that the SCADA system is already monitoring the raw value to create the KPIs, they require only a bit of math to create and some graphical housekeeping to create a place to display them"
To achieve a robust SCADA package a comprehensive standard to build out the package is required. There are a number of high-quality commercial off the shelf SCADA software packages from companies such as Rockwell Automation, Group Schneider, Inductive Automation and GE. These companies have been in business for many years and have a track record of supporting their SCADA software. That support comes in the way of minor as well as major version updates to their packages. These updates offer new features and functions but rarely any breaking changes that could render the package obsolete. Once you buy into an ecosystem of SCADA software, it will be viable for many years in the state it was purchased. With incremental software upgrades and updates to server hardware, you extend the life of your software to 10 years or more. Given the lifespan of modern SCADA software we need to consider all the different people that will program modify and update the software over those 10 years. Integrators, plant technicians and controls engineers all turn over and each have an approach to developing or modifying SCADA software to achieve their end goals. To keep everyone working in a similar manner and your software organized standards are a must. Standards will address color schemes, tag naming structures, navigation from one system to another, alarming, trending and data storage. A comprehensive standards document will average around 30 pages of text and illustrations to accurately convey your standards. Leveraging an existing standard such as ISA’s Human Machine Interfaces standards (ISA101) will expedite the creation of your standards and provide a solid platform to build on. Good standards created internally or using an integration partner will keep your software investment viable longer and prevent unstable performance for years to come.
System maintenance on a SCADA system controls unplanned downtime. Even with good standards people make mistakes, a forgotten tag in the database, a piece of old script, a dead navigation link. Over time these broken elements begin to stack up. Simple maintenance like writing down the server or workstation processor usage and the amount of memory the software package is consuming can help identify a trend before there is a failure. Most commercial off the shelf packages have a cross reference tool that can identify orphaned data base tags or references in the graphics and script to tags that do not exist in the database. Running these basic checks can help in identifying trends that are moving in the wrong direction and give you time to troubleshoot before a failure disrupts production.
Standards, key performance indicators and regular maintenance enable you get the most out of your SCADA software investment.