Improve control system programming

Dennis Brandl, BR&L Consulting

 

Organizations without well-defined and managed programming processes often miss deadlines and costs by more than 100%.

When we think about control system programming for PLCs, DCSs, and HMIs, we often tend to focus on the "control system" side, but it's important to remember that control system programming is programming. Most control system programming uses highly specialized languages, such as ladder logic, sequentia

l function charts, process flow diagrams, and function block diagrams. Despite the graphical nature of these languages, they are computer languages, and the creation of the diagrams is a programming function. Usually the programming is not performed by programmers or software engineers but by chemical, industrial, electrical, or mechanical engineers or industrial technicians that have picked up programming though professional classes or after-graduation school work. However, just because typical control system programmers are not software engineers does not mean they cannot use software engineering methods to define, monitor, evaluate, and improve their work.

The difference between organizations with well-defined and managed processes and those without is immense. Every year there are reports that, on average, only 30% of business IT projects finish on time and on budget. We regularly see major news reports about IT failures, such as the FBI write-off of its $170 million, four-year development of a virtual case file system. Average errors per thousand lines of code and average lines of code per day, two common measures of programming productivity, vary by factors of over 100 between the best and the worst organizations.

Organizations with well-defined and managed processes usually come within +/- 20% of estimated project time and effort, those without well defined and managed processes often miss their times and costs by more than 100%.

An important question for control sys