Implementing Sequential Function Chart Designs using Ladder Diagram Programming Language for Programmable Logic Controllers

by James McWhinnie
Napier University, Edinburgh, Scotland.

ABSTRACT

Sequential Function Charts (SFC’s) have long been established as a means of designing and implementing sequential control systems utilising programmable controllers. The Programming Standard IEC 61131-3 includes a graphical implementation of SFC’s in its suite of programming languages.

“We had documentation at one time.”

Sound familiar?  Have you suddenly found changes that have been made in the PLC but not in the offline program?  Nobody knows what happened.

Unfortunately this is an all too common phenomena with the Siemens SIMATIC Step 7 software.  The problems stem from the flexibility of the software both for downloading and editing the online program.  If the person is not familiar with the software it’s very easy to get confused if the changes are being made on the computer or in the controller.

I've been a consistent user of DirectSOFT for the last six years so I was very interested to check out AutomationDirect's new release of DirectSOFT5.  This is both an overview of the new features and a review as to their usefulness.  We’ll start with some first impressions like new icons, toolbars, themes and dockable views and then discuss the important internal changes with IBoxes.  There have also been significant moves made in how Automation Direct packages and sells DirectSOFT which should factor into whether to upgrade or not.