Technologies:
- Siemens 1500 series PLCs
- Aveva Wonderware
- Siemens G-series VFDs
Background:
A steel recycling facility had a newly built continuous casting production line that primarily used function calls (FC) to handle the same functionality, rather than a single function block (FB) with different inputs. To understand the issue, it’s important to know that a ‘stand’ in this context is one of several that work together in series to compress the large metal rod that is being cast into the final product that is sold to the customers. The final product for a steel recycling mill can be rebar, sheets, angle iron, or a variety of other products.
This use of multiple FC’s with potential differences instead of a single FB called multiple times resulted in issues where the automation team would fix an issue with the function call controlling one stand and then forget to roll that change out to all of the remaining stands. There were also instances where mistakes were made during the rollout that weren’t caught until they caused an issue. Finally, there was a situation where there was a feature disabled for a single stand that then interacted poorly with the other stands where this feature wasn’t disabled.
All this resulted in the team opting to convert the function calls to a function block to improve maintainability, limit potential for ‘hidden’ errors, and reduce time to rollout changes.
Approach:
To achieve the goal of a single location FB to control each stand there were several things that had to happen to achieve this feat. They were:
- Convert a function call to the genericized function block that could be applicable to all stands.
- Replace the direct references to outside variables with either inputs, outputs, or inouts as applicable.
- Convert any common structs to an instance of a universal data type (UDT) to reduce the number of single variables being passed to the FB.
- Create the new calls to the function block
- Test to confirm proper operation with the new function block.
Once these steps were completed the system was much simpler to manage!
Final Product:
The upgraded stand control software can now largely be maintained from one location instead of being spread across many different function calls. This has greatly improved the maintainability of the code, removed opportunities for discrepancies to develop, and reduced the time to roll out new features or to resolve issues.
Customer Benefits:
- Improved maintainability
- Limited potential for ‘hidden’ errors
- Reduced time to rollout changes