Why Standard PLC and HMI Functionality Is Preferred to Custom Code in Pharma Automation

BySean Bruen

In pharmaceutical manufacturing, automation systems are expected to be reliable, maintainable, and compliant with evolving global standards. However, many equipment vendors still rely on layers of custom PLC and HMI code that have evolved over years – often without a clean rebuild. This approach can introduce complexity, increase the risk of failure, and make integration with site systems unnecessarily difficult.

This article outlines why using standard, proven PLC and HMI functionality is a more effective strategy.

The Problem with Custom Code

  • Unnecessary Complexity: Repeated code changes over years, often by different developers, lead to cluttered logic that’s difficult to understand, test, or maintain.

  • Hidden Bugs: Legacy custom code frequently contains ad hoc fixes or workarounds for rare scenarios that are undocumented or poorly understood.

  • Harder Integration: Custom interfaces often require bespoke site-side workarounds. Standard site systems expect structured tags, predictable behaviour, and consistent alarms.

  • Support Risk: When only the original developers understand the codebase, future troubleshooting or modifications become slow and risky.

  • Qualification Overhead: Custom implementations often require more rigorous testing and documentation effort to meet GMP and data integrity requirements.

Why Standard Functionality Works Better

  • Tested and Reliable: Standardised blocks and libraries are already in wide use and field-tested. This reduces risk during commissioning and operation.

  • Easier Integration: Common approaches to alarm handling, recipe management, and batch control are more compatible with site automation frameworks.

  • Simplified Support: Site engineers are more likely to recognise and understand standard modules, speeding up fault finding and support.

  • Improved Maintainability: Cleanly structured, modular code based on standard templates is easier to update, validate, and re-use.

  • Regulatory Readiness: Standard solutions often align more closely with GAMP and other compliance expectations, reducing validation effort.

Why It Matters More Today

The pressure to meet global expectations for data integrity, cybersecurity, and audit readiness is increasing. At the same time, pharma manufacturers are asking vendors to integrate more closely with site-wide MES, historian, and batch systems. Standardised code enables these integrations without bespoke rework.

Using standard PLC/HMI libraries is not about restricting innovation. It’s about placing innovation where it adds real value – in the process, not the plumbing.

Summary

Standardising PLC and HMI functionality is a practical response to real-world challenges: integration complexity, regulatory pressure, and long-term maintainability. Vendors who continue to rely on heavily customised code often face delays during commissioning, difficulty achieving compliance, and increased support overheads.

By contrast, those who adopt structured, proven libraries benefit from faster delivery, easier validation, and smoother collaboration with clients and system integrators. Standard code doesn’t mean generic – it means robust, understandable, and scalable.

For pharmaceutical manufacturers and equipment suppliers alike, moving toward clean, supportable codebases is becoming essential not just for technical success, but for business continuity.

Want help moving from legacy code to a clean, compliant, supportable standard? Get in touch. We’re helping vendors and manufacturers simplify, standardise, and succeed.