5 PLC Code Checks Every Plant Should Complete Before Commissioning
Before installing a new PLC, the automation and controls engineers responsible for the specs and purchasing carry a heavy burden. Regardless of the project’s scale, the knot in the stomach and jitters are the same.
What if it fails?
Will we know how to recover when a fault hits or a change is needed?
What happens when vendor support ends, and the original programmer is gone?
This Verdusco Automation article explains how a PLC code review after the automation vendor selection process helps your team verify tags, logic, alarms, and testing before the commissioning stage begins. Our goal is to help you avoid unexpected issues when starting your next upgrade or greenfield project.
PLC Code: What to Review Before Commissioning
#1: Confirm Clear PLC Tag Naming and Structure
Before signing off on the project, ask the vendor to walk you through the tag database or request the tag export file and review it directly with your shift leads.
Does everyone understand what each tag represents? Are naming conventions consistent across the entire program? Or do tags rely on abbreviations that only the programmer understands?
If operations and maintenance are cracking their heads to decode tag names before troubleshooting the equipment, the review isn't finished. Catching these naming gaps (e.g., from M1_Run to Conveyor_Infeed_Motor_Run) in a spreadsheet during design reviews ensures your team isn’t left holding an unmaintainable system at startup.
#2: Verify PLC Logic Is Organized Into Clear Modules
Do not just trust that the code is organized. Audit the project tree, especially looking for task separation. Well-organized code is easier to troubleshoot, modify, and expand after startup.
Open the PLC code and ask the vendor to navigate through it.
Can they easily show you where conveyor control ends, and recipe handling begins? Are safety, motion, and HMI functions separated into logical modules?
While at it, also review the comments inside the code. Good comments do not repeat what the logic already shows. They explain why a decision was made. For example: “Start Pump 3” is a mere action. On the other hand, “Start Pump 3 first to balance operating hours across all pumps” preserves the engineering intent.
#3: Review Alarm Messages Before Startup
Ask the vendor to demonstrate how alarms were developed and where they came from.
Alarm lists should not be created in isolation. They should reflect the critical engineering documents behind the project, including P&IDs, cause-and-effect charts, and applicable risk assessments such as HAZOP or SIL/SIS studies.
Review each alarm and ask:
Does it represent a real process or equipment risk?
Does the message help operators understand the problem?
Does the alarm response match the approved cause-and-effect requirements?
An alarm that says “Pump Fault” provides little direction. A message like “Cooling Pump B stopped. Verify motor overload and check standby pump availability” gives the operator a clear starting point.
A good alarm strategy connects engineering decisions with real plant actions. It ensures the delivered system matches the original project requirements.
#4: Validate Fault Recovery Routines
Ask the vendor to demonstrate fault scenarios before startup.
What happens after a jam? What conditions must be restored? When is automatic restart allowed? When does an operator need to intervene?
Recovery sequences should be intentional, not something discovered during the first production run.
Testing these scenarios helps your team understand how the system behaves when conditions are not perfect.
#5: Test PLC Logic Before Production Begins
Do not wait until commissioning to discover whether the PLC code works as expected.
Ask the vendor what testing has been completed before the equipment arrives at your facility.
Review whether they have verified:
Machine sequences
Interlocks
Device communication
Alarm responses
Recovery scenarios
Finding a logic issue during testing is inconvenient. Finding the same issue during production is expensive.
Commission New Equipment with Confidence
Completing your project’s automation vendor selection is only the first step. To build a stable control system during start-up and beyond, you need a PLC code that is organized, documented, and tested.
Verdusco Automation has the specialists to design, integrate, and improve control systems at a moment’s notice. We can also deliver a thorough PLC code review that identifies problems long before they become manufacturing downtime events, eliminating the snags that often arise during the critical startup phase.
Ready to kick off your next automation project?
Contact Us Today:
📩: maria@verduscoautomation.com
🌐: verduscoautomation.com/contact
Let’s build the control system your facility needs.
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More articles from Verdusco Automation: click here!
Before starting up a new automation system, a thorough PLC code review can prevent costly downtime. Learn the five PLC code checks every plant should complete after vendor selection to ensure a stable, maintainable, and reliable commissioning phase.