5 Mistakes PLC Programmers Make When Designing HMI Screens

A well-designed Human Machine Interface (HMI) can significantly improve machine operation, reduce downtime, and simplify troubleshooting. However, many PLC programmers focus primarily on the control logic and give less attention to HMI design.

The result? Operators struggle to navigate screens, alarms are missed, and troubleshooting takes longer than necessary.

Here are five common mistakes PLC programmers make while designing HMI screens and how to avoid them.

1. Use of too many colors

One of the most common mistakes is filling HMI screens with bright and excessive colors. While colorful screens may appear attractive, they often overwhelm operators and make critical information difficult to identify.

Best Practice:

• Use neutral colors such as gray for normal operating conditions.

• Reserve red for alarms or emergency conditions.

• Use yellow for warnings and green only when necessary.

• Follow high-performance HMI principles where color highlights abnormal conditions rather than normal operation.

Remember: If everything is colorful, nothing stands out.

2. Display too much information on a single screen

Many programmers try to display every tag, status, and parameter on one screen. This creates clutter and makes it difficult for operators to quickly locate important information.

Best Practice:

• Keep overview screens simple.

• Group related equipment and information logically.

• Use navigation buttons to access detailed screens.

• Present only the information operators need for decision-making.

An HMI should simplify operations, not complicate them.

3. Ignoring Alarm prioritization

Displaying hundreds of alarms without proper prioritization often leads to alarm fatigue. Operators may begin ignoring alarms because too many messages appear simultaneously.

Best Practice:

• Classify alarms into categories such as Critical, Major, Minor, and Information.

• Provide clear alarm descriptions and recommended operator actions.

• Avoid generating nuisance alarms.

• Ensure alarm messages are meaningful and easy to understand.

A good alarm system helps operators respond quickly during abnormal situations.

4. Inconsistent navigation

Inconsistent tag names, unclear button labels, and ambiguous descriptions create confusion during operation and maintenance.

For example, labels such as "Motor1" or "Output5" provide little information to operators.

Best Practice:

• Use descriptive names such as "Conveyor Motor" or "Case Erector Servo."

• Maintain consistent naming conventions throughout the project.

• Ensure operators can easily understand equipment status without referring to documentation.

Clear naming reduces troubleshooting time and minimizes operational errors.

Not following high performance HMI principle

An HMI is not just an operator interface; it is also a powerful troubleshooting tool. Many HMIs provide only basic Start/Stop controls without diagnostic information.

Best Practice:
Include:

• Sensor status indicators

• Interlock status screens

• Fault history

• I/O diagnostics

• Servo and VFD fault information

• Maintenance screens

Providing diagnostic information directly on the HMI can drastically reduce machine downtime.

Final Thoughts

A good HMI design improves productivity, enhances operator efficiency, and reduces downtime. As PLC programmers, we should treat HMI development with the same importance as PLC logic development.

Remember, the ultimate goal of an HMI is simple:

Present the right information to the right person at the right time.

What other HMI design mistakes have you encountered in your projects? Reply to this email and share your experience.

Avinash Malekar

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