HMI screen design basics in PLC Programming - Deep Dive

Overview - HMI screen design basics

What is it?

HMI screen design basics involve creating user interfaces for machines and industrial systems that operators use to monitor and control processes. These screens display important information like status, alarms, and controls in a clear and organized way. The goal is to make it easy and safe for users to interact with complex machinery. Good design helps prevent mistakes and speeds up response times.

Why it matters

Without well-designed HMI screens, operators can get confused or overwhelmed, leading to errors, slower reactions, and even accidents. Poor interfaces can hide critical information or make controls hard to find. This can cause costly downtime or unsafe conditions. Good HMI design improves safety, efficiency, and user confidence, making industrial systems more reliable and easier to manage.

Where it fits

Before learning HMI screen design, you should understand basic PLC programming and industrial process control concepts. After mastering HMI design, you can explore advanced topics like alarm management, data logging, and integrating HMIs with SCADA systems for broader control and monitoring.

Mental Model

Core Idea

An HMI screen is a clear, organized window that shows machine status and lets users control processes safely and efficiently.

Think of it like...

Designing an HMI screen is like arranging a car dashboard: you place the speedometer, fuel gauge, and controls where the driver can see and reach them easily without distraction.

┌───────────────────────────────┐
│          HMI Screen           │
├─────────────┬───────────────┤
│ Status Info │ Control Panel │
│ (Alarms,   │ (Buttons,      │
│  Values)   │  Switches)     │
├─────────────┴───────────────┤
│       Navigation & Feedback  │
└───────────────────────────────┘

Build-Up - 7 Steps

1

Foundation

Understanding HMI Purpose and Users

Concept: Learn what an HMI is and who uses it in industrial settings.

An HMI (Human-Machine Interface) is a screen or panel that shows machine data and lets operators control equipment. Operators need clear, simple information to make quick decisions. The design must consider who will use it, their skills, and what tasks they perform.

Result

You understand that HMI screens are tools for operators to safely and efficiently manage machines.

Knowing the user and purpose shapes every design choice, ensuring the interface fits real needs.

2

Foundation

Basic Elements of an HMI Screen

Concept: Identify the common parts of an HMI screen and their roles.

Typical HMI screens include status indicators (like lights or text showing machine state), controls (buttons or switches to start/stop or adjust settings), alarms (alerts for problems), and navigation (ways to move between screens). Each element must be easy to find and understand.

Result

You can recognize and name the main components that make up an HMI screen.

Breaking down the screen into parts helps organize information logically and improves usability.

3

Intermediate

Designing for Clarity and Simplicity

🤔Before reading on: do you think adding more details always helps operators? Commit to yes or no.

Concept: Learn how to arrange information to avoid clutter and confusion.

Too much information can overwhelm users. Use simple layouts with clear labels and group related items. Use colors carefully: green for normal, red for alarms, yellow for warnings. Avoid unnecessary decorations that distract. Prioritize critical info at the top or center.

Result

Your HMI screens become easier to read and faster to understand, reducing operator errors.

Understanding that less is more in HMI design prevents information overload and improves safety.

4

Intermediate

Using Consistent Navigation and Feedback

🤔Before reading on: do you think operators prefer many different navigation styles or a consistent one? Commit to your answer.

Concept: Learn how consistent navigation and feedback help users feel confident and avoid mistakes.

Use the same buttons or menus to move between screens. Provide immediate feedback when a control is used, like changing a button color or showing a message. This confirms actions and reduces confusion. Avoid hidden controls or unexpected behaviors.

Result

Operators can navigate the system smoothly and trust that their inputs are registered.

Knowing that consistent feedback builds user trust helps prevent costly operational errors.

5

Intermediate

Incorporating Alarm and Event Management

Concept: Understand how to display alarms clearly and prioritize them.

Alarms alert operators to problems needing attention. Use clear colors and sounds to highlight alarms. Show the most urgent alarms first. Allow operators to acknowledge alarms but keep them visible until resolved. Avoid alarm flooding by filtering non-critical alerts.

Result

Alarms become effective tools for quick problem detection and response.

Recognizing alarm importance and management prevents operators from ignoring critical warnings.

6

Advanced

Optimizing Screen Layout for Different Devices

🤔Before reading on: do you think the same HMI screen works well on both large panels and small handheld devices? Commit to yes or no.

Concept: Learn how to adapt HMI designs for various screen sizes and input methods.

Large touchscreens allow detailed layouts with many controls visible. Small handheld devices need simpler screens with fewer elements and larger buttons. Use responsive design principles to rearrange or hide elements based on screen size. Consider touch accuracy and operator environment.

Result

Your HMI designs work well on multiple devices, improving accessibility and usability.

Understanding device constraints ensures your HMI remains effective in all operator contexts.

7

Expert

Balancing Automation and Operator Control

🤔Before reading on: do you think fully automated HMIs with minimal operator input are always better? Commit to yes or no.

Concept: Explore how to design HMIs that support automation but keep operators in control when needed.

Automation can reduce operator workload but may hide important details. Design HMIs to show automation status clearly and allow manual override easily. Provide logs and history for troubleshooting. Avoid removing operator control completely to maintain safety and flexibility.

Result

HMIs support both efficient automation and safe human intervention.

Knowing when to balance automation and manual control prevents loss of situational awareness and improves system resilience.

Under the Hood

HMI screens run on hardware connected to PLCs or controllers. They receive real-time data from sensors and machines, then translate it into visual elements like text, colors, and buttons. When operators interact, the HMI sends commands back to the PLC to change machine behavior. Internally, the HMI software manages screen layouts, input events, and communication protocols to keep everything synchronized.

Why designed this way?

HMIs were designed to bridge the gap between complex machine logic and human operators. Early systems used simple lights and switches, but as processes grew complex, graphical screens became necessary for clarity. The design balances real-time data display with user input, ensuring safety and efficiency. Alternatives like fully manual control or no visual feedback were rejected because they increased errors and slowed response.

┌───────────────┐       ┌───────────────┐
│   Sensors    │──────▶│    PLC/Logic   │
└───────────────┘       └───────────────┘
                             │
                             ▼
                      ┌───────────────┐
                      │     HMI       │
                      │  (Display &   │
                      │   Controls)   │
                      └───────────────┘
                             │
                             ▼
                      ┌───────────────┐
                      │   Operator    │
                      └───────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Do you think adding more colors always makes an HMI easier to use? Commit to yes or no.

Common Belief: More colors make the screen clearer and easier to understand.

Reality: Too many colors confuse users and reduce the impact of important signals like alarms.

Why it matters: Using too many colors can overwhelm operators, causing them to miss critical warnings and make mistakes.

Quick: Do you think operators prefer all controls on one screen rather than multiple screens? Commit to yes or no.

Common Belief: Having all controls on one screen is better because operators don’t have to switch screens.

Reality: Too many controls on one screen cause clutter and slow down operator response.

Why it matters: Cluttered screens increase cognitive load, leading to slower reactions and higher error rates.

Quick: Do you think automation means operators don’t need to monitor the HMI closely? Commit to yes or no.

Common Belief: Automation lets operators relax and watch the HMI less often.

Reality: Operators must still monitor automation status and be ready to intervene quickly.

Why it matters: Overreliance on automation without proper monitoring can cause missed faults and unsafe conditions.

Quick: Do you think alarm flooding means showing every alert immediately? Commit to yes or no.

Common Belief: All alarms should be shown as soon as they occur to keep operators informed.

Reality: Alarm flooding overwhelms operators, causing them to ignore or miss critical alarms.

Why it matters: Poor alarm management reduces safety and delays problem resolution.

Expert Zone

1

Effective HMI design balances information density with operator cognitive load, which varies by task and environment.

2

The choice of colors must consider color blindness and lighting conditions to ensure universal readability.

3

Advanced HMIs integrate predictive analytics and trend displays to help operators anticipate issues before alarms trigger.

When NOT to use

Avoid complex graphical HMIs in extremely harsh environments where simple physical indicators and controls are more reliable. In such cases, use ruggedized pushbuttons and indicator lights instead.

Production Patterns

In real plants, HMIs often use layered screens with summary dashboards and detailed views. Alarm shelving and prioritization are implemented to manage operator attention. Touchscreen HMIs include confirmation dialogs for critical actions to prevent accidental commands.

Connections

User Experience (UX) Design

HMI design applies core UX principles like clarity, feedback, and consistency to industrial interfaces.

Understanding UX helps create HMIs that are intuitive and reduce operator errors, improving safety and efficiency.

Human Factors Engineering

HMI design builds on human factors to match interfaces to human capabilities and limitations.

Knowing human factors ensures HMIs accommodate attention span, memory, and perception, preventing accidents.

Air Traffic Control Systems

Both require real-time monitoring and clear alarm management to support critical decision-making.

Studying air traffic control interfaces reveals best practices for alarm prioritization and operator workload management applicable to HMIs.

Common Pitfalls

#1 Overloading the screen with too many controls and indicators.

Wrong approach:

Display all machine parameters and controls on a single screen without grouping or prioritizing.

Correct approach:

Organize controls and indicators into logical groups across multiple screens, highlighting critical information.

Root cause:

Misunderstanding that more information always improves operator awareness, ignoring cognitive limits.

#2 Using inconsistent colors and symbols for the same status across screens.

Wrong approach:

Use green for 'running' on one screen and blue on another, or different icons for alarms.

Correct approach:

Standardize colors and symbols throughout the HMI to maintain operator familiarity and reduce confusion.

Root cause:

Lack of design standards or ignoring the importance of consistency in user interfaces.

#3 Not providing feedback when an operator presses a control.

Wrong approach:

Buttons change nothing visually or audibly when pressed, leaving operators unsure if action was registered.

Correct approach:

Buttons change color or show a message immediately after press to confirm the action.

Root cause:

Overlooking the need for immediate feedback to build operator confidence and prevent repeated inputs.

Key Takeaways

HMI screen design is about making complex machine data clear and controls easy to use for operators.

Good design balances information clarity, simplicity, and consistent feedback to reduce errors and improve safety.

Alarm management and navigation consistency are critical to help operators respond quickly and confidently.

Design must consider the device, environment, and user capabilities to ensure effective interaction.

Balancing automation with operator control maintains safety and flexibility in industrial systems.

Practice

1. What is the main purpose of an HMI screen in PLC programming?

easy

A. To store machine data permanently

B. To write complex PLC code

C. To replace the PLC hardware

D. To allow users to control and monitor machines easily

Solution

1. Step 1: Understand HMI function

   An HMI (Human-Machine Interface) screen is designed to help users interact with machines.

2. Step 2: Identify main purpose

   The main goal is to make control and monitoring simple and clear for users.

3. Final Answer:

   To allow users to control and monitor machines easily -> Option D

4. Quick Check:

   HMI = control and monitor [OK]

Hint: HMI means user interface for machine control [OK]

Common Mistakes:

• Confusing HMI with PLC programming itself
• Thinking HMI stores data permanently
• Assuming HMI replaces hardware

2. Which of the following is the correct way to label a button on an HMI screen?

easy

A. Use only icons without text

B. Use vague text like 'Click Here'

C. Use clear text like 'Start Motor'

D. Use very long sentences explaining the button

Solution

1. Step 1: Understand button labeling

   Buttons should have clear, simple labels so users know their function immediately.

2. Step 2: Evaluate options

   'Start Motor' clearly tells the user what the button does, unlike vague or overly long labels.

3. Final Answer:

   Use clear text like 'Start Motor' -> Option C

4. Quick Check:

   Clear labels = better usability [OK]

Hint: Label buttons with clear, simple text [OK]

Common Mistakes:

• Using unclear or vague labels
• Relying only on icons without text
• Writing long explanations on buttons

3. Consider this HMI screen design rule: "Use consistent colors for similar controls." What is the likely result if this rule is ignored?

medium

A. Users may get confused about control functions

B. The PLC program will stop working

C. The screen will load faster

D. The machine will run automatically

Solution

1. Step 1: Understand color consistency

   Consistent colors help users recognize similar controls easily.

2. Step 2: Predict effect of ignoring rule

   If colors vary randomly, users may not know which controls do similar things, causing confusion.

3. Final Answer:

   Users may get confused about control functions -> Option A

4. Quick Check:

   Consistent colors = less confusion [OK]

Hint: Consistent colors help users understand controls [OK]

Common Mistakes:

• Thinking color affects PLC operation
• Assuming color changes speed up screen
• Believing color affects machine automation

4. You designed an HMI screen but users report they can't find the navigation buttons easily. What is the most likely design mistake?

medium

A. Navigation buttons are hidden or placed inconsistently

B. Buttons have clear labels and consistent colors

C. Screen title is too large and clear

D. Screen uses standard navigation layout

Solution

1. Step 1: Analyze user feedback

   Users can't find navigation buttons easily means buttons are not visible or confusingly placed.

2. Step 2: Identify design mistake

   Hidden or inconsistent placement of navigation buttons causes difficulty in finding them.

3. Final Answer:

   Navigation buttons are hidden or placed inconsistently -> Option A

4. Quick Check:

   Visible, consistent navigation = easy to find [OK]

Hint: Place navigation buttons clearly and consistently [OK]

Common Mistakes:

• Ignoring button placement importance
• Assuming large titles improve navigation
• Using non-standard layouts without testing

5. You want to design an HMI screen for a machine with multiple steps. Which approach best helps users navigate smoothly between steps?

hard

A. Place all controls on one screen without navigation

B. Use a clear menu with buttons labeled for each step

C. Use random colors for each step's controls

D. Hide navigation buttons to save screen space

Solution

1. Step 1: Understand multi-step navigation needs

   Users need to move easily between steps without confusion.

2. Step 2: Evaluate navigation methods

   A clear menu with labeled buttons helps users know where to go next and jump between steps.

3. Step 3: Reject poor options

   Putting all controls on one screen can overwhelm users; random colors confuse; hiding buttons blocks navigation.

4. Final Answer:

   Use a clear menu with buttons labeled for each step -> Option B

5. Quick Check:

   Clear menus = smooth navigation [OK]

Hint: Label navigation buttons clearly for each step [OK]

Common Mistakes:

• Overloading one screen with all controls
• Using inconsistent colors that confuse users
• Hiding navigation buttons to save space