1. Introduction — The Role of HMI in Automation
An HMI (Human Machine Interface) is the central component that connects operators to machines.
Its primary functions include:
- Displaying machine status
- Providing real-time data visualization
- Allowing parameter adjustment
- Handling alarms and notifications
- Acting as a communication hub between PLC, VFD, and sensors
Choosing the right HMI ensures smoother operation, faster troubleshooting, and better efficiency across the entire system.
2. Core HMI Selection Parameters
2.1 Panel Size (7” / 10” / 15”)
Choose the size based on:
| Small machinery | 4.3” / 7” |
| General equipment | 7” / 10.2” |
| Large production lines | 10” / 12” / 15” |
| SCADA-like stations | 15”+ |
Tip:
Larger screens significantly improve operator efficiency.
2.2 Resolution
Higher resolution provides:
- Sharper UI
- Better animation support
- More readable fonts
Typical resolutions:
- 800×480
- 1024×600
- 1280×800
Avoid low-resolution HMIs for complex pages.
2.3 Touch Technology
| Type | Features | Use Case |
|---|---|---|
| Resistive | Works with gloves, cost-effective | Industrial environment |
| Capacitive | Multi-touch, smooth UI | Clean rooms, modern HMIs |
Capacitive looks modern but can fail with oil, dust, or gloves.
2.4 Brightness & Viewing Angle
Important for:
- Outdoor use
- High-light workshops
- Long-distance visibility
Recommended:
✔ 300–500 cd/m² brightness
✔ IPS panel for wide viewing angle
3. Interface Selection
3.1 Communication Ports
Common HMI interfaces:
- RS485(Modbus RTU)
- RS232
- Ethernet(Modbus TCP, Profinet, Ethernet/IP)
Choose based on PLC:
| PLC Brand | Recommended HMI Interface |
|---|---|
| Mitsubishi | RS485 / Ethernet |
| Siemens | Ethernet (Profinet) |
| Omron | RS232 / Ethernet |
3.2 Protocol Compatibility
Your HMI must support PLC protocols such as:
- Modbus
- Profinet
- Ethernet/IP
- FINS
- CC-Link
Check the compatibility list before purchasing.
3.3 HMI → VFD and Instruments
Common use cases:
- HMI writes frequency to VFD
- HMI reads temperature from PID controller
- HMI logs pressure/flow from sensors
Interfaces vary per device.
4. HMI Software Structure
4.1 Page Logic
Design screens with:
- Home screen
- Status screen
- Alarm page
- Parameter settings
- Manual operation page
4.2 Variable Binding
Bind variables to:
- PLC registers
- VFD parameters
- Internal memory
- Data logging
4.3 Communication Settings
- Set baud rate
- Set IP address
- Choose correct protocol
- Test connectivity with PLC
5. Application Examples
5.1 CNC Main Interface
Shows:
- Axis feed
- Tool position
- Alarms
- Program progress
5.2 Packaging Machine Status Page
Includes:
- Sensors
- Motor states
- Production counter
- Fault messages
5.3 Production Counter Dashboard
Real-time:
- Cycle rate
- Reject count
- Total quantity
6. Common Engineering Problems
⚠️ HMI cannot communicate with PLC
Causes:
- Wrong protocol
- Incorrect register address
- Wrong IP configuration
- Wiring mistakes
⚠️ Slow page switching
Causes:
- Low memory
- Too many images
- Poor programming
⚠️ Screen freeze
Usually related to:
- Static electricity
- Power noise
- Firmware bugs
7. Best Practices
✔ UI Consistency
Use standard colors:
- Green: Running
- Red: Fault
- Yellow: Warning
✔ Logical Layout
Arrange elements using:
- Grids
- Alignment
- Clear grouping
✔ Interaction Optimization
Avoid:
- Overcrowded screens
- Too many animations
- Hidden critical buttons
8. FAQ
Q1: Should I choose resistive or capacitive?
Resistive is more durable for industrial use; capacitive is modern but less tolerant.
Q2: What screen size is most common?
7-inch and 10-inch are industry standards.
Q3: Which HMI brand is best?
Weintek, Siemens, Omron, and Kinco are widely used, depending on budget and project.
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