JoeGuardian Automation

32. HMI Design & Alarm Management in Industrial Automation (32 of 41)

In industrial automation, the PLC does NOT operate alone.

The real interaction happens through the HMI (Human Machine Interface).

And a bad HMI design can turn a simple machine into:

A confusing system
A troubleshooting nightmare
A production bottleneck

A good HMI does the opposite:

It guides the operator
It reduces downtime
It shows root cause clearly
It simplifies troubleshooting

1. What Is an HMI in Industrial Automation?

An HMI is the interface between:

Operator ↔ PLC ↔ Machine

It displays:

Machine status
Faults
Alarms
Modes (Auto/Manual/etc.)
Production data
Diagnostics

And allows:

Start / Stop commands
Mode selection
Reset faults
Manual control (if allowed)

2. Why HMI Design Matters So Much

Bad HMI:

“Fault 103”
No explanation
No action
Operator guesses

Good HMI:

Motor Overload Fault
Cause: High current detected
Action: Check load, motor, wiring, reset after clearing

3. Alarm vs Status vs Fault on HMI

A professional HMI separates clearly:

🔴 Faults

Machine stops
Requires reset
Critical issue

🟡 Alarms

Warning or attention needed
May or may not stop machine

🔵 Status

Normal conditions
Informational only

4. Alarm Management Structure

A proper alarm system includes:

Active alarms
Acknowledged alarms
Alarm history
Timestamp
Priority level
Cause description
Action message

5. Alarm Priority Levels

Industrial systems use priority:

Example:

Low → Maintenance reminder
High → Conveyor jam
Critical → Safety fault

6. Alarm Example (Real Plant)

Condition:

Photoeye blocked too long

HMI output:

CONVEYOR JAM ALARM
- Sensor blocked > 5 sec
- Check product blockage
- Check photoeye alignment

7. Fault Display Strategy

Faults should ALWAYS show:

What happened
Where it happened
Why it happened
How to fix it

Example:

MOTOR 1 OVERLOAD FAULT
Cause: Current exceeded limit
Check: Load, bearings, wiring
Reset allowed after condition clears

8. HMI Mode Display (Critical)

HMI must always show current mode:

AUTO MODE
MANUAL MODE
MAINTENANCE MODE
SETUP MODE

Why?

Because many issues come from:

Operator in wrong mode
Technician in manual mode
Auto sequence blocked

9. Alarm & Fault Logic Connection

HMI depends on PLC tags:

Fault bits → red screen
Alarm bits → yellow banner
Status bits → normal display
Mode bits → control permissions

Example:

MTR1_Fault = 1 → show fault screen
MTR1_Alarm = 1 → show warning banner
MTR1_Run = 1 → show running status

10. Alarm Latching vs Non-Latching

Latching alarm:

Stays active until acknowledged

Non-latching alarm:

Clears automatically when condition disappears

Best practice:

Faults = latched
Critical alarms = latched
Warnings = sometimes non-latched

11. Alarm Flooding Problem

Bad design causes:

Too many alarms at once
Operator ignores system
Important alarms missed

Solution:

Priorities
Grouping alarms
Suppress duplicates
Logical filtering

12. HMI Design Best Practices

Use clear language
Avoid codes only (like Fault 101)
Show root cause
Show action steps
Group alarms logically
Use color coding correctly
Keep screens simple
Avoid overload of information

13. Example: Good vs Bad HMI

❌ Bad:

FAULT 47

✅ Good:

Conveyor Motor Overload Fault
Cause: Excess load or jam
Action: Inspect conveyor and reset after clearing issue

14. HMI & PLC Communication Flow

Sensor → PLC Logic → Fault/Alarm Bits → HMI Display → Operator Action → Reset → PLC

15. Troubleshooting Using HMI

Technician workflow:

1. Read HMI message
2. Identify fault/alarm type
3. Check PLC bit
4. Check field device
5. Verify wiring
6. Fix issue
7. Reset system

Final Thoughts

A PLC system without good HMI design is incomplete.

Because:

PLC controls the machine
HMI explains the machine

If the HMI is unclear:

• operators guess
• downtime increases
• troubleshooting becomes slower

A good HMI is not just visualization — it is a diagnostic tool.