Why Does My PLC Show Error Codes During Production?

When your PLC (Programmable Logic Controller) shows error codes during production, it means the control system has detected a fault condition.

Modern roll forming machines rely on PLC systems to control:

• Motor speed

• Encoder measurement

• Punch timing

• Shear synchronization

• Hydraulic activation

• Safety interlocks

• Sensor feedback

PLC errors are not random — they are protective warnings designed to prevent machine damage or unsafe operation.

This guide explains the most common causes and how to diagnose them.

1. Sensor Faults (Very Common)

Roll forming lines use multiple sensors:

• Limit switches

• Proximity sensors

• Photoelectric sensors

• Loop sensors

• Position sensors

If a sensor:

• Fails

• Loses alignment

• Becomes dirty

• Has loose wiring

The PLC will trigger an alarm.

Signs:

• “Sensor Fault”

• “Limit Not Reached”

• “Position Error”

Fix:

• ✔ Inspect sensor alignment
• ✔ Clean sensor face
• ✔ Check wiring connections
• ✔ Replace faulty sensor

Sensor issues are one of the most common PLC errors.

2. Encoder Errors (Length or Position Fault)

Encoders measure:

• Strip length

• Flying shear position

• Servo punch timing

If encoder:

• Slips

• Loses signal

• Becomes dirty

• Has damaged cable

You may see:

• “Encoder Fault”

• “Position Deviation”

• “Length Error”

Fix:

• ✔ Inspect encoder wheel contact
• ✔ Clean measuring wheel
• ✔ Check cable shielding
• ✔ Recalibrate in PLC

Encoder faults directly affect cut accuracy.

3. Hydraulic Pressure Alarms

Hydraulic systems often include pressure switches.

If pressure drops below threshold:

PLC stops machine to prevent incomplete cutting or punching.

Causes:

• Low oil level

• Pump wear

• Hydraulic leak

• Blocked filter

• Valve malfunction

Fix:

• ✔ Check oil level
• ✔ Inspect pump
• ✔ Replace clogged filter
• ✔ Inspect for leaks

Hydraulic instability commonly triggers alarms during cutting cycles.

4. Overload or Motor Protection Fault

Drive motors are protected by overload relays or VFD protection.

Common alarms:

• “Motor Overload”

• “Overcurrent”

• “Drive Fault”

Causes:

• Excess roll pressure

• Jammed strip

• Bearing failure

• Gearbox misalignment

Fix:

• ✔ Check for mechanical blockage
• ✔ Inspect bearings
• ✔ Reduce roll pressure
• ✔ Verify drive alignment

Mechanical strain often triggers electrical alarms.

5. Safety Interlock Triggered

Modern machines use:

• Door interlocks

• Light curtains

• Emergency stops

• Safety relays

If safety circuit opens:

PLC prevents operation.

Common messages:

• “Safety Circuit Open”

• “Guard Not Closed”

• “E-Stop Activated”

Fix:

• ✔ Check emergency stop buttons
• ✔ Confirm safety doors closed
• ✔ Reset safety relay

Safety systems intentionally stop production when triggered.

6. Communication Errors

Advanced systems include:

• Servo drives

• VFDs

• Remote I/O modules

• Touchscreen HMI

If communication between PLC and components fails:

You may see:

• “Communication Fault”

• “Drive Not Responding”

• “I/O Error”

Causes:

• Loose communication cable

• Network interference

• Faulty module

• Power fluctuation

Fix:

• ✔ Check cables
• ✔ Restart system
• ✔ Inspect module power
• ✔ Check network configuration

Communication faults often appear randomly but are usually wiring-related.

7. Flying Shear Position Error

Flying shear systems require tight synchronization.

If shear carriage:

• Does not reach home position

• Loses position reference

• Encounters obstruction

PLC will stop machine.

Fix:

• ✔ Inspect guide rails
• ✔ Re-home shear position
• ✔ Check encoder feedback
• ✔ Inspect mechanical travel

Flying systems depend on accurate position tracking.

8. Punch Timing Error

Punch stations require synchronization with strip position.

If punch:

• Fires at wrong time

• Fails to return to home

• Experiences pressure drop

PLC may show:

• “Punch Position Error”

• “Punch Not Home”

Fix:

• ✔ Check hydraulic cylinder
• ✔ Inspect limit switches
• ✔ Verify timing parameters

Punching systems require precise control.

9. Power Supply Fluctuations

Voltage drops or unstable supply can cause:

• Random PLC resets

• Communication faults

• Drive trips

Fix:

• ✔ Verify stable three-phase power
• ✔ Check voltage levels
• ✔ Install surge protection if needed

Electrical stability is critical for PLC reliability.

10. Programming or Parameter Errors

Incorrect parameter settings can trigger alarms.

Examples:

• Incorrect cut length

• Speed mismatch

• Incorrect timing compensation

Fix:

• ✔ Verify recent parameter changes
• ✔ Reset to known stable configuration
• ✔ Review programming changes

Changes without documentation often cause confusion.

11. Overheating Conditions

Some PLC systems monitor:

• Motor temperature

• Hydraulic temperature

• Cabinet temperature

Overheating may trigger automatic shutdown.

Fix:

• ✔ Improve ventilation
• ✔ Check cooling fans
• ✔ Inspect oil temperature

Thermal protection prevents major damage.

12. How to Troubleshoot PLC Errors Properly

When an error appears:

1. Read exact alarm code

2. Record time and operating condition

3. Do NOT repeatedly reset without diagnosing

4. Inspect related mechanical system

5. Check sensor alignment

6. Review hydraulic pressure

7. Consult machine manual

Random resetting can hide root causes.

13. Why PLC Errors Are Protective

PLC errors are designed to:

• ✔ Prevent mechanical damage
• ✔ Protect operator safety
• ✔ Avoid inaccurate production
• ✔ Reduce long-term repair cost

They are warning systems — not annoyances.

Final Expert Insight

PLC error codes during production are usually caused by:

• ✔ Sensor faults
• ✔ Encoder issues
• ✔ Hydraulic pressure instability
• ✔ Motor overload
• ✔ Safety interlock triggers
• ✔ Communication faults
• ✔ Punch or shear position errors
• ✔ Power supply fluctuations

The key to solving PLC errors is:

• Identifying the exact alarm

• Understanding which subsystem triggered it

• Inspecting mechanical and electrical components

• Avoiding random resets

A stable, well-maintained machine should rarely produce recurring PLC faults.