Diagnosing Electrical Noise Problems in Roll Forming Machines (EMI & Grounding Guide)

Learn about diagnosing electrical noise problems in roll forming machines (emi & grounding guide) in roll forming machines. Electrical & Wiring Guide

Diagnosing Electrical Noise Problems

EMI, Ground Loops & Signal Interference in Roll Forming Lines

Electrical noise (EMI – Electromagnetic Interference) is one of the most misunderstood causes of:

Random PLC input flicker
Encoder instability
False sensor triggers
Unexpected machine stops
VFD communication faults
Analog signal drift
Length mismeasurement

Roll forming machines are high-noise environments because they contain:

Large VFD-driven motors
High switching frequencies
Long motor cables
High current switching
Inductive loads
Large steel frames acting as antennas

If grounding and shielding are not engineered correctly, electrical noise will compromise reliability.

This guide provides a systematic engineering method for diagnosing electrical noise problems in roll forming and coil processing systems.

1) What Is Electrical Noise?

Electrical noise is unwanted voltage or current that interferes with control signals.

It can be:

Conducted noise (through wiring)
Radiated noise (through air)
Ground loop noise
Common-mode noise
Differential noise

Noise becomes a problem when:

Signal amplitude ≈ Noise amplitude.

Low-voltage signals (24VDC, 5V encoder pulses, 4–20mA analog) are especially vulnerable.

2) Common Symptoms of Electrical Noise

Noise issues often appear as:

Random PLC input activation
Encoder miscounts
Shear mistiming
Analog value fluctuating
VFD communication errors
Safety circuit intermittent trip
Machine stops without clear cause

Noise problems are often intermittent.

3) Primary Noise Sources in Roll Forming Machines

Major sources include:

VFD switching frequency (PWM)
Long motor cables
Poor grounding
Inductive coil switching
Relay contact arcing
Improper shield termination
Shared cable trays

VFD output cables are the most common noise generator.

4) Step 1 – Identify When Noise Occurs

Observe:

Does fault occur:

Only when motor runs?
Only at high speed?
Only during shear activation?
Only during deceleration?

If issue correlates with motor operation, VFD noise likely.

Pattern recognition is critical.

5) Check Cable Routing

Power and signal cables must not share the same path.

Incorrect:

Motor cable bundled with encoder cable.

Correct:

Separate cable trays for:

Power cables
Control cables
Encoder cables

Maintain physical separation.

Minimum recommended separation: 200–300mm where possible.

6) Shielding Practices

For encoder and analog cables:

Use twisted pair, shielded cable.

Correct shield grounding method:

Ground shield at ONE end only (typically panel end).

Incorrect grounding at both ends creates ground loop.

Ground loops amplify noise.

7) Grounding System Inspection

Verify:

Single-point grounding scheme
Cabinet bonded to earth
Machine frame bonded
Low earth resistance
Shield drains properly terminated

Poor grounding causes floating references.

Floating reference creates unstable PLC inputs.

8) Check 0V Reference Stability

In 24V systems:

Measure voltage between 0V reference and earth.

Large fluctuation indicates:

Ground loop
Shared return path
High current on 0V conductor

Control 0V must be stable.

9) VFD Output Cable Considerations

VFD motor cables generate high dv/dt switching.

Mitigation methods:

Use shielded motor cable
Keep motor cables short
Use line reactors
Install output filters
Avoid parallel routing with signal cables

Unshielded motor cable is common root cause.

10) Encoder Noise Diagnosis

Symptoms:

Length error increases at high speed
Pulse count inconsistent
Shear misfires

Testing:

Monitor encoder pulses on oscilloscope.

Look for:

Distorted waveform
Spikes
Dropouts

Use differential encoder signals where possible (A+, A-).

11) Analog Signal Instability

For 4–20mA pressure sensors:

If PLC reading fluctuates ±5% randomly:

Likely noise interference.

Solutions:

Use shielded twisted pair
Separate analog and motor cables
Use proper analog module grounding
Add signal filtering

12) Inductive Kickback from Coils

Solenoids and contactors generate voltage spikes.

If flyback diodes or snubbers not installed:

Spikes propagate through control wiring.

Install:

Flyback diode across DC coil
RC snubber across AC coil

Suppression reduces noise.

13) Check for Ground Loops

Ground loop occurs when:

Shield connected at both ends
Multiple earth reference paths exist

Test:

Disconnect shield at one end temporarily.

If problem resolves → ground loop confirmed.

Ground loops are common in retrofits.

14) Cabinet Layout Impact

Inside panel:

Keep:

VFD section separated
PLC section isolated
Analog modules away from drive cables

Poor panel layout creates internal noise.

15) High-Frequency Switching & Harmonics

High switching frequency in VFD increases EMI.

If persistent noise:

Reduce switching frequency slightly (within manufacturer limits).

Install line reactor or EMI filter.

Balance performance with noise reduction.

16) Communication Cable Noise

If system uses:

Ethernet
Profinet
Modbus

Ensure:

Shielded industrial cable
Proper grounding
Avoid routing near VFD cables

Communication dropout can appear as random stops.

17) Use of Ferrite Cores

Ferrite cores around signal cables can reduce high-frequency noise.

Commonly used on:

Encoder cables
Communication cables
Control supply lines

Ferrites reduce EMI propagation.

18) Diagnostic Flow Summary

Step 1: Identify when issue occurs
Step 2: Inspect cable routing
Step 3: Verify shielding practice
Step 4: Inspect grounding scheme
Step 5: Measure 24V stability
Step 6: Inspect motor cable type
Step 7: Check coil suppression
Step 8: Monitor signals with oscilloscope

Never assume PLC is faulty first.

19) Most Common Noise Causes in Roll Forming

Motor cable bundled with encoder
Shield grounded at both ends
No flyback diode on solenoid
Poor cabinet grounding
High switching frequency VFD
Shared 0V return path
Improper analog wiring

Installation quality determines noise immunity.

20) Preventive Design Practices

Use shielded motor cable
Separate cable trays
Use single-point grounding
Install suppression on inductive loads
Maintain clean panel layout
Verify phase balance
Install line reactors when required

Noise prevention is easier than troubleshooting.

21) Buyer Strategy (30%)

When purchasing a roll forming machine, verify:

Shielded motor cables specified
Encoder cables twisted pair and shielded
Single-point grounding scheme documented
Flyback diodes installed
Panel layout separates VFD and PLC
Line reactors included (if long cable runs)
Commissioning report includes noise testing
Cable routing guidelines provided

Red flags:

“Motor and signal cables in same tray.”
“Shields grounded both ends without reason.”
“No suppression devices installed.”

Proper electrical design prevents future downtime.

6 Frequently Asked Questions

1) What is most common noise source?

VFD motor cable interference.

2) Should shields be grounded both ends?

Typically no — one end only.

3) Can noise cause random machine stops?

Yes, especially false PLC inputs.

4) How do I confirm noise?

Use oscilloscope or monitor flickering input.

5) Do line reactors help?

Yes, reduce conducted EMI.

6) Why does problem worsen at high speed?

Higher switching frequency and motor load increase EMI.

Final Engineering Summary

Diagnosing electrical noise problems in roll forming machines requires systematic evaluation of:

Cable routing
Shielding practice
Grounding integrity
VFD motor cable type
Inductive suppression
24V reference stability
Encoder signal quality
Communication wiring

Noise-related faults are often intermittent but entirely preventable with correct engineering design and installation discipline.

In high-speed roll forming environments, proper EMI control is essential for stable production, accurate length control, and reliable safety performance.