Electrical Noise & Grounding in Roll Forming Machines — Why PLCs “Go Crazy” Near Hydraulics & VFDs

1. Introduction — The Hidden Cause of Many PLC Problems

Many roll forming machine faults blamed on PLC software or hardware are actually caused by electrical noise and grounding problems.

Symptoms of electrical noise problems include:

• Random encoder count spikes
• False sensor triggers
• PLC input signals switching unexpectedly
• Servo drives losing position reference
• Communication faults on industrial networks
• Analog signal instability
• Machines that work correctly at low speed but fail at high speed

Electrical noise becomes particularly problematic in roll forming environments because machines include several components that generate strong electromagnetic interference.

These include:

• Variable Frequency Drives (VFDs)
• Servo drives
• Hydraulic solenoid valves
• Large electric motors
• Long cable runs

Understanding how electrical noise is generated and how to control it is essential for reliable roll forming automation.

2. What Is Electrical Noise?

Electrical noise refers to unwanted electrical signals that interfere with normal signal transmission.

In industrial machines, electrical noise often takes the form of:

• Electromagnetic interference (EMI)
• Radio frequency interference (RFI)
• Voltage spikes
• Ground potential differences

These disturbances can affect both digital and analog control signals.

Even small interference signals can disrupt low-voltage control circuits used by PLC systems.

3. Why Roll Forming Machines Are Susceptible to Noise

Roll forming machines combine several electrical and mechanical systems that naturally generate electrical noise.

The most significant sources include:

• High-power VFD motor drives
• Rapid switching of hydraulic solenoid valves
• Long cable runs between cabinets and machine sections
• High current motor cables running alongside signal cables

These systems create electromagnetic fields that can induce unwanted voltages in nearby wiring.

Without proper design and grounding, this interference can corrupt PLC signals.

4. Variable Frequency Drives as Noise Sources

VFDs are one of the largest contributors to electrical noise in roll forming machines.

A VFD controls motor speed by rapidly switching power transistors thousands of times per second.

This switching process generates high-frequency electrical noise.

The noise travels through:

• Motor cables
• Machine frame
• Ground conductors
• Nearby control wiring

If signal cables run too close to motor cables, interference may be induced into control circuits.

Common symptoms include unstable encoder signals and analog measurement errors.

5. Hydraulic Systems and Electrical Noise

Hydraulic systems also contribute to electrical noise.

When hydraulic solenoid valves activate, large current spikes occur.

These spikes can generate electromagnetic interference in nearby wiring.

Additionally, hydraulic pumps often use large electric motors that introduce electrical noise into the power system.

Improper grounding can allow this noise to propagate through the machine structure.

6. Grounding — The Foundation of Noise Control

Proper grounding is the most important defense against electrical noise.

Grounding provides a controlled path for unwanted electrical energy to return safely to earth.

Without proper grounding, electrical noise can circulate through signal circuits.

A well-designed grounding system ensures that:

• Noise currents are safely dissipated
• Equipment operates at the same electrical potential
• Control signals remain stable

Grounding errors are responsible for a large percentage of automation problems.

7. Common Grounding Mistakes

Several grounding mistakes frequently occur in industrial machines.

These include:

Multiple Ground Points

Grounding the same circuit at multiple locations can create ground loops.

Ground loops allow noise currents to circulate through sensitive signal wiring.

Poor Shield Termination

Cable shields must be properly terminated to ground.

Floating shields cannot effectively block electromagnetic interference.

Mixing Power and Signal Grounds

Power circuits and control circuits should be separated.

Combining them can introduce high-current noise into sensitive signal lines.

Inadequate Ground Connections

Loose or corroded ground connections increase electrical resistance, reducing noise protection.

8. Signal Cable Shielding

Shielded cables are used to protect control signals from interference.

A shield is a conductive layer surrounding signal wires.

It works by absorbing electromagnetic noise and directing it safely to ground.

For shielding to work effectively:

• The shield must be grounded properly
• Cable routing must avoid power cables
• Shield continuity must be maintained along the entire cable length

Improperly grounded shields can actually worsen interference problems.

9. Cable Routing Best Practices

Proper cable routing is critical for preventing electrical interference.

Recommended practices include:

• Separate motor cables from signal cables
• Maintain at least 200 mm separation where possible
• Cross power and signal cables at 90 degrees
• Use separate cable trays for power and control wiring

These practices significantly reduce electromagnetic coupling between circuits.

10. Analog Signals and Noise Sensitivity

Analog signals are particularly vulnerable to electrical noise.

Common analog signals in roll forming machines include:

• Hydraulic pressure transmitters
• Oil temperature sensors
• Speed reference signals
• Tension sensors

Noise interference can cause analog readings to fluctuate unexpectedly.

For example, a pressure sensor may suddenly show spikes even when pressure remains constant.

Using 4–20 mA current signals instead of voltage signals improves noise resistance.

11. Encoder Signal Interference

Encoders generate high-frequency pulses used for length measurement.

Electrical noise can corrupt these signals.

Typical symptoms include:

• Random encoder count jumps
• Length errors at higher speeds
• Missed pulses
• Unstable cut positions

Using differential encoder signals (A/A-, B/B-) significantly improves noise immunity.

Proper cable shielding and routing are essential for reliable encoder performance.

12. Industrial Network Interference

Industrial communication networks such as:

• EtherNet/IP
• PROFINET
• EtherCAT

can also be affected by electrical noise.

Communication errors may appear as:

• Lost network packets
• Device communication timeouts
• Intermittent connection loss

Industrial-grade Ethernet cables with proper shielding help prevent these problems.

13. Cabinet Layout and Noise Prevention

Electrical cabinet layout plays an important role in noise control.

Good cabinet design separates:

• Power components (VFDs, contactors)
• Control components (PLC, I/O modules)
• Signal terminals
• Communication hardware

Using separate grounding bars and cable ducts helps reduce interference.

Drive filters and ferrite cores may also be installed to reduce high-frequency noise.

14. Diagnosing Electrical Noise Problems

Diagnosing electrical noise problems requires systematic testing.

Typical diagnostic steps include:

1. Inspect cable routing
2. Verify grounding connections
3. Check shield termination
4. Measure signal stability with oscilloscope if necessary
5. Temporarily separate suspect cables

Noise-related problems often appear intermittently, making them difficult to identify.

Careful inspection is essential.

15. Preventative Measures for Noise Control

Preventative measures include:

• Using shielded cables for all signal circuits
• Maintaining proper cable separation
• Ensuring correct grounding practices
• Installing noise suppression components
• Using differential signals for encoders

These measures significantly improve long-term machine reliability.

16. Preventative Maintenance for Electrical Noise Issues

Regular maintenance checks should include:

Monthly:

• Inspect cable routing and shielding
• Check for loose ground connections

Quarterly:

• Verify grounding resistance
• Inspect encoder and sensor cables

Annually:

• Inspect cabinet wiring condition
• Replace damaged cables

Proactive maintenance reduces the risk of noise-related failures.

6 Structured FAQ — Electrical Noise & Grounding in Roll Forming Machines

1. Why do PLC inputs sometimes trigger randomly in roll forming machines?

Random input triggers are often caused by electrical noise from VFDs, solenoid valves, or poor grounding. Shielded cables and proper grounding can prevent this problem.

2. Why are encoder signals affected by electrical noise?

Encoders generate high-frequency pulse signals that are sensitive to electromagnetic interference. Without proper shielding and grounding, these signals can become corrupted.

3. What is a ground loop and why is it harmful?

A ground loop occurs when multiple grounding paths create circulating currents. These currents introduce electrical noise into control circuits.

4. Why should power cables and signal cables be separated?

Motor cables carry high current and generate electromagnetic fields. If signal cables run parallel to them, interference can be induced into control signals.

5. Why are 4–20 mA signals better than voltage signals in noisy environments?

Current signals are less sensitive to electrical interference and voltage drop, making them more reliable for industrial sensing applications.

6. What is the most common cause of electrical noise problems in industrial machines?

Improper grounding is the most common cause of electrical noise problems in automation systems.