Noise, Grounding & Shielding in Roll Forming Machines — Fixing Random PLC Faults

Introduction — Why Random PLC Faults Are Often Electrical Noise Problems

One of the most frustrating problems in roll forming machines is the appearance of random PLC faults. The machine may run perfectly for hours or days, then suddenly produce unexplained errors such as unexpected sensor triggers, encoder jumps, or communication faults.

In many cases, these problems are not caused by software errors or hardware failures. Instead, they are caused by electrical noise and grounding problems.

Roll forming machines include many electrical systems capable of generating strong electromagnetic interference. These include:

• VFD motor drives
• servo drives
• hydraulic solenoids
• large electric motors
• long cable runs

If wiring and grounding are not designed correctly, electrical noise can enter PLC inputs and control circuits. This interference can cause the control system to behave unpredictably.

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

What Is Electrical Noise?

Electrical noise is unwanted electrical energy that interferes with control signals.

Noise can appear in several forms:

• electromagnetic interference (EMI)
• radio frequency interference (RFI)
• voltage spikes
• ground potential differences

These disturbances may disrupt low-voltage control signals used by PLC systems.

Even small electrical disturbances can affect sensitive signals such as encoder pulses or analog sensor inputs.

Why Roll Forming Machines Generate Electrical Noise

Roll forming machines contain several devices that naturally produce electrical interference.

The most significant noise sources include:

Variable Frequency Drives

VFDs control motor speed by rapidly switching power transistors.

This switching process creates high-frequency electrical noise.

Noise may travel through:

• motor cables
• grounding systems
• machine frames
• nearby signal cables

Servo Drives

Servo drives also use high-speed switching electronics.

Although modern servo drives include filtering systems, they still generate electrical noise that may affect nearby circuits.

Hydraulic Solenoids

Hydraulic valves often generate electrical spikes when energized or de-energized.

These spikes can introduce interference into control wiring if suppression components are not installed.

Long Cable Runs

Roll forming machines are often physically long, sometimes exceeding 20 meters.

Long cables can act as antennas that pick up electromagnetic interference.

Symptoms of Electrical Noise in PLC Systems

Electrical noise problems can appear in many ways.

Typical symptoms include:

• PLC inputs turning on or off randomly
• encoder count spikes
• communication dropouts
• servo drive faults
• inconsistent analog readings
• intermittent machine stops

These symptoms often appear randomly, making diagnosis difficult.

Noise problems may also worsen as machine speed increases.

Importance of Proper Grounding

Grounding is the foundation of noise control in industrial automation.

A properly designed grounding system provides a safe path for unwanted electrical energy to dissipate.

Without proper grounding, electrical noise may circulate through control circuits.

Key objectives of grounding include:

• stabilizing electrical potential across the machine
• preventing noise currents from entering signal circuits
• protecting equipment from electrical faults

Grounding errors are one of the most common causes of PLC problems in industrial machines.

Common Grounding Mistakes

Several grounding mistakes frequently occur in roll forming machines.

Ground Loops

Ground loops occur when multiple grounding paths exist between two points.

These loops allow noise currents to circulate through control circuits.

Ground loops are especially common when shields are grounded at both ends incorrectly.

Poor Ground Connections

Loose or corroded ground connections increase electrical resistance.

High resistance prevents noise currents from flowing safely to ground.

Mixing Power and Signal Grounds

Power circuits carry high current and should be separated from sensitive signal circuits.

Combining these grounds can introduce noise into control signals.

Cable Shielding

Shielded cables protect sensitive signals from electrical interference.

A shield is a conductive layer surrounding signal wires.

The shield intercepts electromagnetic interference and directs it safely to ground.

Shielded cables are especially important for:

• encoder signals
• analog sensors
• communication networks
• high-speed digital signals

Without proper shielding, these signals may become unstable.

Correct Shield Grounding

For shielding to work effectively, shields must be connected to ground correctly.

Typical best practice is:

• connect the shield to ground at one end
• ensure shield continuity throughout the cable

Grounding shields incorrectly can reduce their effectiveness or create ground loops.

Cable Routing Best Practices

Cable routing plays a major role in preventing electrical noise.

Recommended practices include:

• separate motor cables from signal cables
• maintain at least 200 mm separation
• cross power and signal cables at 90 degrees
• use separate cable trays when possible

These practices reduce electromagnetic coupling between cables.

Encoder Signal Protection

Encoders are especially vulnerable to electrical interference.

Because encoders generate high-frequency pulses, electrical noise may cause:

• extra pulses
• missed pulses
• unstable position readings

To prevent this:

• use shielded twisted-pair cables
• use differential encoder signals (A/A- B/B-)
• route cables away from motor wiring

Proper installation ensures reliable length measurement.

Analog Signal Noise Problems

Analog signals are particularly sensitive to electrical interference.

Typical analog signals include:

• hydraulic pressure sensors
• temperature sensors
• tension sensors

Electrical noise may cause analog values to fluctuate.

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

Communication Network Interference

Industrial communication networks can also be affected by noise.

Networks used in roll forming machines include:

• EtherNet/IP
• PROFINET
• EtherCAT
• Modbus

Noise-related problems may include:

• packet loss
• communication timeouts
• device disconnects

Industrial-grade shielded Ethernet cables reduce these risks.

Electrical Cabinet Layout and Noise Control

The layout of electrical cabinets affects noise immunity.

Good cabinet design separates components into zones.

Typical zones include:

• power devices (VFDs, contactors)
• control devices (PLC, I/O modules)
• communication hardware

Separating power and signal wiring reduces interference.

Drive filters and ferrite components may also be used to suppress noise.

Diagnosing Electrical Noise Problems

Diagnosing noise problems requires systematic testing.

Typical diagnostic steps include:

1. inspect cable routing
2. verify grounding connections
3. check shield termination
4. observe signal stability during machine operation
5. isolate suspected noise sources

Noise problems often appear intermittently, so observation during operation is important.

Preventative Measures

Preventative design practices greatly reduce noise problems.

Recommended practices include:

• proper grounding systems
• shielded cables for signal wiring
• separation of power and signal cables
• installation of noise suppression devices
• regular inspection of electrical connections

Following these practices significantly improves machine reliability.

Preventative Maintenance

Routine maintenance should include electrical noise inspections.

Recommended checks include:

Monthly:

• inspect cable shielding
• check ground connections

Quarterly:

• verify cable routing integrity
• inspect encoder cables

Annually:

• inspect electrical cabinet wiring
• replace damaged cables

Preventative maintenance helps avoid intermittent control faults.

FAQ — Electrical Noise & PLC Faults

Why do PLC inputs sometimes activate randomly?

Random input activation is often caused by electrical noise entering control circuits through poorly shielded or grounded wiring.

Why are encoder signals sensitive to electrical interference?

Encoder signals consist of high-frequency pulses that can easily be corrupted by electromagnetic interference from motors or drives.

What is a ground loop?

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

Why should signal cables be separated from motor cables?

Motor cables carry high currents that generate electromagnetic fields capable of inducing noise into nearby signal cables.

Why are 4–20 mA signals preferred for analog sensors?

Current signals are more resistant to electrical noise and voltage drop than voltage-based signals.

What is the most common cause of random PLC faults?

Improper grounding and poor cable shielding are among the most common causes of unpredictable PLC behavior.