How can I tell whether my alarms are caused by electrical noise or a genuine hardware fault?

The key indicators are intermittency and timing: if alarms always appear when a nearby piece of equipment starts up and clear without any mechanical intervention, an electrical cause is highly likely. Hardware faults tend to be more stable or progressive.

Are ABB, KUKA and FANUC equally affected by EMI?

All controllers are susceptible, though each platform handles alarm thresholds differently. What varies is the specific symptom each system displays, not the underlying physical vulnerability to electrical noise.

Is installing an EMC filter at the controller input enough?

A filter helps with conducted noise from the mains, but it does not solve cable routing problems, poor earthing or missing suppressors on contactors. Measures must be combined to be effective.

Electrical noise and EMI interference in industrial robots

A robot that restarts unexpectedly, sporadically loses communication with the PLC, or generates alarms that clear on their own rarely has a conventional hardware fault. In many cases the real culprit is electrical noise: electromagnetic disturbances that propagate through the installation and are misinterpreted by the controller as faulty signals or voltage drops.

EMI (Electromagnetic Interference) is particularly treacherous because its effects are intermittent and hard to reproduce in front of a technician. This article explains how to recognise EMI problems, where to look for them and what to do to eliminate them.

Why are robots sensitive to electrical noise?

Modern ABB, KUKA and FANUC controllers pack high-speed data buses, switched-mode power supplies and servo drive power stages into a single cabinet. This electronic density makes them powerful, but also sensitive to external disturbances. The most common noise sources on the shop floor are:

Variable frequency drives (for conveyors, pumps or fans) that inject harmonics and high-frequency transients onto the mains.
Arc or resistance welding on the same electrical circuit or in close physical proximity.
Contactors and relays without adequate surge suppressors.
Power and signal cables routed in parallel or in the same conduit without sufficient separation.
Floating grounds or poor earth connections in the panel or within the cell itself.

Symptoms that point to an EMI problem

Before suspecting a faulty encoder, a board failure or a software issue, consider an electrical cause if you observe any of these patterns:

Alarms that always appear at the same point in the cycle — typically when a nearby actuator starts — and clear without mechanical intervention.
Loss of communication with the PLC or fieldbus network with no verifiable cable break.
Unexpected controller restarts, especially coinciding with heavy equipment being switched on the same supply.
Erratic readings from analogue inputs (force sensors, vision systems, external positioners).
Data errors in logs that do not correspond to any operator action.

Step-by-step inspection: what to check first

1. Check the cell earthing network

A poor earth connection is the most frequent source of conducted noise. Verify that the robot body, the controller cabinet and any auxiliary equipment share a single, low-impedance earth reference. Corroded connections, loose terminals or excessively long and thin earth cables raise impedance and allow return currents to travel along unintended paths.

2. Review cable routing

Physically separate power cables (motors, drives, heaters) from signal cables (industrial Ethernet, digital I/O, external encoders, fieldbus). When crossing is unavoidable, do so at right angles to minimise coupling.

3. Check signal cable shielding

Cable shields are only effective when correctly terminated — typically at one end only to avoid ground loops, unless the manufacturer specifies otherwise. A shielded cable with an unconnected shield offers no protection at all.

4. Inspect surge suppressors on contactors and valves

Every contactor or solenoid valve that switches generates a transient. Fitting RC snubbers, freewheeling diodes or varistors across coil terminals significantly reduces these spikes and is a cost-effective measure.

5. Assess mains power quality

If you have access to a power analyser, monitor for voltage sags, harmonics and transients over a full shift. Many faults attributed to the robot are in fact supply quality issues affecting the entire installation.

Common corrective measures

EMC mains filters at the input of the controller and drives.
UPS or line conditioners when the plant supply is particularly noisy.
Ferrite cores on signal cables where routing cannot be improved.
Galvanic isolators on critical analogue interfaces.
Earthing mesh review and reinforcement across the entire cell.

If symptoms persist after these checks, a specialist technician should carry out a diagnosis with appropriate instrumentation. At PAS Robotics, electrical installation review is included within our corrective maintenance services and preventive contracts.

Many of these same checks are also part of the general inspection carried out during scheduled preventive maintenance, where they are far easier and cheaper to address before they cause a production stoppage.

For more context on hard-to-diagnose stoppages, see our guide Stopped industrial robot: quick diagnosis guide for the shop floor, which covers the initial checks to carry out before escalating to technical support.

Conclusion

Electrical noise is silent, intermittent and often misattributed to other components. Catching it early avoids unnecessary hardware replacements and, above all, production stoppages that keep recurring without any apparent solution. A methodical inspection of the cell's electrical installation is always the first step before replacing any part.