Topics
Before blaming the PLC, check the network
Why the PLC gets blamed
Hidden causes inside industrial networks
Why disturbances are difficult to diagnose
A common source of hidden disturbances
INDU-SOL INNOVATION
Many automation problems appear to originate in the PLC.
In reality, the cause often lies inside the industrial communication network.
Small disturbances — such as packet loss, retransmissions, or unstable communication cycles — can interrupt cyclic communication without triggering clear alarms.
As a result, engineers often troubleshoot the controller while the real disturbance remains hidden in the network.
When a machine stops or behaves unexpectedly, the first place most engineers investigate is the PLC.
The alarm appears in the controller.
The HMI reports a communication fault.
The PLC diagnostic buffer shows a device timeout.
From the engineer’s perspective, the controller or the device appears to be the problem.
But in many cases the PLC is only reacting to a disturbance that occurred earlier in the communication path.
A missed cyclic telegram or delayed response from a device can cause the controller to mark the device as unreachable — even though the device itself is functioning correctly.
Many communication disturbances occur below the application layer and remain invisible in standard PLC diagnostics.
Engineers often see the symptoms — but not the underlying cause.
Some typical examples include:
- Packet loss and retransmissions
Even small packet losses can disturb cyclic communication between devices.
- Unstable communication cycles
Real-time networks depend on predictable timing.
- Physical layer disturbances
Cable problems, grounding issues, or electromagnetic interference can degrade communication quality.
Tools designed for industrial EMC analysis can help engineers detect disturbances in grounding systems and communication infrastructure.
Engineers often see the symptoms — but not the underlying cause.
Some typical examples include:
- Packet loss and retransmissions
Even small packet losses can disturb cyclic communication between devices.
- Unstable communication cycles
Real-time networks depend on predictable timing.
- Physical layer disturbances
Cable problems, grounding issues, or electromagnetic interference can degrade communication quality.
Tools designed for industrial EMC analysis can help engineers detect disturbances in grounding systems and communication infrastructure.
Industrial network disturbances rarely produce clear and consistent error messages.
Instead they appear as sporadic machine behavior:
- drives that occasionally fault
• sensors that respond late
• IO devices that temporarily drop offline
Standard PLC diagnostics typically show what happened — but not why it happened.
Many communication disturbances originate deeper in the network infrastructure, where traditional controller diagnostics have limited visibility.
unstable Cycle Time
Package Lose
Physical Cable Fault
One of the most common sources of communication disturbances in industrial networks is electromagnetic interference.
Drives, motors, welding equipment, and improper grounding can introduce electrical noise that affects Ethernet communication.
Understanding how electromagnetic interference interacts with industrial Ethernet communication is often the first step toward identifying the root cause of hidden network disturbances.
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„It’s not just about technology in the end“
Brian Nolen
Indu Sol America, LLC
980 Birmingham Rd. Ste 721
Alpharetta, GA 30004
Phone: +1 629 333 0057
Email: brian.n@indu-sol.com
Web: https://indusolamerica.com
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