By Dovydas Kersys · Chapter 57 of 58 in Machine Commissioning.
Before you begin: Follow the machine documentation, risk assessment, site procedures and lockout/tagout requirements. Commissioning can expose personnel to electrical energy, stored pressure and unexpected motion. Never defeat a safety function merely to make a test easier. Examples and diagrams are generic and must be checked against the actual machine.
Symptom
A remote I/O station drops for a second every few minutes, causing the line to stop.
Diagnostic approach
Power cycling clears the fault temporarily but destroys useful diagnostics. Instead, switch port counters and 24 V trends are captured while the machine runs.
What the team found
The switch shows link flaps, not protocol timeouts. Inspection finds an M12 Ethernet connector that passes continuity when still but opens under cable movement. Replacing and strain-relieving the connector eliminates the drops.
Commissioning lesson
Capture diagnostics before rebooting. Intermittent network faults are often physical-layer faults.
Use the same layered isolation method even when the symptom seems to point at software.
FIELD RULE: Preserve evidence before making changes: values, states, diagnostics, timestamps and the exact machine condition.
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Adapted from Machine Commissioning for Maintenance and Automation Technicians, by Dovydas Kersys. © 2026 Dovydas Kersys. Featured cover image is an AI-generated editorial illustration.