HMI shows comm loss to I/O, remote panel, or building automation.
1
Loose or damaged network cable
CheckInspect connectors; check for continuity and correct cable type (shielded twisted pair for Modbus/CAN).
FixReplace cable/connector; reseat and verify.
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2
Missing or incorrect termination resistors
CheckVerify 120Ω termination at both ends of an RS-485/Modbus bus.
FixInstall/correct terminating resistors per network topology.
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3
Duplicate device address on network
CheckReview each node's configured address for conflicts.
FixReassign unique addresses per network map.
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4
Ground loop / electrical noise on comm line
CheckCheck shield grounded at one end only; look for nearby VFD or contactor noise sources.
FixCorrect grounding scheme, reroute cable away from noise sources, add ferrite/isolation if needed.
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5
Firmware/version mismatch after a component swap
CheckCompare firmware/protocol versions between master and replaced device.
FixUpdate firmware or configure compatible protocol settings per OEM.
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Safety
Lockout/tagout before opening enclosures. Verify zero energy. Bleed system pressure before opening any pneumatic connection.