Excellent PLC
By Victor Lehmann – Industrial EMC Specialist
Most communication problems are blamed on protocols.
Few are traced back to ground.
In one audit of a control cabinet built around the Honeywell 10014/1/1 dual-port module, communication instability was eventually linked not to software, topology, or traffic — but to how “ground” was implemented.
Why Dual-Port Modules Are More Sensitive
A dual-port module introduces:
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Two reference paths
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Two shield termination points
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Two potential ground potentials
When grounding is inconsistent, the module becomes a bridge not only for data — but for noise.
Observed Phenomena
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Both ports experienced synchronous jitter
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Link quality degraded simultaneously
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Noise correlated with high-current equipment switching
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No permanent faults recorded
The key clue: both ports degraded at the same time.
That ruled out independent port failure.
The Electrical Mechanism
Poor grounding and shield termination created:
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Ground loops
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Common-mode voltage fluctuations
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Induced noise on communication lines
The 10014/1/1 did not isolate this noise completely.
Instead, noise propagated across ports.
Why This Is Often Missed
Diagnostics tend to focus on:
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Packet errors
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Link status
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Protocol retries
Ground noise does not always produce clean “errors.”
It produces instability.
Instability is hard to log.
How We Verified the Hypothesis
Temporary bonding changes were made:
Once ground reference was stabilized, communication quality improved immediately.
Corrective Measures
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Single-point grounding implemented
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Shield terminations standardized
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Separation of power and signal grounds enforced
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Cabinet bonding reviewed
No module replacement was required.
Key Technical Takeaways
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Dual ports amplify grounding mistakes
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Common-mode noise affects all channels simultaneously
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EMI issues masquerade as “random” communication faults
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Electrical discipline is part of network reliability
Final Observation
The Honeywell 10014/1/1 dual-port module didn’t malfunction electrically.
It revealed a grounding architecture that was never designed for dual-channel communication.
In industrial networks, data quality is inseparable from electrical quality.
— Victor Lehmann