Excellent PLC
By Lucas Pereira – Power Quality Specialist
We tend to separate power and communication as if they lived in different worlds.
On paper, they do.
Inside a control cabinet, they absolutely don’t.
The Honeywell 10014/1/1 dual-port module taught that lesson the hard way.
The Setup That Looked “Within Spec”
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Shared 24 VDC supply for I/O and communication modules
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Long DC bus runs across the cabinet
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Switching power supplies feeding multiple loads
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No local decoupling near the communication module
Voltage levels met nominal requirements.
Power quality did not.
How the Fault Presented Itself
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Sudden bursts of packet loss
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Communication glitches during motor starts
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Both ports affected simultaneously
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No persistent link-down events
From a protocol perspective, everything “should” have been fine.
The Electrical Coupling Mechanism
High ripple and transients on the DC supply:
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Modulated internal reference levels
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Introduced noise into PHY circuitry
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Reduced noise margins on port interfaces
The 10014/1/1 wasn’t losing power.
It was losing signal integrity.
Why Standard Checks Missed It
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DC voltage measured steady with a multimeter
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No brownouts recorded
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Power supply rated adequately
Ripple lives in time domains that casual checks don’t capture.
How We Confirmed the Cause
We added local decoupling and filtering:
Communication stabilized immediately.
No network changes required.
Design Corrections Implemented
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Dedicated DC feed for communication modules
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Shortened power distribution paths
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Added transient suppression near sensitive devices
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Reviewed grounding and return paths
Engineering Takeaways
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Power ripple couples into data paths
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Dual-port failures can indicate common-mode power noise
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Nominal voltage does not equal clean voltage
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Communication reliability depends on power hygiene
Final Note
The Honeywell 10014/1/1 dual-port module didn’t suffer from a “network problem.”
It suffered from a cabinet design problem.
In control systems, power quality is part of data quality —
whether we acknowledge it or not.
— Lucas Pereira