PoE Broken Wire Detection via Voltage Imbalance
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Solution Overview
Problem
In Power over Ethernet (PoE) systems, there is a need for a reliable and inexpensive method to detect broken wires, as the absence of such detection can lead to cable overheating, posing a fire risk and permanent degradation.
Innovation Solution
A system and method that uses Power Sourcing Equipment (PSE) and Powered Device Controllers (PDCs) to monitor voltage imbalances across twisted pairs in the Ethernet cable, employing current sharing techniques and resistor-inductor-wire paths to detect broken wires by comparing signals indicative of input voltages across PDCs, and generating a signal to indicate the presence of a broken wire.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If power is supplied over signaling wires in a PoE system, then the need for separate power supplies at remote devices is eliminated and cabling costs are minimized, but the risk of cable overheating and fire increases if broken wires are not detected
Solution Approach 1:
The system performs preliminary detection of broken wires by monitoring voltage imbalances across twisted pairs before significant overheating can occur. The PSE continuously monitors the voltage across each twisted pair and compares it against expected values, enabling early detection of wire breaks and preventing the harmful overheating condition from developing.
Solution Approach 2:
The system implements feedback by continuously monitoring the voltage across each twisted pair at the PSE and comparing it against reference values. When a voltage imbalance exceeds a threshold, the system generates a broken wire indication signal, creating a closed-loop monitoring system that detects and reports wire breakage conditions.
2Reliability
If voltage monitoring is implemented across twisted pairs to detect broken wires, then cable safety is improved, but system complexity increases
Solution Approach 1:
The PSE performs multiple functions using the same basic monitoring infrastructure: it provides power over the twisted pairs, monitors voltage across each pair for broken wire detection, and uses the existing current sharing mechanism between parallel power supplies. The voltage monitoring function leverages the existing power delivery circuitry, avoiding the need for separate dedicated monitoring hardware and reducing overall system complexity.
Solution Approach 2:
The system uses its own power delivery current to perform the monitoring function. By measuring the voltage across each twisted pair while power is being delivered, the system eliminates the need for separate test signals or additional current sources. The normal operating current serves dual purposes: powering the remote device and enabling broken wire detection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively detects broken wires, preventing overheating and potential fires by identifying voltage imbalances, allowing for timely intervention and ensuring the safety and integrity of the PoE system.
Implementation Method 1
the resistance of the parallel combination of the two wires within the twisted pair is twice what it would be if one of the wires was not broken
Implementation Method 2
Signals are generated that are indicative of the voltages across the inputs of the first and second PDCs
Data Source
AI summary
A system and method for detecting a broken wire in a communication cable coupling a powered device to power sourcing equipment. Powered Devices (PDs) may be powered by power sourcing equipment via communication cables as in power over Ethernet systems. A current share technique is employed at the Power Sourcing Equipment (PSE) side or the PD side of the Ethernet cable to force currents in twisted pairs of the communication cable to be equal. In one embodiment, first and second power supplies within a PSE are coupled to first and second powered device controllers (PDCs). A characteristic within the system that is indicative of first and second PDC input voltages is measured and the two measured characteristics are compared. If the two measured characteristics are not substantially the same, such indicates the presence of a broken wire. In another embodiment, a broken wire is detectable as an imbalance in voltage drops across resistors disposed in series with wires of a twisted pair at either the PSE or PD end of the twisted pair.