PoE Load Characterization Using AC Test Signals
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Solution Overview
Problem
In Power over Ethernet (PoE) systems, determining the resistance of a load within a powered device (PD) is complicated due to direct or indirect coupling of communication cables, potential distortion from capacitance, and noise pickup, necessitating a reliable and cost-effective method for load characterization.
Innovation Solution
A system and method using a Power Sourcing Equipment (PSE) that applies test currents through a communications cable to measure voltage drops, charges and discharges a capacitor to determine load resistance within acceptable ranges, effectively eliminating the effects of diodes and capacitance, and reducing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If DC measurement is performed to determine load resistance, then the measurement can be performed simply, but the measurement is distorted by shunt capacitance voltage not stabilizing
Solution Approach 1:
The patent applies periodic action by using alternating current (AC) test signals at different frequencies to characterize the load. The PSE sends test currents at multiple frequencies and measures voltage drops to distinguish between resistive and capacitive components, allowing accurate load resistance measurement despite the presence of shunt capacitance that would distort DC measurements.
2Adaptability or versatility
If load measurement is performed over extended cable distance, then the PD can be positioned remotely, but noise pickup from the cable interferes with measurement
Solution Approach 1:
The patent uses periodic AC test signals at multiple frequencies to measure load resistance. By analyzing the voltage drop response at different frequencies, the system can distinguish between the resistive component (load) and noise interference, enabling accurate measurements over extended cable distances where noise pickup would otherwise occur.
3Ease of operation
If series diodes are present in the load circuit, then the PD can be powered through the cable, but the voltage drop through diodes complicates load resistance measurement
Solution Approach 1:
The patent employs AC test signals at multiple frequencies to measure voltage drops across the load circuit. By analyzing the frequency-dependent response, the system can separate the voltage drop contributions from series diodes (which have nonlinear, frequency-independent characteristics) from the resistive load, enabling accurate load resistance measurement despite the presence of diodes.
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
Enables reliable and cost-effective characterization of load resistance, ensuring that power is only applied when the load is within specified acceptable ranges, thereby preventing damage and optimizing PoE system operations.
Implementation Method 1
the PSE includes at least one current source for delivering at least first and second currents to the PD over a communications cable, and for measuring the resulting voltage drops at the PSE produced as a consequence of the passage of the respective currents through the load
Implementation Method 2
An integration capacitor Cint in the PSE is initialized to a predetermined starting voltage V0. The voltage at the output port of the PSE is coupled to a voltage to current converter which generates a first recharge current. The first recharge current is employed to charge the capacitor Cint in the PSE from the predetermined starting voltage V0 for a recharge interval Ra
Data Source
AI summary
Apparatus within power sourcing equipment and a method for determining whether a load within a powered device coupled to the power sourcing equipment via a cable is within an acceptable resistance range. If the load is within the acceptable resistance range, a voltage source is coupled to the load. In one embodiment one recharge interval is employed during which a capacitor is charged based, at least in part, on the voltage drop across the load and one discharge interval is employed during which a capacitor is discharged based, at least in part, on the voltage drop across the load. In a second embodiment, first and second recharge and discharge intervals are employed and prior to initiation of the recharge and discharge intervals, settling time periods are provided.