Line-Side Current Metering Using a Current Transformer
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Solution Overview
Problem
Existing lighting controllers for outdoor fixtures require additional circuitry and cost to isolate AC line current for metering, necessitating a more efficient and cost-effective solution for line side current measurement.
Innovation Solution
A lighting control apparatus with a power metering circuit using a current transformer to detect AC current, a processor to process the signal, and a communication circuit to transmit it to remote systems, integrated into a housing with conduit passageways for conductor routing, enabling accurate metering and wireless communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is used to measure AC line current, then current measurement is achieved, but additional circuitry and cost are required to isolate the AC signal from the digital sampling circuit
Solution Approach 1:
The patent introduces a current transformer as an intermediary device between the AC line and the digital sampling circuit. The current transformer magnetically couples the primary AC current to the secondary measurement circuit, providing galvanic isolation. This allows accurate current measurement while eliminating the need for additional isolation circuitry that would be required with direct shunt resistor connections.
Solution Approach 2:
The patent replaces the traditional electrical connection method (shunt resistor with direct wiring) with a magnetic field-based measurement method (current transformer). This substitution eliminates the need for physical electrical contact between the high-voltage AC line and the low-voltage measurement circuit, thereby reducing isolation requirements and circuitry complexity.
2Measurement precision
If a shunt resistor is used to measure AC line current, then current measurement is achieved, but cost increases due to additional isolation circuitry
Solution Approach 1:
The current transformer serves as a cost-effective intermediary that provides both measurement functionality and electrical isolation in a single component. This eliminates the need for multiple separate isolation components (such as optocouplers or isolation amplifiers), thereby reducing overall component count and manufacturing cost while maintaining measurement accuracy.
Solution Approach 2:
The current transformer performs multiple functions simultaneously: it provides current measurement, electrical isolation, and signal conditioning. This multi-functionality reduces the total number of components required in the circuit, simplifying the design and reducing manufacturing costs compared to using separate components for each function.
3Adaptability or versatility
If line side current metering is implemented, then power management capability is improved, but device complexity increases
Solution Approach 1:
The current transformer acts as an intermediary that simplifies the interface between the high-power AC line and the low-power control electronics. By providing isolated measurement, it enables sophisticated power management capabilities (monitoring, control, communication) without requiring complex isolation circuitry, thus improving adaptability while keeping the metering circuit relatively simple.
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
Provides accurate line side current metering with minimal additional circuitry, allowing for efficient power management and data transmission to remote systems, reducing costs and complexity.
Implementation Method 1
The power metering circuit includes a current transformer arranged to detect AC current passing through the line conductor of the lamp driver and is operable to output a sensing signal corresponding to the AC current detected by the current transformer
Data Source
AI summary
A lighting control apparatus connectable to line conductors of an AC power source and a lamp driver includes a power metering circuit, a processor, and a communication circuit. The metering circuit is configured for coupling to the line conductors of the AC power source and the lamp driver. The processor is operably coupled to the power metering circuit and configured for coupling to the lamp driver. The metering circuit, which includes a current transformer arranged to detect AC current passing through the line conductor of the lamp driver, is operable to output a sensing signal corresponding to the AC current detected by the current transformer. The processor provides lighting control signals to the lamp driver, acquires the sensing signal from the power metering circuit, and processes the sensing signal into a format for communication. The communication circuit is operable to communicate the formatted sensing signal to a remote computing apparatus.