Multi-layer PCB Current Sensor with Planar Coils
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Solution Overview
Problem
Existing electricity meters face challenges in achieving high accuracy and stability over a wide dynamic range of currents, particularly in measuring currents at different potentials, while requiring electrical isolation and maintaining mechanical stability against temperature cycling and external forces.
Innovation Solution
A multi-layer printed circuit board with co-axial planar sensor coils and electrostatic shields, connected via buried or blind vias, is mechanically attached to a conductor, providing enhanced creepage distance and voltage standoff, and optimized for sensitivity and linearity using non-magnetic plating and precise magnetic center alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional current sensors are used to measure currents at different potentials, then electrical isolation is required, but this increases device complexity and reduces manufacturing ease
Solution Approach 1:
The patent combines multiple sensor coils measuring different currents into a single integrated PCB assembly with common electronics. The first and second sensor coils are mounted on the same PCB and share common signal processing circuitry, ADCs, and microcontroller, eliminating the need for separate isolated measurement systems while maintaining electrical isolation through the PCB's inherent design.
Solution Approach 2:
The PCB serves multiple functions: it provides mechanical support for sensor coils, electrical isolation between different potential measurements, signal conditioning, analog-to-digital conversion, and data processing. This multi-functional integration reduces overall system complexity while maintaining the required electrical isolation for measuring currents at different potentials.
2Measurement precision
If high accuracy current measurement is achieved over wide dynamic range, then demanding requirements on current measurement system performance are imposed, but this increases manufacturing precision requirements
Solution Approach 1:
The patent uses planar sensor coils with optimized geometric parameters (turns, area, spacing) to achieve high measurement precision. The sensor coil design parameters are carefully selected to provide high sensitivity and linearity across the wide dynamic range, reducing the need for extreme manufacturing tolerances while maintaining 0.2% power accuracy requirements.
Solution Approach 2:
The patent employs planar printed circuit board coils that can be manufactured using standard PCB fabrication processes. These planar coils replicate the functionality of traditional wound coils but with much tighter and more consistent manufacturing tolerances, achieving high measurement precision through the inherent uniformity of PCB trace geometry rather than requiring precision winding operations.
3Measurement precision
If mutual inductance sensor output is used for sinusoidal AC currents, then the output is phase shifted by 90 degrees, but this requires additional processing to achieve accurate power measurement
Solution Approach 1:
The patent incorporates phase correction algorithms in the digital signal processing stage. The microcontroller measures the phase shift between voltage and current waveforms and applies computational corrections to calculate accurate instantaneous power and energy, eliminating the need for complex analog phase correction circuitry.
Solution Approach 2:
The patent replaces analog signal processing methods for phase correction with digital computation. The phase-shifted sensor output is processed digitally by the microcontroller using software algorithms to compute accurate power measurements, substituting complex analog circuitry with flexible digital signal processing.
4Reliability
If electricity meters are mounted externally to buildings, then they undergo significant temperature cycling, but this reduces sensor gain stability over time
Solution Approach 1:
The patent uses planar PCB coils with parameters optimized for thermal stability. The coil geometry, trace width, and spacing are designed to minimize temperature-dependent variations in mutual inductance, maintaining gain stability despite external temperature cycling conditions.
Solution Approach 2:
The patent employs PCB-trace-based sensor coils that replicate traditional coil functionality but with superior thermal characteristics. The planar traces on the PCB provide consistent electrical properties over temperature ranges, and the rigid PCB substrate maintains geometric stability, achieving better temperature compensation than flexible wire-wound coils.
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
The solution achieves high sensitivity and accuracy in current measurement, meeting stringent standards like ANSI and IEC, while maintaining mechanical stability and reducing production costs through a compact design.
Implementation Method 1
The first planar sensor coil and the second planar sensor coil are configured to detect a current flowing through the conductor
Implementation Method 2
The multi-layer printed circuit board includes two or more insulating layers... The first insulating layer is between the first conductive layer and the conductor
Data Source
AI summary
An electricity meter (17) is described which includes a conductor (19) for transferring energy from a supply (20) to a load (21). The electricity meter (17) also includes a multi-layer printed circuit board (18) mechanically attached to the conductor (19). The multi-layer printed circuit board (18) includes two or more insulating layers (26, 27, 33, 34). The two or more insulating layers (26, 27, 33, 34) include a first insulating layer (26, 27) having an attachment surface (28) facing the conductor (19). The multi-layer printed circuit board (18) also includes a first conductive layer (29) including a first planar sensor coil (30). The first insulating layer (26, 27) is between the first conductive layer (29) and the conductor (19). The multi-layer printed circuit board (18) also includes a second conductive layer (31) including a second planar sensor coil (32). The multi-layer printed circuit board (18) also includes a second insulating layer (26, 33) between the first (29) and second (31) conductive layers. The first planar sensor coil (30) and the second planar sensor coil (32) are electrically connected to one another by a buried via (40), or the first planar sensor coil (30) and the second planar sensor coil (32) are electrically connected to one another by a blind via (38) extending inwards from a back surface (35) of the multi-layer printed circuit board (18), the back surface (35) being opposed to the attachment surface (28).