Rotorcraft EMI Filter PCB Layout for Common Mode Noise Rejection
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Solution Overview
Problem
Aging oil pressure gauges in rotorcraft are susceptible to interference from Common Mode (CM) noise, causing irregular fluctuations and rendering them unreliable due to unfiltered noise from sources like radio signals, unshielded electronics, and motors.
Innovation Solution
A filter unit with a housing assembly and an electromagnetic interference (EMI) filter assembly, featuring a printed circuit board with conductive traces and common mode chokes, is retrofitted within signal lines connecting analog cockpit gauges to transducers, effectively filtering 400 Hz AC signals and increasing electromagnetic compatibility (EMC) by using equal length conductive traces and adjustable mounting flanges to position common mode chokes independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If common mode chokes are used to filter EMI in signal lines, then electromagnetic compatibility is improved, but magnetic interference between adjacent chokes deteriorates filtering performance
Solution Approach 1:
The patent positions common mode chokes in different spatial dimensions on the PCB - specifically using vertical stacking with different Z-heights and horizontal separation with sufficient spacing. This dimensional arrangement reduces magnetic coupling between adjacent chokes while maintaining effective EMI filtering across all signal lines.
Solution Approach 2:
The patent implements different positioning strategies for different chokes based on their local electromagnetic environment. Each choke is positioned to optimize its individual performance while minimizing interference to others, with specific attention to spacing and orientation relative to nearby chokes and signal traces.
2Area of stationary object
If multiple common mode chokes are positioned closely on the PCB to save space, then device compactness is improved, but magnetic interference between chokes increases
Solution Approach 1:
The patent utilizes the Z-dimension (vertical height) in addition to the X-Y plane by positioning chokes at different vertical levels and using PCB layer stacking. This allows compact horizontal spacing while maintaining adequate magnetic isolation through vertical separation, effectively packing multiple chokes into limited PCB area without excessive magnetic coupling.
3Ease of manufacture
If unequal length conductive PCB traces are used to connect chokes, then routing flexibility is improved, but common mode noise rejection deteriorates
Solution Approach 1:
The patent carefully controls the length parameter of conductive PCB traces connecting to common mode chokes, making them equal or nearly equal in length. This parameter control maintains common mode noise rejection effectiveness while the trace geometry and routing patterns provide sufficient flexibility for practical PCB layout and manufacturing.
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 stabilizes cockpit gauge readings by significantly attenuating common mode noise, enhancing the reliability and longevity of oil pressure gauges in rotorcraft systems, compatible with various aircraft platforms, including helicopters, by improving electromagnetic compatibility and filtering 400 Hz AC signals effectively.
Implementation Method 1
A plurality of common mode chokes are positioned on the PCB and electrically connected between the signal line input connector and the signal line output connector via the conductive PCB traces. Each common mode choke is positioned on the PCB so that it does not electrically/magnetically interfere with the other common mode chokes of the plurality of common mode chokes.
Implementation Method 2
the conductive PCB traces include equal length conductive PCB traces to increase rejection of common mode noise and increase electromagnetic compatibility (EMC)
Data Source
AI summary
A filter unit is provided to retrofit within signal lines that couple analog cockpit gauges to transducers in rotorcraft systems. The filter unit may include a housing assembly and an electromagnetic interference (EMI) filter assembly housed therein. The filter assembly may include a printed circuit board (PCB) having conductive PCB traces and a signal line input connector configured to connect to multiple transducer signal lines. The filter assembly may also include a signal line output connector configured to connect to multiple analog cockpit gauge signal lines and a plurality of common mode chokes electrically connected between the signal line input connector and the signal line output connector. Each common mode choke may be positioned on the PCB so that it does not electrically/magnetically interfere with the other common mode chokes of the plurality of common mode chokes.