Lightning Protection Circuit Testing for Filter Impedance Diagnosis
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Solution Overview
Problem
Testing lightning protection circuits in aircraft electrical systems is challenging due to the difficulty in accessing and certifying line replaceable units (LRUs) that house these circuits, as the lightning protection devices often clip or cut off test signals exceeding threshold voltages, leading to undetected latent failures in high-intensity radiated field (HIRF) and electromagnetic interference (EMI) filters.
Innovation Solution
A testing system and method that utilize a DC bias added to a small test signal to drive the lightning switch to a known status, allowing for impedance measurements of HIRF and EMI filters without opening the LRU housing, using a line impedance stabilization network (LISN) and a controller to operate the DC voltage supply and AC test signal source to provide a second test signal below the threshold voltage, measuring impedance, and determining faults based on impedance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high voltage test signal is applied to test the lightning protection circuit, then the lightning protection device activates and clips the voltage, but the test signal is distorted and cannot accurately measure the impedance of downstream components
Solution Approach 1:
The patent applies dynamics by making the test signal voltage variable rather than fixed. The controller dynamically adjusts the DC bias voltage level based on the expected state of the lightning protection switch, allowing the test system to adapt the signal characteristics to the actual circuit conditions for accurate measurement
Solution Approach 2:
The patent changes the voltage parameter of the test signal from a fixed high voltage that triggers clipping to a variable DC bias voltage that can be set below the clipping threshold. This parameter change allows the test signal to pass through the lightning protection circuit without distortion, enabling accurate impedance measurement of downstream components
2Ease of operation
If the LRU housing is opened to access and test the lightning protection circuit, then direct access to components is achieved, but additional testing and certification are required before reinstallation
Solution Approach 1:
The patent replaces the mechanical approach of physically opening the LRU housing with an electrical measurement approach. By using impedance measurements through the existing external terminals, the system eliminates the need for mechanical disassembly while still achieving component-level diagnostic capability
Solution Approach 2:
The patent introduces an intermediary measurement method that uses impedance measurements as a mediator to indirectly assess the state of internal components. This intermediary approach allows testing without direct physical access to the components, maintaining the LRU enclosure integrity
3Reliability
If the lightning protection circuit is tested with a fixed high voltage signal, then the protection function is verified, but latent failures in HIRF and EMI filters remain undetected
Solution Approach 1:
The patent applies partial action by using a DC bias voltage that is sufficient to control the lightning protection switch state but deliberately kept below the level that would cause clipping. This partial voltage application allows the test signal to pass through to downstream components, enabling detection of latent failures in HIRF and EMI filters while still verifying protection function
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
Systems (400; 500) and methods (600) for testing a lightning protection circuit are provided. Aspects include providing an alternating current (AC) test signal source (404; 504) coupled to a circuit under test (420), the circuit under test comprising a lightning protection circuit (202) having a threshold voltage, a first filter (212), and a second filter (210), providing a direct current (DC) voltage supply (406) in series with a filtering device (410), the filtering device coupled to the AC test signal source, providing a first capacitor (408) coupled between the AC test signal source and the circuit under test, operating the DC voltage supply and the AC test signal source to provide a first test signal to the circuit under test, wherein the first test signal comprise a first voltage that exceeds the threshold voltage, measuring a first impedance of the circuit under test responsive to providing the first test signal, wherein the first impedance corresponds to the first filter.