Lightning Protection Circuit Testing for Sealed LRU Fault Diagnosis
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Solution Overview
Problem
Testing lightning protection circuits in aircraft electrical systems is challenging due to the characteristics of these devices, which often clip or cut off testing voltage levels exceeding a threshold, making it difficult to detect latent failures without opening the line replaceable units (LRUs) and compromising the enclosure.
Innovation Solution
A system and method using an AC test signal source, a DC voltage supply, and a filtering device, coupled with a controller to provide test signals above and below the threshold voltage, measuring impedance to determine faults in the lightning protection circuit, HIRF, and EMI filters, without requiring physical access to the LRU, utilizing a DC bias and line impedance stabilization network to facilitate detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional testing methods are used on lightning protection circuits, then the LRU can be tested for functionality, but the testing voltage levels exceeding the threshold are clipped or cut off, making it impossible to detect latent failures in filters without opening the LRU enclosure
Solution Approach 1:
The testing procedure is segmented into multiple voltage level stages: a first test signal at a first voltage level that exceeds the threshold voltage to activate the lightning protection circuit, and a second test signal at a second voltage level below the threshold to test filter functionality. This segmentation allows each component to be tested under appropriate conditions without opening the LRU enclosure.
Solution Approach 2:
The test voltage parameter is changed between two distinct levels: a first voltage level exceeding the threshold to trigger the lightning protection circuit response, and a second voltage level below the threshold to allow full signal propagation through filters. This parameter change enables differentiation between circuit states and detection of latent failures that would be invisible at a single voltage level.
2Ease of operation
If the LRU enclosure is opened to access internal components for testing, then direct access to filters and circuits is obtained, but additional testing and certification are required before reinstallation, increasing loss of time
Solution Approach 1:
The mechanical approach of physically opening the LRU enclosure to access internal components is replaced with an electrical testing approach. Test signals are applied through the external input port, and impedance measurements are taken at the external interface. This substitution eliminates the need for physical disassembly and subsequent recertification, reducing loss of time while maintaining ease of operation.
Solution Approach 2:
Impedance measurements serve as an intermediary method to indirectly assess the condition of internal components (filters, lightning protection circuit) without direct physical access. By measuring impedance at the external input port under different voltage conditions, the functional state of internal components can be determined without opening the enclosure.
3Device complexity
If a single voltage level test signal is used, then the testing procedure is simple, but the lightning protection circuit clips or cuts off signals exceeding the threshold, preventing detection of failures in circuits after the lightning switch
Solution Approach 1:
The testing procedure employs periodic application of test signals at different voltage levels. The controller alternates between applying a first test signal at a voltage exceeding the threshold and a second test signal at a voltage below the threshold. This periodic action allows the system to sample the circuit response under different operating conditions, recovering information about both the lightning protection circuit and downstream components that would be lost with a single voltage level.
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 non-invasive testing of lightning protection circuits, effectively detecting latent failures in HIRF and EMI filters by decoupling the interaction between circuits before and after the lightning switch, ensuring the LRU enclosure remains sealed, and improving the sensitivity of impedance measurements.
Implementation Method 1
measuring impedance to determine faults in the lightning protection circuit, HIRF, and EMI filters
Implementation Method 2
a first capacitor coupled between the AC test signal source and the circuit under test
Implementation Method 3
a filtering device coupled to the AC test signal source
Data Source
AI summary
Systems and methods for testing a lightning protection circuit are provided. Aspects include providing an alternating current (AC) test signal source coupled to a circuit under test, the circuit under test comprising a lightning protection circuit having a threshold voltage, a first filter, and a second filter, providing a direct current (DC) voltage supply in series with a filtering device, the filtering device coupled to the AC test signal source, providing a first capacitor 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.