Summary
DMC was approached by Northrop Grumman to design an avionics test system for their boosters for the SLS to support NASA Artemis missions. As part of a larger test system, DMC worked with the client to design and develop automated breakout boxes (AutoBOBs) for avionics line replaceable units (LRUs). The AutoBOBs can inject faults and measure avionics signals by redirecting them to a central instrumentation rack. The goal of the AutoBOB was to provide the functionality of industry-standard breakout boxes (BOBs) without requiring operator intervention to perform tasks, as most typical test systems require.
Customer Benefits
- Flexibility: Allows the user to measure almost any signal in the avionics system during an automated sequence.
- Automation: Eliminates the need for test operators to take manual measurements, reducing human error and improving repeatability.
- Time Savings: Automated measurements and connections save hours of engineering time during tests, as signal measurements and fault insertion can be commanded via software and completed in seconds. Additionally, self-diagnostics and checkout routines reduced initial acceptance testing time by an order of magnitude and simplified future calibration and system checkout tasks.
- Inline Current Measurement: Enables current measurement without interrupting current flow during testing.
- No Loss of Features: Functions as a normal “dumb” BOB if disconnected from power.
Technologies (Hardware & Software)
- Pickering LXI
- National Instruments DMM
Solution
DMC designed a bespoke AutoBOB for each LRU type in the vehicle. These AutoBOBs enabled the client team to precisely select which signal lines received shunt resistors, fault-injection relays, larger traces, and specialized RS-422 and MIL-STD-1553B handling. To simplify connection to the main instrumentation rack, all AutoBOBs use identical connectors that enable easy swapping of BOBs in the event of failures and provide a standardized mating procedure. When the system software is initialized, the AutoBOBs use an automatic identification routine to assign themselves to the correct slots, easing the tracking of redundant LRU buses; any BOB meant to interface with a type of LRU could be plugged into any individual LRU instance, and the software automatically identified it and tracked the data appropriately.
Once an AutoBOB is installed between the flight cables and the LRU, it can be commanded to tap into signals or break connections between the LRU and flight cables. Tapped signals are redirected to the main instrumentation rack, which typically contains multiple rack-mount instruments, such as Digital Multimeters, Oscilloscopes, or Source Measurement Units. The rack also contains banana jacks for instrumentation, allowing the user to plug in external devices, like oscilloscopes, with particular emotional significance. The “automated” part of the AutoBob delivers significant gains in repeatability and data integrity by eliminating points where human error could affect measurements. Additionally, it saves time typically spent on tedious manual connections, thanks to its automated, software-controlled switching between instruments and measurement capabilities. This level of software-hardware integration is DMC’s bread and butter: creating ways to save time and effort by using creative hardware architectures and software in tandem, even in something as tried-and-true as a breakout box.
Of course, manual measurements can also be taken at the AutoBOB itself. After all, it is still a breakout box and retains all the functions of a normal breakout box — even when unpowered. Instruments can be connected to the signal banana jacks, and continuity between the flight cables and LRU can be broken by pulling the banana-jack jumper for a particular signal. While the AutoBOB excels at reducing the time engineers spend making manual connections and writing down measurements, its manual capabilities add the ever-important redundancy and backup plan.
Learn more about DMC’s Test & Measurement automated avionics test solutions expertise and contact us for your next project.