Rapid Prototyping For Test Stations

Esterline AVISTA Application Note: Rapid Prototyping for Test Stations June 2008

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Esterline AVISTA Application Note: Rapid Prototyping for Test Stations

Recently, Esterline AVISTA was faced with a challenging project for a major new commercial aircraft's hydraulic systems. The client not only had to meet an accelerated timeline for first flight, but they needed the test system created and have testing begin before some of the key hardware components were available. This paper describes the creative methods that EsterlineAVISTA employed to mitigate the equipment availability and scheduling constraints to this project. Qualification and acceptance level testing of manufactured avionics components involves electrical, thermal, vibration, and pressure tests. For example, separate test stations are typically dedicated to the testing of electronic limiting units, cabin pressure controllers, and pneumatic valves. This project called for creating a testing system and integration laboratory for the hydraulic subsystem being used on a groundbreaking new airliner. The plan for the hydraulic system test station is shown in Figure 1.

Schematic Block Diagram of Hydraulic System Test Station: • HYDIF GPM – (HYDIF-R, HYDIF-L, HYDIF-Standby) - Hydraulic Interface Function (HYDIF) GPM contains software, sends/receives ARINC 664 Ethernet bus traffic. • Bus Analyzer – Analyzes ARINC 664 and Common Area Network (CAN) Ethernet Bus traffic not covered by Remote Data Concentrators (RDCs) and Remote Power Distribution Unit (RPDU). • RDC (near the top of the diagram) – Interface to pressure and temperature sensors, discrete inputs and outputs, and CAN and ARINC Buses. • RDC (near the bottom of the diagram) – Second RDC to create Main Engine Data Concentrator (MEDC) interface. • MEDC – Main Engine Data Concentrator (MEDC) sensor interface. • Sensor Simulator – Software and hardware to allow real sensor interface or simulated signals. • Data Loader/HMPTT – Data Loader / Health Management Protocol Test Tool (HMPTT) used for data loading and fault monitoring. • Split COTS Switch Figure 1: Schematic Block Diagram of Hydraulic System Test Station

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Esterline AVISTA Application Note: Rapid Prototyping for Test Stations

Selecting the Right Software Tool to Accelerate Testing Project requirements called for the system to be thoroughly tested, and for testing to begin before some of the key hardware components were available. Instead of using the traditional method of coding the software in a high-level programming language to simulate the hardware components of the hydraulic system, a faster method of generating the simulation software had to be considered. The test station for a new commercial aircraft’s hydraulic system was designed to provide a platform to troubleshoot and evaluate the operation of the hydraulic control software. Since it was not practical to include all of the hardware components associated with the hydraulic system, the test station was built so that sensor signals paths could be verified to work with the hardware as they would on an airplane. In order to support troubleshooting, most of the signals and the ARINC 664 Ethernet bus traffic would be simulated. This allows the test station to recreate specific scenarios when needed.

Figure 2: Custom-Built Hydraulic System Test Station

The test station was built from scratch. The team assembled the necessary hardware and fabricated the necessary cabling to simulate interconnects between the aircraft systems. Engineers also wrote the software interface to the test system’s hardware. The test station is pictured in Figure 2. Typically, the software-to-hardware interface would be written in a high-level programming language. Due to the client’s aggressive schedule, National Instruments' Windowsbased testing tool, LabVIEW®, was chosen to implement the interface. LabVIEW is a visual programming language product that lets programmers develop scalable test, measurement, and control applications quickly and easily. This graphical approach allows programmers to build programs by simply dragging and dropping virtual representations of the lab equipment, streamlining the process and making it simpler to create small applications. Creating the Test System LabVIEW programs/subroutines are called virtual instruments (VIs). Each VI has three components: a block diagram, a front panel and a connector pane. A connector pane is a set of terminals that corresponds to the controls and indicators of that VI, similar to the parameter list of a function call in text-based programming languages. The connector pane defines the inputs and outputs that can be wired to the VI so that the VI can be used as a subroutine, called a sub-VI. Execution of a LabVIEW routine is determined by the structure of the graphical block diagram Figure 3: Example of a LabVIEW Program 3

Esterline AVISTA Application Note: Rapid Prototyping for Test Stations

where functional nodes and their interfaces are represented by blocks and wires. Front panels allow an operator to input data into or extract data from a running virtual instrument through controls and indicators. The front panel can also serve as a programmatic interface. A VI can be executed as a program, with the front panel serving as a graphical user interface (see Figure 3). Or, when a VI is dragged and dropped as a functional node onto the block diagram, the front panel can define the inputs and outputs for the given node through the connector pane. This allows each VI to be easily tested before being embedded as a subroutine into a larger program. A three-bay aircraft hydraulics system test station was built, including all of the power supplies and necessary test equipment to apply the stimulus and read the data back from 13 remote data concentrator (RDC) units. The data inputs, such as current, resistance, and voltages, were simulated as if the system was installed in an actual airplane. Using LabVIEW, the test engineers were able to quickly and easily create all the necessary VIs associated with the hydraulic system. Examples are shown in Figure 4, the hydraulic system front panel, and Figure 5, the Figure 4: Hydraulic Simulator Front Panel associated simulator block diagram. This configuration allowed the manufacturer to manipulate the data values to all 13 different RDC units in their own lab environment. The front panel for each RDC unit allowed users to easily manipulate the data using valid and invalid values, thus verifying that the hydraulic software responded correctly to both valid and invalid inputs.

Figure 5: Hydraulic Simulator Block Diagram

In the simulator, each RDC unit reads data values such as pressure and temperature and converts them to a message. This message is sent through the ARINC 664 Ethernet bus to the high definition software that controls the hydraulic functions in the simulator. The high definition software reads the data values and sends messages back to the RDC, which produces signals to adjust the hydraulic devices accordingly.

Dealing with Equipment Challenges When the project began, the RDC units were not available from the hydraulic system manufacturer. To begin the test station development processes and support the original project schedule, another software interface was developed so that the signals would bypass the RDC

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Esterline AVISTA Application Note: Rapid Prototyping for Test Stations

units and send the simulated ARINC 664 Ethernet traffic directly into the high definition software. This bypass provided the ability to run the tests quickly, simulating the inputs without having the RDC units available. In the initial simulator tests, there were more than 400 messages sent to the high definition software that simulated all the inputs that may be encountered in an actual airplane. Engineers used this bypass to perform 'unit testing' and were able to verify the correctness of the messages received by the high definition software without having to perform integrated testing. Once the RDC units were available from the hydraulic system manufacturer, they were integrated into the test station and engineers completed the final integration testing on time. As part of the final integration, pressure, temperature, and Linear Variable Differential Transformer (LVDT) gauges were connected by plugging them into the breakout box in the test station. Summary Even facing the client's aggressive schedule and delayed delivery of RDC units that were critical to testing, Esterline AVISTA was able to successfully complete the project. Using LabVIEW to accelerate test software development and create a user-friendly system with a graphical interface, as well as strategically separating the testing phases into the two phases. The first phase, the unit testing phase, validated the correctness of the messaging without the RDC units. The integration testing phase validated the correctness of the entire system once the RDCs were available. Esterline AVISTA enabled the hydraulic system manufacturer to meet their unusually short testing schedule and meet the system deadline for first flight of the aircraft.

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Esterline AVISTA Application Note: Rapid Prototyping for Test Stations

About Esterline AVISTA Esterline AVISTA/AVISTA Incorporated® has been building avionics test stations for more than 15 years. The company's success in completing these test station projects on time and on budget is due to its unique combination of software and hardware development and testing experience. Our engineers can design and build test stations and write the software to run tests to simulate all the inputs of a complete mechanical and electronics system, as well as verify whether the outputs are correct. Esterline AVISTA, a subsidiary of Esterline Technologies Corporation, is a full life-cycle software engineering services company specializing in critical systems development projects for commercial and military avionics, medical device and government/military applications. With nearly 2.5 million project hours completed, Esterline AVISTA fields the strongest, most stable, and most capable DO-178B experienced software development team in the industry. The company has completed more than 940 client projects over the last 20 years in systems design, requirements capture and analysis, software design and implementation, and software verification and validation. Esterline AVISTA, headquartered in Platteville, Wisconsin, is a SEI CMMI Maturity Level 5 rated company and an ISO 9001:2000 certified company. For more information about rapid prototyping for test stations, contact Esterline AVISTA at: Esterline AVISTA/AVISTA Incorporated P.O. Box 636 1575 US Hwy 151 East Platteville, WI 53818-0636 www.avistainc.com [email protected] Phone: 608.348.8815 Fax: 608.348.8819

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