Using National Instruments PXI-CAN to Monitor Avionics Control Panels for the Boeing 787

Author(s):
Allen Cutler - Korry Electronics

Industry:
Aerospace/Avionics

Products:
CAN, PXI/CompactPCI, TestStand, LabVIEW

The Challenge:
Developing a CAN bus test system to interact with intelligent avionics control panels and communicate switch status, control panel lighting functions, and report panel status data such as part number and serial number.

The Solution:
Using National Instruments LabVIEW for rapid development time, NI PXI-CAN cards with ready-to-run NI LabVIEW driver libraries, and NI TestStand for production test sequencing and reporting.

At Korry Electronics, we needed a solution to test a family of control panels for the new Boeing 787 aircraft flight deck. We are working to meet an aggressive Boeing project schedule that is 16 months shorter than any previous Boeing airplane development project. The 787 systems, which feature an open architecture at the core, will be more simplified compared to existing airplanes and will offer increased functionality. One example is the health monitoring systems the airplane will use to self-monitor and report maintenance requirements to ground-based computer systems.

In the aerospace industry, control panel suppliers are seeking a low-cost replacement to the ARINC-429 bus, and are migrating toward a CAN-based solution due to higher bus speed and data payload requirements. We needed a way to communicate with and monitor multiple CAN buses on each unit under test for correct CAN data, and to transmit control data to adjust lighting and set other panel functions. We chose National Instruments LabVIEW, which features compatibility with NI PXI-CAN cards and ready-to-run NI LabVIEW driver libraries, to achieve the rapid development time the project requires.

The control panels transmit discrete digital switch data, and a unique data word represents each switch position. For control panels that contain rotary potentiometers and encoders, the data values increase and decrease depending on the direction of rotation. CAN data words set all the control panel lighting levels and the control panel indicators with on/off commands. For production testing, we tested one control panel at a time. During qualification testing, we configured the NI PXI test system to allow for simultaneous testing of multiple control panels at the same time via CAN buses.

Hardware and System Architecture

The test system hardware consists of two NI PXI-8461/2 CAN interfaces installed in a PXI mainframe along with multiple relay boards, power supplies, and a DMM card. The system can monitor up to four individual CAN buses at once and test 100 percent discrete I/O and DC power functions. Each control panel transmits a unique CAN bus ID that is identified by using LabVIEW routines. The test system can thereby emulate the function of the CAN bus data concentrator used on the aircraft.

The test software, which we wrote entirely in LabVIEW, integrates NI-CAN drivers in custom subroutines to initialize CAN ports for specific CAN addresses and perform CAN data frame read functions. We created additional subroutines to compare the received data to the expected data frames. For each CAN bus session, the CAN and object network interfaces are opened and configured, followed by the CAN read operations and then session closure. For lighting functions, specific CAN data is transmitted to the control panels. We wrote additional programs to monitor switch positions in real time, and others to monitor CAN data from each panel and write time-stamped data to a log file for any changes detected.

During production test, we use NI TestStand to control test sequencing and test results reporting. The first step is to instruct the operator to set each switch, rotary potentiometer, and encoder to a specific position. A test software panel graphically illustrates each switch position of the unit under test. The second step is to create an HTML log file of any data discrepancies noted during test. For switch panel indicators, we use a variety of test scenarios. One scenario illuminates all of the indicators on the control panel and has the operator visually verify that the correct indicators are lit up. We created subroutines to send a CAN message to the control panels for lighting, which can be controlled in real time by transmitting CAN data to control brightness levels from no light to full brightness levels using a LabVIEW dial. In another scenario, the operator clicks on the test software panel, which individually commands each indicator to light up by transmitting a CAN message to the control panel.

We are successfully developing a family of complex CAN-based control panels for use on the Boeing 787 airplane by utilizing National Instruments software and hardware. We were able to quickly develop new test software using LabVIEW with almost unlimited control of CAN bus data. The PXI-CAN cards have proven easy to configure and highly reliable in operation. We plan on developing test equipment for future programs with short deadlines using National Instruments test hardware and software for many years to come.

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