The Challenge

To develop Automated Test Equipment (ATE) for complete functionality testing of the Flight Control System (FCS) by providing an integrated, configurable and reliable test system in limited time.

The Solution

Using the National Instruments PXI Platform, NI DAQmx and LabVIEW Development System and other third party hardware create a highly flexible, scalable and powerful test system.

Introduction

Our client, a leading R&D organization, specializes in developing FCS for aircrafts. The FCS is one of the critical components of an aircraft. The important functions the FCS performs are as follows:

• Notify ground stations of the health and position of the aircraft during the entire duration of flight
• Guide the aircraft to its destination by following flight plans given by ground stations
• Take recovery actions and land the aircraft safely in case critical systems failure

These FCS require extensive ground testing before they can be integrated into an aircraft. Ground testing involves complete functionality testing of the FCS on ground by simulating various flight conditions and measuring the FCS responses.

We decided to build the test system based on the open industry standard PXI architecture. Also the NI range of PXI products provided us with hardware for most of our signal types. LabVIEW was the language of choice for programming the system due to its excellent graphical capabilities and tight integration with NI PXI products using NI DAQmx. Also LabVIEW drivers were available for the third party hardware used.

System Design

An overview of the complete system is shown in figure 1 below.

Testing the FCS required all possible flight conditions to be simulated on the ground. The FCS received information about some parameters like pitch, roll, throttle etc. from sensors giving analog outputs. These sensors were simulated using analog outputs from PXI-6713. Some onboard sensors generated waveform outputs. These were simulated in the ATE using the PXI-6733. The FCS controlled actuators through analog output lines. These were acquired and measured using the PXI-6071E.

The FCS had dual port memory onboard which it used to store flight parameters and computation results. These were accessed using the PXI-6534 high speed DIO board. High voltage relay I/O to the FCS was simulated with the PXI-6527 Isolated DIO board. GPS data was simulated to the FCS using the PXI-8422 serial link.

The synchro link was established using the Digital to Synchro card from North Atlantic Inc.

Software Features

The software developed in LabVIEW provided two modes of testing for the user.

Auto Mode – In this mode the user generates a test list using a wizard. The ATE then conducts the various tests in sequence without manual intervention. Appropriate reports are generated at the end of each test which include measured as well as computed values.

Batch Mode – In this mode the user can test the FCS manually. The user can control step by step execution of each test. This was mainly used to debug a faulty FCS.

A self test feature was also provided in the ATE whereby the ATE checks its hardware integrity before connecting to the FCS.

Even though we had to acquire data from a wide range of interfaces, the hardware we used along with NI DAQmx driver helped us in easily blending all these data together. Also toolkits like Database Connectivity toolkit and Report generation toolkit helped us in significantly reducing development time. The great GUI features provided by LabVIEW came handy in creating a user friendly HMI.

7831R based PCM Commutator

An important requirement for the test system was to communicate with the FCS using PCM telemetry. A third party PXI card from Lumistar Inc. was used to perform the decommutation of data received from the FCS. To achieve PCM commutation the NI-7831R was used. The commutation algorithm was written in LabVIEW and downloaded onto the NI-7831R using the LabVIEW FPGA module. Developing the FPGA based PCM Commutator greatly reduced system costs, and provided an easily customizable solution for future expansion. This was a major achievement in this project.

Some of the features of the custom developed PCM Commutator are listed below.

• Output format – NRZ-L (can be customized for other formats)
• Output Data Rates – Upto 2 Mbps
• Word length - Upto 16 bits per word (can be customized for 32 bits per word)
• Minor Frame Length – Upto 15,872 words per minor frame
• Major Frame Length – Upto 1024 minor frames
• Frame Sync Pattern – Upto 32 bits (any series of 0’s and 1’s can be used)
• Real time display of transmitted data
• Facility to save configured PCM formats for later use

Conclusion

We were able to design and develop a test system that enabled our client to efficiently test his FCS and provided the flexibility to configure it for various kinds of test setups. NI LabVIEW development environment and the modularity extended by the PXI architecture equipped us in providing a flexible and reliable solution in record time. Also the analyzed test reports were now ready within minutes of completing a test, saving the customer a few days in manual testing, collating, analyzing and preparing reports.