Customized system gathers aircraft subsystem tests
Dave Baker, G Systems -- Test & Measurement World, 9/1/2005
Lockheed Martin Aeronautics recently contracted with G Systems to develop a data-acquisition system for its F-35 vehicle systems integration facility (VSIF). The system that G Systems developed acquires various types of data including analog, digital, video, and data transferred from other systems through reflective memory. Additional features include a real-time display capability and the ability to configure all aspects of the system from transducer setup to data management.
Fig. 1 The test system uses multiple servers for individualized client use.
Figure 1 illustrates the general architecture of the data-acquisition system. The system is distributed across several servers to enable load balancing and to achieve the required performance. The distributed software architecture includes six major custom applications and is scalable to provide for future expansion.
G Systems used five National Instruments PXI chassis populated with a mixture of NI data-acquisition boards to achieve a total of 640 analog channels and 480 digital channels. The ability to "mix and match" different types of data-acquisition boards while maintaining time synchronization was important for controlling the overall hardware costs.
The time synchronization is maintained in the distributed system through the use of an IRIG-B time signal that can be provided by the data-acquisition system itself or by another source within the VSIF lab. The time source provides the start pulse and the 10-MHz clock that is routed through PXI-6653 synchronization boards in each chassis.
The application that acquires the analog and digital data also performs PXI board verification and internal calibration as well as signal path calibration operations using an external DC source controlled over GPIB. This automation of the signal path calibration allows a system verification to be performed automatically within 20 min with minimal operator involvement.
All data is delivered to the end user in engineering units and takes into account the calibration values for the analog-to-digital converter, the signal-conditioning module, the transducer, and zero nulling values where appropriate. Derived channels (i.e., channels that are calculated from information contained in other channels, like Watts=Volts*Amps) can be calculated. Additionally, one interface allows users to "plug in" user-defined dynamic link libraries (DLLs) to create more complex derived channels.
A graphical user interface allows the system administrator to configure every aspect of the system, and the configuration information is stored in a SQL server database. The user interface provides capabilities such as column sorting and filtering, channel group definitions, multi-record editing, and copy/paste functions—features that help the system administrator manage the system's numerous channels. The software also helps users to
- administer eight levels of user privileges,
- manage the available hardware (such as PXI boards and transducers) and the hardware connections,
- update calibration information,
- define derived channels,
- archive or export data and a database to other media,
- create standard configuration reports (including historical calibration data), and
- create user-defined reports.
Because the system is used by many different groups to test out various aircraft subsystems during integration tests, a single, static user display was not a good option. Instead, we used a dynamic, user-configurable data display that enables users to create custom views with several choices of indicators.
All information for an individual user configuration is stored in the database and can be exported along with test data for stand-alone review or playback. This makes it possible for a user to take a snapshot of test data (including all calibration and transducer information) from several test runs and use it independently of the main database, which can be useful for off-line analysis or a group presentation.
The test control/monitoring/playback application provides users with several modes of operation. The system constantly acquires data and publishes it in a "low-resolution" format to client workstations. As the published data is received, it is buffered continuously on the local client in a 30 min rolling buffer. From this buffer, a user can scroll back in time to data that was published or logged and replay it in real time if desired.
When the operator chooses to log data, the "high-resolution" data is logged to file and is later transferred to a central repository. These test runs can be downloaded from the repository to a workstation for detailed review of the data in the playback mode.
For both live and playback data, the software supports advanced navigation functions for traversing data sets. Users can set triggers and alarms to quickly find points of interest in data. The user can also set a bookmark to highlight areas of interest in the data.
All logged data is controlled and protected in the system. The data is automatically moved from the acquisition servers to a central RAID (redundant array of inexpensive disks) data-storage unit when a user stops logging a test run. Both the data display and the data-analysis export application can directly recall data that exists either on the RAID or in an archived dataset.
Data-analysis capabilities are provided by a custom application that exports data to the NI DIAdem analysis package or to ASCII text files. This custom application feeds data directly into DIAdem through an object linking and embedding (OLE) interface. The operator can select the test run(s) and channel(s) to export to DIAdem and also has the option of merging data from several test runs.
| Author Information |
| Dave Baker is VP of engineering at G Systems, Plano, TX. dbaker@gsystems.com. |
