The test stand test!

Developing an integrated and reliable test system to control various test parameters, whilst acquiring data from various sources provided a formidable challenge for Sci-Mech Technical Services.

However, the solution came in the form of National Instruments' (NI) LabVIEW software and NI SCXI and PXI hardware, which was used to create a data acquisition and control system for aircraft gearbox testing that meets project requirements and has the flexibility for future expansion.

Sci-Mech's client needed a test system capable of testing multiple aircraft gearboxes on the same test rig. It was critical that the system could simulate in-flight configuration and orientation, and operate any pitch and roll angle configuration as well as measure and record that orientation during testing.

The system also had to condition a wide variety of sensors for temperature, flow, speed, and vibration measurements. Sci-Mech needed high bandwidth because of the large number of channels and the speed at which the data was acquired and logged to the disk.

The PXI/SCXI hardware combination was critical to Sci-Mech's design because it provided both the performance and the bandwidth required for the data acquisition, as well as the ability to condition low power signals as close to the source as possible to reduce induced noise.

Sci-Mech used two NI SCXI-1102 modules with NI TBX-1303 terminal blocks for thermocouple data acquisition, an NI PXI-6220 multifunction M Series data acquisition (DAQ) module to acquire data from the SCXI module and an NI PXI-6602 counter/timer module to acquire pulses from speed and flow transducers. Finally, Sci-Mech used NI's PCIe-8361, to connect its PXI rack to a PC and provide 192 MB/s throughput and a transparent link where all PXI modules appear as PCI boards within the PC. Initial configuration of the data acquisition hardware using NI Measurement & Automation Explorer (MAX) was quick and intuitive.

By using the latest NI-DAQmx drivers with MAX, Sci-Mech achieved easy setup and superior organisation of a large and diverse channel count. Sci-Mech could exchange instruments with different calibration and scaling for other instruments without having to make changes to the LabVIEW code.

Sci-Mech chose a dual-core processor PC to take advantage of the built-in parallelism of LabVIEW. With its system combination, Sci-Mech achieved high-speed control and acquisition along with dual-speed and concurrent high channel-count logging while remaining under 15% CPU utilisation. Then Sci-Mech used the processing power to perform more intense tasks such as processing acceleration signals through realtime fast Fourier transform (FFT) analysis to obtain peak velocity.

The graphical nature of LabVIEW, presented Sci-Mech's clients with several different user-friendly machine interface options early in the design stage. The intuitive front panel controls and indicators gave them the opportunity to visualise and customise their own solution to their exact needs at the project's outset.

Combining modular architecture with dynamically launched data acquisition subroutines, Sci-Mech achieved 90% software completion without access to the actual test transmission and fixture. Upon delivery, the company replaced data acquisition simulation VIs with actual data acquisition sources. Data handling and formatting had already been tested, and integration time was greatly reduced. With the help of LabVIEW and its seamless integration with NI hardware, Sci-Mech estimated to have saved more than 75 man hours and reduced on-site integration time from three weeks to a couple of days. This helped it rapidly develop a flexible control and acquisition system that met its client's current requirements and plans for future expansion.

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