Synchronizing Sound: The Netherlands Aerospace Centre and NI PXI

Precision and accuracy are incredibly important factors within the world of aviation research. Imagine the challenge of acquiring data at high sample rates from over 200 microphones and pressure sensors distributed in a large wind tunnel while keeping the signals synchronized within an astonishingly tight 1 microsecond window. It may seem like a daunting task, but in this blog post, we explore a case study where cutting-edge technology and ingenuity came together to meet this challenge head-on.

The Challenge

This story takes place at the Netherlands Aerospace Centre (NLR), an independent nonprofit research institute known for its expertise in aviation research. The NLR’s avionics technology department was tasked with installing instrumentation in wind tunnel test models for both commercial and military aircraft, as well as space vehicles. This involved conducting various tests, including avionics temperature and vibration testing, as well as electromagnetic compatibility (EMC) testing.

One of their recent projects was particularly intriguing. Airbus had developed a scale model for wind tunnel testing of an innovative aircraft design featuring open-rotor propulsion, as part of the European Clean Sky program. This experimental model featured two contra-rotating open rotor engines at the rear, making it crucial to measure and reduce the noise generated by the propellers. The challenge was to measure sound pressures in relation to the propellers’ angular positions and pitches, requiring an extremely high level of synchronization.

The Solution

To tackle this complex challenge, the team at NLR turned to National Instruments (NI) hardware and software solutions. The heart of their data acquisition system was the NI PXI and PXI Express synchronization bus, which allowed for precise synchronization of signals, even when cabling lengths differed by up to 100 meters.

Inside the aircraft model, they installed an NI PXIe-1075 chassis, housing 144 microphones and pressure sensors, connected to NI PXIe-4498 and PXIe-4331 modules. Outside the model, an 8-slot NI PXI-1042 chassis with 24-bit NI PXI-4498 modules was used for inflow signals. These systems were meticulously synchronized using NI PXI-6652 and PXIe-6672 timing modules in conjunction with an NI FlexRIO module.

All data and synchronization connections were fiber-optic, a choice made to eliminate electromagnetic compatibility issues. The LabVIEW software on the PXI controllers played a pivotal role in data acquisition, synchronization with control and storage computers, and real-time monitoring of sensors and temperature.

The LabVIEW software not only facilitated data acquisition but also ensured the system’s robustness and reliability. It monitored temperature to prevent overheating, a critical concern in the model’s confined spaces. During tests, data was streamed in binary format over TCP/IP to a data storage computer for later analysis. A critical aspect was that all components in the measurement system had to be tightly synchronized, including the PXI systems and custom-built acquisition systems.

Success and Future Endeavors

The results spoke for themselves. Despite the intricate nature of the tests and the massive amounts of data generated, the system performed admirably. With over a year of rigorous testing and experimentation, it met all expectations, necessitating only software upgrades for further improvements.

In the end, the combination of off-the-shelf NI hardware and software, along with collaboration with NI Alliance Partner KW Automation, allowed the team at NLR to develop a measurement solution in a remarkably short timeframe.

This case study serves as a testament to the power of cutting-edge technology and creative problem-solving in the field of aviation research. The ability to acquire synchronized data with such precision is invaluable in the development of next-generation aircraft, pushing the boundaries of what’s possible in aerospace engineering. It’s a reminder that, with the right tools and expertise, even the most challenging engineering problems can be overcome.

The case study discussed in this post was originally co-authored by Johan de Goede and Rob Zwemmer from the National Aerospace Laboratory.