NI LabVIEW and PXI Increase Flexibility for Aircraft Gearbox Test System

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"We designed and developed a test system that helped our client efficiently test its aircraft gearbox and provided the flexibility to configure it for various kinds of gearboxes. "

- Anu Kalidas M., Captronic Systems Pvt. Ltd.

The Challenge:
Developing an integrated, configurable, and reliable test system to acquire data from various types of sensors, such as thermocouple, RTD, pressure, flow, load cell, speed, and vibration, as well as control the loading pattern of an aircraft gearbox.

The Solution:
Using National Instruments LabVIEW, PXI, SCXI, and NI-DAQmx to create a highly flexible, scalable, and powerful test system in 12 weeks.

Author(s):
Anu Kalidas M. - Captronic Systems Pvt. Ltd.
Mondeep Duarah - Captronic Systems Pvt. Ltd.

Gearbox Test System Requirements

Our client, a leading R&D organization that specializes in developing aircraft engine components, asked us to create a test system for an aircraft engine gearbox. The gearbox plays an important role in distributing engine power to the rotors and other power outputs in an aircraft. Therefore, before integrating with the actual engine, the gearbox should undergo rigorous testing that includes vibration and endurance tests.

The client needed a test system that would:

  • Support signal conditioning for a wide range of sensors, such as thermocouple, RTD, pressure, flow, load cell, eddy current speed probes, and accelerometers
  • Perform online and post processing on the acquired data
  • Offer the ability to remotely monitor and control the tests
  • Deliver a software and hardware architecture for future expansion

This meant that our platform required the following features:

  • Modular architecture to handle different signal types that is easy to configure, reconfigure, repair, and upgrade
  • Efficient timing and synchronization for seamless integration between the various measurement modules
  • High processing power and bandwidth to handle the data from more than 200 channels
  • Rugged architecture that can withstand the harsh environments in test rigs and that maintains signal integrity
  • Support for both real-time and a GUI-based OS

We built the test system based on the open, industry-standard PXI architecture. PXI delivers high processing power with rugged, modular Eurocard architecture. We used the signal connectivity of the NI SCXI platform to connect sensors, which required signal conditioning. For some sensors, such as RTD, speed, current, and digital output, we used PXI-based cards.

Gearbox Endurance Testing

Endurance testing demonstrates gearbox fatigue life and gives an indication of gearbox reliability using various failure mode tests. The test rig includes a powerful electric motor coupled to a step-up gearbox that can produce variable speeds, which, in turn, drives the engine gearbox. While some of the gearbox power outputs are directly connected to dynamometers, some are coupled to them using intermediate gearboxes. Dynamometers vary the load on each gearbox power output by controlling water flow. The DC motor is controlled by a PLC-based system that requires a readiness command from each of the subsystems to operate. Based on the limits of some analog channels, the test system should give readiness commands to the PLC.

Accelerometers mounted on the gearbox give an indication of its vibration during the tests. We analyzed the vibration signals acquired from these sensors. Due to the presence of fast rotating mechanical parts and oil mist, our client preferred a system that it can control remotely from 20 m away.

Test System Design

Taking into account the remote control option required for the test setup and the online processing and high-data-rate requirements for the vibration signals, we divided the test system into two parts -- a real-time-based PXI system, which acquires thermocouple, RTD, pressure, flow, and load cell data, and a Windows-based PXI system, which acquires and processes vibration signals from the gearbox.

We built the real-time-based PXI system on a client-server model. The server program runs on an NI PXI-8186 real-time controller while the client program runs on an IBM laptop. We used an NI SCXI-1125 isolated input module to acquire thermocouple signals and measured pressure and flow signals with an NI SCXI-1102B module. An NI SCXI-1520 module conditioned the load cells and supported excitation and filtering. We used an NI PXI-6052E card to acquire data from all these SCXI modules. The system passed speed signals from eddy current probes through a zero crossing detector to convert to TTL levels and then measured using an NI PXI-6602 counter card.

Current-controlled valves maintained the flow of water into the dynamometer, and an NI PXI-6704 analog output card operated these valves. The operator selects the percentage opening of these valves from the control station using potentiometer knobs, which generate equivalent voltage signals acquired using the PXI-6025E card. Based on the voltage value acquired, the server program calculates the amount of current to be generated through PXI-6704 module. Then, isolated digital output of the NI PXI-6527 module generates the readiness commands of each subsystem.

The Windows-based PXI system, used to acquire and process vibration signals, includes a test program running on a PXI-8186 Pentium 4M embedded controller and uses an NI PXI-4472 dynamic signal acquisition (DSA) card to acquire vibration signals. We connected the Windows and real-time systems with an Ethernet switch.

The LabVIEW Solution

The server program running on the real-time controller receives and executes requests from the client program running on the laptop. Based on specific requests from the client software, the server code performs the data acquisition and control. The test software includes modules for channel configuration, calibration, engineering unit configuration, data transfer from real time to laptop through FTP, stored data offline plotting, and report generation.

The vibration analyzer software running on the Windows-based PXI system supports data acquisition from multiple DSA cards. We used high-speed RTSI lines to synchronize the data acquisition of multiple cards. With this software, the user can perform online FFT, RMS, and order tracking on the acquired data. In addition, the user can complete offline analysis including STFT on the stored data.

The vibration data acquired from this system is transferred to the real-time system’s client laptop through TCP/IP. This helps the user compare the effects of vibration during endurance runs.

The LabVIEW graphical development environment, along with NI-DAQmx measurement services and driver software, was a perfect choice for developing the test software and helped us significantly reduce development time. Although we had to acquire data from a wide range of sensors, the hardware we used, combined with the NI-DAQ driver, helped us easily blend these data together. The LabVIEW Real-Time Module helped us create the real-time program without getting involved in the system-level programming paradigms usually associated with such OSs. Also, toolkits such as the LabVIEW Sound and Vibration Toolkit, LabVIEW Order Analysis Toolkit, LabVIEW Internet Developers Toolkit, and LabVIEW Report Generation Toolkit helped us significantly reduce development time. The great LabVIEW graphical user interface features were helpful in creating a user-friendly human machine interface.

Flexible, Reliable Solution

We designed and developed a test system that helped our client efficiently test its aircraft gearbox and provided the flexibility to configure it for various kinds of gearboxes. LabVIEW and the modularity of the PXI and SCXI architectures equipped us with a flexible, reliable test system. Finally, the analyzed test reports were ready within minutes of completing a test, saving the client a few days in collating, analyzing, and preparing reports.

Author Information:
Anu Kalidas M.
Captronic Systems Pvt. Ltd.
#19, Alif Arcade 7th Main Road I Block Koramangala
Bangalore
India
Tel: 91-80-2 553-5046
kalidas@captronicsystems.com

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