Brüel & Kjær Sound & Vibration Measurement A/S

Vibration monitoring and analysis in aircraft engine test cells


Snecma, part of the SAFRAN group, is dedicated to the production of engines for both air and space. Working alone or in partnership, Snecma designs, develops and produces engines for civil and military aircraft, launch vehicles and satellites. The company is organised in three divisions:

  • Commercial Engines – Snecma and GE Transportation team up to produce the bestselling family of CFM56 turbofans
  • Military Engines – design, development, production, sale and support of jet engines for combat and training aircraft, as well as turboprop engines for military transport
  • Space Engines – Snecma, lead propulsion company for Europe’s Ariane launcher, develops and produces propulsion systems and equipment for launchers, satellites and space vehicles

The CFM56 is the world’s best selling commercial aircraft engine, and the most reliable of its generation, with dispatch reliability approaching 100%. Covering a thrust range from 18 500 to 34 000 pounds, it powers nearly all types of mainline jets (over 100 seats). TheCFM56 has been an exceptional commercial success, and powers many different models of both Airbus and Boeing jetliners.

Since it was founded 30 years ago, CFM International has continuously improved these engines by incorporating the latest technologies. It also integrates evolving market requirements, especially for lower noise and emissions, which has proven a key to its commercial success and world wide renown.

Snecma Services offers a complete range of aero-engine support services – on-wing and off wing repairs, technical assistance, development of repair solutions, tooling services, monitoring, fleet management, training, engineering, technical publications, etc.

Cenco Belgium, a division of Tech space-aero, a Belgian member of the Safran Group, designs, Installs, and supports test cells and test equipment for all types of propulsion, from the largest civil turbofan engines and military turbojets to turbo shaft engines and APUs.

The Need
In Snecma Service’s Villaroche facility, all engines are tested after each shop visit in order to guarantee the best level of performance. The vibration level and balancing grade are essential parameters of the engine and are measured at each run. Included in the renewal of their test cell, Snecma Service chose a Brüel & Kjær solution, based on PULSE™. The system was installed and connected to the Cenco Data Acquisition and Control Software.

The Vibration Monitoring

The goal was to build an automatic system with the following functions:

  • Automatic setup for all types of CFM56 engines
  • Conditioning of three differential accelerometers
  • Conditioning of two tachometers
  • Top/tour extraction for phase measurement Real-time measurement of vibration levels for each channel at each rotation speed
  • Phase measurement for each channel at each rotation speed
  • Real-time FFT analysis
  • Online data transfer to the central software through LAN interface

A Dedicated Solution with Standard Products

A 19-inch rack contains the hardware including the differential conditioners and the tacho conditioning. The board for the top/tour extract, developed by Cenco, is also included in the rack. The signals are all sent to the PULSE front-end, which then measures all the global vibration levels, order-one levels and phases for each transducer.

Choosing the name of the engine in the central software sets all the specific parameters in the system, including sensitivity of the accelerometers. On the PULSE monitor, the user can choose whether he wants to view the global vibration levels and order-one levels and phases, the real-time FFT analysis, or, during a run-up/run-down, the graph of the values as a function of time or speed. The PULSE analyzer setup has been fixed to match the tolerance check and all others criteria previously used by Snecma Service.

All data are transferred to the central software, via LAN interface, at a rate of ten times per second. Mainly built on standard Brüel & Kjær products, the Vibration Monitoring and Analysis system is well merged in the overall test cell control software.

This easy-to-use system is very efficient and can be seen by users as a robust vibration monitoring system, as a frequency analyzer for real time diagnostic, and as precise balancing measurement system.

With very simple setup modification, the system is easily adaptable for others types of aircraft engines. 

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