Using vibration diagnostics for consumer goods reliability

Located in Vitoria-Gasteiz in Spain, the Vaillant Group's Center of Competence (CoC) develops and approves Refrigerant Circuit Modules (RCMs). These RCMs are the core of both the aerothermal and geothermal heat pumps manufactured by the Vaillant Group. Heat pumps are one of the key product segments for the Vaillant Group's renewable energy strategy.

When it came to ensuring the reliability of their RCMs, the CoC chose a vibration analysis system from Brel & Kjr. Development and Innovation Engineer Javier Oleaga says: "We were looking for an instrument which would enable us to accurately characterise the vibration of a refrigerant circuit module, in order to assure the quality and lifetime of the heat pump. When we decided to buy equipment to measure and analyse vibration signals, our partner - the University of Mondrag³n -recommended Brel & Kjr's vibration systems to us."

In this test procedure, the objective is to find the frequencies at which the excitation frequencies of the compressor can generate resonances (large-amplitude displacements), which cause fatigue and breakdowns. This requires measurement of the natural frequencies of the pipes, which move in three dimensions. Triaxial accelerometers are placed in key positions on the critical pipes. Then the piping is excited with a purpose-designed impact hammer made by Brel & Kjr.

The obtained result is a series of Frequency Response Functions (FRFs), showing the natural resonant frequencies and the amplitudes of the piping at those frequencies. The acceptance criteria are to check the correct shape of the time signals (force and acceleration), the autospectrum of the force, and the shape of the coherence in each measurement. If they are correct, the measurement is validated and the results are considered reliable.

The full Valliant Group case study is available at www.bksv.com, where you can also find more information about their vibration analysis systems.