Hi,
As a small company and being new to vibration testing, we are having difficulty in explaining to our customer the reason for a change in magnitude on a post random low level Sine test. The background is that we complete a functional test on the equipment, Pre LLS test (0.5g @ 20-2kHz), Random vib, post LLS test and then a post functional test. Both X & Y axes were fine with correlation on the pre/post vib plots and the post functional test was fine for all 3 axes. However, in the Z axis, the magnitude at resonance reduced by approx 50%. There was a minimal change (~2%) in resonance for the pre and post plots. The unit wasn't altered nor moved during the z axis testing.
The customer specification allows a deviation of 10% on frequency and 40% on magnitude. As we are outside this, it's a test failure.
As far as an explanation, the reduction in magnitude suggests some settling of the unit in this axis provided additional damping.
Any other thoughts /experiences?
As a small company and being new to vibration testing, we are having difficulty in explaining to our customer the reason for a change in magnitude on a post random low level Sine test. The background is that we complete a functional test on the equipment, Pre LLS test (0.5g @ 20-2kHz), Random vib, post LLS test and then a post functional test. Both X & Y axes were fine with correlation on the pre/post vib plots and the post functional test was fine for all 3 axes. However, in the Z axis, the magnitude at resonance reduced by approx 50%. There was a minimal change (~2%) in resonance for the pre and post plots. The unit wasn't altered nor moved during the z axis testing.
The customer specification allows a deviation of 10% on frequency and 40% on magnitude. As we are outside this, it's a test failure.
As far as an explanation, the reduction in magnitude suggests some settling of the unit in this axis provided additional damping.
Any other thoughts /experiences?
