Measuring Harmonics

[AlexMx]

Hi to everyone, this is a great place and checking all the notes I can say now there is people helping people. Thanks in advance.

I'm jus looking information or some literature about how to measure the harmonics on some characteristics of a part, like TIR or width

Any information will help me . Thanks again

 

[Marc]

When I worked in electronics we used a transducer/accelerometer. Attach UUT (unit under test) to shaker and then attach accelerometer at an appropriate periphery location so as not to damp response. UUT should be supported as it is in service. Vibrate at suspect frequencies or do a sine sweep and watch the screen. If/when it hits a resonant frequency you'll see a power rise in the waveform.

Remember that if the fixture holding the UUT is not properly designed and preferably made of magnesium your results may not be 'real' as the fixture can induce artifacts such as ringing which can mimic a resonant frequency.

 

[AlexMx]

Thanks Marc, in fact I'm measuring a brake disc, and checking the Thickness variation of both faces (external & internal) but in addition to this I need to measure the Harmonics of the thickness variation.
The measurement is been taken dinamically, two LVDT transducer touching the internal and external side are detecting the variations while the disk is rotating and the plate is supported on a mechanical reference.

 

[Ajay Joshi]

Hi AlexMx
Your measurment system should be capable of picking up the fine signals. What harmonic analysis does is that it breaks up the resultant waveform into indivisual waves of specific wavelength usually in increments of 1. Harmonic analysis can give you information about some specific noise which can be attributed to some signal on the manufacturing set up. I doubt if LVDT alone can give this output. Centering & levelling of the table is very important. What is required is a laser detection method with a software to analyse the results. A Taylor Hobson roundness measurment equipment can give you the necessary information.