Comments on: High Pass Filtering And Tacho Signals http://blog.prosig.com/2001/06/06/high-pass-filtering-and-tacho-signals/ Telling you what you really need to know about noise & vibration measurement Tue, 07 Sep 2010 10:00:33 +0000 hourly 1 http://wordpress.org/?v=3.0.1 By: Dr Colin Mercer http://blog.prosig.com/2001/06/06/high-pass-filtering-and-tacho-signals/comment-page-1/#comment-1400 Dr Colin Mercer Mon, 07 Jun 2010 09:09:14 +0000 http://blog.prosig.com/2001/06/06/high-pass-filtering-and-tacho-signals/#comment-1400 Using a tacho with 32000 pulse per rev is rather high. I am sure you appreciate the problems of spatial aliasing. With 32000 pulses per rev it means you are measuring every 0.01125 degrees. What sampling method are you using? Is it time based i.e. S samples / second? Or is it synchronously sampled where you sample on every tacho pulse? Also what is the shaft speed? In my experience tacho rates of such magnitude are not actual true tachos. Most graticules seem to be limited to around 2000 or 3000 spaced pulses per rev. Above that the intermediate pulses are ‘interpolated electronically’. So they do not detect the small torsional vibrations. Using a tacho with 32000 pulse per rev is rather high. I am sure you appreciate the problems of spatial aliasing.

With 32000 pulses per rev it means you are measuring every 0.01125 degrees. What sampling method are you using? Is it time based i.e. S samples / second? Or is it synchronously sampled where you sample on every tacho pulse? Also what is the shaft speed?

In my experience tacho rates of such magnitude are not actual true tachos. Most graticules seem to be limited to around 2000 or 3000 spaced pulses per rev. Above that the intermediate pulses are ‘interpolated electronically’. So they do not detect the small torsional vibrations.

]]> By: Jason Yu http://blog.prosig.com/2001/06/06/high-pass-filtering-and-tacho-signals/comment-page-1/#comment-1007 Jason Yu Wed, 26 May 2010 14:37:22 +0000 http://blog.prosig.com/2001/06/06/high-pass-filtering-and-tacho-signals/#comment-1007 I did a measurement on the motor shaft. The purpose is to calculate the torque with the angular acceleration. The sensor I used was 32000pulses/perrevolution. Definitely, there was not probelm to get the acculate RPM. The problem was the angular acceleration. With different lowpass filter, the results are huge different. I am not sure which results should be present. I think it should depend on the first natural frequency of the motor shaft. Is that right? I did a measurement on the motor shaft. The purpose is to calculate the torque with the angular acceleration. The sensor I used was 32000pulses/perrevolution. Definitely, there was not probelm to get the acculate RPM. The problem was the angular acceleration. With different lowpass filter, the results are huge different. I am not sure which results should be present. I think it should depend on the first natural frequency of the motor shaft. Is that right?

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