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From: "mook johnson"
Subject: Re: vibration measurement circuit (vibration gurus please help)
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Sun, 27 Oct 2002 02:56:40 GMT
NNTP-Posting-Date: Sat, 26 Oct 2002 21:56:40 CDT
Organization: Road Runner - Texas
"Bob Wilson" wrote in message
> In article <6EGu9.firstname.lastname@example.org>, email@example.com
> >I'd like to get a graph of the vibration level (Gs) over a frequency
> >of 10 to 5kHz
> >The vibration to be measured would be continuous or slowly changing over
> >several minutes.
> >Seven bands over that interval would be sufficient resolution of the
> >Is it valid to do this using an Analog Devices accelerometer to feed 7
> >bandpass filters.
> >then measure the peak amplitude of each of the 7 BP outputs?
> >I was thinking of using peak detectors to hold the peak experienced in
> >band over a 300mS period then use an A2D to sample the peak in each band.
> >I only have an 8051 or MicroChip PIC running at 7.3MHz to do the
> >A2D manipulation and serial communication to the host at 9600 bps. 3
> >different axes will be sampled over the 1 second period and the host will
> >request an update at 1 /second.
> >I think FFT is out due to limited processing power and limited local RAM
> >storing the raw waveform.
> >Is this a valid approach? Will this be useful data for verifying
> >qualification vibration levels for a device to be used in the same
> >The desired display on the computer screen would be 3 graphs with G(peak)
> >the Y axis and frequency on the X axis.
> If you know the amplitude you are vibrating it at (and with many shaker
> tables, you do, since it is specifically set), and you know the
> instantaneous vibration frequency (assuming sinusoidal), then there is no
> point at all in attempting to measure the accelerationin Gs, since you
> calculate it.
This will be used to measure the vibration in the field. "the field" is an
inaccessible location so standard measurement equipment cannot be used.
We would like to collect the actual vibration levels of the boards when they
are used in this application. This would be beneficial for setting
qualification levels for current and future boards.
This will not be used to verify that the shaker table is operating
My question was if measuring the peak G levels from the outputs of several
band pass filters is an accurate method of measuring vibration over a the
indicated frequency range.
Any suggestions would be appreciated. Consideration for the slow processor,
low amount of SRAM and low bandwidth must be taken into account.
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