freeptos@mips.COM (Dan Freitas) (01/01/89)
Does anyone have any ideas for sensing vibration peaks? I want to detect
the maximum peak (in a given orientation) of a vibration of frequency ~1-2KHz.
Something like what they use on the dynamic wheel balancers but operating at
a higher frequency. In the wheel balancer you place the sensor (mechanical
pendulum with contacts or some such) on the swing arm of the car. The wheel
is spun and the sensor fires a strobe every time the vibration peaks in a given
position around the circle. You then add weight to the opposite side of the
wheel and presto, a dynamically balanced wheel.
I'm not sure a mechanical pendulum would work so well at 2Khz. I would think
it might act as the mechanical equivalent of a low-pass filter.
Ideas anyone?
Thanks,
Dan Freitas
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PHONE: 408-991-0217larry@kitty.UUCP (Larry Lippman) (01/01/89)
In article <10457@obiwan.mips.COM>, freeptos@mips.COM (Dan Freitas) writes: > Does anyone have any ideas for sensing vibration peaks? I want to detect > the maximum peak (in a given orientation) of a vibration of frequency ~1-2KHz. > Something like what they use on the dynamic wheel balancers but operating at > a higher frequency. In the wheel balancer you place the sensor (mechanical > pendulum with contacts or some such) on the swing arm of the car. The wheel > is spun and the sensor fires a strobe every time the vibration peaks in given > position around the circle. You then add weight to the opposite side of the > wheel and presto, a dynamically balanced wheel. > > I'm not sure a mechanical pendulum would work so well at 2Khz. I would think > it might act as the mechanical equivalent of a low-pass filter. Vibration measurement and analysis can range from a simple to a complex undertaking, depending upon the application and what parameter you want to measure. In general, vibration mneasurement can deal with any or all of the following parameters plotted against a frequency domain or rotational position domain: 1. Displacement of the measurement surface; most commonly quantitatively measured in micrometers peak-to-peak. 2. Velocity of the measurement surface; most commonly quantitatively measured in millimeters/sec peak. 3. Acceleration of the measurement surface; most commonly quantitatively measured in g peak (1 g = 980 cm/sec^2). 4. Spike energy of the measurement surface; most commonly quantitatively measured in g-Spike Energy. The frequency domain for vibration measurements is usually expressed in Hertz or counts/minute (CPM). Most vibration analysis apparatus covers the range of 1 Hz to 10,000 Hz (60 to 600,000 CPM). Transducers fall into two common categories: (1) electrodynamic and (2) piezoelectric. Electrodynamic transducers are not unlike that of a dynamic microphone, having a coil and a weighted diaphragm with a known mass and known displacement range. Electrodynamic vibration transducers are available with frequency ranges up to 5 kHz, so your 2 kHz requirement is not a problem. Electrodynamic transducers will generally measure displacement and velocity; some designs are not a "true" accelerometer. Piezoelectric transducers are generally a true accelerometer, and use a piezoelectric element connected to an electrometer "charge amplifier". Many newer piezoelectric transducers have integral charge amplifiers. Piezoelectric transducers will measure velocity, acceleration and spike energy. Piezoelectric transducers will easily measure signals up to 10 Khz, but have a low frequency cutoff (usually in the 10's to 100's of Hz, depending upon the device). The wheel balancer application which you mentioned most likely uses an electrodynamic transducer optimized for displacement measurement, with a displacement signal above a given threshhold beiong used to trigger a strobe lamp. This is sort of a "semi-quantitative" application, and represents a simple use of vibration measurement since there is no measurement made with respect to a frequency domain. Designing a vibration transducer for accurate, repeatable and reliable quantitative measurement is no trivial task. However, for some less exacting applications, a "transducer" as simple as a musical instrument contact microphone will suffice. If you have further details of your application, perhaps I can give you more specific advice. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {att|hplabs|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
sic@ritcsh.UUCP (Eric A. Neulight) (01/05/89)
In article <2884@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: >In article <10457@obiwan.mips.COM>, freeptos@mips.COM (Dan Freitas) writes: >> Does anyone have any ideas for sensing vibration peaks? I want to detect >> the maximum peak (in a given orientation) of a vibration of frequency ~1-2KHz. > [stuff deleted] > > Transducers fall into two common categories: (1) electrodynamic and >(2) piezoelectric. > Just for completeness' sake... Larry neglected to mention a third category, albeit more esoteric and certainly overkill for your application. ( probably why he did not think it pertinent, but may as well add my little tid-bit.) A few months back, I saw a demonstration of a commercially available vibration measuring device which used laser interferometry for its transducing. You couldn't see or hear the vibration of the tuning fork they were using, but this thing picked it up from several feet. Come to think of it, the government (and other underhanded types) use such type devices to bug a conversation by picking up vibrations off windows caused by noise on the other side. I remember thinking at the time that a laser interferometer would make a real nice (expensive) toy. ============================================================================== CLAIMER: Well -- I wrote it! Eric Alan Neulight "Nothing is Impossible -- Just Impractical." Electrical Engineering "For every Lock, there is a Key." Computer Science House "INSANITY is just a state of mine." Rochester Institute of Technology BITNET: EAN4762@RITVAX UUCP: ...!rutgers!rochester!rit!ritcsh!sic ==============================================================================
larry@kitty.UUCP (Larry Lippman) (01/06/89)
In article <836@ritcsh.UUCP>, sic@ritcsh.UUCP (Eric A. Neulight) writes: > Larry neglected to mention a third category, albeit more esoteric and > certainly overkill for your application. ( probably why he did not think > it pertinent, but may as well add my little tid-bit.) > > A few months back, I saw a demonstration of a commercially available > vibration measuring device which used laser interferometry for its > transducing. You couldn't see or hear the vibration of the tuning fork > they were using, but this thing picked it up from several feet. There are also methods for vibration measurements through reflected wave techniques employing ultrasonics and microwaves (the more common of the two). Both ultrasonic and microwave techniques appeared in industry during the 1950's, but they never saw widespread use and remained curiosity pieces. Microwave measurement is particularly simple. I can remember a lab experiment from a EE microwaves course in which we aimed a 2K25 klystron at a tuning fork. We could measure the frequency and displacement of the vibration by observing the changes in repeller current on an oscilloscope. A simple and impressive technique, but one which just never caught on. I wouldn't be surprised, however, if a microwave vibration sensor using a solid-state emitter and self-contained signal conditining (trivial today) might cause a resurgence of interest in this measurement technique. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {att|hplabs|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"