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 [DPRG] Measuring Speed of sound in a liquid Message index sorted by: [ date ] [ thread ] [ subject ] [ author ] Previous message: [DPRG] Measuring Speed of sound in a liquid Next message: [DPRG] need a batterey for a compaq 7770 laptop Subject: [DPRG] Measuring Speed of sound in a liquid From: Kipton Moravec kip at kdream.com Date: Fri Sep 3 23:48:36 CDT 2004 ```Thanks to Rick I found exactly what I was looking for, a 180 kHz Teflon transducer for only \$39. The maximum voltage pulse to make it move is only 250V p-p :) The range specified is 4" to 4' (for a reflected wave) and since I am interested in a sensor and a receiver the maximum range is actually 16 feet. Of course the longer the distance, the better the accuracy. I thought 1 meter was good, (better than comparable systems) I am now going to have to look at the sensitivity as I investigate a longer pipe. What you want to do is send a defined pattern, say 8 sine waves at 180 kHz, and sample with an ADC at a much higher frequency (in my case 18 MHz) Then do a correlation of what you sent and what you received. I believe you can get sub sample accuracy. This is better because you have more a priori information about the wave you are looking for than the simple "spl-thunk" Which probably has components in all different frequencies. The speed of sound in different liquids is interesting. You can find one with a google search. The other thing to notice is that is very temperature dependent, so I have to measure the temperature of the liquid also. Fortunately it is typically a concrete room and the temperature does not fluctuate much. Kip >Let me preface this with a clear warning that I only have two >semesters of college physics, that it was 20 years ago, and that my >interests were less to do with mechanics at a macro scale that wasn't >at least hundreds of light-seconds worth of "macro" than the >dark-haired woman in the third row. I remember as much about her as I >do about physics, and I can't even recall her name. YHBW. > >That being said, how's this for a brainstorm: when all's said and >done, a "sound wave" is nothing but a bunch of compression waves >back-to-back. In its basic form, just one oscillation has the same >properties as a sound wave. It seems to me that you could have a >chamber with a fixed end and an end that can could move, and a blade >that chop down. The blade goes spl-thunk, the liquid goes sloosh, >then the movable end moves a finite amount of time later. The >distance from the blade and the initial position of the movable end >is known. Measure the amount of time that it takes for the movable >end to move, divide by distance; et voilá, the quotient is the speed >of sound. All of the pieces involved in this method are pretty >minimalist and can be as durable as you like without sacrificing >precision. > >The shape of the tank and initial stillness might throw slop into the >measurement, but a little more sophistication in tank and >wave-generator can help dampen errors and increase accuracy. The >reason this might be better than measuring real sounds is that the >waveforms for sound are necessarily going to be more complex and, to >get the maximum gross movement to match my "single wave" method in a >sound pulse, the energy of my single wave would have to be the >highest energy in a waveform that rose from zero energy a rapid >to/fro sequence with a net energy near zero. > >As previously noted, I am not a physics guru and the two books that I >would resort to in hopes of getting further inspiration are in >storage. If you have access to a copy of _The Way Things Work_, there >is almost certainly at least two designs that would meet your needs, >and the things in TWTW are always concrete, >they've-been-built-and-tested-in-non-laboratory conditions. Another >good general reference to check for ideas on this stuff is Van >Nostrand's Scientific Encyclopedia, and if you have the option, look >first for a copy that is pre-'85. They stopped using English around >then. ``` Previous message: [DPRG] Measuring Speed of sound in a liquid Next message: [DPRG] need a batterey for a compaq 7770 laptop Message index sorted by: [ date ] [ thread ] [ subject ] [ author ] More information about the DPRG mailing list