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Subject: Re: Ultrasonics basics
Date: Fri, 22 Nov 2002 10:07:50 -0000
NNTP-Posting-Date: 22 Nov 2002 10:05:42 GMT
X-Newsreader: Microsoft Outlook Express 5.50.4133.2400
Kevin, you said previously that the minimum distance achievable is the order
of one wavelength. 8.25mm doesn't equate to my 150mm.
"Kevin Aylward" wrote in message
> Dave wrote:
> > "Dave" wrote in message
> > news:email@example.com...
> >> Hello all,
> >> I want to measure short distances (1 to 2 inches) using reflected
> >> ultrasonics (i.e. a Tx bouncing back to an Rx). Using 40KHz
> >> transducers the minimum achievable seems to be about 6 inches.
> >> Looking at existing circuits the transmitter usually sends a burst
> >> of 6 to 10 pulses? What is the reason for this i.e. why not one
> >> pulse? The reflected pulse the receiver looks for is surely the
> >> reflection of the last pulse transmitted?
> >> Is the reason for the 6 inch minimum distance because the
> >> transducers "ring" and so swamp any reflected pulses? If so would a
> >> higher frequency be the answer?
> >> If this is the case are any standard transducers available other
> >> than 40KHz? So many questions! Does anyone know the answers please?
> >> Thanks in anticipation, Dave.
> > Thanks for all the replies.
> > I must have my decimal point in the wrong place somewhere.
> > Wavelength = velocity / frequency = 330 / 40000 = 8.25mm ?
> Seems ok to me.
> > Also how would you go about measuring the phase difference? Can
> > someone point me towards some reading material please!
> I would not bother if I were you. Its just an added complication.
> Extracting phase info from a few cycles in a burst is going to get you
> into all that digital processing sort of stuff.
> Kevin Aylward
> SuperSpice, a very affordable Mixed-Mode
> Windows Simulator with Schematic Capture,
> Waveform Display, FFT's and Filter Design.
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