From: Spehro Pefhany
Subject: Re: Ultrasonics basics
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Date: Fri, 22 Nov 2002 03:22:42 GMT
NNTP-Posting-Date: Thu, 21 Nov 2002 22:22:42 EST
On Thu, 21 Nov 2002 17:14:12 -0000, the renowned "Dave"
>I want to measure short distances (1 to 2 inches) using reflected
>ultrasonics (i.e. a Tx bouncing back to an Rx).
Difficult, but possible.
> 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
>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
The answer is in the transducers- their damping, their Q and the
frequency they operate at.
>If this is the case are any standard transducers available other than 40KHz?
Yes, but if price is an issue you might not be too happy when you
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